U.S. patent application number 16/556021 was filed with the patent office on 2020-01-16 for selectively permeable graphene oxide membrane.
The applicant listed for this patent is NITTO DENKO CORPORATION. Invention is credited to Craig Roger Bartels, Masahiko Hirose, Isamu Kitahara, Makoto Kobuke, Weiping Lin, Shunsuke Noumi, Peng Wang, Yuji Yamashiro, Shijun Zheng.
Application Number | 20200017377 16/556021 |
Document ID | / |
Family ID | 57750636 |
Filed Date | 2020-01-16 |
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United States Patent
Application |
20200017377 |
Kind Code |
A1 |
Zheng; Shijun ; et
al. |
January 16, 2020 |
SELECTIVELY PERMEABLE GRAPHENE OXIDE MEMBRANE
Abstract
Described herein is a graphene material-based membrane that
provides selective resistance for solutes or gas while providing
water permeability. A selectively permeable membrane comprising
graphene oxide, reduced graphene oxide, and also functionalized or
crosslinked between the graphene, that provides enhanced salt
separation from water or gas permeability resistance, methods for
making such membranes, and methods of using the membranes for
dehydrating or removing solutes from water are also described.
Inventors: |
Zheng; Shijun; (San Diego,
CA) ; Kitahara; Isamu; (San Diego, CA) ;
Kobuke; Makoto; (Osaka, JP) ; Wang; Peng; (San
Diego, CA) ; Bartels; Craig Roger; (San Diego,
CA) ; Yamashiro; Yuji; (Osaka, JP) ; Hirose;
Masahiko; (Kusatsu Shiga, JP) ; Noumi; Shunsuke;
(Kusatsu Shiga, JP) ; Lin; Weiping; (Carlsbad,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NITTO DENKO CORPORATION |
Osaka |
|
JP |
|
|
Family ID: |
57750636 |
Appl. No.: |
16/556021 |
Filed: |
August 29, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15380797 |
Dec 15, 2016 |
10442709 |
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16556021 |
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62268835 |
Dec 17, 2015 |
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62339589 |
May 20, 2016 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B01D 63/02 20130101;
B01D 61/025 20130101; B01D 67/0044 20130101; B01D 69/08 20130101;
C02F 1/44 20130101; B01D 69/12 20130101; B01D 67/0079 20130101;
B01D 2323/30 20130101; B01D 69/125 20130101; B01D 67/0083 20130101;
B01D 71/024 20130101; B01D 67/0006 20130101; B01D 69/148 20130101;
B01D 71/56 20130101 |
International
Class: |
C02F 1/44 20060101
C02F001/44; B01D 67/00 20060101 B01D067/00; B01D 69/08 20060101
B01D069/08; B01D 69/12 20060101 B01D069/12; B01D 71/02 20060101
B01D071/02 |
Claims
1. A membrane comprising: a porous substrate; and a graphene oxide
layer comprising an optionally substituted cross-linked graphene
oxide in fluid communication with the porous substrate; wherein the
optionally substituted cross-linked graphene oxide comprises an
optionally substituted graphene oxide and a cross-linkage
represented by the Formula: ##STR00010## wherein R is H, CO.sub.2H,
CO.sub.2Li, CO.sub.2Na, or CO.sub.2K.
2. The membrane of claim 1, wherein the cross-linkage is:
##STR00011##
3. The membrane of claim 1, wherein the porous substrate comprises
a polymer or hollow fibers.
4. The membrane of claim 1, wherein the optionally substituted
graphene oxide material comprises platelets.
5. The membrane of claim 4, wherein the platelets have a size that
is about 0.05 .mu.m to about 50 .mu.m.
6. The membrane of claim 1, wherein the optionally substituted
cross-linked graphene oxide is about 20 atom % to about 90 atom %
carbon.
7. The membrane of claim 1, wherein the optionally substituted
cross-linked graphene oxide is prepared by reacting an optionally
substituted meta-phenylenediamine (MPD) with an optionally
substituted graphene oxide (GO), wherein the weight ratio of
optionally substituted meta-phenylenediamine to optionally
substituted graphene oxide (MPD/GO) is in a range of about 0.1 to
about 100.
8. The membrane of claim 7, wherein the weight ratio of the
optionally substituted meta-phenylenediamine to the optionally
substituted graphene oxide (MPD/GO) is in a range of 1 to 10.
9. The membrane of claim 1, wherein the optionally substituted
graphene oxide is a non-functionalized graphene oxide,
reduced-graphene oxide, functionalized graphene oxide,
functionalized and reduced-graphene oxide, or a combination
thereof.
10. The membrane of claim 1, further comprising a salt rejection
layer.
11. The membrane of claim 10, wherein the salt rejection layer is
disposed on the graphene oxide layer.
12. The membrane of claim 10, wherein the salt rejection layer
comprises a polyamide prepared by reacting meta-phenylenediamine
with trimesoyl chloride.
13. The membrane of claim 1, wherein the membrane further comprises
a protective layer, wherein the protective layer comprises a
hydrophilic polymer.
14. The membrane of claim 1, wherein the thickness of the graphene
oxide layer is about 5 nm to about 200 nm.
15. A method for dehydrating an unprocessed fluid, comprising
exposing the unprocessed fluid to the membrane of claim 1.
16. A method for removing a solute from an unprocessed solution,
comprising exposing the unprocessed solution to the membrane of
claim 1.
17. The method of claim 16, further comprising passing the
unprocessed solution through the membrane.
18. The method of claim 17, wherein passing the unprocessed
solution through the membrane is achieved by applying a pressure
gradient across the membrane.
19. A method of making a membrane, comprising: (a) resting a
solution comprising an optionally substituted graphene oxide and a
water soluble cross-linker for about 30 minutes to about 12 hours
to create a coating mixture; (b) applying the coating mixture to a
substrate; (c) repeating step (b) as necessary to achieve the
desired thickness or number of layers; and (d) curing the
optionally substituted graphene oxide and water soluble
cross-linker upon the substrate at about 50.degree. C. to about
120.degree. C. for about 15 minutes to about 2 hours so that the
optionally substituted graphene oxide and the water soluble
cross-linker are covalently bonded.
20. A method of making a membrane from an optionally substituted
meta-phenylenediamine cross-linker and an optionally substituted
graphene oxide, comprising: (a) separately applying to a substrate:
1) an aqueous solution of an optionally substituted graphene oxide
and 2) an aqueous solution of an optionally substituted
meta-phenylenediamine cross-linker; (b) repeating step (a) as
necessary to achieve the desired thickness or number of layers; and
(c) curing the optionally substituted graphene oxide and
cross-linker upon the substrate at about 50.degree. C. to about
120.degree. C. for about 15 minutes to about 2 hours until the
optionally substituted graphene oxide and optionally substituted
meta-phenylenediamine cross-linker are covalently bonded.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is a Continuation of U.S. application Ser.
No. 15/380,797, filed on Dec. 15, 2016, which claims the benefit of
U.S. Provisional Application 62/268,835 filed Dec. 17, 2015, and
U.S. Provisional Application 62/339,589 filed May 20, 2016, which
are incorporated by reference for their entirety.
FIELD
[0002] The present embodiments are related to polymeric membranes,
including membranes comprising graphene materials for uses such as
water treatment, desalination of saline water, or water
removal.
BACKGROUND
[0003] Due to the increase of human population and water
consumption coupled with limited freshwater resources on earth,
technologies such as seawater desalination and water
treatment/recycle to provide safe and fresh water have become more
important to our society. The desalination process using reverse
osmosis (RO) membrane is the leading technology for producing fresh
water from saline water. Most of current commercial RO membranes
adopt a thin-film composite (TFC) configuration consisting of a
thin aromatic polyamide selective layer on top of a microporous
substrate; typically, a polysulfone membrane on non-woven
polyester. Although these RO membranes can provide excellent salt
rejection rate, higher water flux; thinner and more hydrophilic
membranes are still desired to further improve energy efficiency of
RO. Therefore, new membrane materials and synthetic methods are in
high demand to achieve the desired properties as described
above.
SUMMARY
[0004] This disclosure relates to a GO membrane composition
suitable for high water flux applications. The GO membrane
composition may be prepared by using a water soluble cross-linker.
The water soluble cross-linker may be one that is compatible with
the polyamide coating of a reverse osmosis membrane. Methods of
efficiently and economically making these GO membrane compositions
are also described. Water can be used as a solvent in preparing
these GO membrane compositions, which makes the membrane
preparation process more environmentally friendly and more cost
effective.
[0005] Some embodiments include a selectively permeable polymeric
membrane, such as a membrane comprising the high-water flux GO
membrane composition, for water treatment and desalination of
saline water. Some embodiments include a GO-MPD
(meta-phenylenediamine) membrane comprising a porous substrate, and
a graphene oxide layer comprising an optionally substituted
cross-linked graphene oxide in fluid communication with the porous
substrate, wherein the optionally substituted cross-linked graphene
oxide comprises an optionally substituted graphene oxide and a
cross-linkage represented by Formula I or Formula 1M:
##STR00001##
wherein R is H, or an organic acid group or a salt thereof, such as
CO.sub.2H, CO.sub.2Li, CO.sub.2Na, or CO.sub.2K. In some
embodiments, the resulting membrane containing GO-MPD composite as
described herein further comprises a salt rejection layer, and/or a
protection layer.
[0006] Some embodiments include a method of dehydrating an
unprocessed fluid comprising exposing the unprocessed fluid to the
above described membranes, or removing a solute, such as
desalination, from an unprocessed solution comprising exposing or
passing the unprocessed solution to the aforementioned membranes.
In some embodiments, passing the unprocessed solution through the
membrane is achieved by applying a pressure gradient across the
membrane.
[0007] Some embodiments include a method of making a membrane, such
as dehydration membrane or desalination membrane, comprising mixing
an optionally substituted graphene oxide (GO) and a cross-linker,
such as an optionally substituted meta-phenylenediamine to get an
aqueous solution, followed by resting to get a coating mixture and
applying the coating mixture to a substrate, and curing the GO and
the cross-linker on the substrate until they are covalently bonded.
Some embodiments include separately applying the optionally
substituted GO aqueous solution and an optionally substituted
meta-phenylenediamine cross-linker aqueous solution to a substrate
followed by the same process and conditions of curing until they
are covalently bonded. In some embodiments, the method further
comprising applying a salt rejection layer, and/or a protection
layer.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is a diagram showing the graphene oxide layers of a
GO-MPD membrane.
[0009] FIGS. 2A-2B is a depiction of two possible embodiments of
membranes without a salt rejection layer or a protective
coating.
[0010] FIGS. 3A-3B is a depiction of two possible embodiments of
membranes without a salt rejection layer but with a protective
coating.
[0011] FIGS. 4A-4B is a depiction of two possible embodiments of
membranes with a salt rejection layer but without a protective
coating.
[0012] FIGS. 5A-5B is a depiction of two possible embodiments of
membranes with a salt rejection layer and a protective coating.
[0013] FIG. 6 is a depiction of a possible embodiment for the
method for making a membrane--Layer-by-Layer Method.
[0014] FIG. 7 is a depiction of a possible embodiment for the
method of making a membrane--Filter Method
[0015] FIG. 8 is a depiction of a possible embodiment for the
method of making a membrane--Mixture Coating Method.
[0016] FIGS. 9A-9B shows SEM data of a membrane showing a
substrate, the GO-MPD layer, and a protective coating (resin).
[0017] FIG. 10 is a plot of XRD data for GO and GO-MPD each on a
glass slide with control plots for each glass slide.
[0018] FIG. 11 is a plot showing the infrared (IR) spectra
comparison of GO and GO-MPD.
[0019] FIG. 12 is a diagram depicting the experimental setup for
the water vapor permeability and gas leakage testing.
DETAILED DESCRIPTION
I. General:
[0020] A selectively permeable membrane includes a membrane that is
relatively permeable for one material and relatively impermeable
for another material. For example, a membrane may be relatively
permeable to water or water vapor and relatively impermeable to
organic liquids or oxygen or nitrogen gas.
[0021] As used herein the term "rest," "resting," or "rested"
includes the act of leaving a solution stand undisturbed at room
temperature and atmospheric pressure for a specific duration of
time.
