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WO2013170249A1 - Membranes nanocomposites de nanotubes de carbone fonctionnalisés et leurs procédés de fabrication - Google Patents

Membranes nanocomposites de nanotubes de carbone fonctionnalisés et leurs procédés de fabrication Download PDF

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Publication number
WO2013170249A1
WO2013170249A1 PCT/US2013/040744 US2013040744W WO2013170249A1 WO 2013170249 A1 WO2013170249 A1 WO 2013170249A1 US 2013040744 W US2013040744 W US 2013040744W WO 2013170249 A1 WO2013170249 A1 WO 2013170249A1
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Prior art keywords
carbon nanotubes
membrane
carbon
support
zwitterions
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Inventor
Eva Marand
Anil K. SURAPATHI
Wai Fong CHEN
Karl Johnson
Hangyan CHEN
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Virginia Tech Intellectual Properties Inc
University of Pittsburgh
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Virginia Tech Intellectual Properties Inc
University of Pittsburgh
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
    • B01D69/10—Supported membranes; Membrane supports
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
    • B01D69/14—Dynamic membranes
    • B01D69/141—Heterogeneous membranes, e.g. containing dispersed material; Mixed matrix membranes
    • B01D69/148—Organic/inorganic mixed matrix membranes
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
    • B01D71/02—Inorganic material
    • B01D71/021—Carbon
    • B01D71/0212—Carbon nanotubes
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
    • B01D71/06—Organic material
    • B01D71/56—Polyamides, e.g. polyester-amides

