U.S. patent application number 11/057698 was filed with the patent office on 2005-10-06 for nanoporous chelating fibers.
Invention is credited to Economy, James, Liu, Chunqing.
Application Number | 20050221087 11/057698 |
Document ID | / |
Family ID | 35054685 |
Filed Date | 2005-10-06 |
United States Patent
Application |
20050221087 |
Kind Code |
A1 |
Economy, James ; et
al. |
October 6, 2005 |
Nanoporous chelating fibers
Abstract
A composite includes substrate fibers, and an organosilica
coating including a structure-directing template, on the substrate
fibers. The composite may be formed by coating substrate fibers
with an organosilica sol containing a structure-directing template,
and curing the organosilica sol to form an organosilica coating. A
nanoporous chelating fiber includes a substrate fiber and a
nanoporous chelating coating, on the substrate fiber. Nanoporous
chelating fibers may be formed by removing the structure-directing
template from a composite to form a nanoporous chelating coating on
the substrate fibers. Contaminants may be removed from a fluid by
contacting nanoporous chelating fibers with a fluid containing at
least one contaminant.
Inventors: |
Economy, James; (Urbana,
IL) ; Liu, Chunqing; (Mount Prospect, IL) |
Correspondence
Address: |
EVAN LAW GROUP LLC
566 WEST ADAMS, SUITE 350
CHICAGO
IL
60661
US
|
Family ID: |
35054685 |
Appl. No.: |
11/057698 |
Filed: |
February 14, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60544847 |
Feb 13, 2004 |
|
|
|
Current U.S.
Class: |
428/375 |
Current CPC
Class: |
D06M 11/79 20130101;
D06M 15/643 20130101; C03C 25/24 20130101; D06M 2400/02 20130101;
B01J 45/00 20130101; B01J 47/127 20170101; Y10T 428/2933 20150115;
B01J 20/2808 20130101 |
Class at
Publication: |
428/375 |
International
Class: |
D06L 001/00 |
Goverment Interests
[0002] The subject matter of this application may have been funded
in part under a research grants from the Science and Technology
Center (STC) program of the National Science Foundation (NSF),
under Agreement Number CTS-0120978. The U.S. Government may have
rights in this invention.
Claims
1. A nanoporous chelating fiber, comprising: a substrate fiber; and
a nanoporous chelating coating, on the substrate fiber.
2. The nanoporous chelating fiber of claim 1, wherein the
nanoporous chelating coating comprises an organosilica comprising a
plurality of chelating groups.
3. The nanoporous chelating fiber of claim 2, wherein the plurality
of chelating groups comprises at least one chelating group selected
from the group consisting of a thiol, an alcohol, a primary amine,
a secondary amine, an ammonium group, and a calix[n]arene.
4. The nanoporous chelating fiber of claim 2, wherein the plurality
of chelating groups comprises thiol groups.
5. The nanoporous chelating fiber of claim 1, wherein the substrate
fiber comprises a material selected from the group consisting of
glass, mineral, ceramic, metal, natural fiber and polymer.
6. The nanoporous chelating fiber of claim 1, wherein the substrate
fiber is present with a plurality of substrate fibers in a form
selected from the group consisting of papers, fabrics, felts and
mats.
7. A composite, comprising: substrate fibers; and an organosilica
coating comprising a structure-directing template, on the substrate
fibers.
8. The composite of claim 7, wherein the structure-directing
template comprises a member selected from the group consisting of
cetyltrimethylammonium bromide, cetyltrimethylammonium chloride,
CH.sub.3(CH.sub.2).sub.15(OCH.sub.2CH.sub.2).sub.10OH,
(EO).sub.20(PO).sub.70(EO).sub.20,
(EO).sub.105(PO).sub.70(EO).sub.105, dibenzoyl-/-tartaric acid and
a cyclodextrin.
9. The composite of claim 7, wherein the organosilica coating
further comprises a plurality of chelating groups.
10. The composite of claim 9, wherein the plurality of chelating
groups comprises at least one chelating group selected from the
group consisting of a thiol, an alcohol, a primary amine, a
secondary amine, an ammonium group, and a calix[n]arene.
11. A method of forming a composite, comprising: coating substrate
fibers with an organosilica sol comprising a structure-directing
template; and curing the organosilica sol to form an organosilica
coating.
12. The method of claim 11, wherein the organosilica sol is formed
by combining ingredients comprising an organotrialkoxysilane
comprising a chelating group, a tetraalkoxysilane, a
structure-directing template, an acid catalyst, water, and a
volatile solvent.
13. The method of claim 12, wherein the combining comprises:
forming a homogeneous monomer mixture comprising the
organotrialkoxysilane, the tetraalkoxysilane, the acid catalyst,
water, and the volatile solvent; and adding the structure-directing
template to the homogeneous monomer mixture.
14. The method of claim 12, wherein the organotrialkoxysilane
comprises a compound having the structure of formula
(I):R(CH.sub.2).sub.nSi(OR.sup.5- ).sub.3 (I)wherein --R is the
chelating group, n is an integer from 0 to 20, and --R.sup.5 is a
C1-C8 hydrocarbon group.
15. The method of claim 12, wherein the chelating group is selected
from the group consisting of a thiol, an alcohol, a primary amine,
a secondary amine, an ammonium group, and a calix[n]arene.
16. The method of claim 12, wherein the chelating group is a
thiol.
17. The method of claim 11, wherein the structure-directing
template comprises a member selected from the group consisting of
cetyltrimethylammonium bromide, cetyltrimethylammonium chloride,
CH.sub.3(CH.sub.2).sub.15(OCH.sub.2CH.sub.2).sub.10OH,
(EO).sub.20(PO).sub.70(EO).sub.20,
(EO).sub.105(PO).sub.70(EO).sub.105, dibenzoyl-/-tartaric acid and
a cyclodextrin.
18. A method of forming nanoporous chelating fibers, comprising:
removing the structure-directing template from the composite of
claim 7 to form a nanoporous chelating coating on the substrate
fibers.
19. The method of claim 18, wherein the removing the
structure-directing template comprises contacting the organosilica
coating with a mixture comprising an acid and a volatile
solvent.
20. A method of removing a contaminant from a fluid, comprising:
contacting the nanoporous chelating fiber of claim 1 with a fluid
comprising at least one contaminant.
Description
REFERENCE To RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application No. 60/544,847 entitled "Nanoporous Organic/Inorganic
Hybrid Chelating Fibers" filed Feb. 13, 2004, which is incorporated
by reference in its entirety.
