US20050221087A1

US20050221087A1 - Nanoporous chelating fibers

Info

Publication number: US20050221087A1
Application number: US11/057,698
Authority: US
Inventors: James Economy; Chunqing Liu
Original assignee: University of Illinois
Current assignee: University of Illinois
Priority date: 2004-02-13
Filing date: 2005-02-14
Publication date: 2005-10-06

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.

Description

REFERENCE To RELATED APPLICATIONS

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.

FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

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.

BACKGROUND

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.
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.
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.
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.
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

In one aspect, the invention provides a nanoporous chelating fiber that includes a substrate fiber and a nanoporous chelating coating, on the substrate fiber.
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.
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.
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.
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(CH₂)_nSi (OR⁵)₃ (1)
wherein —R is the chelating group, n is an integer from 0 to 20, and —R⁵is a C1-C8 hydrocarbon group.
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.
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, CH₃(CH₂)₁₅(OCH₂CH₂)₁₀OH, (EO)₂₀(PO)₇₀(EO)₂₀, (EO)₁₀₅(PO)₇₀(EO)₁₀₅, dibenzoyl-/-tartaric acid and a cyclodextrin.
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

The invention can be better understood with reference to the following drawings and description.
FIG. 1 is a flowchart illustrating schematically the preparation of an example of nanoporous thiol-functionalized organosilica chelating fibers.
FIG. 2 is a graph illustrating the FTIR spectra of (a) original Crane-230 glass fiber substrate and (b) MP-silica-20%-NC fibers.
FIG. 3 is a graph illustrating solid-state ¹³C NMR spectrum of MP-silica-10%-NC fibers.
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.
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,
FIG. 6 is a TEM image of MP-silica-10%-NC material coated on the glass fiber substrate.
FIG. 7 is a SEM image of MP-silica-10%-NC fibers.
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.
FIG. 9 is a flowchart illustrating schematically a regeneration study on an example of mercury-loaded MP-silica-10%-NC fibers.

DETAILED DESCRIPTION

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.
The term “nanoporous,” as used herein, means a substance containing pores having an average diameter of 100 nanometers (nm) or smaller.
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.
The term “organosilica,” as used herein, means a silica (SiO_x) network containing organic chemical groups.
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.
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.

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™, 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 TiO₂, SiC, and BN; metal fibers such as iron, nickel and platinum; polymer fibers such as TYVEK™; 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° C.

TABLE 1


Commercially Available Substrate Fibers

Company	Product Line	Description

CRANE & CO.	Crane 230 (6.5 μm)	Non-woven Fiber
		Glass Mats
	Crane 232 (7.5 μm)	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 ® 7529	Non-woven Fiber
	(11 μm))	Glass Mats
LYDALL MANNING	MANNIGLAS ®	Non-woven Fiber
		Glass Mats
DUPONT	TYVEK ®	HDPE Spun
		Bonded Paper

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):

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 (—NH₂) and secondary amines (—NR¹H); ammonium groups, including trialkyl ammonium groups (—[NR²R³R⁴]⁺); calix[n]arenes; and mixtures thereof, where R¹, R², R³and R⁴may be alkyl or aryl groups. Specific examples of —R groups include —SH, —OH, —NH₂, —NR¹H, —(CH₂)_nNH(CH₂)₂NH₂, —OCH₂CH(OH)CH₂N(CH₂CH₂OH)₂, calix[n]arenes (n=4, 6, or 8), —[NCH₃((CH₂)_aCH₃)₂]⁺ Cl⁻, —[N(CH₂)₁₇CH₃(CH₃)₂]⁺Cl⁻, —[N(CH₃)₃]⁺ Cl⁻, —[N(CH₂CH₃)₃]⁺ Cl⁻, and —[N(CH₂CH₂CH₂CH₃)₃]⁺ Cl⁻.
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.
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° 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.
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 CH₃(CH₂)₁₅(OCH₂CH₂)₁₀OH (Brij-56; UNIQEMA, New Castle, DE), (EO)₂₀(PO)₇₀(EO)₂₀(Pluronic-P123, where EO is ethylene oxide and PO is propylene oxide; BASF Corporation, Mount Olive, N.J.), (EO)₁₀₅(PO)₇₀(EO)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.
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):1-10:0.5-5:1×10⁻⁵−10×10⁻⁵, 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.
The organotrialkoxysilane monomer may be a compound having the structure of formula (I):
R(CH₂)_nSi(OR⁵)₃ (1)
in which —R is a chelating group, n is an integer from 0 to 20, and —R⁵is a C1-C8 hydrocarbon group. Examples of chelating groups include thiols (—SH); alcohols (—OH); amines, including primary amines (—NH₂) and secondary amines (—NR¹H); ammonium groups, including trialkyl ammonium groups (—[NR²R³R⁴]⁺); calix[n]arenes; and mixtures thereof, where R¹, R², R³and R⁴may be alkyl or aryl groups. Specific examples of —R groups include —SH, —OH, —NH₂, —NR¹H, —(CH₂)_nNH(CH₂)₂NH₂, —OCH₂CH(OH)CH₂N(CH₂CH₂OH)₂, calix[n]arenes (n=4, 6, or 8), —[NCH₃((CH₂)₉CH₃)₂]⁺ Cl⁻, [N(CH₂)₁₇CH₃(CH₃)₂]⁺ Cl⁻, —[N(CH₃)₃]⁺ Cl⁻, —[N(CH₂CH₃)₃]⁺Cl⁻, and —[N(CH₂CH₂CH₂CH₃)₃]⁺ Cl⁻.
The tetraalkoxysilane monomer may be a compound having the structure of formula (III):
SI(OR⁶)₄ (III)
in which —R⁶is a C1-C8 hydrocarbon group.
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.
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° 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.
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.
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° 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° C., to form nanoporous chelating fibers.
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 Å to 1 mm in diameter. Preferably, the fibers have an aspect ratio of at least 10.
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.
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.
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.
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.
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_dfor 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.
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.
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.
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

