U.S. patent application number 17/005573 was filed with the patent office on 2021-02-18 for methods of membrane modification.
The applicant listed for this patent is King Abdullah University of Science and Technology. Invention is credited to Iran D. CHARRY PRADA, Suzana NUNES.
Application Number | 20210046429 17/005573 |
Document ID | / |
Family ID | 1000005196791 |
Filed Date | 2021-02-18 |
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United States Patent
Application |
20210046429 |
Kind Code |
A1 |
NUNES; Suzana ; et
al. |
February 18, 2021 |
METHODS OF MEMBRANE MODIFICATION
Abstract
A porous membrane can include a nanoparticle.
Inventors: |
NUNES; Suzana; (Thuwal,
SA) ; CHARRY PRADA; Iran D.; (Thuwal, SA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
King Abdullah University of Science and Technology |
Thuwal |
|
SA |
|
|
Family ID: |
1000005196791 |
Appl. No.: |
17/005573 |
Filed: |
August 28, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13861818 |
Apr 12, 2013 |
10780402 |
|
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17005573 |
|
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61636699 |
Apr 22, 2012 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B01D 71/024 20130101;
B01D 69/02 20130101; B01D 69/148 20130101; B01D 2325/36 20130101;
B01D 67/0093 20130101; B01D 2325/48 20130101; B01D 67/0079
20130101; B01D 2323/38 20130101; B01D 71/60 20130101 |
International
Class: |
B01D 69/02 20060101
B01D069/02; B01D 67/00 20060101 B01D067/00; B01D 69/14 20060101
B01D069/14 |
Claims
1-16. (canceled)
17. A membrane comprising: a porous polymer layer including a
functionalizing agent and a nanoparticle.
18. The membrane of claim 17, wherein the functionalizing agent
includes a metal alkoxide.
19. The membrane of claim 18, wherein the functionalizing agent
includes a Z-terminated alkoxy and wherein Z is a moiety that is
compatible with, soluble within, or reacts with at least one of the
nanoparticles or a functional group on the nanoparticles.
20. The membrane of claim 19, wherein Z is hydroxy, sulfhydryl,
sulfinate, sulfinic acid, epoxy, sulfonate, sulfonic acid,
disulphide, carboxyl, carboxylate, amine, amide, alkoxysilyl,
halosilyl, phosphate, phosphonic acid, phosphonate ester,
phosphinate, phosphinic acid, or phosphinate ester.
21. The membrane of claim 17, wherein the functionalizing agent is
a silane.
22. The membrane of claim 21, wherein the silane includes
tetraethylorthosilicate, silicon tetrachloride, silanol-terminated
polydimethylsiloxane, chlorine-terminated polydimethylsiloxane,
ethoxy-terminated polydimethylsiloxane, methoxy-terminated
polydimethylsiloxane, triethoxysilylethyl-terminated
polydimethylsiloxane, dimethylamino-terminated
polydimethylsiloxane, (3-glycidyloxypropyl)trimethoxysilane, or
N1-(3-trimethoxysilylpropyl)diethylenetriamine.
23. The membrane of claim 19, wherein the silane includes a
Z-terminated halo silane and wherein Z is a moiety that is
compatible with, soluble within, or reacts with at least one of the
nanoparticles or a functional group on the nanoparticles.
24. The membrane of claim 23, wherein Z is hydroxy, sulfhydryl,
sulfinate, sulfinic acid, epoxy, sulfonate, sulfonic acid,
disulphide, carboxyl, carboxylate, amine, amide, alkoxysilyl,
halosilyl, phosphate, phosphonic acid, phosphonate ester,
phosphinate, phosphinic acid, or phosphinate ester.
25. The membrane of claim 17, wherein the porous polymer layer
further includes an organic polymer and wherein the organic polymer
is selected from polyolefins, ethylene-propylene rubbers,
ethylene-propylene-diene monomer terpolymers (EPDM), polystyrenes,
polyvinylchloride (PVC), polyamides, polyacrylates, celluloses,
polyesters, polyethers, polysulphones, polyazoles,
polyvinylhalides, polyhalocarbons, polyethyleneimine, polymers or
copolymers of ethylene, propylene, isobutene, butene, hexene,
octene, vinyl acetate, vinyl chloride, vinyl propionate, vinyl
isobutyrate, vinyl alcohol, allyl alcohol, allyl acetate, allyl
acetone, allyl benzene, allyl ether, ethyl acrylate, methyl
acrylate, acrylic acid, and methacrylic acid.
26. The membrane of claim 25, wherein the organic polymer is
selected from polyetherimides, polyacrylonitriles, poly sulfones,
polyoxadiazoles, polytriazoles, and polyvinylfluorides.