BACKGROUND
[0003] The removal of contaminants from air, water and oil in
industrial, commercial, or residential environments is a problem
that is becoming more serious in recent years, prompting the
establishment of increasingly stringent government regulations
demanding that levels of contaminants be lowered. In particular,
the removal of contaminants such as organic compounds, heavy
metals, and radioactive metals from air, water, and oil is the
focus of much research. The contamination of groundwater and,
ultimately, drinking water is the driving force behind the
extensive research being conducted in order to remove toxic and
hazardous contaminants from wastewater. The wastewater contains
contaminants such as mercury, arsenic and iron, which react with
oxygen; negatively charged metals such as arsenic, molybdenum, and
chromium; and positively charged heavy metals such as silver, lead,
and nickel. Disposing of wastewater is not only very expensive and
time consuming, but also extremely harmful to the environment.
Current processes for the removal of contaminants from air, water,
and oil include incineration, adsorption, impingement,
electrostatic attraction, centrifugation, sonic agglomeration,
ozonization, membrane separation, ion exchange, and solvent
extraction. However, all of these processes have some impediments
for use in industrial applications. For example, there are a number
of drawbacks associated with the traditional approach to ion
exchange bead synthesis. During functionalization of the polymeric
systems, swelling agents must be used to reduce effects of osmotic
shock and to maintain the spherical form of the bead. Furthermore,
environmentally unfriendly solvents including toluene, methylene
chloride, perchloethylene and carbon tetrachloride, etc. are used
in the synthesis and carry an added expense not only in their
initial cost but also in the EPA requirements for handling spent
solvents.
[0004] Recently, hybrid mesoporous powder materials with
functionalized monolayers containing thiol groups have been used as
adsorbents to remove heavy metals from waste streams. See, for
example, Feng et al. Science 276: 923-6 (1997); Liu et al. Chem.
Eng. Tech. 21: 97-100 (1998); Mercier et al. Environ. Sci. Tech.
32: 2749-54 (1998); and Liu et al. Adv. Mater. 10: 161 +(1998); and
PCT Application Publication No. WO 98/34723, all of which are
incorporated herein by reference. These functionalized hybrid
materials show selectivity and high loading capacity for mercury
(II) ions and many other heavy metals. Although these
functionalized hybrid materials show potential as heavy metal
adsorbents, the requirements of mesoporosity, high ordering, and
high surface areas make the synthesis of these materials quite
complex. In addition, the ligand loading capacity of these
materials is limited by the quantity and availability of anchoring
residual silanol groups on the pore surface. Furthermore,
environmentally hazardous solvents, such as toluene, were used in
the functionalization process of the materials.
[0005] Glass fibers coated with ion-exchange polymers have been
investigated as a low cost approach to contaminant removal. See,
for example, Economy et al., Ind. Eng. Chem. Res. 41: 6436-42
(2002); Dominguez et al., Polym. Adv. Tech. 12: 197-05 (2001); and
U.S. Pat. No. 6,706,361 B1, all of which are expressly incorporated
herein by reference. These polymeric ion exchange fibers have the
potential to remove a wide range of contaminant ions from water
such as mercury, cadmium, lead, and cyanide ions. It would be
desirable to improve certain properties of these fibers, such as
selectivity and efficiency in removal of toxic heavy metal ions and
radioactive metal ions from air, water, and oil in the presence of
high concentrations of nontoxic competing ions such as sodium and
potassium.
[0006] Nonporous polymeric chelating fibers have been investigated
for selective removal of trace levels of mercury and radioactive
cesium ions from water. See, for example, Liu et al., Environ. Sci.
Tech., 37: 4261-4268 (2003); Liu et al., C&E News, September
15: p21 (2003), each of which is expressly incorporated herein by
reference. It would be desirable to improve certain properties of
these fibers, such as the loading capacity and sorption kinetics
for contaminants.
[0007] It would be desirable to provide more effective and
efficient materials and methods to remove contaminants,
particularly toxic heavy metal ions and radioactive metal ions from
the air, water, and oil.
SUMMARY
[0008] In one aspect, the invention provides a nanoporous chelating
fiber that includes a substrate fiber and a nanoporous chelating
coating, on the substrate fiber.
[0009] In another aspect of the invention, there is a composite
that includes substrate fibers, and an organosilica coating that
includes a structure-directing template, on the substrate
fibers.
[0010] In yet another aspect of the invention, there is a method of
forming a composite that includes coating substrate fibers with an
organosilica sol containing a structure-directing template, and
curing the organosilica sol to form an organosilica coating.
[0011] In yet another aspect of the invention, there is a method of
forming nanoporous chelating fibers that includes removing the
structure-directing template from a composite to form a nanoporous
chelating coating on the substrate fibers.
[0012] These aspects may include methods of forming composites
and/or nanoporous chelating fibers wherein the organosilica sol is
formed by combining ingredients including an organotrialkoxysilane
having a chelating group, a tetraalkoxysilane, a
structure-directing template, an acid catalyst, water, and a
volatile solvent. The combining may include forming a homogeneous
monomer mixture including the organotrialkoxysilane, the
tetraalkoxysilane, the acid catalyst, water, and the volatile
solvent; and adding the structure-directing template to the
homogeneous monomer mixture. The removing the structure-directing
template may include contacting the organosilica coating with a
mixture including acid and a volatile solvent. The
organotrialkoxysilane may include a compound having the structure
of formula (I):
R(CH.sub.2).sub.nSi (OR.sup.5).sub.3 (1)
[0013] wherein --R is the chelating group, n is an integer from 0
to 20, and --R.sup.5 is a C1-C8 hydrocarbon group.
[0014] In yet another aspect of the invention, there is a method of
removing a contaminant from a fluid that includes contacting a
nanoporous chelating fiber with a fluid containing at least one
contaminant. The fluid may include a substance selected from the
group consisting of water, an oil and a gas; the at least one
contaminant may include a substance selected from the group
consisting of an alkali metal compound, an alkali earth metal
compound, a transition metal compound, a group III-VIII compound, a
lanthanide compound and an actinide compound; and the at least one
contaminant may include a substance selected from the group
consisting of a copper compound, a chromium compound, a mercury
compound, a lead compound, a silver compound, a zinc compound and
an arsenic compound. The method may further include regenerating
the nanoporous chelating fiber after the contacting, where the
regenerating includes treating the nanoporous chelating fiber with
an aqueous acid solution.