[0022] Unless otherwise indicated, when a compound or a chemical
structure, such as graphene oxide or phenylenediamine is referred
to as being "optionally substituted," it includes a compound or a
chemical structure that either has no substituents (i.e.,
unsubstituted), or has one or more substituents (i.e.,
substituted). The term "substituent" has the broadest meaning known
in the art and includes a moiety that replaces one or more hydrogen
atoms attached to a parent compound or structure. In some
embodiments, a substituent may be any type of group that may be
present on a structure of an organic compound, which may have a
molecular weight (e.g., the sum of the atomic masses of the atoms
of the substituent) of 15-50 g/mol, 15-100 g/mol, 15-150 g/mol,
15-200 g/mol, 15-300 g/mol, or 15-500 g/mol. In some embodiments, a
substituent comprises, or consists of: 0-30, 0-20, 0-10, or 0-5
carbon atoms; and 0-30, 0-20, 0-10, or 0-5 heteroatoms, wherein
each heteroatom may independently be: N, O, S, Si, F, Cl, Br, or I;
provided that the substituent includes one C, N, O, S, Si, F, Cl,
Br, or I atom. Examples of substituents include, but are not
limited to, alkyl, alkenyl, alkynyl, heteroalkyl, heteroalkenyl,
heteroalkynyl, aryl, heteroaryl, hydroxy, alkoxy, aryloxy, acyl,
acyloxy, alkylcarboxylate, thiol, alkylthio, cyano, halo,
thiocarbonyl, O-carbamyl, N-carbamyl, O-thiocarbamyl,
N-thiocarbamyl, C-amido, N-amido, S-sulfonamido, N-sulfonamido,
isocyanato, thiocyanato, isothiocyanato, nitro, silyl, sulfenyl,
sulfinyl, sulfonyl, haloalkyl, haloalkoxyl, trihalomethanesulfonyl,
trihalomethanesulfonamido, amino, etc.
[0023] For convenience, the term "molecular weight" is used with
respect to a moiety or part of a molecule to indicate the sum of
the atomic masses of the atoms in the moiety or part of a molecule,
even though it may not be a complete molecule.
[0024] As used herein the term "fluid" includes any substance that
continually deforms, or flows, under an applied shear stress. Such
non-limiting examples of fluids include Newtonian and/or
non-Newtonian fluids. In some embodiments, examples of Newtonian
can be gases, liquids, and/or plasmas. In some embodiments,
non-Newtonian fluids can be plastic solids (e.g., corn starch
aqueous solution, toothpaste).
[0025] As used herein, the term "fluid communication" means that a
fluid can pass through a first component and travel to and through
a second component or more components regardless of whether they
are in physical communication or the order of arrangement.
II. Membrane:
[0026] The present disclosure relates to water separation membranes
where a highly hydrophilic membrane with low organic compound
permeability and high mechanical and chemical stability may be
useful to support the polyamide salt rejection layer in a reverse
osmosis (RO) membrane. This membrane material may be suitable for
solute removal from an unprocessed fluid, such as desalination from
saline water, or purifying drinking water, such as waste water
treatment. This membrane material may be suitable in the
dehydration or water/water vapor removal from an unprocessed fluid.
Some selective water permeable membranes described herein are
GO-MPD membranes having a high-water flux, which may improve the
energy efficiency of RO membranes and improve water
recovery/separation efficiency. The water permeable GO-MPD membrane
comprises an optionally substituted graphene oxide (GO) crosslinked
with an optionally substituted arylenediamine, such as an
optionally substituted water-soluble metal phenylenediamine (MPD).
Thus, using the hydrophilic GO material and the water soluble
cross-linkers such as MPD may provide the membranes with broad
applications where high-water permeability with high selectivity of
permeability is important. These GO-MPD membranes may also be
prepared using water as a solvent, which can make the manufacturing
process much more environmentally friendly and cost effective.
[0027] In some embodiments, the selectively permeable membrane
further comprises a porous substrate or support, such as a porous
support comprising a polymer or hollow fibers. For some membranes,
the GO-MPD layer or membrane is disposed on the porous support. The
GO-MPD layer or membrane may further be in fluid communication with
the substrate. Additional optional layers may also be included such
as a salt rejection layer disposed on the GO-MPD layer, a
protective layer, and etc. In some embodiments, the protective
layer can comprise a hydrophilic polymer. In some embodiments, the
fluid passing through the membrane travels through all the
components regardless of whether they are in physical communication
or the order of arrangement.
[0028] A substrate may be any suitable material and in any suitable
form upon which a layer, such as a layer of a GO-MBD membrane, may
be deposited or disposed. In some embodiments, the substrate may
comprise a porous material, such as a polymer or a hollow fiber. In
some embodiments, the polymer may be polyethylene (PE),
polypropalene (PP), polysulfone (PSF), polyether sulfone (PES),
polyvinylidene fluoride (PVDF), polyamide (Nylon), polyimide (PI),
and/or mixtures thereof. In some embodiments, the polymer may be
polysulfone. In some embodiments, the porous material may comprise
a polysulfone based ultrafiltration membrane. In some embodiments,
the porous material may comprise hollow fibers. The hollow fibers
may be casted or extruded. The hollow fibers may be made, for
example, as described in U.S. Pat. Nos. 4,900,626; 6,805,730 and U.
S. Patent Application Publication No. 2015/0165389, which are
incorporated by reference for their disclosure related to methods
of preparing hollow fibers.
[0029] Some membranes further comprise a salt rejection layer, e.g.
disposed on the GO-MPD layer. A salt rejection layer may comprise
any material that is suitable for preventing the passage of salts.
Some salt rejection layers comprise a polymer, such as a polyamide
or a mixture of polyamides. In some embodiments, the polyamide can
be a polyamide made from an amine (e.g. meta-phenylenediamine,
para-phenylenediamine, ortho-phenylenediamine, piperazine,
polyethylenimine, polyvinylamine, or the like) and an acyl chloride
(e.g. trimesoyl chloride, isophthaloyl chloride, or the like). In
some embodiments, the amine can be meta-phenylenediamine. In some
embodiments, the acyl chloride can be trimesoyl chloride. In some
embodiments, the polyamide can be made from a meta-phenylenediamine
and a trimesoyl chloride (e.g. by polymerization of
meta-phenylenediamine and/or trimesoyl chloride). In some
embodiments, having the salt rejection layer include the same type
of structural feature as the GO-MPD membrane (also made from MPD)
upon which it is disposed can avoid adverse interaction between the
two layers.
[0030] As mentioned above, some membranes may further comprise a
protective coating. For example, the protective coating can be
disposed on top of the membrane to protect it from the environment.
The protective coating may have any composition suitable for
protecting a membrane from the environment, Many polymers are
suitable for use in a protective coating such as one or a mixture
of hydrophilic polymers, e.g. polyvinyl alcohol (PVA), polyvinyl
pyrrolidone (PVP), polyethylene glycol (PEG), polyethylene oxide
(PEO), polyoxyethylene (POE), polyacrylic acid (PAA),
polymethacrylic acid (PMMA) and polyacrylamide (PAM),
polyethylenimine (PEI), poly(2-oxazoline), polyethersulfone (PES),
methyl cellulose (MC), chitosan, poly (allylamine hydrochloride)
(PAH) and poly (sodium 4-styrene sulfonate) (PSS), and any
combinations thereof. In some embodiments, the protective coating
can comprise PVA.
[0031] Some non-limiting examples of a membrane 100 without a salt
rejection layer may be configured as shown in FIGS. 2A, 2B, 3A and
3B. The membrane 100 can comprise at least a substrate 120 and a
cross-linked graphene material layer 110. In some embodiments, as
shown in FIGS. 3A and 3B, the membrane may further comprise a
protective coating, 140. In some embodiments, as shown in FIGS. 2A
and 2B, the membrane can be without a protective coating. In some
embodiments, the cross-linked graphene material layer, 110, can be
initially constructed to have alternating layers of graphene oxide,
111, and cross-linker, 112. In some embodiments, the cross-linked
graphene material layer may comprise a single layer of a mixture of
graphene oxide and cross-linker, 113. In some embodiments, the
substrate may be sandwiched between two aforementioned membranes.
In some embodiments, the membrane can allow the passage of water
and/or water vapor but resists the passage of gases. In some
embodiments, as a result of the layers, the membrane may provide a
means of removal of water from a control volume by allowing water
vapor to pass through but excluding the passage of other gases;
resulting in passive dehydration.
[0032] In some embodiments, the membrane can be used to remove
water or water vapor from a control volume while hindering the
passage of solutes or other fluids, such as gases. In some
embodiments, a membrane may be disposed between or separate a
fluidly communicated first fluid reservoir and a second fluid
reservoir. In some embodiments, the first reservoir may contain a
feed fluid upstream and/or at the membrane. In some embodiments,
the fluid upstream can comprise a gas and water vapor. In some
embodiments, the second reservoir may contain a processed fluid
downstream and/or at the membrane. In some embodiments, the fluid
downstream can have less humidity than that of the first reservoir.
In some embodiments, the membrane selectively allows water or water
vapor to pass through while resisting the passage of gas, solute,
or liquid material from passing through. In some embodiments, the
membrane may provide a filter to selectively remove solute and/or
suspended contaminants from feed fluid. In some embodiments, the
membrane has a desired flow rate. In some embodiments, the membrane
may comprise ultrafiltration material.
[0033] In some embodiments, the membrane can exhibit a water vapor
permeability of about 15-100 .mu.gm.sup.-2s.sup.-1Pa.sup.-1, about
20-90 .mu.gm.sup.-2s.sup.-1Pa.sup.-1, about 25-90
.mu.gm.sup.-2s.sup.-1Pa.sup.-1, about 30-60
.mu.gm.sup.-2s.sup.-1Pa.sup.-1, about 30-40
.mu.gm.sup.-2s.sup.-1Pa.sup.-1 about 40-60
.mu.gm.sup.-1s.sup.-1Pa.sup.-1, about 40-50
.mu.gm.sup.-2s.sup.-1Pa.sup.-1, or about 50-60
.mu.gm.sup.-2s.sup.-1Pa.sup.-1. In some embodiments, the membrane
can also have a maximum N.sub.2 gas leakage rate of about 1000
cc/min, about 500 cc/min, about 100 cc/min, about 40 cc/min, about
25 cc/min, about 5 cc/min, less than 10 cc/min, or less than 5
cc/min.
[0034] Some non-limiting examples of a membrane 200 comprising a
salt rejection layer 130 may be configured as shown in FIGS. 4A,
4B, 5A, and 5B. In some embodiments, the membrane 200 can comprise
at least a substrate 120 a cross-linked graphene material layer 110
and a salt rejection layer 130. In some embodiments, the salt
rejection layer 130 may be disposed on top of the cross-linked
graphene material layer 110. In some embodiments, as shown in FIGS.
5A and 5B, the membrane may further comprise a protective coating,
140, wherein the protective coating can protect the components of
the membrane from harsh environments. In some embodiments, as shown
in FIGS. 4A and 4B, the membrane can be without a protective
coating. In some embodiments, the cross-linked graphene material
layer 110 may be initially constructed to have an alternating layer
of graphene material 111 and cross-linker 112. In some embodiments,
the cross-linked graphene material layer may comprise a single
layer of a mixture of graphene material and cross-linker 113. In
some embodiments, the substrate may be sandwiched between two
layers comprising GO-MPD.
[0035] In some embodiments, the membrane selectively allows water
or water vapor to pass through while keeping gas, solute, or liquid
material from passing through. In some embodiments, as a result of
the layers, the membrane may provide a durable desalination system
that can be selectively permeable to water, and less permeable to
salts. In some embodiments, as a result of the layers, the membrane
may provide a durable reverse osmosis system that may effectively
filter saline water, polluted water or feed fluids.
[0036] In some embodiments, the membrane exhibits a normalized
volumetric water flow rate of about 10-1000
galft.sup.-2day.sup.-1bar.sup.-1; about 20-750
galft.sup.-2day.sup.-1bar.sup.-1; about 100-500
galft.sup.-2day.sup.-1bar.sup.-1; about 200-400
galft.sup.-2day.sup.-1bar.sup.-1, at least about 10
galft.sup.-2day.sup.-1bar.sup.-1, about 20
galft.sup.-2day.sup.-1bar.sup.-1, about 100
galft.sup.-2day.sup.-1bar.sup.-1, about 200
galft.sup.-2day.sup.-1bar.sup.-1 or a normalized volumetric water
flow rate in a range bounded by any of these values.
[0037] In some embodiments, the cross-linked graphene oxide layer
may have an average pore size or fluid passageway of an average
diameter of about 0.01 .mu.m (10 nm) to about 0.1 .mu.m (100 nm),
and/or about 0.01 .mu.m (10 nm) to about 0.05 .mu.m (50 nm).