27. The membrane of claim 17, wherein the nanoparticles include Ag,
Au, titania, zirconia, ceria, a rare earth oxide, or silica.
28. The membrane of claim 17, wherein the nanoparticles are
functionalized with a functional group selected from the group
consisting of a hydroxy, a thio, an amino, and a carboxy.
29. The membrane of claim 17, wherein the nanoparticles are surface
functionalized by reaction with a second silane.
30. The membrane of claim 29, wherein the second silane includes an
amino silane.
31. The membrane of claim 29, wherein the second silane includes
N1-(3-trimethoxysilylpropyl)diethylenetriamine.
32. The membrane of claim 17, wherein the functionalizing agent
includes an epoxy-terminated alkoxy or halo silane and the
nanoparticles are functionalized by reaction with an amino
silane.
33. The membrane of claim 32, wherein the epoxy group and the amino
group react to covalently attach the functionalized nanoparticles
to the porous layer.
34. The membrane of claim 17, wherein the functionalizing agent
includes glycidoxypropyltrimethoxysilane (GMS) and wherein the
nanoparticles are functionalized by reaction with
N1-(3-trimethoxysilylpropyl)diethylenetriamine.
35. The membrane of claim 17, wherein the nanoparticles include
TiO.sub.2 nanoparticles.
36. The membrane of claim 17, wherein the organic polymer includes
polyetherimide or polyetherimide sulfone.
37. The membrane of claim 17, wherein the membrane is an asymmetric
membrane and wherein the nanoparticles are covalently attached to
the porous layer.
Description
CLAIM OF PRIORITY
[0001] This application is a divisional of U.S. application Ser.
No. 13/861,818, filed on Apr. 12, 2013, which claims the benefit of
prior U.S. Provisional Application No. 61/636,699, filed on Apr.
22, 2012, which is incorporated by reference in its entirety.
TECHNICAL FIELD
[0002] This invention relates to a modified polymer membranes and
methods of manufacturing modified polymer membranes.
BACKGROUND OF THE INVENTION
[0003] Polymer membranes can be used in a variety of applications.
For example, polymer membranes can be used in water separation or
purification systems, gas separation or purification systems,
membrane reactors, electrochemical cells, drug delivery devices and
other systems. The properties of the surfaces and pores of the
membrane can determine the usefulness of the membrane for
particular applications.
SUMMARY
[0004] A method of forming the membrane can include dissolving the
polymer in an organic solvent and casting the membrane. For
example, casting the membrane can include phase inversion
casting.
[0005] In one aspect, a method of manufacturing a membrane includes
forming the membrane from the dissolved polymer in the presence of
a functionalizing agent, and exposing the functionalizing agent to
a nanoparticle to form a modified membrane.
[0006] In another aspect, a membrane includes a porous polymer
layer including a functionalizing agent and a nanoparticle.
[0007] In certain embodiments, the method includes casting the
membrane. The method can further include dissolving the polymer in
an organic solvent.
[0008] Forming the membrane can include phase inversion.
[0009] The nanoparticle can include functional groups. The
nanoparticle can be Ag, Au, titania, zirconia, ceria, a rare earth
oxide or silica. The functionalizing agent can include a metal
alkoxide or silane. The silane can be tetraethylorthosilicate,
silicon tetrachloride, silanol-terminated polydimethylsiloxane,
chlorine-terminated polydimethylsiloxane, ethoxy-terminated
polydimethylsiloxane, methoxy-terminated polydimethylsiloxane,
triethoxysilylethyl-terminated polydimethylsiloxane,
dimethylamino-terminated polydimethylsiloxane,
(3-glycidyloxypropyl)trimethoxysilane,
N.sup.1-(3-trimethoxysilylpropyl)diethylenetriamine, or a
Z-terminated alkoxy or halo silane in which Z is a moiety that is
compatible with, soluble within, or reacts with a nanoparticle or a
functional group on the nanoparticle. Z can be hydroxy, sulfhydryl,
sulfinate, sulfinic acid, epoxy, sulfonate, sulfonic acid,
disulphide, carboxyl, carboxylate, amine, amide, alkoxysilyl,
halosilyl, phosphate, phosphonic acid, phosphonate ester,
phosphinate, phosphinic acid, or phosphinate ester.
[0010] Other aspects, embodiments, and features will be apparent
from the following description, the drawings, and the claims.
DETAILED DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a diagram depicting a general surface
nanostructure process of: a) functionalization of a nanoparticle;
b) a polysiloxanes network in a polymer matrix; or c) selective
attachment of nanoparticles onto a membrane surface.