[0015] These aspects may include nanoporous chelating fibers,
composites, methods of forming the nanoporous chelating fibers
and/or composites, and methods of removing contaminants wherein the
nanoporous chelating coating includes an organosilica having a
plurality of chelating groups; wherein the plurality of chelating
groups includes at least one chelating group selected from the
group consisting of a thiol, an alcohol, a primary amine, a
secondary amine, an ammonium group, and a calix[n]arene; wherein
the plurality of chelating groups includes thiol groups; wherein
the substrate fiber includes a material selected from the group
consisting of glass, mineral, ceramic, metal, natural fiber and
polymer; wherein the substrate fiber is present with a plurality of
substrate fibers in a form selected from the group consisting of
papers, fabrics, felts and mats; and wherein the
structure-directing template includes a member selected from the
group consisting of cetyltrimethylammonium bromide,
cetyltrimethylammonium chloride,
CH.sub.3(CH.sub.2).sub.15(OCH.sub.2CH.su- b.2).sub.10OH,
(EO).sub.20(PO).sub.70(EO).sub.20, (EO).sub.105(PO).sub.70(-
EO).sub.105, dibenzoyl-/-tartaric acid and a cyclodextrin.
[0016] The scope of the present invention is defined solely by the
appended claims and is not affected by the statements within this
summary.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The invention can be better understood with reference to the
following drawings and description.
[0018] FIG. 1 is a flowchart illustrating schematically the
preparation of an example of nanoporous thiol-functionalized
organosilica chelating fibers.
[0019] FIG. 2 is a graph illustrating the FTIR spectra of (a)
original Crane-230 glass fiber substrate and (b) MP-silica-20%-NC
fibers.
[0020] FIG. 3 is a graph illustrating solid-state .sup.13C NMR
spectrum of MP-silica-10%-NC fibers.
[0021] FIG. 4 is a graph illustrating the nitrogen
adsorption-desorption isotherms of (a) MP-silica-10%-NC, (b)
MP-silica-20%-NC, and (c) MP-silica-50%-NC fibers.
[0022] FIG. 5 is a graph illustrating the pore size distributions
for (a) MP-silica-10%-NC, (b) MP-silica-20%-NC, and (c)
MP-silica-50%-NC fibers,
[0023] FIG. 6 is a TEM image of MP-silica-10%-NC material coated on
the glass fiber substrate.
[0024] FIG. 7 is a SEM image of MP-silica-10%-NC fibers.
[0025] FIG. 8 is a graph illustrating the changes of mercury
concentrations as a function of time in the sorption reaction of
MP-silica-10%-NC and MP-silica-50%-NC fibers. Initial Hg
concentration: 3.7 ppm, 10 mL of solution with 2250 ppm of sodium
ions, 0.1 g of MP-silica-10%-NC or MP-silica-50%-NC fibers.
[0026] FIG. 9 is a flowchart illustrating schematically a
regeneration study on an example of mercury-loaded MP-silica-10%-NC
fibers.
DETAILED DESCRIPTION
[0027] Nanoporous chelating fibers include substrate fibers and a
nanoporous chelating coating, on the substrate fibers. These
nanoporous chelating fibers may be formed from a composite that
includes substrate fibers, and an organosilica coating containing a
structure-directing template, on the fibers. This type of composite
may be formed by coating substrate fibers with an organosilica sol
containing the structure-directing template, and then curing the
organosilica sol. The composite may then be converted into
nanoporous chelating fibers by removing the structure-directing
template. Nanoporous chelating fibers may be used to remove
contaminants from fluids such as water, oil, gases and mixtures
thereof.
[0028] The term "nanoporous," as used herein, means a substance
containing pores having an average diameter of 100 nanometers (nm)
or smaller.
[0029] The term "chelating," as used herein, means a substance that
binds a metal atom with two or more ligands. At the molecular
level, a chelating group is any chemical group that forms a ligand
with a metal atom.
[0030] The term "organosilica," as used herein, means a silica
(SiO.sub.x) network containing organic chemical groups.
[0031] The term "nanoporous organosilica chelating coating," as
used herein, means an organosilica that contains organic chelating
groups, thus allowing the material to chelate specific metal
ions.
[0032] Nanoporous chelating fibers can exhibit advantages over
conventional materials for purification of fluids. For example,
nanoporous chelating fibers can provide for increased kinetic rates
of reaction and regeneration, reduced fracture and breakage, and
improved strength and dimensional stability relative to
conventional ion exchange resins in the form of beads. In another
example, nanoporous chelating fibers can display improved
selectivity for specific toxic metal ions in air, water, and oil in
the presence of high concentrations of nontoxic metal ions, as
compared with polymeric ion exchange fibers. In yet another
example, nanoporous chelating fibers may be manufactured more
easily and less expensively than hybrid mesoporous powder materials
due to the relatively simple synthetic procedures, and can provide
better mechanical integrity and wear resistance. A wide variety of
nanoporous chelating fibers with different organic chelating
groups, which are capable of chelating/adsorbing a number of
different contaminant metal ions from air, water, and oil, can be
produced by using different nanoporous chelating materials. In a
specific example, nanoporous organosilica chelating fibers may have
desirable properties including low-cost, high surface areas,
controlled pore sizes, high mechanical and dimensional stabilities,
and reduced swelling, as well as ease of fabrication into felts,
papers, or fabrics for scaling-up and commercialization.
[0033] Nanoporous chelating fibers include substrate fibers, and a
nanoporous chelating coating, on the surface of the substrate
fibers. The substrate fibers may include any material that can
tolerate the conditions necessary to form the insoluble nanoporous
chelating coating. Examples include natural fibers, e-glass fibers,
HEPA filters, synthetic fibers used in clothing, polyesters,
polyethylene, polyethylene terephthalate, nylon 6, nylon 66,
polypropylene, KEVLAR.TM., liquid crystalline polyesters, and
syndiotactic polystyrene. Other examples include natural and
synthetic fibers, for example: glass fibers; mineral fibers such as
asbestos and basalt; ceramic fibers such as TiO.sub.2, SiC, and BN;
metal fibers such as iron, nickel and platinum; polymer fibers such
as TYVEK.TM.; natural fibers such as cellulose and animal hair; and
combinations thereof. Some preferred substrate fibers are listed in
Table 1. Preferably the fibers have a softening or decomposition
temperature of at most 350.degree. C.