[0038] In some embodiments, a membrane may be a selectively
permeable. In some embodiments, the membrane may be an osmosis
membrane. In some embodiments, the membrane may be a water
separation membrane. In some embodiments, a water permeable- and/or
solute impermeable membrane containing graphene material, such as
graphene oxide, may provide desired selective gas, liquid, and/or
vapor permeability resistance. In some embodiments, the membrane
may be a reverse osmosis (RO) membrane. In some embodiments, the
selectively permeable membrane may comprise multiple layers,
wherein at least one layer contains graphene material.
III. Cross-Linked GO
[0039] The membranes described herein have a cross-linked
optionally substituted graphene oxide. These optionally substituted
cross-linked graphene oxides include an optionally substituted
graphene that is cross-linked with a water-soluble cross-linkage,
or which are a product cross-linking graphene oxide with a
water-soluble cross-linking agent.
A. Graphene Oxide
[0040] Graphene materials have many attractive properties, such as
a 2-dimensional sheet-like structure with extraordinary high
mechanical strength and nanometer scale thickness. The graphene
oxide (GO), an exfoliated oxidation of graphite, can be mass
produced at low cost. With its high degree of oxidation, graphene
oxide has high water permeability and also exhibits versatility to
be functionalized by many functional groups, such as amines or
alcohols to form various membrane structures. Unlike traditional
membranes, where the water is transported through the pores of the
material, in graphene oxide membranes the transportation of water
can be between the interlayer spaces. Graphene oxide's capillary
effect can result in long water slip lengths that offer fast water
transportation rate. Additionally, the membrane's selectivity and
water flux can be controlled by adjusting the interlayer distance
of graphene sheets.
[0041] Layered GO membranes with lamellar structure can be
fabricated by vacuum filtration process of GO aqueous solution but
may be highly susceptible to be dispersed in aqueous environment
under high flux. To solve this issue, the GO sheets can be
cross-linked firmly to withstand the water flux while keeping the
lamellar structure.
[0042] It is believed that there may be a large number (.about.30%)
of epoxy groups on the basal plane of GO, which may be readily
reactive with amine groups at elevated temperatures. It is also
believed that GO sheets have an extraordinary high aspect ratio
which provides a large available gas/water diffusion surface as
compared to other materials, and it has the ability to decrease the
effective pore diameter of any substrate supporting material to
minimize contaminant infusion while retaining flux rates. It is
also believed that the epoxy or hydroxyl groups increases the
hydrophilicity of the materials, and thus contributes to the
increase in water vapor permeability and selectivity of the
membrane.
[0043] In some embodiments, the optionally substituted graphene
oxide may be in the form of sheets, planes or flakes. In some
embodiments, the graphene material may have a surface area of about
100 m.sup.2/g to about 5000 m.sup.2/g, about 150 m.sup.2/g to about
4000 m.sup.2/g, about 200 m.sup.2/g to about 1000 m.sup.2/g, about
500 m.sup.2/g to 1000 m.sup.2/g, about 1000 m.sup.2/g to about 2500
m.sup.2/g, about 2000 m.sup.2/g to about 3000 m.sup.2/g, about 100
m.sup.2/g to 500 m.sup.2/g, about 400 m.sup.2/g to about 500
m.sup.2/g, or any surface area in a range bounded by any of these
values.
[0044] In some embodiments, the graphene oxide may be platelets
having 1, 2, or 3 dimensions with size of each dimension
independently in the nanometer to micron range. In some
embodiments, the graphene may have a platelet size in any one of
the dimensions, or may have a square root of the area of the
largest surface of the platelet, of about 0.05-100 .mu.m, about
0.05-50 .mu.m, about 0.1-50 .mu.m, about 0.5-10 .mu.m, about 1-5
.mu.m, about 0.1-2 .mu.m, about 1-3 .mu.m, about 2-4 .mu.m, about
3-5 .mu.m, about 4-6 .mu.m, about 5-7 .mu.m, about 6-8 .mu.m, about
7-10 .mu.m, about 10-15 .mu.m, about 15-20 .mu.m, about 50-100
.mu.m, about 60-80 .mu.m, about 50-60 .mu.m, about 25-50 .mu.m, or
any platelet size in a range bounded by any of these values.
[0045] In some embodiments, the graphene material can comprise at
least 70%, at least 75%, at least 80%, at least 85%, at least 90%,
at least 95%, at least 97%, or at least 99% of graphene material
having a molecular weight of about 5000 Daltons to about 200,000
Daltons.
[0046] In some embodiments, the optionally substituted graphene
oxide may be unsubstituted. In some embodiments, the optionally
substituted graphene oxide may comprise a non-functionalized
graphene base. In some embodiments, the graphene material may
comprise a functionalized graphene base. Functionalized graphene
includes one or more functional groups not present in graphene
oxide, such as functional groups that are not OH, COOH or epoxide
group directly attached to a C-atom of the graphene base. Examples
of functional groups that may be present in functionalized graphene
include halogen, alkene, alkyne, CN, ester, amide, or amine.
[0047] Graphene oxide includes any graphene having epoxy
substituents and saturated carbon atoms. In some embodiments, the
graphene material, such as optionally substituted graphene oxide,
may comprise a functionalized graphene base. In some embodiments,
more than: about 90%, about 80%, about 70%, about 60% about 50%,
about 40%, about 30%, about 20%, or about 10% of the optionally
substituted graphene oxide may be functionalized. In other
embodiments, the majority of optionally substituted graphene oxide
may be functionalized. In still other embodiments, substantially
all the optionally substituted graphene oxide may be
functionalized. In some embodiments, the functionalized graphene
oxide may comprise a graphene base and functional compound. In some
embodiments, the graphene base can be graphene oxide (GO),
reduced-graphene oxide (RGO), functionalized graphene oxide,
functionalized and reduced-graphene oxide, or any combination
thereof.
[0048] In some embodiments, the functionalized graphene contains
multiple types of functional groups in addition to at least one
epoxide group. In some embodiments, there is only one type of
functional groups in the functionalized graphene.
[0049] In some embodiments, the epoxide groups can be the
by-product of oxidation of the graphene to create graphene oxide.
In some embodiments, the epoxide groups are formed on the surface
of the graphene base by additional chemical reactions. In some
embodiments, the epoxide groups are formed during oxidation and
additional chemical reactions.
[0050] In some embodiments, the mass percentage of the graphene
base relative to the total composition of the graphene containing
layer can be about 1 wt % to about 95 wt %, about 10 wt % to about
95 wt %, about 30 wt % to about 80 wt %, about 20-50 wt %, about
30-50 wt %, about 40-60 wt %, about 60-80 wt %, or 80-95 wt %.
[0051] In some embodiments, the selectively permeable membrane can
comprise crosslinked, optionally substituted graphene oxide. In
some embodiments, the crosslinked, optionally substituted graphene
oxide comprises a cross-linking group covalently bonding adjacent
optionally substituted graphene oxides. In some embodiments, the
optionally substituted graphene material may be a crosslinked
graphene, where the graphene material may be crosslinked with at
least one other graphene base by a cross-linker material/bridge. it
is believed that crosslinking the graphene material can enhance the
membrane's mechanical strength and water permeable properties by
creating strong chemical bonding and wide channels between graphene
platelets to allow water to pass through the platelets easily. In
some embodiments, the graphene material may comprise crosslinked
graphene material at the graphene bases having at least about 1%,
about 5%, about 10%, about 20%, about 30%, about 40% about 50%,
about 60%, about 70%, about 80%, about 90%, about 95%, or all of
the graphene material crosslinked. In some embodiments, the
majority of the graphene material may be crosslinked. In some
embodiments, some of the graphene material may be crosslinked with
at least 5% of the graphene material crosslinked with other
graphene material. The amount of crosslinking may be estimated
based on the weight of the cross-linker as compared with the total
amount of graphene material. In some embodiments, one or more of
the graphene base(s) that are crosslinked may also be
functionalized. In some embodiments, the graphene material may
comprise both crosslinked and non-crosslinked graphene, as well as
crosslinked, functionalized, functionalized and non-crosslinked
graphene.
[0052] In some embodiments, the adjacent optionally substituted
graphene oxides can be covalently bonded to each other by an
optionally substituted phenylenediamine cross-linker. The resulting
cross-linked graphene oxide can be represented as following:
##STR00002##
[0053] wherein GO represents an optionally substituted graphene
oxide and Ph represents an optionally substituted phenylene.
[0054] In some embodiments, the phenylenediamine cross-linker is an
optionally substituted meta-phenylenediamine as shown in Formula
2:
##STR00003##
[0055] wherein R is H, or an optionally substituted carboxylic
acid. In some embodiments, the substituents can be Na, K, or Li. In
some embodiments, R is H, CO.sub.2H, CO.sub.2Li, CO.sub.2Na, and/or
CO.sub.2K. For example, the optionally substituted
meta-phenylenediamine can be:
##STR00004##
[0056] When the cross-linker is a salt, such as sodium salt,
potassium salt, or lithium salt, the hydrophilicity of the
resulting GO membrane could be increased, thereby increasing the
total water flux.
[0057] In some embodiments, a cross-linkage containing two C--N
bonds between optionally substituted graphene oxides (GOs) can be
generated by a ring opening reaction of an epoxide group in each of
the optionally substituted graphene oxide with each of the 2 amine
groups of a phenylene diamine cross-linker. Examples of the
reactions are shown in Scheme 1 below where unsubstituted
meta-phenylenediamine is used.
##STR00005##
[0058] In some embodiments, the reaction between the optionally
substituted meta-phenylenediamine and the optionally substituted
graphene oxides can form a cross-linkage between two vertically
stacked graphene oxides as represented in Scheme 2 below.
##STR00006##
[0059] In some embodiments, an optionally substituted
phenylenediamine crosslinker, such as substituted
meta-phenylenediamine or unsubstituted meta-phenylenediamine
crosslinks to a first interior carbon atom on a face of the first
optionally substituted graphene oxide platelet and to a second
interior carbon atom on a face of the second optionally substituted
graphene oxide platelet. An interior carbon atom on a face of an
optionally substituted graphene oxide platelet is a carbon atom
that is not on an outer border of the optionally substituted
graphene oxide platelet. For example, for the graphene oxide
platelet depicted below, the interior carbon atoms on the face of
the GO are shown in bold, and the remaining carbon atoms are on the
outer border of GO. The structure below is depicted only to
illustrate the principle of an interior carbon atom and does not
limit the structure of a graphene oxide.
##STR00007##
[0060] As carboxyl groups are predominantly on the edge of the
graphene oxides instead of in the body or planar interior of the
graphene where majority of the epoxide groups are located, as
depicted above, it is believed that forming C--N bonds from the
epoxide functional groups instead of forming amide bonds from
carboxylic acid groups on the GOs via reactions with crosslinkers
can result in higher degree of crosslinking between vertically
stacked graphene oxides (i.e., crosslinks to the graphene's
surfaces). Furthermore, this in-plane bonding between adjacent
graphene materials may allow for a lamellar layered GO structure to
resist dispersion in water without the need for polymers in
addition to the cross-linker.
[0061] In some embodiments, the weight ratio of MPD/GO (weight
ratio=weight of meta-phenylenediamine cross-linker/weight of
optionally substituted graphene oxide) can be about 0.05-100, about
0.1-100, about 0.2-50, about 1-10, about 1-5, about 5-10, about
5-8, about 6-10, about 6-8, or about 7 (for example 7 mg of
meta-phenylenediamine cross-linker and 1 mg of optionally
substituted graphene oxide), or any ratio in a range bounded by any
of these values.
[0062] In some embodiments, an optionally substituted graphene
oxide, crosslinked with a substituted phenylenediamine, such as a
substituted m-phenylenediamine or an unsubstituted
phenylenediamine, such as unsubstituted m-phenylenediamine, can
have about 5-60 atom %, about 5-10 atom %, about 10-15 atom %,
about 15-20 atom %, about 15-25 atom %, about 20-40 atom %, about
20-25 atom %, about 30-35 atom %, about 40-60 atom %; at least:
about 5 atom %, about 7 atom %, about 10 atom %, about 12 atom %,
about 14 atom %, about 15 atom %, about 16 atom %, about 17 atom %,
about 18 atom %, about 19 atom %, or about 20 atom %; about 21 atom
%, about 34%, or about 33%; or any atom % of oxygen atom in a range
bounded by any of these values. The percentage of crosslinking can
be determined by X-ray photoelectron spectroscopy (XPS).