[0012] FIG. 2 is a graph depicting contact angle, pore size and
field emission scanning electron micrographs (FESEM) microscopy of
membranes prepared from polyethyleneimine (PEI) casting solutions
with and without polysilsesquioxane from polycondensation of
N.sup.1-(3-trimethoxysilylpropyl)diethylenetriamine (GMS) in
different coagulation baths; larger area of (f) membrane prepared
from PEI/GMS casting solution coagulated in 65.degree. C.
nanoparticle dispersion (all membranes FESEM image with the same
magnification).
[0013] FIG. 3 is a series of micrographs depicting detailed cross
section field emission scanning electron micrographs (FESEM) of
asymmetric PEI membrane modified with nanoparticles.
[0014] FIG. 4 is a series of micrographs depicting secondary
electron image of a functionalized membrane cross-section (from top
(0 micrometer) to bottom (85 micrometer)) and its Energy Dispersive
Spectroscopy Analysis (EDS): Line-scan and elemental mapping of Si
and Ti.
[0015] FIG. 5 is a graph depicting .sup.1H NMR (600 MHz, 297K,
CDC13, ppm) spectra of PEI membranes with and without
polysilsesquioxane.
[0016] FIG. 6 is a graph depicting experimental DSC-thermograms of
the PEI membranes.
[0017] FIG. 7 is a graph depicting thermal gravimetrical analysis
(TGA-DT) of the asymmetric PEI membrane with polysilsesquioxane and
modified with TiO.sub.2 nanoparticles.
DETAILED DESCRIPTION OF THE INVENTION
[0018] Membranes are important in separation processes, such as
water reuse, for instance ultrafiltration and forward osmosis or
other membrane technologies. A well-known problem in the membrane
field is fouling during the separation process, for example, by the
adhesion of mainly organic solutes or biological microorganisms to
the surface of membranes. The fouling can cause flux reduction and
can lead to pore blocking. Surface functionalization can make the
membrane more hydrophilic. Alternatively, or in addition, creation
of surface nanostructures can help reduce or minimize the fouling
problem. In order to reduce or prevent biofouling, for example,
biocide nanoparticles such as silver, copper or metallic oxides can
be affixed to the membrane surface or pores. Another application
for modified membranes is in membrane reactors. For example,
metallic particles or nanoparticles affixed to a surface of a
porous polymer membrane can be used as a catalyst. Uniform
distribution of the particles, stability and accessibility on the
membrane can be provided, improving the use of the modified
membrane in a reactor.
[0019] In general, a method of forming a polymer membrane can
include attaching nanoparticles to a surface or pores of the
membrane can produce modified membranes that are tailored for
particular uses. The method achieves a good distribution of
nanoparticles throughout the membrane, and can provide access to
the particles on the surface of the membrane while having a strong
and stable connection to the membrane. These features can improve
the lifespan of the membrane for the purpose, and can avoid
leaching out or other degradation during operation. The method
provides a simple way to attach particles to the surface, without
additional polymer functionalization.
[0020] Examples of potential uses for modified membranes include
for organic-inorganic membranes for fuel cells (see, for example,
EP1191621 B1, which is incorporated by reference in its entirety),
heteropolyacid modified membranes (see, for example, M. L. Ponce,
L. A. S. de A. Prado, V. Silva and S. P. Nunes "Membranes for
direct methanol fuel cell based on modified heteropolyacids"
Desalination, 162 (1-3): 383-391 (2004), which is incorporated by
reference in its entirety), or silane functional polymer membranes
(see, for example, S. P. Nunes, K. V. Peinemann, K. Ohlrogge, A.
Alpers, M. Keller and A. T. N. Pires. "Membranes of poly(ether
imide) and nanodispersed silica." Journal of Membrane Science 157
(1999) 219, which is incorporated by reference in its entirety. In
each of these examples, benefits would be obtained by using the
modified membranes described herein.
[0021] There are two exemplary approaches to making the modified
membrane utilizing a functionalizing action, such as a metal
alkoxide or silane, and a nanoparticle or polymer.
[0022] In one approach, a preformed membrane can be immersed in a
dispersion containing nanoparticles, which have been previously
functionalized with active groups, which react with the groups
available in the membrane. In certain embodiments, heat or
irradiation can be used to promote the reaction. For example, a
preformed membrane can be immersed in the dispersion of
functionalized particles and heat it just enough to promote the
reaction between a particle functional groups (such as an amine)
and a chemical groups added by a silane to the modified membranes
(such as an epoxy). Organically modified silanes can be
commercially available as coupling agents and as long the
morphology of the membrane is controlled, a suitable organically
modified silane can be added to the polymer casting solution.
Alternatively, it can be possible to chemically modify the organic
polymer of the membrane to react with nanoparticles.