1TABLE 1 Commercially Available Substrate Fibers Company Product
Line Description CRANE & CO. Crane 230 (6.5 .mu.m) Non-woven
Fiber Glass Mats Crane 232 (7.5 .mu.m) Non-woven Fiber Glass Mats
FIBER GLAST 519 (0.75 oz.) Wovens 573 (9 oz.) Wovens HOLLINGSWORTH
& BG05095 Glass Paper or Felts VOSE HE1021 JOHNS MANVILLE
DURAGLASS .RTM. 7529 Non-woven Fiber (11 .mu.m)) Glass Mats LYDALL
MANNING MANNIGLAS .RTM. Non-woven Fiber Glass Mats DUPONT TYVEK
.RTM. HDPE Spun Bonded Paper
[0034] The nanoporous chelating coating material may be any
nanoporous material that contains chelating groups. Preferably the
nanoporous material is a nanoporous organosilica. Examples of
nanoporous organosilica include materials having the structure of
formula (II): 1
[0035] in which --R is a chelating group, and n is an integer from
0 to 20. The chelating group may be neutral or ionic, as long as
the group forms a ligand with a metal atom. A chelating coating may
include a single type of chelating group, or it may include more
than one type of chelating group. Examples of chelating groups
include thiols (--SH); alcohols (--OH); amines, including primary
amines (--NH.sub.2) and secondary amines (--NR.sup.1H); ammonium
groups, including trialkyl ammonium groups
(--[NR.sup.2R.sup.3R.sup.4].sup.+); calix[n]arenes; and mixtures
thereof, where R.sup.1, R.sup.2, R.sup.3 and R.sup.4 may be alkyl
or aryl groups. Specific examples of --R groups include --SH, --OH,
--NH.sub.2, --NR.sup.1H,
--(CH.sub.2).sub.nNH(CH.sub.2).sub.2NH.sub.2,
--OCH.sub.2CH(OH)CH.sub.2N(CH.sub.2CH.sub.2OH).sub.2,
calix[n]arenes (n=4, 6, or 8),
--[NCH.sub.3((CH.sub.2).sub.aCH.sub.3).sub.2].sup.+ Cl.sup.-,
--[N(CH.sub.2).sub.17CH.sub.3(CH.sub.3).sub.2].sup.+Cl.sup.-,
--[N(CH.sub.3).sub.3].sup.+ Cl.sup.-,
--[N(CH.sub.2CH.sub.3).sub.3].sup.+ Cl.sup.-, and
--[N(CH.sub.2CH.sub.2CH.sub.2CH.sub.3).sub.3].sup.+ Cl.sup.-.
[0036] Nanoporous chelating fibers may be prepared by coating
substrate fibers with a template-directed organosilica sol to form
an organosilica coating on the surface of the substrate fibers.
Curing of the organosilica coating forms a composite having an
insoluble organosilica coating on the surface of the substrate
fibers. Subsequent removal of the template from the insoluble
organosilica coating produces nanoporous chelating fibers having an
organosilica chelating coating.
[0037] A template-directed organosilica sol may be prepared by
mixing an organotrialkoxysilane, a tetraalkoxysilane, a
structure-directing template, an acid catalyst, water, and a
volatile solvent. The ratio of organotrialkoxysilane to
tetraalkoxysilane in the template-directed organosilica sol may be
varied from 0:100 to 100:100. This sol contains an organosilica
network organized around micelles of the structure-directing
template. The sol may be applied to the fibers by a variety of
coating methods and then dried. Examples of coating methods include
dip-coating and spray coating. The coated fibers may be cured, for
example at 100-150.degree. C., to form an insoluble organosilica
network on the surface of the substrate fibers. Removal of the
template results in the formation of nanoporous organosilica
chelating fibers.
[0038] Structure-directing templates may be ionic surfactants,
neutral surfactants, or non-surfactants. Examples of
structure-directing templates include ionic surfactants, such as
cetyltrimethylammonium bromide (CTABr) and cetyltrimethylammonium
chloride (CTACl); neutral surfacants such as
CH.sub.3(CH.sub.2).sub.15(OCH.sub.2CH.sub.2).sub.10OH (Brij-56;
UNIQEMA, New Castle, DE), (EO).sub.20(PO).sub.70(EO).sub.20
(Pluronic-P123, where EO is ethylene oxide and PO is propylene
oxide; BASF Corporation, Mount Olive, N.J.),
(EO).sub.105(PO).sub.70(EO).sub.105 (Pluronic-F127, where EO is
ethylene oxide and PO is propylene oxide; BASF); non-surfactants
such as dibenzoyl-/-tartaric acid and cyclodextrins; and
derivatives and analogs thereof.
[0039] In one example, a method of forming the nanoporous chelating
coating on the surface of substrate fibers includes synthesizing an
organosilica sol using a structure-directing template, and then
applying the solution to the substrate fibers. The
template-directed organosilica sol may be provided by first
preparing a homogeneous organosilane monomer solution by mixing
organotrialkoxysilane monomer and tetraalkoxysilane monomer, water,
an acid catalyst and a volatile solvent. The molar percentage (mol
%) of organotrialkoxysilane monomer to the total amount of monomer
may be from zero to 100, and preferably is from 5 to 40 mol %.
Preferably the water is deionized water. In one example, a
homogeneous organosilane monomer solution contains a molar ratio of
organotrialkoxysilane to tetraalkoxysilane to volatile solvent to
deionized water to acid catalyst of
x:(1-x):1-10:0.5-5:1.times.10.sup.-5-- 10.times.10.sup.-5, where x
is a number from zero to 1. Examples of acid catalysts include
hydrochloric acid, phosphoric acid, sulfonic acid, acetic acid, and
mixtures thereof. Examples of volatile solvents include alcohols
such as ethanol or methanol; ethers such as diethyl ether; ketones
such as acetone; and mixtures thereof.