[0063] In some embodiments, an optionally substituted graphene
oxide, crosslinked with a substituted phenylenediamine, such as a
substituted m-phenylenediamine or an unsubstituted
phenylenediamine, such as unsubstituted m-phenylenediamine, can
have about 20-90 atom %, about 30-80 atom %, about 40-75 atom %,
about 60-75 atom %, about 60-70 atom %, about 50-70 atom %, about
60-65 atom %, about 68%, about 63% of carbon atom, or any atom % of
carbon atom in a range bounded by any of these values. The
percentage of carbon atom can be determined by XPS.
[0064] In some embodiments, an optionally substituted graphene
oxide, crosslinked with a substituted phenylenediamine, such as a
substituted m-phenylenediamine or an unsubstituted
phenylenediamine, such as unsubstituted m-phenylenediamine, can
have a carbon to oxygen atom ratio (C/O) of about 1-5.5, about
1.5-5, about 1-5, about 1-4, about 1-3, about 2-5, about 2-4, about
2-3, about 1.6-4, about 1.7-3.5, about 1.8-3.3, about 3-4, about
3-3.5, about 1-2, about 1.5-2, about 3.2, or about 1.9, or any atom
ratio of C/O in a range bounded by any of these values.
[0065] In some embodiments, an optionally substituted graphene
oxide, crosslinked with a substituted phenylenediamine, such as a
substituted m-phenylenediamine or an unsubstituted
phenylenediamine, such as unsubstituted m-phenylenediamine, can
have less than about 20 atom %, less than about 15 atom %, less
than about 13 atom %, less than 11.5 atom %, less than about 11
atom %, less than about 10 atom %, about 10-11 atom %, about 10.9
atom %, about 1-20 atom %, about 3-6 atom %, about 5-15 atom %,
about 9-13 atom %, about 10-12 atom % of nitrogen, or any atom
percent in a range bounded by any of these values. The percentage
of nitrogen atoms, which may reflect the degree of crosslinking in
GO-MPD membrane, can be determined by XPS.
[0066] In some embodiments, an optionally substituted graphene
oxide, crosslinked with a substituted phenylenediamine, such as a
substituted m-phenylenediamine or an unsubstituted
phenylenediamine, such as unsubstituted m-phenylenediamine, can
have an interlayer distance or d-spacing of about 0.5-3 nm, about
0.6-2 nm, about 0.7-1.7 nm, about 0.8-1.5 nm, about 0.9-1.5 nm,
about 1.4-1.5 nm, about 0.9-1 nm, about 1.4 nm, about 1.43, about
0.9 nm, about 0.93 nm, or any distance in a range bounded by any of
these values. The d-spacing can be determined by x-ray powder
diffraction (XRD).
[0067] The GO-MPD layer may have any suitable thickness. For
example, some GO-MPD layers may have a thickness of about 5-200 nm,
10-100 nm, about 10-50 nm, about 10-20 nm, about 20-30 nm, about
30-40 nm, about 40-50 nm, about 50-70 nm, about 70-100 nm about 10
nm, 12 nm, about 20 nm, about 30 nm, about 40 nm, about 50 nm,
about 60 nm, about 80 nm, about 100 nm, or any thickness in a range
bounded by any of these values.
IV. Methods of Controlling Water or Solute Content
[0068] Some embodiments include methods for controlling the water
content in a fluid. In some embodiments, the fluid can comprise a
liquid. In some embodiments, the fluid can comprise a gas. In some
embodiments, the gas can comprise multiple gases including water
vapor. In some embodiments, the method controls the concentration
of water vapor in a gas. In some embodiments, the method controls
the concentration of water in a liquid. In some embodiments, the
fluid containing high concentration of water can be an unprocessed
fluid. In some embodiments, the method can provide removal of water
from the unprocessed fluid, or dehydration, to reach desired water
concentrations of the unprocessed fluid; thereby to yield a
processed fluid.
[0069] In some embodiments, a method of dehydrating of an
unprocessed fluid comprises contacting the unprocessed fluid to the
one or more of the aforementioned membranes. In some embodiments,
contacting the unprocessed fluid to the membrane can result in
allowing the water to pass through the membrane to a second fluid,
or effluent. In some embodiments, exposing the unprocessed fluid to
the membrane further comprises allowing sufficient time for the
water to pass through the membrane so that the processed fluid
achieves the desired water concentration. In some embodiments, the
unprocessed fluid is in a gaseous phase, wherein the water being
removed is water vapor. In some embodiments, the unprocessed fluid
is in the liquid phase, wherein the water being removed is liquid
water. In some embodiments, the method comprises allowing water
vapor to pass through the membrane. In some embodiments, the method
comprises allowing liquid water to pass through the membrane. In
some embodiments, the method comprises allowing a combination of
water vapor and liquid water to pass through the membrane. The
desired water concentration can be a concentration (but not limited
to), of water vapor content in an enclosed space that is below the
level which would result in condensation, mold growth, and/or
spoliation of food.
[0070] In some embodiments, passing the water through the membrane
can be by osmosis, or under the power of osmotic pressure. In some
embodiments, the method further comprises providing a pressure
gradient across the membrane to force the water passing through the
membrane to overcome osmotic back pressure.
[0071] In some embodiments, methods of extracting liquid water from
an aqueous solution containing dissolved solutes, for applications
such as pollutant removal or desalination are described. In some
embodiments, a method for removing a solute from an unprocessed
solution can comprise contacting the unprocessed solution to one or
more of the aforementioned membranes. In some embodiments, the
method further comprises passing the solution through the membrane.
In some embodiments, passing the water containing solute through
the membrane can be accomplished by supplying a means of producing
head pressure. In some embodiments, the head pressure can be
sufficient to overcome osmotic back pressure. In some embodiments,
the method comprises retaining the solutes by the membrane while
allowing water to pass through, thereby reducing the solute content
of the water. In some embodiments, the method can further comprise
providing a pressure gradient across the membrane.
[0072] In some embodiments, providing a pressure gradient across
the membrane can be achieved by producing a positive pressure in
the first reservoir, producing a negative pressure in the second
reservoir, or producing a positive pressure in the first reservoir
and producing a negative pressure in the second reservoir. In some
embodiments, a means of producing a positive pressure in the first
reservoir can be accomplished by using a piston, a pump, a gravity
drop, and/or a hydraulic ram. In some embodiments, a means of
producing a negative pressure in the second reservoir can be
achieved by applying a vacuum or withdrawing fluid from the second
reservoir.
V. Methods of Fabricating Membranes
[0073] Some embodiments include methods for making a membrane
comprising: preparing solutions of graphene oxide and a
cross-linker, applying the solutions to a substrate, and curing the
mixture on a substrate. In some embodiments, a layer-by-layer
method is used, wherein applying the solutions to the substrate
comprises applying layer by layer of a plurality of alternating
layers of graphene oxide and cross-linker to the substrate. A
non-limiting example is shown in FIG. 6. In some embodiments, a
filtering method is used, wherein applying the solutions to the
substrate comprises applying a single layer of a mixed graphene
oxide and cross-linker solution and then filtering the resulting
coating solution through the pretreated substrate. A non-limiting
example is shown in FIG. 7. In some embodiments, a mixture coating
method is used, wherein applying a single layer or a plurality of
layers of a mixed graphene oxide and cross-linker coating solution
to the pretreated substrate to form one or a plurality of layers. A
non-limiting example is shown in FIG. 8. In some embodiments, the
graphene oxide comprises optionally substituted graphene oxide. In
some embodiments, the cross-linker comprises optionally substituted
meta-phenylenediamine.
[0074] In some embodiments, the method of making a membrane
comprises: (a) mixing an optionally substituted graphene oxide and
a cross-linker to get an aqueous solution; (b) resting the solution
for 30 minutes to 12 hours to create a coating mixture; (c)
applying the coating mixture to a substrate; (d) repeating step (c)
as necessary to achieve the desired thickness or number of layers;
and (e) curing the optionally substituted graphene oxide and the
cross-linker upon the substrate at 50.degree. C. to 120.degree. C.
for 15 minutes to 2 hours so that the optionally substituted
graphene oxide and the cross-linker are covalently bonded. In some
embodiments, applying the coating mixture to the substrate can be
achieved by immersing the substrate into the coating mixture first,
and then drawing the solution onto the substrate by applying a
negative pressure gradient across the substrate until the desired
coating thickness can be achieved. In some embodiments, applying
the coating mixture to the substrate can be achieved by blade
coating, spray coating, dip coating, or spin coating. In some
embodiments, the method can further comprise rinsing the substrate
with deionized water after application of the coating mixture. In
some embodiments, the method can further comprise applying a salt
rejection layer.
[0075] Some embodiments include a method of making a membrane from
an optionally substituted meta-phenylenediamine cross-linker and an
optionally substituted graphene oxide comprising: (a) separately
applying an optionally substituted graphene oxide aqueous solution
and an optionally substituted meta-phenylenediamine cross-linker
aqueous solution to a substrate; (b) repeating step (a) as
necessary to achieve the desired thickness or number of layers; and
(c) curing the optionally substituted graphene oxide and the
cross-linker upon the substrate at 50-120.degree. C. for 15 minutes
to 2 hours so that the optionally substituted graphene oxide and
optionally substituted meta-phenylenediamine cross-linker can
covalently bond. Applying the aqueous solutions to the substrate
can be achieved by methods such as blade coating, spray coating,
dip coating, spin coating, etc. Some methods can further comprise
rinsing the substrate with deionized water after each application
of either an optionally substituted meta-phenylenediamine
cross-linker aqueous solution or an optionally substituted graphene
oxide aqueous solution. In some embodiments, the method can further
comprise applying a salt rejection layer.
[0076] In some embodiments, the method comprises optionally
pre-treating a substrate to assist in the adhesion of the graphene
oxide to the substrate. In some embodiments, pretreating the
substrate comprises treating the substrate with a dopamine
solution. In some embodiments, the dopamine solution can be
polymerized to form polydopamine on the substrate. In some
embodiments, the method comprises drying the pretreated substrate
at about 40-90.degree. C. In some embodiments, the pretreated
substrate can be dried at about 65.degree. C.
[0077] In some embodiments, the method comprises applying a
graphene oxide aqueous solution and a cross-linker aqueous solution
to the substrate. In some embodiments, applying a graphene oxide
aqueous solution and a cross-linker aqueous solution to the
substrate can be achieved by layer-by-layer method, filter method,
or mixture coating method, which results a coated substrate. In
some embodiments, the application procedure can be repeated until
the desired thickness or number of layers of the graphene oxide and
the cross-linker are achieved. In some embodiments, the thickness
or number of layers is defined so that the resulting membrane meets
the aforementioned membrane performance criteria. In some
embodiments, the desired thickness of membrane can range from about
5-2000 nm, about 5-1000 nm, about 1000-2000 nm, about 10-500 nm,
about 500-1000 nm, about 50-300 nm, about 10-200 nm, about 10-100
nm, about 10-50 nm, about 20-50 nm, or about 50-100. In some
embodiments, the number of layers can range from 1 to 250, from 1
to 100, from 1 to 50, from 1 to 20, from 1 to 15, from 1 to 10, or
from 1 to 5. This process results in a fully coated substrate. In
some embodiments, the method further comprises heating the fully
coated substrate to facilitate the crosslinking, or forming
covalent bonding, of the graphene oxide and the cross-linker. In
some embodiments, the fully coated substrate can be heated in an
oven at about 50-120.degree. C., about 40-150.degree. C., about
50-100.degree. C., about 80-90.degree. C., about 40-60.degree. C.,
about 120.degree. C., about 50.degree. C., or about 80.degree. C.
In some embodiments, the fully coated substrate can be heated for a
period of about 15 minutes to about 2 hours, about 0.5-1 h, about 1
hour, or about 30 minutes to result a membrane.