[0023] In another approach, the membrane can be coagulated in a
bath containing functionalized nanoparticles and can be allowed to
react at the same time that the pores are formed through the
process of reactive phase inversion. This approach can be extended
also to other systems, without nanoparticles, including with other
reactive monomers, crosslinkers, or other compound, in a
coagulation bath. Reactive phase inversion could use a reactive
polymer instead of nanoparticles. A typical procedure of
preparation of asymmetric porous membranes can include dissolving
the polymer, casting the solution with doctor blade on a substrate,
such as a glass plate or non-woven support, and immersing the
membrane in water. By a process, known in the membrane field as
phase inversion process, an asymmetric porous structure is formed,
with smaller pores on the top of the membrane and a gradient of
pores with increasing pore size down to the bottom of the membrane.
The water can be in a coagulation bath. By forming the membrane in
a reactive solution, where functionalized nanoparticles are
dispersed and the functional groups are available for reaction,
reactive phase inversion (RPI), and leading to the modified
membrane structure. Other reactive agents like crosslinker could be
present in the coagulation bath and react with chemical groups in
the incipient membrane during the pore formation. The resulting
membrane can be stable to solvents or can induce target
functionalization inside the pores while they are being formed.
[0024] For example, the nanoparticles can be attached by adding
organically functionalized silanes to a casting solution and
promoting silane polymerization to form an inorganic polymer
(polysilsesquioxane). The silane is chosen to contain a functional
group that is reactive with the nanoparticles. The functional group
can be, for example, an epoxy, which can be used to attach to the
nanoparticles. For example, an asymmetric porous membrane can be
prepared by a conventional phase inversion method whereby an epoxy
group becomes exposed to pore walls of the membrane and the
membrane surface.
[0025] Suitable polymers can include polyolefins,
ethylene-propylene rubbers, ethylene-propylene-diene monomer
terpolymers (EPDM), polystyrenes, polyvinylchloride (PVC),
polyamides, polyacrylates, celluloses, polyesters, polyethers,
polysulphones, polyazoles (ie., diazole, triazole),
polyvinylhalides, polyhalocarbons, polyethyleneimine, or polymers
or copolymers of ethylene, propylene, isobutene, butene, hexene,
octene, vinyl acetate, vinyl chloride, vinyl propionate, vinyl
isobutyrate, vinyl alcohol, allyl alcohol, allyl acetate, allyl
acetone, allyl benzene, allyl ether, ethyl acrylate, methyl
acrylate, acrylic acid, or methacrylic acid. Preferred polymer
materials include polyetherimides, polyacrylonitriles,
polysulfones, polyoxadiazoles, polytriazoles, or
polyvinylfluorides.
[0026] Suitable nanoparticles can include inorganic particles,
clusters, or nanowires, such as inorganic, organic, semiconducting,
metallic, metal oxide, transition metal oxide, crystalline, or
magnetic particles. Examples include Ag, Au, titania, zirconia,
ceria, a rare earth oxide or silica. Other examples of
nanoparticles are described, for example, in U.S. Patent
Publication 20110039105, U.S. Pat. Nos. 8,124,230, and 7,148,282,
each of which is incorporated in its entirety. In certain
embodiments, the nanoparticle includes one or more functional
groups on a surface of the nanoparticle. The functional group can
be hydroxy, thio, amino, carboxy, or any other group capable of
reacting with the functionalizing agent.
[0027] Suitable functionalization agent can include a metal
alkoxide or a silane. The silane can include
tetraethylorthosilicate, silicon tetrachloride, silanol-terminated
polydimethylsiloxane, chlorine-terminated polydimethylsiloxane,
ethoxy-terminated polydimethylsiloxane, methoxy-terminated
polydimethylsiloxane, triethoxysilylethyl-terminated
polydimethylsiloxane, dimethylamino-terminated
polydimethylsiloxane, (3-glycidyloxypropyl)trimethoxysilane,
N.sup.1-(3-trimethoxysilylpropyl)diethylenetriamine, or a
Z-terminated alkoxy or halo silane in which Z is a moiety that is
compatible with, soluble within, or reacts with a nanoparticle or a
functional group on the nanoparticle. For example, Z can be
hydroxy, sulfhydryl, sulfinate, sulfinic acid, epoxy, sulfonate,
sulfonic acid, disulphide, carboxyl, carboxylate, amine, amide,
alkoxysilyl, halosilyl, phosphate, phosphonic acid, phosphonate
ester, phosphinate, phosphinic acid, or phosphinate ester.
[0028] Suitable silanes, functionalized nanoparticles or other
materials can be purchased commercially or prepared by ordinary
synthetic organic techniques.
[0029] For example, membranes with very regular distribution of
TiO.sub.2 nanoparticles were prepared aiming at antifouling and/or
separation coupled to photocatalytic applications. Particles and
membrane surfaces were modified with organoalkylsilanes having
reactive functional groups. Reaction between added epoxy and amino
functional groups led to asymmetric polyetherimide porous membranes
with TiO.sub.2 decorated surface. Leaching tests confirmed the
strong attachment of the particles to the polymer surface.