[0040] The organotrialkoxysilane monomer may be a compound having
the structure of formula (I):
R(CH.sub.2).sub.nSi(OR.sup.5).sub.3 (1)
[0041] in which --R is a chelating group, n is an integer from 0 to
20, and --R.sup.5 is a C1-C8 hydrocarbon group. Examples of
chelating groups include thiols (--SH); alcohols (--OH); amines,
including primary amines (--NH.sub.2) and secondary amines
(--NR.sup.1H); ammonium groups, including trialkyl ammonium groups
(--[NR.sup.2R.sup.3R.sup.4].sup.+); calix[n]arenes; and mixtures
thereof, where R.sup.1, R.sup.2, R.sup.3 and R.sup.4 may be alkyl
or aryl groups. Specific examples of --R groups include --SH, --OH,
--NH.sub.2, --NR.sup.1H, --(CH.sub.2).sub.nNH(CH.sub.-
2).sub.2NH.sub.2,
--OCH.sub.2CH(OH)CH.sub.2N(CH.sub.2CH.sub.2OH).sub.2,
calix[n]arenes (n=4, 6, or 8),
--[NCH.sub.3((CH.sub.2).sub.9CH.sub.3).sub- .2].sup.+ Cl.sup.-,
[N(CH.sub.2).sub.17CH.sub.3(CH.sub.3).sub.2].sup.+ Cl.sup.-,
--[N(CH.sub.3).sub.3].sup.+ Cl.sup.-, --[N(CH.sub.2CH.sub.3).su-
b.3].sup.+Cl.sup.-, and
--[N(CH.sub.2CH.sub.2CH.sub.2CH.sub.3).sub.3].sup.- + Cl.sup.-.
[0042] The tetraalkoxysilane monomer may be a compound having the
structure of formula (III):
SI(OR.sup.6).sub.4 (III)
[0043] in which --R.sup.6 is a C1-C8 hydrocarbon group.
[0044] A structure-directing template-may then be added to this
homogeneous organosilane monomer solution. The structure-directing
template may be added directly to the homogeneous organosilane
monomer solution, or it may be combined with other substances to
form a template solution, which may then be added to the monomer
solution. A template solution may contain a mixture of the
structure-directing template in a liquid such as water and/or a
volatile solvent, and may contain an acid catalyst. Examples of
volatile solvents include alcohols such as ethanol or methanol;
ethers such as diethyl ether; ketones such as acetone; and mixtures
thereof. Examples of acid catalysts include hydrochloric acid,
phosphoric acid, sulfonic acid, acetic acid, and mixtures thereof.
In one example, a template solution contains a molar ratio of
volatile solvent to deionized water to acid catalyst to
structure-directing template of 1-20:0.5-5:0.001-0.005:0.1-0.3.
[0045] In a specific example of preparing an organosilica sol using
a structure-directing template, a homogeneous organosilane monomer
solution in deionized water may be refluxed at for example
60.degree. C. for 0.5-5 hours and then cooled to room temperature
to provide a pre-hydrolyzed sol solution. To this pre-hydrolyzed
sol is added a template solution containing deionized water, an
acid catalyst, a structure-directing template, and a volatile
solvent. The solution is aged for 1-14 days to allow for the silica
network to adequately organize around the template micelles to
produce the final template-directed organosilica sol used for
coating the substrate fibers.
[0046] The coated fibers may be exposed to air to dry the
organosilica coating. The dried organosilica coating may then be
cured in air or in vacuo by heating to form an insoluble
organosilica chelating coating on the fibers. The
structure-directing templates in the insoluble organosilica
chelating coating can be removed from this composite by gently
stirring the coated fibers in a solution of acid.
[0047] In one example, the structure-directing templates are
removed from a composite by stirring the coated fibers in a mixture
of 36 weight percent (wt %) aqueous HCl and a volatile solvent,
such that the weight ratio of the fiber to HCl to volatile solvent
is 1: 1-1.5:150-200. The fibers may be stirred in this mixture at
elevated temperature, such as 50.degree. C., for about 2 hours. The
coated fibers are then washed repeatedly with the volatile solvent,
and dried in air or in vacuo by heating, for example to about
120.degree. C., to form nanoporous chelating fibers.
[0048] The nanoporous chelating fibers may be present in any form.
Examples include loose fibers, woven and non-woven fabrics, papers,
felts and mats. The nanoporous chelating fibers may be made from
substrate fibers already present in a specific form, or the
nanoporous chelating fibers may first be prepared from loose
substrate fibers, and made into the specific form. The nanoporous
chelating coating may be used as an adhesive to hold the fibers
together. The length of the nanoporous chelating fibers is not
limited, and may be, for example, 0.01 mm to 100 m in length. The
nanoporous chelating fibers may be prepared from longer substrate
fibers, then cut or chopped. The diameter of the nanoporous
chelating fibers is also not limited, and may be, for example 100
.ANG. to 1 mm in diameter. Preferably, the fibers have an aspect
ratio of at least 10.
[0049] The nanoporous chelating coating on the nanoporous chelating
fibers may be present on isolated regions on the surface of the
substrate fibers, may completely enclose the substrate fibers, or
enclose all of the substrate fibers except the ends of the
substrate fibers. For example, if the substrate fibers were
completely enclosed by the nanoporous chelating coating, then
chopping would result in the ends of the fibers being exposed.
[0050] The weight ratio between the nanoporous chelating coating
and the substrate fibers is not limited, but may affect the final
properties of the nanoporous chelating fibers. For example, if the
amount of the nanoporous chelating coating is very large compared
to the amount of substrate fibers, the brittleness of the coating
may reduce the flexibility of the nanoporous chelating fibers.
Preferably, the nanoporous chelating fibers include 10 to 90% by
weight of the nanoporous chelating coating, more preferably 20 to
80% by weight of the nanoporous chelating coating, including 30%,
40%, 50%, 60%, and 70% by weight of the nanoporous chelating
coating.
[0051] Nanoporous chelating fibers may be used to remove
contaminants from fluids such as water, oil, gases and mixtures
thereof. In this application, nanoporous chelating fibers can
display selectivity for specific toxic metal ions in air, water,
and oil in the presence of high concentrations of nontoxic metal
ions. For example, nanoporous chelating fibers can exhibit high
loading capacities for metal ions, high selectivities for specific
metal ions in the presence of high concentrations of competing
ions, and quite rapid sorption kinetics for toxic metal ions such
as mercury, silver, lead, etc.
[0052] Contaminants that can be removed include alkali metal
compounds, alkali earth metal compounds, transition metal
compounds, group III-VIII compounds, lanthanide compounds, and
actinide compounds. Specific examples of contaminants that can be
removed include copper compounds, chromium compounds, mercury
compounds, lead compounds, silver compounds, zinc compounds, and
arsenic compounds. The fluids from which contaminants may be
removed include liquids, such as water, oil and mixtures thereof,
and includes gases, such as air.