[0078] In some embodiments, the method for fabricating membranes
further comprises applying a salt rejection layer to the membrane
or a cured substrate to yield a membrane with a salt rejection
layer. In some embodiments, the salt rejection layer can be applied
by dipping the cured substrate into a solution of precursors in
mixed solvents. In some embodiments, the precursors can comprise an
amine and an acyl chloride. In some embodiments, the precursors can
comprise meta-phenylenediamine and trimesoyl chloride. In some
embodiments, the concentration of meta-phenylenediamine can range
from about 0.01-10 wt %, about 0.1-5 wt %, about 5-10 wt %, about
1-5 wt %, about 2-4 wt %, about 4 wt %, about 2 wt %, or about 3 wt
%. In some embodiments, the trimesoyl chloride concentration can
range from about 0.001 vol % to about 1 vol %, about 0.01-1 vol %,
about 0.1-0.5 vol %, about 0.1-0.3 vol %, about 0.2-0.3 vol %,
about 0.1-0.2 vol %, or about 0.14 vol %. In some embodiments, the
mixture of meta-phenylenediamine and trimesoyl chloride can be
allowed to rest for a sufficient amount of time such that
polymerization can take place before the dipping occurs. In some
embodiments, the method comprises resting the mixture at room
temperature for about 1-6 hours, about 5 hours, about 2 hours, or
about 3 hours. In some embodiments, the method comprises dipping
the cured substrate in the coating mixture for about 15 seconds to
about 15 minutes; about 5 seconds to about 5 minutes, about 10
seconds to about 10 minutes, about 5-15 minutes, about 10-15
minutes, about 5-10 minutes, or about 10-15 seconds.
[0079] In other embodiments, the salt rejection layer can be
applied by coating the cured substrate in separate solutions of
aqueous meta-phenylenediamine and a solution of trimesoyl chloride
in an organic solvent. In some embodiments, the
meta-phenylenediamine solution can have a concentration in a range
of about 0.01-10 wt %, about 0.1-5 wt %, about 5-10 wt %, about 1-5
wt %, about 2-4 wt %, about 4 wt %, about 2 wt %, or about 3 wt %.
In some embodiments, the trimesoyl chloride solution can have a
concentration in a range of about 0.001-1 vol %, about 0.01-1 vol
%, about 0.1-0.5 vol %, about 0.1-0.3 vol %, about 0.2-0.3 vol %,
about 0.1-0.2 vol %, or about 0.14 vol %. In some embodiments, the
method comprises dipping the cured substrate in the aqueous
meta-phenylenediamine for a period of about 1 second to about 30
minutes, about 15 seconds to about 15 minutes; or about 10 seconds
to about 10 minutes. In some embodiments, the method then comprises
removing excess meta-phenylenediamine from the cured substrate. In
some embodiments, the method then comprises dipping the cured
substrate into the trimesoyl chloride solution for a period of
about 30 seconds to about 10 minutes, about 45 seconds to about 2.5
minutes, or about 1 minute. In some embodiments, the method
comprises subsequently drying the cured substrate in an oven to
yield a membrane with a salt rejection layer. In some embodiments,
the cured substrate can be dried at about 45.degree. C. to about
200.degree. C. for a period about 5 minutes to about 20 minutes, at
about 75.degree. C. to about 120.degree. C. for a period of about 5
minutes to about 15 minutes, or at about 90.degree. C. for about 10
minutes. This process results in a membrane with a salt rejection
layer.
[0080] In some embodiments, the method for fabricating a membrane
further comprises subsequently applying a protective coating on the
membrane. In some embodiments, the applying a protective coating
comprises adding a hydrophilic polymer layer. In some embodiments,
applying a protective coating comprises coating the membrane with a
PVA aqueous solution. Applying a protective layer can be achieved
by methods such as blade coating, spray coating, dip coating, spin
coating, and etc. In some embodiments, applying a protective layer
can be achieved by dip coating of the membrane in a protective
coating solution for about 1 minute to about 10 minutes, about 1-5
minutes, about 5 minutes, or about 2 minutes. In some embodiments,
the method further comprises drying the membrane at a about
75.degree. C. to about 120.degree. C. for about 5 minutes to about
15 minutes, or at about 90.degree. C. for about 10 minutes. This
results in a membrane with a protective coating.
[0081] Three methods of applying an optionally substituted graphene
oxide (GO) and a cross-linker, such as an optionally substituted
meta-phenylenediamine to a substrate, are described below in more
detail.
1. Layer-by-Layer Method:
[0082] In some embodiments, a layer-by-layer method is used to
apply a graphene oxide aqueous solution and a cross-linker aqueous
solution, such as an optionally substituted meta-phenylenediamine,
to a substrate, wherein the method comprises applying the
aforementioned solutions separately layer by layer to form a
plurality of layers. In some embodiments, the number of layers can
range from 1-100, 1-50, 1-20, 1-15, 1-10, or 1-5, or is 10, wherein
a coating of graphene oxide and a coating of optionally substituted
meta-phenylenediamine cross-linker is considered a single layer. In
some embodiments, the aqueous graphene oxide solution can have a
concentration ranging from about 0.0001-0.01 wt %. In some
embodiments, the optionally substituted meta-phenylenediamine
cross-linker aqueous solution can have a concentration ranging from
0.0001-0.01 wt %. In some embodiments, applying the optionally
substituted meta-phenylenediamine cross-linker aqueous solution can
be followed by applying the graphene oxide aqueous solution. In
other embodiments, applying the graphene oxide aqueous solution can
be followed by applying the optionally substituted
meta-phenylenediamine cross-linker aqueous solution. In some
embodiments, applying the aqueous solutions can be achieved
independently by blade coating, spray coating, dip coating, spin
coating, or other methods known in the art. In some embodiments,
applying the solutions can be done by dip coating the substrate in
the respective solution for about 1 minute to about 10 minutes,
about 1-5 minutes, or about 5 minutes.
[0083] In some embodiments, the layer-by-layer method further
comprises rinsing the resulting substrate in deionized (DI) water
to remove excess material after the application of either the
graphene oxide aqueous solution and/or the optionally substituted
meta-phenylenediamine cross-linker aqueous solution to yield a
coated substrate.
2. Filtering Method:
[0084] In some embodiments, a filtering method is used to apply a
graphene oxide aqueous solution and a cross-linker aqueous solution
to a substrate, wherein the method comprises creating a mixed
coating solution, resting the coating solution to form a coating
mixture, and then filtering the coating mixture through the
substrate to generate a coated substrate.
[0085] In some embodiments, creating a mixed coating solution
comprises preparing a single mixed coating solution by mixing
aqueous solutions of a graphene oxide and a cross-linker. In some
embodiments, creating a mixed coating solution comprises mixing the
graphene oxide aqueous solution with a concentration of about
0.0001-0.01 wt %, and the cross-linker aqueous solution with a
concentration of about 0.0001-0.01 wt % to yield a coating
solution.
[0086] In some embodiments, the filtering method comprises resting
the coating solution at about room temperature for a period of
about 30 minutes to about 12 hours, about 1-6 hours, about 2-5
hours, 2-4 hours, about 5 hours, or about 3 hours. It is believed
that resting the coating solution could allow the graphene oxide
and the cross-linker to begin covalently bonding to facilitate the
generation of a final crosslinked layer. In some embodiments, the
filtering method comprises immersing the substrate in the coating
mixture. In some embodiments, the method further comprises drawing
the coating mixture into the substrate by applying a negative
pressure gradient across the substrate. It is believed that by
forcing the liquid of the coating mixture to move through the
substrate, some portion of coating mixture can be disposed on the
substrate's surface resulting in the thickness of a layer being
proportional to the duration of mixture movement through the
substrate. In some embodiments, the negative pressure gradient can
be applied through a vacuum on one side of the substrate. In some
embodiments, the duration of the drawing of the mixture can be
varied such that a desired total thickness of the resulting coating
layer is achieved, e.g., about 10-100 nm, about 10-50 nm, about 10
nm, 12 nm, about 20 nm, about 30 nm, about 40 nm, about 50 nm, or
about 100 nm.
[0087] In some embodiments, the filtering method further comprises
rinsing the resulting substrate with deionized (DI) water to remove
excess material after application of the coating mixture to yield a
coated substrate.
3. Mixture Coating Method:
[0088] In some embodiments, a mixture coating method is used to
apply a graphene oxide aqueous solution and a cross-linker aqueous
solution to a substrate, wherein the method comprises creating a
mixed coating solution, resting the coating solution to form a
coating mixture, and then applying the coating mixture to form a
plurality of layers on the substrate. In some embodiments, the
number of layers can range from 1 to about 100, where a single
mixed layer in considered a single layer.
[0089] In some embodiments, creating a mixed coating solution
comprises creating a single mixed coating solution by mixing
aqueous solutions of a graphene oxide and a cross-linker. In some
embodiments, creating a mixed coating solution comprises mixing the
graphene oxide solution with concentration of about 0.0001-0.01 wt
% and the cross-linker aqueous solution with concentration of about
0.0001-0.01 wt % to yield a coating solution.
[0090] In some embodiments, the mixture coating method comprises
resting the coating solution at about room temperature for about 30
minutes to about 12 hours, about 1-6 hours, about 5 hours, or about
3 hours. It is believed that resting the coating solution allows
the graphene oxide and the cross-linker to begin covalently bonding
to facilitate the generation of a final crosslinked layer.
[0091] In some embodiments, the mixture coating method further
comprises applying the coating mixture to the substrate. In some
embodiments, applying a coating mixture to the substrate can be
accomplished by blade coating, spray coating, dip coating, spin
coating, or other methods known in the art. In some embodiments,
applying a coating mixture can be achieved by spray coating the
substrate.
[0092] In some embodiments, the mixture coating method optionally
comprises rinsing the resulting substrate with DI water after
application of the coating mixture to remove excess materials,
which yields a coated substrate.
EMBODIMENTS
[0093] The following embodiments are specifically contemplated:
Embodiment 1
[0094] A membrane comprising:
[0095] a porous substrate; and
[0096] a graphene oxide layer comprising an optionally substituted
cross-linked graphene oxide in fluid communication with the porous
substrate;
[0097] wherein the optionally substituted cross-linked graphene
oxide comprises an optionally substituted graphene oxide and a
cross-linkage represented by Formula 1:
##STR00008##
[0098] wherein R is H, CO.sub.2H, CO.sub.2Li, CO.sub.2Na, or
CO.sub.2K.
Embodiment 2
[0099] The membrane of embodiment 1, wherein the cross-linkage
is:
##STR00009##
Embodiment 3
[0100] The membrane of embodiment 1 or 2, wherein the porous
substrate comprises a polymer or hollow fibers.
Embodiment 4
[0101] The membrane of embodiment 1, 2, or 3, wherein the
optionally substituted graphene oxide comprises platelets.
Embodiment 5
[0102] The membrane of embodiment 4, wherein the size of the
platelets are about 0.05 .mu.m to about 50 .mu.m.
Embodiment 6
[0103] The membrane of embodiment 1, 2, 3, 4, or 5, wherein the
optionally substituted cross-linked graphene oxide is about 20 atom
% to about 90 atom % carbon.
Embodiment 7
[0104] The membrane of embodiment 1, 2, 3, 4, or 5, wherein the
optionally substituted cross-linked graphene oxide material is
about 1 atom % to about 20 atom % nitrogen.
Embodiment 8
[0105] The membrane of embodiment 1, 2, 3, 4, or 5, wherein the
optionally substituted cross-linked graphene oxide material is
about 3 atom % to about 6 atom % nitrogen.
Embodiment 9
[0106] The membrane of embodiment 1, 2, 3, 4, or 5, wherein the
optionally substituted cross-linked graphene oxide material is
about 5 atom % to about 15 atom % nitrogen.
Embodiment 10
[0107] The membrane of embodiment 1, 2, 3, 4, or 5, wherein the
optionally substituted cross-linked graphene oxide material is
about 9 atom % to about 13 atom % nitrogen.
Embodiment 11
[0108] The membrane of embodiment 1, 2, 3, 4, or 5, wherein the
optionally substituted cross-linked graphene oxide material is
about 10 atom % to about 12 atom % nitrogen.
Embodiment 12
[0109] The membrane of embodiment 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or
11, wherein the optionally substituted cross-linked graphene oxide
is prepared by reacting an optionally substituted
meta-phenylenediamine (MPD) with an optionally substituted graphene
oxide (GO), wherein the weight ratio of optionally substituted
meta-phenylenediamine to optionally substituted graphene oxide
(MPD/GO) is in a range of about 0.1 to about 100.
Embodiment 13
[0110] The membrane of embodiment 12, wherein the weight ratio of
optionally substituted meta-phenylenediamine to optionally
substituted graphene oxide (MPD/GO) is in a range of 1 to 10.
Embodiment 14
[0111] The membrane of embodiment 13, wherein the weight ratio of
optionally substituted meta-phenylenediamine to optionally
substituted graphene oxide (MPD/GO) is about 1, about 3, or about
7.
Embodiment 15
[0112] The membrane of embodiment 13, wherein the weight ratio of
optionally substituted meta-phenylenediamine to optionally
substituted graphene oxide (MPD/GO) is about 3, or about 7.