Excellent properties were obtained, such as hydrophilicity and
thermal stability up to temperatures close to 260.degree. C. The
average pore size was 134.+-.17 nm, in the range of
ultrafiltration. The particle size and electrophoretic mobility was
measured by dynamic light scattering (DLS); thermal stability was
confirmed by TGA and DSC. Chemical characterization was performed
by FTIR, NMR and EDS. Wettability was evaluated by contact angle
measurements and the morphology was investigated by FESEM.
[0030] Among metal oxide nanoparticles, TiO.sub.2 has attracted
interest for application in membrane technology due to its
bifouling control ability, photocatalytic and ultrahydrophilicity
properties. In terms of fouling mitigation, TiO.sub.2 has proved to
diminish the irreversible fouling without compromising the flux of
ultrafiltration and reverse osmosis membranes. They also exhibit
antibacterial effect against Escherichia coli (E. coli) [1-3]. The
photocatalytic and ultra-hydrophilicity properties are related to
self-cleaning performance added to surfaces. Photocatalytic
activity leads to total or partial decomposition of organic matter
as trichlorophenol, recalcitrant pollutants and toxic organic
substances [3-5]. Ultrahydrophilicity allows eliminating the
remaining contaminants from the surface by simple rinsing [4, 6].
In addition, some other well-known attractive properties of
TiO.sub.2 particles include a good chemical stability, UV-filter
capability, optical properties, wide availability and low cost
[7,8]. The integration of TiO.sub.2 nanoparticles and polymeric
membranes has been reported through different techniques, which
include the blending of nanoparticles into the membrane and the
deposition onto the membrane surface. Mixed-matrix membranes have
been prepared by trapping or assembly in the bulk, but they have
shown a very poor distribution and alteration of the mechanical
membrane properties [3, 9, 10]. Particle surface coating has been
reported by spray deposition technique [11], and low
temperature-hydrothermal (LTH) process [10], which resulted in
particles aggregation, then being more useful for nonporous solid
surfaces or fibers; also coating by plasma treated surfaces and by
pulse-frequency d.c. reactive magnetum sputtering methods have been
explored [12], which due to the high interaction of the pulse
frequency with the surface not only alter the pore properties but
also tend to produce a non-homogeneous coating and even damage to
the membrane. Moreover, bulk incorporation of TiO.sub.2
nanoparticles with combination of subsequent dipping in particles
suspension for membranes has been documented but with aggregation
at the surface of polysulfone membranes [6]. They also may cause
pore plugging and instability of the coating layer [9]. However,
even with the reported drawbacks the use of organic-inorganic
materials for membrane preparation can be very successful if
carefully explored. Organoalkoxysilanes have been previously used
for building a phosphonated network or incorporating phosphate
particles to increase proton conductivity of polymer membranes for
fuel cell application as reported by Pezzin et al and Nunes et al
[13, 14]. Organoalkoxysilanes have been used also to improve the
mechanical resistance to membranes under pressure [15] and reduce
swelling of membranes used for gas separation and direct alcohol
fuel cell [14, 16].
[0031] Silane coupling agents have proved to be effective for
grafting onto particles surface [7]. They can be used for surface
modification of nanoparticles and for improving dielectric and
wetting properties of organic-inorganic composites. The first step
for a successful membrane surface modification with nanoparticles
is the functionalization of the particles alone. Stabilization of
colloidal dispersion is needed to avoid aggregation. In this work
the particle functionalization has also the final goal of chemical
binding on the membrane functionalized surface.
[0032] In summary, the main objective of this work is the
preparation and characterization of a novel nanostructured membrane
with TiO.sub.2 nanoparticles, with excellent distribution and
stable attachment on the membrane surface and in the pore walls. A
combination phase inversion for membrane preparation with reactive
processes facilitates stable and homogeneous functionalization.
[0033] Experimental
[0034] For the surface functionalization of TiO.sub.2 particles,
commercial TiO.sub.2 nanoparticles, a mixture of rutile and anatase
(<150 nm particle size (DLS), dispersion, 33-37 wt. % in
H.sub.2O) and N1-(3-trimethoxysilylpropyl) diethylenetriamine were
bought from Sigma-Aldrich. The particles were purified by dialysis
using SnakeSkin dialysis tubing (7K MWCO 35 ft. (10.5 m)) supplied
by Thermo-Scientific.
[0035] Polyetherimide-sulfone (PEI), Extern XH1015, was kindly
supplied by Sabic and anhydrous dimethylformamide (DMF) from Sigma
Aldrich was used for preparation of asymmetric porous membranes.