[0053] In one example, nanoporous organosilica chelating fibers
having thiol chelating groups shows a loading capacity for mercury
ions up to 269 mg Hg/g of coating. These fibers also show high
selectivities for mercury ions, with a measured K.sub.d for Hg
greater than 637800 mL/g, as well as rapid sorption kinetics for
mercury ions, removing >99 % of Hg within 30 min at a
solution-to-solid ratio of 100 mL/g.
[0054] Once nanoporous chelating fibers have been used to remove
contaminants from fluids, the chelating properties can be
regenerated, allowing the fibers to be used again for removal of
contaminants from a fluid. For example, nanoporous chelating fibers
that have been loaded with metal ions can be treated with an
aqueous acid solution, and this treatment may result in 100%
regeneration of the chelation capacity of the fibers.
[0055] In a specific example, a method of regenerating the
contaminant-loaded nanoporous chelating fibers includes soaking the
contaminant-loaded nanoporous chelating fibers in an 1.0-12.1 molar
(M) aqueous acid solution for 2-12 hours. The leached fibers may be
rinsed repeatedly with deionized water and dried in air or in vacuo
to result in 100% regeneration of the nanoporous chelating fibers.
Examples of acids that may be used for regeneration include
hydrochloric acid, phosphoric acid, sulfonic acid, acetic acid, and
mixtures thereof.
[0056] The following examples are provided to illustrate one or
more preferred embodiments of the invention. Numerous variations
can be made to the following examples that lie within the scope of
the invention.
EXAMPLES
Example 1
Synthesis of Organosilica Chelating Fibers with CTABr Templates
[0057] Thiol-functionalized organosilica sol solutions were
prepared by a micellar templating technique. A typical synthetic
procedure required a molar ratio of 1Si:20EtOH:5H.sub.2O:0.004
HCl:0.14CTABr. Tetraethoxysilane (TEOS) and
mercaptopropyltrimethoxysilane (MPTMS) were used as the Si sources.
Sol solutions were prepared with MPTMS to the total amount of Si
molar ratios of x/100 (MP-silica-x %-CTABr sol solution, x=0-100).
A mixture of MPTMS and TEOS corresponding to the appropriate mole
fraction, with a total of 72 mmol Si (for example, 1.4 g (7.2 mmol)
of MPTMS and 13.5 g (64.8 mmol) of TEOS for MP-silica-1 0%-CTABr
sol solution), was mixed with a solution containing 1.3 g (72 mmol)
of Dl water, 0.13 mg of HCI and 9.9 g (216 mmol) of ethanol. The
homogeneous solution was refluxed at 60.degree. C. for 1 h and then
cooled to room temperature to result in a pre-hydrolyzed sol
solution. Then a solution consisting of 5.18 g (288 mmol) of Dl
water, 10.4 mg of HCl, 3.67 g (10.1 mmol) of CTABr, and 56.3 g
(1.22 mol) of ethanol was added to the pre-hydrolyzed sol solution.
The solution was aged for 7 days to allow for the silica network to
adequately organize around the CTABr micelles. The final
homogeneous sol solution was then used as the dipping solution.
[0058] Crane-230 glass fibers were dip-coated with a MP-silica-x
%-CTABr sol solution for 10 min, and placed on a fine mesh screen.
The coated glass fibers were dried in a hood at room temperature
for 12 h. The dried fibers were cured at 120.degree. C. for 48 h in
an oven. The cured MP-silica-x %-CTABr fibers were allowed to cool
to room temperature slowly and weighed immediately.
[0059] The extraction of CTABr surfactant templates was performed
by gently stirring a mixture of 1.0 g of MP-silica-x %-CTABr fibers
in a solution of 1.0 g of hydrochloric acid (36 wt. %) and 180 g of
methanol in a 60.degree. C. water bath for 4 h. The
surfactant-extracted MP-silica-x %-NC fibers were washed repeatedly
with methanol, and dried for 24 h at 80.degree. C. in vacuo.
[0060] This synthetic procedure is illustrated schematically in
FIG. 1. FIG. 1 also applies in general to the synthetic procedures
of Examples 2-4.
Example 2
Synthesis of Organosilica Chelating Fibers with Brij-56
Templates
[0061] Thiol-functionalized organosilica sol solutions were
prepared by a micellar templating technique. A typical synthetic
procedure required a molar ratio of 1Si:20EtOH:5H.sub.2O:0.004
HCl:0.14 CH.sub.3(CH.sub.2).sub.15(OCH.sub.2CH.sub.2).sub.10OH
(Brij-56). Tetraethoxysilane (TEOS) and
mercaptopropyltrimethoxysilane (MPTMS) were used as the Si sources.
Sol solutions were prepared with MPTMS to the total amount of Si
molar ratios of x/100 (MP-silica-x %-Brij sol solution, x=0-100). A
mixture of MPTMS and TEOS corresponding to the appropriate mole
fraction, with a total of 72 mmol Si (for example, 1.4 g (7.2 mmol)
of MPTMS and 13.5 g (64.8 mmol) of TEOS for MP-silica-10%-Brij sol
solution), was mixed with a solution containing 1.3 g (72 mmol) of
Dl water, 0.13 mg of HCI and 9.9 g (216 mmol) of ethanol. The
homogeneous solution was refluxed at 60.degree. C. for 1 h and then
cooled to room temperature to result in a pre-hydrolyzed sol
solution. Then a solution consisting of 5.18 g (288 mmol) of Dl
water, 10.4 mg of HCl, 6.89 g (10.1 mmol) of Brij-56, and 56.3 g
(1.22 mol) of ethanol was added to the pre-hydrolyzed sol solution.
The solution was aged for 7 days to allow for the silica network to
adequately organize around the Brij-56 micelles. The final
homogeneous sol solution was then used as the dipping solution.
[0062] Crane-230 glass fibers were dip-coated with a MP-silica-x
%-Brij sol solution for 10 min, and placed on a fine mesh screen.
The coated glass fibers were dried in a hood at room temperature
for 12 h. The dried fibers were cured at 120.degree. C. for 48 h in
an oven. The cured MP-silica-x %-Brij fibers were allowed to cool
to room temperature slowly and weighed immediately.
[0063] The extraction of Brij-56 templates was performed by gently
stirring a mixture of 1.0 g of MP-silica-x %-Brij fibers in a
solution of 1.0 g of hydrochloric acid (36 wt. %) and 180 g of
methanol in a 60.degree. C. water bath for 4 h. The
template-extracted MP-silica-x %-NB fibers were washed repeatedly
with methanol, and dried for 24 h at 80.degree. C. in vacuo.