Embodiment 16
[0113] The membrane of embodiment 13, wherein the weight ratio of
optionally substituted meta-phenylenediamine to optionally
substituted graphene oxide (MPD/GO) is about 7.
Embodiment 17
[0114] The membrane of embodiment 1, 2, 3, 4, 5, 6, 7, 8, 9, 10,
11, 12, 13, 14, 15, or 16, wherein the optionally substituted
graphene oxide is a non-functionalized graphene oxide,
reduced-graphene oxide, functionalized graphene oxide,
functionalized and reduced-graphene oxide, or a combination
thereof.
Embodiment 18
[0115] The membrane of embodiment 1, 2, 3, 4, 5, 6, 7, 8, 9, 10,
11, 12, 13, 14, 15, or 16, further comprising a salt rejection
layer.
Embodiment 19
[0116] The membrane of embodiment 18, wherein the salt rejection
layer is disposed on the graphene oxide layer.
Embodiment 20
[0117] The membrane of embodiment 18 or 19, wherein the salt
rejection layer comprises a polyamide prepared by reacting a
meta-phenylenediamine with trimesoyl chloride.
Embodiment 21
[0118] The membrane of embodiment 1, 2, 3, 4, 5, 6, 7, 8, 9, 10,
11, 12, 13, 14, 15, 16, 17, 18, 19, or 20, wherein the membrane
further comprises a protective layer, wherein the protective layer
comprises a hydrophilic polymer.
Embodiment 22
[0119] The membrane of embodiment 1, 2, 3, 4, 5, 6, 7, 8, 9, 10,
11, 12, 13, 14, 15, 16, 17, 18, 19, 20, or 21, wherein the
thickness of the graphene oxide layer is about 5 nm to about 200
nm.
Embodiment 23
[0120] The membrane of embodiment 22, the thickness of the graphene
oxide layer is about 10 nm to about 100 nm.
Embodiment 24
[0121] The membrane of embodiment 1, 2, 3, 4, 5, 6, 7, 8, 9, 10,
11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, or 23, comprising 1
to about 100 graphene oxide layers.
Embodiment 25
[0122] The membrane of embodiment 19, comprising 1 layer to 10
layers of coating of GO and MPD.
Embodiment 26
[0123] A method for dehydrating an unprocessed fluid, comprising
exposing the unprocessed fluid to the membrane of embodiment 1, 2,
3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20,
21, 22, 23, 24, or 25.
Embodiment 27
[0124] A method for removing a solute from an unprocessed solution,
comprising exposing the unprocessed solution to the membrane of
embodiment 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16,
17, 18, 19, 20, 21, 22, 23, 24, or 25.
Embodiment 28
[0125] The method of embodiment 27, further comprising passing the
unprocessed solution through the membrane.
Embodiment 29
[0126] The method of embodiment 28, wherein passing the unprocessed
solution through the membrane is achieved by applying a pressure
gradient across the membrane.
Embodiment 30
[0127] A method of making a membrane, comprising: [0128] (a)
resting a solution comprising an optionally substituted graphene
oxide and a water soluble cross-linker for about 30 minutes to
about 12 hours to create a coating mixture; [0129] (b) applying the
coating mixture to a substrate; [0130] (c) repeating step (b) as
necessary to achieve the desired thickness or number of layers; and
[0131] (d) curing the optionally substituted graphene oxide and
water soluble cross-linker upon the substrate at about 50.degree.
C. to about 120.degree. C. for about 15 minutes to about 2 hours so
that the optionally substituted graphene oxide and the water
soluble cross-linker are covalently bonded.
Embodiment 31
[0132] The method of embodiment 30, wherein the applying the
coating mixture to the substrate comprises immersing the substrate
into the coating mixture and then drawing the coating mixture into
the substrate by applying a negative pressure gradient across the
substrate until the desired coating thickness is achieved.
Embodiment 32
[0133] The method of embodiment 30, wherein the applying the
coating mixture to the substrate comprises blade coating, spray
coating, dip coating, or spin coating.
Embodiment 33
[0134] The method of embodiment 30, 31, or 32, further comprising
rinsing the substrate with deionized water after application of the
coating mixture.
Embodiment 34
[0135] A method of making a membrane from an optionally substituted
meta-phenylenediamine cross-linker and an optionally substituted
graphene oxide, comprising: [0136] (a) separately applying to a
substrate: 1) an aqueous solution of an optionally substituted
graphene oxide, and 2) an aqueous solution of an optionally
substituted meta-phenylenediamine cross-linker; [0137] (b)
repeating step (a) as necessary to achieve the desired thickness or
number of layers; and [0138] (c) curing the optionally substituted
graphene oxide and cross-linker upon the substrate at about
50.degree. C. to about 120.degree. C. for about 15 minutes to about
2 hours until the optionally substituted graphene oxide and
optionally substituted meta-phenylenediamine cross-linker are
covalently bonded.
Embodiment 35
[0139] The method of embodiment 34, wherein step (a) is achieved by
blade coating, spray coating, dip coating, or spin coating of one
or both of the aqueous solutions.
Embodiment 36
[0140] The method of embodiment 34 or 35, further comprising
rinsing the substrate with deionized water after each application
of aqueous solution.
Embodiment 37
[0141] The method of embodiment 30, 31, 32, 33, 34, 35 or 36,
further comprising applying a salt rejection layer.
Embodiment 38
[0142] The method of embodiment 37, wherein the salt rejection
layer comprises a polyamide prepared by a method comprising
reacting a meta-phenylenediamine with trimesoyl chloride.
EXAMPLES
[0143] It has been discovered that embodiments of the selectively
permeable membranes described herein have improved permeability
resistance to both oxygen gas and vapor with acceptable material
properties as compared to other selectively permeable membranes.
These benefits are further demonstrated by the following examples,
which are intended to be illustrative of the disclosure, but are
not intended to limit the scope or underlying principles in any
way.
Example 1.1.1: Synthesis of Graphene Oxide Dispersion (GC-1)
[0144] GO Preparation: GO was prepared from graphite using the
modified Hummers method. Graphite flakes (2.0 g) (Sigma Aldrich,
St. Louis, Mo., USA, 100 mesh) were oxidized in a mixture of 2.0 g
of NaNO.sub.3 (Aldrich), 10 g KMnO.sub.4 of (Aldrich) and 96 mL of
concentrated H.sub.2SO.sub.4 (Aldrich, 98%) at 50.degree. C. for 15
hours. The resulting paste like mixture was poured into 400 g of
ice followed by adding 30 mL of hydrogen peroxide (Aldrich, 30%).
The resulting solution was then stirred at room temperature for 2
hours to reduce the manganese dioxide, then filtered through a
filter paper and washed with DI water. The solid was collected and
then dispersed in DI water with stirring, centrifuged at 6300 rpm
for 40 minutes, and the aqueous layer was decanted. The remaining
solid was then dispersed in DI water again and the washing process
was repeated 4 times. The purified GO was then dispersed in DI
water under sonication (power of 20 W) for 2.5 hours to get the GO
dispersion (0.4 wt %) as GC-1.
Example 2.1.1: Preparation of a Membrane by Filtration
[0145] Substrate Pretreatment:
[0146] A supporting membrane, polyamide (Nylon) (0.1 .mu.m pore,
Aldrich), was used as a substrate; and it was dip-coated in a
dopamine solution (2 g/L dopamine (Aldrich) and 1.3 g/L of Trizma
base buffer (Aldrich)) at pH 8.5. The dopamine was polymerized to
form polydopamine on the substrate. Then, the polydopamine-coated
substrate was dried in oven (DX400, Yamato Scientific Co., Ltd.
Tokyo, Japan) at 65.degree. C. This process resulted in a
pre-treated substrate.
[0147] GO-MPD Application/Filtration Method:
[0148] First the GO dispersion, GC-1, was diluted with DI water to
create a 0.1 wt % GO aqueous solution. Second, a 0.1 wt % of
meta-phenylenediamine (MPD) aqueous solution was prepared by
dissolving an appropriate amount of MPD (Aldrich) in DI water.
Then, a coating mixture was created by dissolving the aqueous
solutions of 0.1 wt % MPD and 0.1 wt % GO in DI water at a weight
ratio of 1:1. The resulting solution was then rested for about 3
hours, or normally until the GO and amine have finished reacting.
The resulting coating mixture was then filtered through the
pretreated substrate under vacuum to draw the solution through the
substrate. After solvent was filtered through the substrate, the
resulting membrane with the mixture deposited on its surface was
then placed in an oven (DX400, Yamato Scientific) at 80.degree. C.
for 30 minutes to facilitate further crosslinking. This process
generated a membrane without a salt rejection layer
(MD-1.1.1.1.1).
Example 2.1.1.1: Preparation of Additional Membranes by
Filtration
[0149] Additional membranes MD-1.1.1.1.2 through MD-1.1.2.1.4 were
constructed using the methods similar to Example 2.1.1, with the
exception that parameters were varied for the specific membranes as
shown in Table 1. Specifically, the substrate [e.g., polysulfone
(PSF), polyether sulfone (PES), polyamide (Nylon), polyimide (PI),
or polyvinylidene fluoride (PVDF)], layer thickness, cross-linker
[e.g., MPD or 3, 5-diaminobenzoic acid (MPD w/ COOH) (Aldrich)],
and mass ratio of cross-linker to GO were varied.
TABLE-US-00001 TABLE 1 Membranes Made without a Salt Rejection
Layer. Mass ratio of Coating Crosslinker Thickness Membrane Method
Crosslinker to GO Substrate Material (nm or lyr) MD-1.1.1.1.1
Filtration MPD 1:1 Nylon 0.1 .mu.m Pore 12 MD-1.1.1.1.2 Filtration
MPD 1:1 PVDF 12 MD-1.1.1.1.3 Filtration MPD 1:1 PES 36 MD-1.1.1.1.4
Filtration MPD 1:1 PI 36 MD-1.1.1.1.5 Filtration MPD 1:1 Nylon 0.1
.mu.m Pore 20 MD-1.1.1.1.6 Filtration MPD 3:1 Nylon 0.1 .mu.m Pore
20 MD-1.1.1.1.7 Filtration MPD 7:1 Nylon 0.1 .mu.m Pore 20
MD-1.1.1.1.8 Filtration MPD 7:1 Nylon 0.45 .mu.m Pore 40
MD-1.1.1.1.9 Filtration MPD 7:1 Nylon 0.45 .mu.m Pore 100
MD-1.1.1.1.10 Filtration MPD 7:1 Stretched PP 16 MD-1.1.1.1.11
Filtration MPD 7:1 Stretched PP 26 MD-1.1.1.1.12 Filtration MPD 7:1
Stretched PP 40 MD-1.1.1.1.13 Filtration MPD 7:1 Stretched PP 60
MD-1.1.1.1.14 Filtration MPD 7:1 Stretched PP 80 MD-1.1.2.1.1
Filtration MPD w/COOH 3:1 Nylon 0.1 .mu.m Pore 20 MD-1.1.2.1.2
Filtration MPD w/COOH 7:1 Nylon 0.1 .mu.m Pore 20 MD-1.1.2.1.3
Filtration MPD w/COOH 7:1 Stretched PP 40 MD-1.1.2.1.4 Filtration
MPD w/COOH 7:1 Stretched PP 80 MD-1.2.1.1.1 Mixture MPD 1:1 Nylon
0.1 .mu.m Pore 20 (Prop.) MD-1.3.1.1.1 Layer by Layer MPD 1:1 PSF 1
layer.sup. MD-1.3.1.1.2 Layer by Layer MPD 1:1 PSF 5 layers
MD-1.3.1.1.3 Layer by Layer MPD 1:1 PSF 10 layers Notes: [1]
Numbering Scheme is MD-J.K.L.M.N, wherein J = 1--no salt rejection
layer; 2--salt rejection layer K = 1--by filtration method; 2--by
mixture-coating method, 3--by layer by layer method L = 1--MPD;
2--MPD w/COOH; M = 1--no protective coating; 2--with protective
coating N = membrane # within category [2] All PP and PVA/PP
substrates are approximately 30 .mu.m thick; whereas the nylon
substrate varies from 65 to 125 .mu.m thick. [3] (Prop.)--Indicates
a proposed example.
Example 2.1.2: Preparation of a Membrane by Mixture Coating
(Proposed)
[0150] The GO preparation and substrate preparation can use the
same method as that in Example 2.1.1 with the exception of the
GO-MPD preparation method, which varies as described below.