Glycidoxypropyltrimethoxysilane (GMS) from Acros Organics was used
for the membrane functionalization.
[0036] The particles were prepared and the membranes were casted
using deionized water prepared with a MilliQ water purification
system. Chemicals were used without further purification.
[0037] The surface functionalization of commercial TiO.sub.2
nanoparticles was performed mixing 150 mL of IM TiO.sub.2
nanoparticles dispersion in DI water and 10 mL of 10 vol % solution
of N1-(3-trimethoxysilylpropyl)diethylenetriamine. The dispersion
was placed into a Parr reactor at 60.degree. C. and 60 bar of
CO.sub.2 for 8 hours under stirring at 300 rpm.
[0038] Afterwards, the solution was dialyzed up to four days to
remove any unreacted chemical remaining in solution. Finally, the
colloidal dispersion was diluted 10 times in volume.
[0039] Membrane Functionalization with Epoxy-Organopolysiloxane
Network
[0040] Glycidoxypropyltrimethoxysilane (10 wt % to PEI) was added
dropwise to 20 wt % polyetherimide solutions in DMF. After 2 hours,
HCl 0.1M was added to the mixture (3:2 acid molar ratio to silane).
The resulted mixture was stirred for three days in order to promote
the network formation by sol-gel process.
[0041] Membranes Preparation
[0042] The preparation of asymmetric membranes by phase inversion
consisted of the following steps: (1) casting of a 100-.mu.m-thick
film on a glass plate with a doctor blade, (2) immersion in a
coagulation bath (water) at two different evaluated conditions:
room temperature and 65.degree. C. for 12 hours, and (3) drying at
ambient conditions.
[0043] For surface attachment of TiO.sub.2 nanoparticles, the usual
non-solvent bath (water) was substituted by a particles dispersion.
Remaining steps were developed as explained before.
[0044] Size and electrophoretic mobility were determined on a
Malvern Zetasizer Nano-ZS.
[0045] Fourier Transform Infrared-Attenuated Total Reflectance
(FTIR-ATR) spectra were recorded on a FTIR Nicolet iS10 with a
Universal ATR accessory equipped with a single reflection diamond
crystal for membranes samples and KBr pellets for powders.
[0046] .sup.1H NMR spectra of 5-10% (w/w) solutions of the final
polymers in DMF-d7 with Si(CH.sub.3)4 as an internal standard were
recorded at room temperature at 600 MHz SB Liquid NMR Spectrometer
(Bruker).
[0047] Differential scanning calorimetry (DSC) was carried out on a
Perkin-Elmer DSC 204 Fl NETZSCH under nitrogen flow. The heating
rate was 5.degree. C.-min-.sup.1 and the cooling rate was
10.degree. C.-min-.sup.1 in the range of temperature from 25 to
220.degree. C. The samples were placed in aluminum pans and heated
from 25 to 220.degree. C. under nitrogen flow rate. For all
samples, an isotherm was recorded at 220.degree. C. for 15 minutes.
The glass transition temperature (Tg) of each sample was determined
from the second heating scan.
[0048] Thermogravimetric analysis (TGA) was conducted on TA
instrument TA/TGA Q50 with a heating rate of 5.degree.
C.-min-.sup.1 under nitrogen flow up to 800.degree. C. Colloidal
dispersions were previously freeze-dried for this
characterization.
[0049] Surface and cross section morphology were examined by field
emission scanning electron microscopy (FESEM) in a PEI Nova.TM.
NanoSEM 630. The samples were sputter coated with platinum for 30 s
at 20 mA to prevent electron charging. All the images were taken
using a TLD--secondary electrons detector in immersion mode, 2 KV
voltage, working distance of 3 mm and spot size between 1.5 and 2.
Images were obtained at different magnifications. The samples for
cross-sectional images were previously freeze-fractured in liquid
nitrogen.
[0050] Composition analyses for the membranes were acquired from
characteristic Energy-dispersive X-ray spectroscopy (EDS) at 10 KV,
working distance of 5mm and spot size 6. Different EDAX techniques
were explored on this work such as elemental analysis, and line and
mapping scans.
[0051] Stationary contact angle measurements for the membranes were
performed in Kruss Easydrop equipment.
[0052] Leaching Tests
[0053] The strength of the interaction between particles and PEI
membranes was evaluated by leaching tests using DI water as
solvent, for three days. The samples were washed with periodic
changes of water in order to avoid the saturation of the aqueous
phase with inorganic components.