Example 3
Synthesis of Organosilica Chelating Fibers with Pluronic-P123
Templates
[0064] The thiol-functionalized organosilica sol solutions were
prepared by a micellar templating technique. A typical synthetic
procedure required a molar ratio of
1Si:20EtOH:5H.sub.2O:0.004HCl:0.14(EO).sub.20(P-
O).sub.70(EO).sub.20 (Pluronic-P123, where EO is ethylene oxide and
PO is propylene oxide). Tetraethoxysilane (TEOS) and
mercaptopropyltrimethoxysi- lane (MPTMS) were used as the Si
sources. Sol solutions were prepared with MPTMS to the total amount
of Si molar ratios of x/100 (MP-silica-x %-P123 sol solution,
x=0-100). A mixture of MPTMS and TEOS corresponding to the
appropriate mole fraction, with a total of 72 mmol Si (for example,
1.4 g (7.2 mmol) of MPTMS and 13.5 g (64.8 mmol) of TEOS for
MP-silica-10%-P123 sol solution), was mixed with a solution
containing 1.3 g (72 mmol) of Dl water, 0.13 mg of HCl and 9.9 g
(216 mmol) of ethanol. The homogeneous solution was refluxed at
60.degree. C. for 1 h and then cooled to room temperature to result
in a pre-hydrolyzed sol solution. Then a solution consisting of
5.18 g (288 mmol) of Dl water, 10.4 mg of HCl, 10.1 mmol of
Pluronic-P123, and 56.3 g (1.22 mol) of ethanol was added to the
pre-hydrolyzed sol solution. The solution was aged for 7 days to
allow for the silica network to adequately organize around the
Pluronic-P123 micelles. The final homogeneous sol solution was then
used as the dipping solution.
[0065] Crane-230 glass fibers were dip-coated with a MP-silica-x
%-P123 sol solution for 10 min, and placed on a fine mesh screen.
The coated glass fibers were dried in a hood at room temperature
for 12 h. The dried fibers were cured at 120.degree. C. for 48 h in
an oven. The cured MP-silica-x %-P123 fibers were allowed to cool
to room temperature slowly and weighed immediately.
[0066] The extraction of Pluronic-P123 templates was performed by
gently stirring a mixture of 1.0 g of MP-silica-x %-P1 23 fibers in
a solution of 1.0 g of hydrochloric acid (36 wt. %) and 180 g of
methanol in a 60.degree. C. water bath for 4 h. The
template-extracted MP-silica-x %-NP fibers were washed repeatedly
with methanol, and dried for 24 h at 80.degree. C. in vacuo.
Example 4
Synthesis of Organosilica Chelating Fibers with Pluronic-F127
Templates
[0067] Thiol-functionalized organosilica sol solutions were
prepared by a micellar templating technique. A typical synthetic
procedure required a molar ratio of
1Si:20EtOH:5H.sub.2O:0.004HCl:0.14(EO).sub.105(PO).sub.70(-
EO).sub.105 (Pluronic-F127, where EO is ethylene oxide and PO is
propylene oxide). Tetraethoxysilane (TEOS) and
mercaptopropyltrimethoxysilane (MPTMS) were used as the Si sources.
Sol solutions were prepared with MPTMS to the total amount of Si
molar ratios of x/100 (MP-silica-x %-F127 sol solution, x=0-100). A
mixture of MPTMS and TEOS corresponding to the appropriate mole
fraction, with a total of 72 mmol Si (for example, 1.4 g (7.2 mmol)
of MPTMS and 13.5 g (64.8 mmol) of TEOS for MP-silica-10%-F127 sol
solution), was mixed with a solution containing 1.3 g (72 mmol) of
Dl water, 0.13 mg of HCl and 9.9 g (216 mmol) of ethanol. The
homogeneous solution was refluxed at 60.degree. C. for 1 h and then
cooled to room temperature to result in a pre-hydrolyzed sol
solution. Then a solution consisting of 5.18 g (288 mmol) of Dl
water, 10.4 mg of HCl, 10.1 mmol of Pluronic-F127, and 56.3 g (1.22
mol) of ethanol was added to the pre-hydrolyzed sol solution. The
solution was aged for 7 days to allow for the silica network to
adequately organize around the pluronic-F127 micelles. The final
homogeneous sol solution was then used as the dipping solution.
[0068] Crane-230 glass fibers were dip-coated with a MP-silica-x
%-F127 sol solution for 10 min, and placed on a fine mesh screen.
The coated glass fibers were dried in a hood at room temperature
for 12 h. The dried fibers were cured at 120.degree. C. for 48 h in
an oven. The cured MP-silica-x %-F127 fibers were allowed to cool
to room temperature slowly and weighed immediately.
[0069] The extraction of Pluronic-F127 templates was performed by
gently stirring a mixture of 1.0 g of MP-silica-x %-F127 fibers in
a solution of 1.0 g of hydrochloric acid (36 wt. %) and 180 g of
methanol in a 60.degree. C. water bath for 4 h. The
template-extracted MP-silica-x %-NF fibers were washed repeatedly
with methanol, and dried for 24 h at 80.degree. C. in vacuo.
Example 5
Analysis of Organosilica Chelating MP-silica-x %-CTABr Fibers
[0070] The chemical and physical properties of the nanoporous
organosilica chelating fibers of Example 1 were characterized by a
variety of methods. Table 2 lists some of these properties of the
MP-silica-x %-NC fibers.
[0071] The chemical structures of the fibers were characterized by
infrared spectroscopy (IR) and solid-state .sup.13C and .sup.29Si
nuclear magnetic resonance (NMR). FTIR spectra of the nanoporous
organosilica chelating fibers were obtained on KBr pellets using a
Nicolet Magna IR TM spectrophotometer 550. High-resolution .sup.13C
solid-state NMR spectra were run at 75.5 MHz on a Varian VXR300
spectrometer with a ZrO.sub.2 rotor and two aurum caps. The
spinning speed was 6 kHz. FIG. 2 shows the FTIR spectra of (a)
original Crane-230 glass fiber substrate and (b) MP-silica-20%-NC
fibers. FIG. 3 shows the solid-state .sup.13C NMR spectrum of
MP-silica-10%-NC fibers. The results not only indicated that the
organosilica chelating materials were successfully coated on the
substrate fibers, but also proved that the organic chelating groups
were covalently bound to silica.