[0151] GO-MPD Application/Mixture Coating Method (Dip Coating):
[0152] First, the GO dispersion, GC-1, can be diluted with DI water
to create a 0.1 wt % GO aqueous solution. Second, a 0.1 wt % MPD
aqueous solution can be prepared by dissolving an appropriate
amount of MPD (Aldrich) in DI water. Then, a coating solution can
be created by dissolving the aqueous solutions of 0.1 wt % GO and
0.1% MPD in DI water at a weight ratio of 1:1. The resulting
coating solution can be rested for about 3 hours, or normally until
the GO and the amine have been pre-reacted. This process can result
in a coating mixture.
[0153] The polydopamine-coated substrate can be then coated with
the above described coating mixture by dipping the substrate in the
coating mixture. Next, the substrate can be rinsed thoroughly in DI
water to remove any excess particles. The aforementioned process
can be repeated, that is dipping the substrate into the coating
mixture and then rinsing with DI water for a number of cycles to
get the desired number of layers or thickness of GO and MPD. The
resulting membrane can be then kept in an oven (DX400, Yamato
Scientific) at 80.degree. C. for 30 minutes to facilitate further
crosslinking. This process can result in a membrane without a salt
rejection layer.
Example 2.1.3: Preparation of a Membrane Via Layer-by-Layer
Application (MD-1.3.1.1.1)
[0154] The GO preparation and substrate preparation used the same
method as that in Example 2.1.1 with the exception that the GO-MPD
application method varied as described below and polysulfone (PSF)
was used as a substrate.
[0155] GO-MPD Application/Layer-by-Layer Method:
[0156] A 0.1 wt % MPD aqueous solution was prepared by dissolving
an appropriate amount of MPD (Aldrich) in DI water. A 0.1 wt % GO
aqueous solution was made by diluting the GO dispersion, GC-1 in DI
water. The polydopamine-coated substrate was then soaked in 0.1 wt
% MPD aqueous solution for 5 minutes, rinsed thoroughly with DI
water, and subsequently soaked in 0.1 wt % GO solution for 5
minutes to attach the first layer of GO. Next, the membrane was
rinsed with DI water to remove excess GO. This process can be
repeated, alternately dipping the substrate into MPD and GO
solution, for a number of cycles to get the desired number of
layers of GO and MPD. In this particular example, the membrane with
one layer was prepared. The resulting membrane was then kept in an
oven (DX400, Yamato Scientific) at 80.degree. C. for 30 minutes to
facilitate further crosslinking. This process resulted in a
membrane without a salt rejection layer (MD-1.3.1.1.1).
Example 2.1.3.1: Preparation of Additional Membranes Via
Layer-by-Layer Application
[0157] The sensitivity of the number of layers was examined. For
membranes MD-1.3.1.1.2 and MD-1.3.1.1.3, the method used was the
same as that in Example 2.1.3, with the exception that the number
of layers was varied as shown in 2 or specifically from 1 layer up
to 10 layers respectively.
Example 2.2.1: Addition of a Salt Rejection Layer to a Membrane
[0158] To enhance the salt rejection capability of the membrane,
MD-1.1.1.1.1 was additionally coated with a polyamide salt
rejection layer. A 3.0 wt % MPD aqueous solution was prepared by
diluting an appropriate amount of MPD (Aldrich) in DI water. A 0.14
vol % trimesoyl chloride solution was made by diluting an
appropriate amount of trimesoyl chloride (Aldrich) in isoparrifin
solvent (Isopar E & G, Exxon Mobil Chemical, Houston Tex.,
USA). The GO-MPD coated membrane was then dipped in the aqueous
solution of 3.0 wt % of MPD (Aldrich) for a period of 10 seconds to
10 minutes depending on the substrate and then removed. Excess
solution remaining on the membrane was then removed by air dry.
Then, the membrane was dipped into the 0.14 vol % trimesoyl
chloride solution for 10 seconds and removed. The resulting
assembly was then dried in an oven (DX400, Yamato Scientific) at
120.degree. C. for 3 minutes. This process resulted in a membrane
with a salt rejection layer (MD-2.1.1.1.1).
Example 2.2.1.1: Addition of a Salt Rejection Layer to Additional
Membranes
[0159] Additional membranes, MD-1.1.1.1.2 through MD-1.1.1.1.7,
MD-1.1.2.1.1, MD-1.1.2.1.2 and MD-2.3.1.1.3, were coated with a
salt rejection layer using a similar procedure as that in Example
2.2.1. The resulting configurations of the new membranes created
are presented in Table 2.
TABLE-US-00002 TABLE 2 Membranes with a Salt Rejection Layer. Mass
Ratio of Coating Crosslinker Thickness Membrane Method Crosslinker
to GO Substrate Material (nm or layer) MD-2.1.1.1.1 Filtration MPD
1:1 Nylon 0.1 .mu.m Pore 12 MD-2.1.1.1.2 Filtration MPD 1:1 PVDF 12
MD-2.1.1.1.3 Filtration MPD 1:1 PES 36 MD-2.1.1.1.4 Filtration MPD
1:1 PI 36 MD-2.1.1.1.5 Filtration MPD 1:1 Nylon 0.1 .mu.m Pore 20
MD-2.1.1.1.6 Filtration MPD 3:1 Nylon 0.1 .mu.m Pore 20
MD-2.1.1.1.7 Filtration MPD 7:1 Nylon 0.1 .mu.m Pore 20
MD-2.1.2.1.1 Filtration MPD w/COOH 3:1 Nylon 0.1 .mu.m Pore 20
MD-2.1.2.1.2 Filtration MPD w/COOH 7:1 Nylon 0.1 .mu.m Pore 20
MD-2.3.1.1.3 Layer by Layer MPD 1:1 PSF 10 layers Notes: [1]
Numbering Scheme is MD-J.K.L.M.N, wherein J = 1--no salt rejection
layer; 2--salt rejection layer K = 1--filtration method;
2--mixture-coating method; 3--layer by layer method L = 1--MPD;
2--MPD w/COOH; M = 1--no protective coating; 2--protective coating
N = membrane # within category [2] All PP and PVA/PP substrates are
approximately 30 .mu.m thick; whereas the nylon substrate varies
from 65 to125 .mu.m in thickness. [3] (Prop.)--Represents a
proposed example.
Example 2.2.2: Preparation of a Membrane with a Protective
Coating
[0160] A sample of MD-1.3.1.1.3, a 10-layer membrane prepared via
the layer-by-layer coating of GO and MPD on a substrate of PSF, was
coated with a protective resin to yield MD-1.3.1.2.3, as shown in
FIG. 9. This coating was made by known methods in the art.
[0161] Other selected membranes can be coated with protective
layers. First, a PVA solution of 2.0 wt % can be prepared by
stirring 20 g of PVA (Aldrich) in 1 L of DI water at 90.degree. C.
for 20 minutes until all granules dissolve. The solution was then
cooled to room temperature. The selected substrates can be immersed
in the solution for 10 minutes and then removed. Excess solution
remaining on the membrane can then be removed by paper wipes. The
resulting assembly can then be dried in an oven (DX400, Yamato
Scientific) at 90.degree. C. for 30 minutes. A membrane with a
protective coating can thus be obtained.
Comparative Example 2.1.1: Preparation of Comparative Membranes
[0162] Comparative membranes (CMDs), CMD-1.1 through CMD-1.2 were
created using commercially available substrate components of
polysulfone membrane (PSF) (Sterlitech Corporation, Kent, Wash.,
USA) and polypropylene (PP) filtration membrane (Celgard LLC,
Charlotte, N.C., USA). CMD-1.3, a PVA/PP membrane, was created by
immersing a PP filtration membrane in a PVA/water solution
(Aldrich) for 10 minutes and then drying the resulting membrane in
an oven (DX400, Yamato Scientific) at 90.degree. C. for about 30
minutes.
Comparative Example 2.1.2: Preparation of Additional Comparative
Membranes
[0163] Comparative membranes CMD-2.1.1 through CMD-2.2.2 were made
using methods similar to those used in Example 2.1.1 with the
variations outlined in Table 3.
TABLE-US-00003 TABLE 3 Comparative Membranes. Mass Ratio of Coating
Crosslinker Substrate Thickness Membrane Method Crosslinker to GO
Material (nm) CMD-1.1 n/a -- -- PSF -- CMD-1.2 n/a -- -- Stretched
PP -- CMD-1.3 n/a -- -- Stretched PP/PVA n/a CMD-2.1.1 Filtration
EDA 1:1 Nylon 0.1 .mu.m Pore 20 CMD-2.1.2 Filtration EDA 3:1 Nylon
0.1 .mu.m Pore 20 CMD-2.1.3 Filtration EDA 7:1 Nylon 0.1 .mu.m Pore
20 CMD-2.2.1 Filtration PPD 3:1 Nylon 0.1 .mu.m Pore 20 CMD-2.2.2
Filtration PPD 7:1 Nylon 0.1 .mu.m Pore 20 Notes: [1] All PP and
PVA/PP substrates are approximately 30 .mu.m thick; whereas the
nylon substrate varies from 65 to 125 .mu.m in thickness.
Example 3.1: Membrane Characterization
[0164] TEM Analysis:
[0165] Membrane MD-1.1.1.1.1 was analyzed with a Transmission
Electron Microscope (TEM). The TEM procedures are similar to those
known in the art. The TEM cross-section analysis of GO-MPD membrane
is shown in FIG. 9. The membrane thickness is about 5-10 nm and is
continuous along the substrate.
[0166] XPS Analysis:
[0167] Membrane MD-1.1.1.1.1 was analyzed by X-ray photoelectron
spectroscopy (XPS) to determine the relative distribution of the
atomic spectra. The procedures for XPS are similar to those known
in the art. The XPS analysis, shown in Table 4, indicates a
significant increase of nitrogen in the GO-MPD membrane, due to the
cross-linking of MPD with GO, and partial reduction of oxygen as
the epoxide was significantly reduced.
TABLE-US-00004 TABLE 4 XPS Analysis Result of GO and GO-MPD
Membranes. Samples C N O S Cl Ref (GO) 65.2 -- 34.0 0.8 -- GO-MPD
67.5 10.9 20.8 0.5 0.3 GO-MPD 62.6 4.4 32.5 0.5 -- w/COOH
[0168] XRD Analysis:
[0169] The basic GO-MPD membrane structure in a representative
MD-1.1.1.1.1 membrane was characterized by X-ray Diffraction (XRD)
as shown in FIG. 10. The structure was the same as MD-1.1.1.1.1
except that the substrate was a nylon substrate to facilitate
testing. The d-spacing of the lattice was calculated by Bragg
equation: 2d sin .theta.=n.lamda., which shows that the GO-MPD has
a longer interlayer distance than unmodified GO, see Table 5. The
increase in interlayer distance is likely due to the effect of the
MPD cross-linking.
TABLE-US-00005 TABLE 5 Interlayer Distance of GO-MPD Membrane.
2.theta. (deg) D-spacing (nm) GO 9.5 0.93 GO-MPD 6.16 1.43
[0170] IR Analysis:
[0171] An infrared (IR) analysis of GO-MPD structure in the
MD-1.1.1.1.1 membrane was performed using methods known in the art.
The IR analysis, as shown in FIG. 11 for both GO and GO-MPD
indicating the formation of C--N and N--H bonds. The existence of
the C--N and N--H bonds suggests that cross-linking has
occurred.
Example 4.1: Dehydration/Water Separation Performance Testing of
Selected Membranes
[0172] Dehydration Characteristics--Water Vapor Permeability
Testing:
[0173] The water vapor permeability of the membranes was tested.
For the gas leakage, Nitrogen was chosen to mimic air.
[0174] A sample diagram of the setup is shown in FIG. 12. The test
setup consisted of a cross-flow test cell (CF016A, Sterlitech)
which forms two plenums on either side, each with its own inlet and
an outlet. The membrane being measured was placed in the 45
mm.times.45 mm testing chamber and sandwiched between the two
halves of the test cell to create two sealed plenums when the
shells are mated, each plenum in fluid communication only through
the membrane. Then the inlets and outlets were chosen such that the
fluid flow in each plenum was in a counter-flow configuration. The
wet N.sub.2 gas was sent into the setup from the wet side, the
first side, and then exited with some residual water vapor and gas
permeated from the membrane sample into the second side, the dry
side. The sweep or dry N.sub.2 gas was sent into the setup and then
vented, with the wet gas being entrained from the membrane.