[0054] A simple method of porous membrane functionalization was
directed at improved fouling resistance, as well as the possibility
of extending the application for catalytic active systems. The idea
is to add complementing reactive functionalities to particles and
membranes, by working with organosilanes. The use of silanes for
modification of polymeric membranes has been reported to improve
the mechanical stability as far as compaction and resistance to
swelling is concerned [14-16]. Careful morphology control is
required when silane is added to the casting solution. The
preparation steps include (i) particle functionalization with amino
silane (FIG. 1a), (ii) casting of organo-inorganic solution with
epoxy-functionalized surface (FIG. 1b) and (iii) reactive/phase
inversion in water with dispersed functionalized TiO.sub.2 leading
to covalent attachment onto membrane surface (FIG. 1e).
Surface Functionalization of TiO2 Nanoparticles
[0055] TiO.sub.2 nanoparticles were modified by grafting amino
functional groups onto the particles surface, by reaction with
amino silanes. FIG. 1(a) shows the possible chemical titania
functionalization, which result from the silane reaction on the
particles surface. The most probable reaction is directly between
the surface hydroxyl groups and silane through --Si--O-- groups, as
part of the condensation and hydrolysis process; however bonding of
primary amino to --OH groups is also possible, as well as
electrostatic interaction between NH.sub.3+ (protonated amine) and
--OH groups [7, 17]. The zeta potential increases from (0.5.+-.1.5)
mV to (42.+-.9) mV after modification of TiO.sub.2 particles,
indicating that protonation has taken place, According to DLS
measurements, the functionalization process led to an increase in
particles size from -47 nm to -92 nm probably due to bridging after
condensation between different alkoxysilane chains linked to
different particles in the dispersion. The grafting success was
confirmed by FTIR.
Organo-Inorganic Membrane Casting and Pore Morphology Control
[0056] FIG. 1(b) represents the polyetherimide/polysilsesquioxane
blend with reactive epoxy groups, which constitutes the membrane to
be linked to amino-functionalized particles. The polysilsesquioxane
formation was optimized, by taking in account classical sol-gel
reports of Brinker [19] and Witucki [20] to avoid reverse reaction
from siloxane network to silanol. Acid catalysis (0.1M HCl),
H.sub.2O/Si molar ratio 1.5 and 3 days stirring of solutions in DMF
at room temperature. FTIR spectra evidenced the network formation
at the optimized conditions.
[0057] Asymmetric porous membranes were prepared by casting PEI
solutions on glass plates, followed by immersion in water. When the
temperature of the coagulation bath is increased, larger pores are
formed and the contact angle slightly decreases (Comparison between
FIGS. 3a and 3b). It is known that surface texture influences the
contact angle and porosity can lead to super hydrophobicity as well
as super hydrophilicity, according to Cassie and Wenzel models
[21-24]. A marginal contact angle decrease is observed when
epoxysilsesquioxane is incorporated (FIGS. 3c and 3d). Much lower
contact angles could be measured when TiO.sub.2 functionalized
particles were attached to the membranes (FIGS. 3e and 3f). For
that the particle functionalization itself, which is highly
hydrophilic, might have a large contribution. Furthermore the
Wenzel equation [23, 25] predicts a decrease of contact angle when
the features at the surface favor the liquid penetration into the
roughness grooves (gaps between the peaks). The attached particles
act as features (FIG. 3f), which are smaller in size than the water
drop dimension, increasing the wettability of analogous
non-functionalized PEI membranes [23, 25] with similar pore size
(FIG. 3b).
[0058] Without the epoxy-silsesquioxane network, the particles tend
to aggregate on the membrane surface and plug the pores.
Reactive Phase Inversion and Surface Attachment of TiO.sub.2
Nanoparticles onto PEI Membranes
[0059] One of the best nanostructured membrane was cast from PEI
solutions containing epoxy polysilsesquioxane immersed in the
dispersion of TiO.sub.2 particles. The sol-gel process leading to
the formation of polysilsesquioxane in the PEI solution does not
open the epoxy groups as confirmed by NMR. The characterization is
shown as supplementary information (FIG. 5). For the successful
attachment of TiO.sub.2 particles the phase inversion process
usually leading to the formation of asymmetric porous membranes was
also a reactive process. As the incipient membrane is being formed,
with the usual water-solvent exchange, followed by pore formation,
the casting solution and particularly the epoxy groups are exposed
to the amino-functionalized particles. Reaction between amino and
epoxy groups takes place as depicted in FIG. 1e. During the
immersion/coagulation step the polymer (PEI and polysilsesquioxane)
chains have high mobility. As phase separation takes place to form
and solidify the pore structure, it is expected that the epoxy
groups tend to be preferentially placed in the polymer-water
interface and react to amino groups available in the functionalized
particles. Reactions of primary amine/epoxy and secondary
amine/epoxy are possible at 65.degree. C. In absence of a proton
donor, the secondary amine has a dual role not only by forming an
intermediate complex with the epoxy, but also as a nucleophilic
reagent attacking preformed epoxy-amine complexes.