[0072] The surface areas of all the fibers were determined by
N.sub.2 adsorption at 77 K using an Autosorb-1 volumetric sorption
analyzer controlled by Autosorb-1 for windows 1.19 software
(Quantachrome). All samples were outgassed at 80.degree. C. until
the test of outgas pressure rise was passed by 10 .mu.Hg/min prior
to their analysis. FIG. 4 illustrates the nitrogen
adsorption-desorption isotherms of (a) MP-silica-10%-NC, (b)
MP-silica-20%-NC, and (c) MP-silica-50%-NC fibers. FIG. 5
illustrates the pore size distributions for (a) MP-silica-10%-NC,
(b) MP-silica-20%-NC, and (c) MP-silica-50%-NC fibers. Nitrogen
adsorption-desorption measurements on the nanoporous organosilica
chelating fibers showed that the nanoporous organosilica chelating
fibers had high surface areas with average pore diameters of <20
nm.
[0073] TEM images were recorded on a Hitachi HF-2000 transmission
electron microscope. FIG. 6 shows the TEM image of MP-silica-10%-NC
material coated on the glass fiber substrate. Transmission electron
microscopy (TEM) images of the nanoporous organosilica chelating
fibers showed that the nanoporous organosilica chelating fibers had
many nanopores without ordered arrays.
[0074] SEM images were acquired using a Hitachi S4700 scanning
electron microscope with an acceleration voltage of 5 kV. FIG. 7
illustrates the SEM image of MP-silica-10%-NC fibers. Scanning
electron microscopy (SEM) images of the nanoporous organosilica
chelating fibers showed that although some bridging exists, most of
the nanoporous organosilica chelating material was coated on the
surface of the fibers rather than occurring randomly within all the
void volumes between the fibers. The remaining void volume and the
nanoporous organosilica chelating coating would work together to
facilitate the diffusion and access of contaminants to the
chelating groups.
[0075] Mercury was determined in adsorption isotherm solutions with
a PS Analytical Cold Vapor Atomic Fluorescence Spectrometer.
[0076] Thermogravimetric (TGA) measurements were performed on a
Hi-Res TA Instruments 2950 Thermogravimetric Analyzer. TGA analysis
revealed that the nanoporous organosilica chelating fibers were
thermally stable up to 200.degree. C.
2TABLE 2 Physicochemical characteristics of MP-silica-x %-NC
fibers. Silica coating BET surface area Pore Hg.sup.2+ loading
capacity content m.sup.2g.sup.-1 of m.sup.2g.sup.-1 of diameter
mgg.sup.-1 of mgg.sup.-1 of Material (wt. %) material coating (nm)
material coating MP-silica- 36.6 245 669 1.84 -- -- 0%-NC
MP-silica- 44.2 275 622 1.75 70.8 160.2 10%-NC MP-silica- 39.5 183
463 1.49 90.0 228.0 20%-NC MP-silica- 44.8 0 0 -- -- -- 50%-NC
Example 6
Equilibration Adsorption Isotherm Experiments of MP-silica-x %-NC
Fibers with Mercury Solutions
[0077] Tenth gram samples of MP-silica-x %-NC fibers from Example 1
were equilibrated with 10 mL solutions containing various
concentrations of mercury at room temperature. After the mixtures
were shaken for 2 h, they were filtered through a 0.22 .mu.m Nylon
66 filter and analyzed by atomic fluorescence for residual metal
content. A Thermo Elemental ExCell Inductively Coupled Plasma Mass
Spectrometer (ICP-MS) was used to determine solution concentrations
of sodium and other toxic metal ions such as silver, lead, cesium,
etc. Mercury was determined in adsorption isotherm solutions with a
PS Analytical Cold Vapor Atomic Fluorescence Spectrometer. Table 3
lists the analyzed concentrations of metal ions in aqueous
solutions of mercury after treatment with MP-silica-x %-NC
fibers.
3TABLE 3 Analyzed concentrations of metal ions in aqueous solutions
of mercury after treatment with MP-silica-x %-NC fibers. Ion
concentrations after treatment (ppm) Solution 1* Solution 2**
Material Hg Hg Na K.sub.d of Hg (mLg.sup.-1) MP-silica-0%-NC 2.5
3.4 2170 -- MP-silica-10%-NC 0.00037 0.00058 2100 637 800
MP-silica-20%-NC 0.0005 0.0012 2140 308 233 MP-silica-50%-NC 0.0081
0.0092 2150 40 117 *Initial concentration of Hg in solution 1 is
2.5 ppm. **Initial concentrations of Hg and Na in solution 2 are
3.7 ppm and 2170 ppm, respectively.
Example 7
Mercury Sorption Kinetics for MP-silica-x %-NC Fibers
[0078] Kinetic experiments were conducted for MP-silica-x %-NC
fibers from Example 1 in the same fashion as the adsorption
isotherm experiments, except that the mixtures were shaken for 1
min, 3 min, 5 min, 10 min, 30 min, 60 min and 120 min,
respectively, and then filtered through a 0.22 .mu.m Nylon 66
filter and analyzed by atomic fluorescence for residual metal
content. FIG. 8 shows the changes of mercury concentrations as a
function of time in the sorption reaction of MP-silica-10%-NC and
MP-silica-50%-NC fibers.
Example 8
Regeneration Studies on Mercury-Loaded MP-silica-x %-NC Fibers
[0079] MP-silica-x %-NC fibers from Example 1 that had been loaded
with mercury were soaked in an aqueous HCl solution (5.0 M) for 6
h. The mixture was filtered and the mercury concentration in the
filtrate was determined by Atomic Fluorescence Spectrometry. The
leached fibers were rinsed repeatedly with Dl water and oven dried
at 60.degree. C. overnight prior to reuse. Tenth gram samples of
leached MP-silica-x %-NC fibers were allowed to equilibrate in 10
mL solutions of 3.7 ppm mercury and 2170 ppm sodium for 2 h with
shaking at room temperature. The solution was filtered through a
0.22 .mu.m Nylon 66 filter and analyzed for mercury by Atomic
Fluorescence Spectrometry and for sodium by ICP-MS. FIG. 9
schematically illustrates the regeneration study on the
mercury-loaded MP-silica-10%-NC fibers.
[0080] While various embodiments of the invention have been
described, it will be apparent to those of ordinary skill in the
art that other embodiments and implementations are possible within
the scope of the invention. Accordingly, the invention is not to be
restricted except in light of the attached claims and their
equivalents.
* * * * *