Humidity and Temperature were measured at three positions: input
and output on the wet N.sub.2 gas side, and output on the dry
N.sub.2 gas side using a Humidity/Temperature Transmitters
(RHXL3SD, Omega Engineering, Inc., Stamford, Conn., USA). In
addition, the flow rate was also measured for both wet and dry
sides by two Air Flow Sensors (FLR1204-D, Omega). The gas pressure
was also measured on both the wet and dry side by two Digital
Pressure Gauges (Media Gauge MGA-30-A-9V-R, SSI Technologies, Inc.,
Janesville, Wis., USA).
[0175] For the measurements, selected membranes were placed in the
setup and the wet side inlet was set to a relative humidity of
between about 80% to about 90%. The dry side inlet had a relative
humidity of 0%. The upstream pressure for the wet gas stream was
set to 0.13 psig. The upstream pressure for the dry gas stream was
set to 0.03 psig. From the instruments, the water vapor pressure
and absolute humidity at the three measurement stations were
derived/calculated from the measured temperature and humidity data.
Then the water vapor transmission rate was derived from the
difference in absolute humidity, flow rate, and exposed area of the
membrane. Lastly, the water vapor permeability was derived from the
water vapor transmission rate and the water vapor pressure
difference between the two plenums. The nitrogen flow rate was
derived from the dry N.sub.2 output and the wet N.sub.2 inputs as
well as the water vapor transmission rate.
[0176] Dehydration Characteristics--Nitrogen Leakage Testing:
[0177] The gas leakage of the membranes was tested. Nitrogen was
chosen to mimic air. For these tests, the same test setup was used
as that in the Water Vapor Permeability testing with the exception
that the dry N.sub.2 air inlet was closed and the dry N.sub.2
outlet was, instead of being vented to atmosphere, vented to a flow
measurement instrument (D800286 Gilibrator-2 Standard Air Flow
Calibrator; Sensidyne, St. Petersburg, Fla., USA) with a normal
test cell (20 cc to 6 LPM, Sensidyne) or a low-flow test cell (1
cc/min to 250 cc/min, Sensidyne) to measure the flow leakage
through the membrane. For N.sub.2 flow rates at about 1 cc/min or
below, a 0.5 mL manual bubble flow meter was used (#23771,
Aldrich), which has a range of about 0.03 cc/min to about 5 cc/min,
to determine the leakage rate instead of using the flow measurement
instrument described above.
[0178] For the measurements, the selected membranes were placed in
the setup and the wet side inlet was set to a relative humidity of
between about 80% to about 90%. The dry side inlet was closed to
seal off the portion upstream of the flow measurement instrument so
that only gas leaked through the membrane would go to the flow
measurement instrument. The upstream pressure for the wet gas
stream was set to 0.13 psig and the leakage of the N.sub.2 through
the membrane was measured.
TABLE-US-00006 TABLE 6 Water Vapor Permeability Measurements for
Various Membranes. Coating H.sub.2O vapor N.sub.2 Gas Thickness
permeability Flow Rate Membrane (nm) (.mu.g/m.sup.2 s Pa) (cc/min)
GO-MPD 1:7 on Nylon 0.1 20 nm 46.7 -- .mu.m Pore (MD-1.1.1.1.7)
GO-MPD 1:7 on Nylon 0.45 40 nm 49.4 27.25 .mu.m Pore (MD-1.1.1.1.8)
GO-MPD 1:7 on Nylon 0.45 100 nm 51.2 5.45 .mu.m Pore (MD-1.1.1.1.9)
GO-MPD w/COOH 1:7 on 20 nm 44.5 -- Nylon 0.1 .mu.m Pore (MD-
1.1.2.1.2)
[0179] As shown in Table 6, water permeability can be maintained by
using larger substrate pores. Additionally, for the larger
substrates, the effect of defects due to the large pore sizes can
be minimized by increasing the GO-MPD layer thickness resulting in
high water vapor permeability with the exclusion of other
gases.
TABLE-US-00007 TABLE 7 Vapor Permeability Measurements for Various
Membranes (without Salt Rejection Layer). Coating H.sub.2O vapor
N.sub.2 Gas Thickness permeability Flow Rate Membrane (nm)
(.mu.g/m.sup.2 s Pa) (cc/min) Stretched PP Substrate -- 55.1 75.29
(CMD-1.2) Stretched PP/PVA -- 51.8 90.00 Substrate (CMD-1.3) 1:7
GO-MPD on Stretched 16 nm 44.9 2.67 PP (MD-1.1.1.1.10) 1:7 GO-MPD
on Stretched 26 nm 51.2 0.10 PP (MD-1.1.1.1.11) 1:7 GO-MPD on
Stretched 40 nm 38.9 0.19 PP (MD-1.1.1.1.12) 1:7 GO-MPD on
Stretched 60 nm 41.4 0.28 PP (MD-1.1.1.1.13) 1:7 GO-MPD on
Stretched 80 nm 36.9 0.24 PP (MD-1.1.1.1.14) 1:7 GO-MPD w/COOH on
40 nm 32.3 0.24 Stretched PP (MD- 1.1.2.1.3) 1:7 GO-MPD w/COOH on
80 nm 28.4 0.14 Stretched PP (MD- 1.1.2.1.4)
[0180] As shown in Table 7, the GO-MPD coated PP substrates
exhibited a distinct drop in permeability of other gases such as
N.sub.2 besides water when the thickness was above 16 nm.
Additionally, the water vapor permeability remains at least 50% of
that of the uncoated substrates (CMD-1.2 or CMD-1.3 membrane)
demonstrating the ability of the membrane to reject other gases
while maintaining water vapor flux across the membrane.
Example 4.2: Reverse Osmosis Performance Testing of Selected
Membranes
[0181] Water Flux and Salt Rejection Testing:
[0182] The water flux of GO-MPD membrane coated on varies porous
substrates were found to be very high, which is comparable with
porous polysulfone substrate widely used in current reverse osmosis
membranes.
[0183] For the membranes made via layer-by-layer method, the
sensitivity of water flux relates to the numbers of layers in the
membranes was investigated, and the results are shown in Table 8.
As shown in the Table 8, there is no appreciable variation on water
flux as the result of the increase in the number of GO-MPD
layers.
TABLE-US-00008 TABLE 8 Water Flux and Salt Rejection of GO-MPD
Membranes Prepared by Layer-By-Layer (LBL) Method DI water DI water
DI water 1500 ppm NaCl NaCl flux @50 flux @100 flux @200 Flux @225
Rejection. psi (GFD) psi (GFD) psi (GFD) psi (GFD) (%) PSF
(dopamine coated) 289 -- -- -- -- (CMD-1.1) GP-MPD on PSF 136 267
457 307 16 (dopamine coated) 1 layer (MD-1.3.1.1.1) GO-MPD on PSF
39 152 258 323 12 (dopamine coated) 5 layers (MD-1.3.1.1.2) GO-MPD
on PSF 122 213 335 223 16 (dopamine coated) 10 layers
(MD-1.3.1.1.3)
[0184] For the filter method, the various membranes created were
examined to see the variations on water flux under the same head
pressure. The results are presented in Table 9 which shows that for
the membrane (ME-1.1.1.1.2), even with coating of GO-MPD substrate,
the water flux can exceed an uncoated PSF membrane (CMD-1.1).
TABLE-US-00009 TABLE 9 Water Flux Data of GO-MPD Membranes Prepared
by Filtration Method Versus Thickness and Substrate Differences.
PSF (no GO-MPD on GO-MPD on GO-MPD on GO-MPD on coating) Nylon
substrate PVDF substrate PES substrate PI substrate (CMD-1.1)
(MD-1.1.1.1.1) (ME-1.1.1.1.2) (ME-1.1.1.1.3) (ME-1.1.1.1.4) Coating
Thickness n/a 12 nm 12 nm 36 nm 36 nm Water flux @30 psi (GFD) 243
208 854 199 64
[0185] To test the salt rejection capability, the reverse osmosis
membrane comprising a 10-layer GO-MPD coated substrate (ME-3C) was
first tested to determine the membrane's ability to reject salt and
retain adequate water flux. As seen in Table 10, the membrane has
demonstrated high NaCl salt rejection and good water flux. In
addition, the salt rejection capability of membranes with various
cross-linkers were also tested to determine the effect of different
cross-linker materials and compared to the comparative examples to
determine the relative effect of the new cross-linker
materials.
TABLE-US-00010 TABLE 10 Performance of Selected Polyamide Coated
Membranes. 1500 ppm NaCl Water Flux Membrane Rejection (%) (GFD) PA
+ 10-layer 95.99 16.8 1:1 GO-MPD (MD-2.3.1.1.3) PA + 20 nm Filtered
76 4.6 1:1 GO-MPD Unsub. (MD-2.1.1.1.5) PA + 20 nm Filtered 30 9.9
1:1 GO-EDA (CMD-2.1.1) PA + 20 nm Filtered 91 3.7 3:1 GO-MPD Unsub.
(MD-2.1.1.1.6) PA + 20 nm Filtered 93 7.0 3:1 GO-MPD w/COOH
(MD-2.1.2.1.1) PA + 20 nm Filtered 59 5.7 3:1 GO-PPD (CMD-2.2.1) PA
+ 20 nm Filtered 94 2.9 7:1 GO-MPD (MD-2.1.1.1.7) PA + 20 nm
Filtered 95.7 6.4 7:1 GO-MPD w/COOH (MD-2.1.2.1.2) PA + 20 nm
Filtered 81 2.5 7:1 GO-EDA (CMD-2.1.3) PA + 20 nm Filtered 35 10.7
7:1 GO-PPD (CMD-2.2.2) Notes: [1] PA: polyamide coating (salt
rejection layer) [2] Cell Testing Conditions: pressure: 225 psi,
temperature: 25.degree. C., pH: 6.5-7.0, run flow: 1.5 L/min
[0186] From the data collected, it was shown that the GO with a
meta-phenylenediamine (MPD) cross-linker outperformed comparable GO
membranes with ethylenediamine (EDA) or para-phenylenediamine (PPD)
cross-linkers in terms of salt rejection with comparable water flux
rates. In addition, the GO-MPD w/ COOH membrane (MD-2.1.2.1.1)
showed higher salt rejection and a high-water flux than the GO-MPD
without substitutions (CMD-2.2.1).
[0187] Unless otherwise indicated, all numbers expressing
quantities of ingredients, properties such as molecular weight,
reaction conditions, and etc. used in herein are to be understood
as being modified in all instances by the term "about." Each
numerical parameter should at least be construed in light of the
number of reported significant digits and by applying ordinary
rounding techniques. Accordingly, unless indicated to the contrary,
the numerical parameters may be modified according to the desired
properties sought to be achieved, and should, therefore, be
considered as part of the disclosure. At the very least, the
examples shown herein are for illustration only, not as an attempt
to limit the scope of the disclosure.
[0188] The terms "a," "an," "the" and similar referents used in the
context of describing embodiments of the present disclosure
(especially in the context of the following claims) are to be
construed to cover both the singular and the plural, unless
otherwise indicated herein or clearly contradicted by context. All
methods described herein may be performed in any suitable order
unless otherwise indicated herein or otherwise clearly contradicted
by context. The use of any and all examples, or exemplary language
(e.g., "such as") provided herein is intended merely to better
illustrate embodiments of the present disclosure and does not pose
a limitation on the scope of any claim. No language in the
specification should be construed as indicating any non-claimed
element essential to the practice of the embodiments of the present
disclosure.
[0189] Groupings of alternative elements or embodiments disclosed
herein are not to be construed as limitations. Each group member
may be referred to and claimed individually or in any combination
with other members of the group or other elements found herein. It
is anticipated that one or more members of a group may be included
in, or deleted from, a group for reasons of convenience and/or
patentability.
[0190] Certain embodiments are described herein, including the best
mode known to the inventors for carrying out the embodiments. Of
course, variations on these described embodiments will become
apparent to those of ordinary skill in the art upon reading the
foregoing description. The inventor expects skilled artisans to
employ such variations as appropriate, and the inventors intend for
the embodiments of the present disclosure to be practiced otherwise
than specifically described herein. Accordingly, the claims include
all modifications and equivalents of the subject matter recited in
the claims as permitted by applicable law. Moreover, any
combination of the above-described elements in all possible
variations thereof is contemplated unless otherwise indicated
herein or otherwise clearly contradicted by context.
[0191] In closing, it is to be understood that the embodiments
disclosed herein are illustrative of the principles of the claims.
Other modifications that may be employed are within the scope of
the claims. Thus, by way of example, but not of limitation,
alternative embodiments may be utilized in accordance with the
teachings herein. Accordingly, the claims are not limited to
embodiments precisely as shown and described.
* * * * *