Thiol-functionalized organosilica sol solutions were prepared by a micellar templating technique. A typical synthetic procedure required a molar ratio of 1Si:20EtOH:5H₂O: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° 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.
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° 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.
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° 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° C. in vacuo.
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

Thiol-functionalized organosilica sol solutions were prepared by a micellar templating technique. A typical synthetic procedure required a molar ratio of 1Si:20EtOH:5H₂O:0.004 HCl:0.14 CH₃(CH₂)₁₅(OCH₂CH₂)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° 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.
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° 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.
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° 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° C. in vacuo.

Example 3

Synthesis of Organosilica Chelating Fibers with Pluronic-P123 Templates

The thiol-functionalized organosilica sol solutions were prepared by a micellar templating technique. A typical synthetic procedure required a molar ratio of 1Si:20EtOH:5H₂O:0.004HCl:0.14(EO)₂₀(PO)₇₀(EO)₂₀(Pluronic-P123, 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 %-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° 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.
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° 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.
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° 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° C. in vacuo.

Example 4

Synthesis of Organosilica Chelating Fibers with Pluronic-F127 Templates

Thiol-functionalized organosilica sol solutions were prepared by a micellar templating technique. A typical synthetic procedure required a molar ratio of 1Si:20EtOH:5H₂O:0.004HCl:0.14(EO)₁₀₅(PO)₇₀(EO)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° 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.
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° 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.
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° 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° C. in vacuo.

Example 5

Analysis of Organosilica Chelating MP-silica-x %-CTABr Fibers

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.
The chemical structures of the fibers were characterized by infrared spectroscopy (IR) and solid-state ¹³C and 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 ¹³C solid-state NMR spectra were run at 75.5 MHz on a Varian VXR300 spectrometer with a ZrO₂rotor 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 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.
The surface areas of all the fibers were determined by N₂adsorption 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° C. until the test of outgas pressure rise was passed by 10 μHg/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.
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.
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.
Mercury was determined in adsorption isotherm solutions with a PS Analytical Cold Vapor Atomic Fluorescence Spectrometer.
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° C.

TABLE 2

Physicochemical characteristics of MP-silica-x %-NC fibers.

Silica coating BET surface area Pore Hg²⁺loading capacity

content m²g⁻¹of m²g⁻¹of diameter mgg⁻¹of mgg⁻¹of

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

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 μm 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.

TABLE 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_dof Hg (mLg⁻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

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 μm 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

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° 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 μm 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.
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.

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, CH₃(CH₂)₁₅(OCH₂CH₂)₁₀OH, (EO)₂₀(PO)₇₀(EO)₂₀, (EO)₁₀₅(PO)₇₀(EO)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(CH₂)_nSi(OR⁵)₃ (I)

wherein —R is the chelating group, n is an integer from 0 to 20, and —R⁵is 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, CH₃(CH₂)₁₅(OCH₂CH₂)₁₀OH, (EO)₂₀(PO)₇₀(EO)₂₀, (EO)₁₀₅(PO)₇₀(EO)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.