[0060] The reactive phase inversion led to uniformly attached
particles onto PEI surface. The observed mean pore diameter was
134.+-.17 nm, making the membrane suitable for ultrafiltration
applications such as waste water treatment with photocatalytic and
biofouling control properties coming from the attached inorganic
particles. In addition, this membrane exhibited good wettability as
shown in the FIG. 3f.
[0061] Cross-section FESEM images of the functionalized asymmetric
membrane with TiO.sub.2 nanoparticles are shown in the FIG. 4.
Sponge-like morphology dominates, which is positive from the point
of view of mechanical stability and resistance to compaction when
working at high pressure. Finger-like cavities are only present in
the center of the membrane. It is clear that the TiO.sub.2
particles are preferentially distributed in the external membrane
layers, which were in more direct contact to the particle
dispersion during the membrane formation. Particularly in the top
layer a large density of TiO.sub.2 particles can be seen, which are
not only on the membrane top surface, but mostly placed on the pore
walls. This is relevant since in operation not only the top flat
surface should be protected from fouling, but also the pore
entrance. Furthermore when catalytic activity is aimed, the pore
functionalization offers a longer contact time between active
particles and pollutant molecules to be converted.
[0062] The distribution of inorganic phase in the PEI porous
membrane was confirmed by Energy Dispersive X-Ray Spectroscopic
Analysis (EDS) shown in FIG. 5 along the cross-section. Sis present
only in the organic polymer (sulfone groups) and the Ti signal
comes exclusively from the TiO.sub.2 particles. The Ti/S ratio
(line-scan) is a semi-quantitative indication of how the particles
are distributed. They are mostly attached in the surface layers,
the highest particle density being found up to 3 .mu.m from the
surface (both sides). The Si signal comes from the
polysilsesquioxane and from the functionalization of the TiO.sub.2
particles. The Si/S ratio is relatively uniform in the center (up
to 5 .mu.m from the surface) of the membrane cross-section. If we
discount the small increase of Si sign close to the surface, which
can be assigned to the attached particles, we can conclude that the
polysilsesquioxane phase is homogeneously distributed all over the
membrane. This is confirmed by the images obtained in elemental
mapping mode both for Si and Ti.
[0063] The thermal properties and stability of the prepared
membranes have been analyzed and the results are shown in FIGS. 6
and 7. The glass transition temperature measured by DSC, T.sub.g,
is 267.degree. C. Practically no shift could be detected with the
functionalization, as expected, since the amount or silane added is
only around 10 wt %. The decomposition temperature measured by TGA,
Td, is around 495.degree. C. for the modified membrane with
functionalized TiO.sub.2 nanoparticles. This makes this membrane
able to operate at temperatures close to 260.degree. C., conditions
in which most of polymeric membranes are not stable enough.
[0064] The stability of the particle attachment was evaluated by
washing the membranes for three days, continuously changing the
water. The Ti/S and Si/S ratios evaluated by EDS are shown in Table
1 for all the samples before and after washing. The analyzed
membranes are similar to those characterized in FIGS. 3b, 3e and
3f. It can be clearly seen that when TiO.sub.2 particles are added
without previously functionalization with epoxysilanes, the
particles easily detach after strong washing since Ti/S ratio
dramatically decreases. Different behavior is observed for the
functionalized PEI membrane previously functionalized with
epoxysilanes, which exhibited negligible change in the Ti/S and
Si/S ratio, confirming the formation of strong link with covalent
bond between the porous membrane and the functionalized TiO.sub.2
particles.
TABLE-US-00001 TABLE 1 EDS analysis on the top of the membrane
surfaces Before WashinQ After WashinQ Ti/S wt Si/S wt Ti/S wt Si/S
wt Membrane ratio ratio ratio ratio PEI/Ti0 2 402 5.7 0.27 0.014
PEI/ 3.6 0.37 3.3 0.36 Polysilsesquioxane/ Ti02
[0065] TiO.sub.2 has been reported to increase the fouling
resistance of membranes, and has been explored as photocatalyst for
pollutant conversion to less toxic products. However the effective
use of TiO.sub.2 particles for membrane modification only makes
sense if their attachment is stable under operation and if the
particles are well distributed and accessible in the membrane
surface and pore walls. A new method of membrane functionalization
has been proposed to address all these requirements. The method
combines conventional phase inversion technology of asymmetric
porous membrane preparation and reaction during the membrane
coagulation. Hydrophilic ultrafiltration membranes with stable
attachment of TiO.sub.2 nanoparticles on the surface and in the
pores with penetration depth around 2.5-3.5 .mu.m were
obtained.
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[0091] Other embodiments are within the scope of the following
claims.
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