Definitions

  • the present invention relates to membranes for use in desalination and other applications, as well as to methods of fabricating such membranes. More particularly, embodiments of the invention relate to zwitterion-functtonafeed carbon nanotube nanocomposite membranes and methods of their fabrication.
  • Carbon nanotubes are promising materials for use in membranes because they have been shown to exhibit remarkably high flux, (See Holt, J. .; Park, H. G.; Wang, Y.; Stadermann, M.; Artyukhin, A. B.; Grigoropouios, C. P.; Noy, A.; Bakajin, O., Fast Mass Transport Through Sub-2-Nanometer Carbon Nanotubes, Science, 312, 1034-1037 (2006) (“Holt et at., 2006” ⁇ ; and see Kim, S.; Chen, L; Johnson, J. K.; arand, E., Polysulfone and FunctionaSized Carbon Nanotube ixed Matrix Membranes for Gas Separation; Theory and Experiment.
  • Yu et a/ also studied ion transport through carbon nanotube membranes using larger diameter (3 nm) carbon nanotubes. See Yu, M.; Funke, H. H,; Falconer, J. L; Noble, R. D., Gated Son Transport through Dense Carbon Nanotube Membranes, J. Am. Chem. Soc, 132, 8285-8290 (2010) ⁇ "Yu et at, 2010"). These larger diameter nanotubes did not exhibit any ion rejection properties, but did display gated transport due to water wettability, that could be tuned by temperature, sonication, or addition of solutes (Yu et a/., 2010).
  • nanoporous graphene is a system that is similar to carbon nanotubes; both are one-atom thick materials composed of carbon. Atomistic simulations have been used to predict that porous graphene coutd also be used for desalination by tuning the size of the pores. See Sint, K,; Wang, EL; Krai, P., Selective Ion Passage through Functionalized Graphene Nanopores, Journal of the American Chemical Society, 130, 16448-16449 (2008). Cohen- Tanugi, D.; Grossman, J. C, Water Desalination across Nanoporous Graphene, Nano Letters, 12, 3602-3608 (2012) fCohen-Tanugi and Grossman, 2012").
  • an electrically conductive polymer-nanocomposite membrane containing carbon nanotubes is highly resistant to biofiim formation when an electrical potential is applied across the membrane. See de Lannoy, C.-F.; Jassby, D.,; Gioe, K.; Gordon, A. D.; Wiesner, M, R., Aquatic Biofou!ing Prevention by Electrically Charged Nanocomposite Polymer Thin Film Membranes, Environmental Science & Technology (2013).
  • zwitterion-functionalized nanotubes could function in a similar way, but without the need for the imposed electrical potential, because the groups have permanent charges.
  • zwitterion groups that can be used include those having the structure: -GOO- Non-equilibrium !VID simulations can be used to calculate both water and ion transport through idealized membranes and it has been found that addition of two zwttterions per tube end can completely block ion transport in membranes having carbon nanotubes with diameters of 15.6 A.
  • the inventors have synthesized carbon nanotube/po!yamide nanocomposite membranes using a procedure that partially aligns the carbon nanotubes within the polyamide layer through flow filtration (Kim, Jinschek, Chen, Sholl, and Marland, 2007). Additionally, the performance of the membranes as a function of the concentration of the carbon nanotubes has been measured, it has been found that increasing the weight fraction of carbon nanotubes leads to an increase of both water transport and ion rejection, indicating that the zwitterion-functionalized carbon nanotubes are effective at both conducting water and blocking ion transport.
  • Another objective includes providing a membrane that may be useful for desalination and other filtering applications as a result of these methods.
  • the present invention provides methods of fabricating a functiona!ized carbon nanotube nanocomposite membrane.
  • the carbon nanotubes may be functionalized with zwitterions, or other functional groups, to block transport of ions through the carbon nanotubes while allowing the passage of water molecules.
  • the invention provides a method of fabricating functionalized carbon nanotube nanocomposite membranes, comprising carbon nanotube functionalization, wherein carbon nanotubes are functionalized with zwitterionic functional groups; deposition, wherein said functionalized carbon nanotubes are deposited on a membrane support; and polymerization, wherein a polymer matrix is deposited over, on, around, and/or in operable communication with, the membrane support and deposited funetionaiized carbon nanotubes; wherein the zwitterionic functional groups consist of less than 18 carbon atoms and the polymer is po!yamide.
  • the carbon nanotubes may be singSe-walied nanotubes.
  • the zwitterionic functional groups may consist of less than 18 carbon atoms, less than 14 carbon atoms, less than 12 carbon atoms, less than 10 carbon atoms, less than 8 carbon atoms, or less than 6 carbon atoms.
  • the invention provides a method of carbon nanoiube functionaiization comprising: a reflux step, wherein carbon nanotubes are refluxed in a combination of sulfuric acid and nitric acid; a thionyl chloride addition step; a 3-(dimethyfamino)propan-1-oi addition step; and a ⁇ - propiolactone addition step,
  • the invention provides a method of deposition of carbon nanotubes on a membrane support comprising; pretreatment of said membrane support with a surfactant; and filtration of a solution of said carbon nanotubes through said membrane support.
  • the invention provides a method of intrafacia! polymerization of polyamide on a membrane support, wherein the membrane support comprises a polyester side and polysulfone side, comprising; contacting the polyester side of the said membrane support with an aqueous solution comprising a diamine; removing said aqueous solution from said membrane support; and contacting the polysulfone side of said membrane support with an organic solution comprising an acid chloride,
  • the invention provides a functionalized carbon nanotube nanocomposite membrane, comprising a membrane support; carbon nanotubes functionalized with zwitterionic functional groups deposited on the membrane support; and a po!ymer matrix overlaying the carbon nanotubes and membrane support; wherein the zwitterionic functional groups consist of less than 18 carbon atoms and the polymer is poiyamide.
  • FIG. 1 is a schematic diagram showing an exemplary embodiment of a carbon nanotube functionalization method according to the invention.
  • FIG. 2A is a photo showing an exemplary embodiment of a filtration cell for use in a method according to the invention.
  • FIG. 2B is a photo showing a polyethersuSfone (PES) support membrane with carbon nanotubes deposited using a high-pressure filtration technique according to the invention.
  • PES polyethersuSfone
  • FIGS. 3A-C are schematic diagrams depicting an exemplary method according to embodiments of the invention for fabricating a carbon nanotube nanocomposite membrane according to the invention.
  • FIG. 3D is a photo showing the top of a functionalized carbon nanotube nanocomposite membrane prepared in accordance with embodiments of the method illustrated in FIGS. 3A-C.
  • FIG. 4 is a fable illustrating different gas permeabilities of non- Simiting examples of carbon nanotube nanocomposite membranes according to the invention.
  • FIG. 5A is a table illustrating water flow and sait rejectio of a non- limiting example of a carbon nanotube nanocomposite membrane according to embodiments of the invention.
  • FIG. 58 is a graph illustrating water flow and salt rejection of a non- limiting example of a carbon nanoiube nanocomposste membrane according to embodiments of the invention.
  • FSG. 6 is a computer rendered image depicting a simulation setup for simulation studies of nanotubes to model the effects of water and ion transport through functionalized single-wall nanoiube membranes.
  • FIG. 7A is a graph illustrating a computer simulation of the flux of salt ions through a pristine single-walled carbon nanoiube membrane.
  • FIG. 7B is a graph illustrating a computer simulation of the flux of salt ions through a single-walled carbon nanoiube functionalized with two zwitterions on the end of each nanoiube.
  • FIG. 8 is a computer rendered image depicting a simulation cell containing a membrane composed of four carbon nanotubes embedded between two graphene sheets with saltwater on either side of the membrane, wherein each end of the tube is functionalized with two zwitterionic groups.
  • FIGS. 9A and 98 are graphs illustrating conductance of water and ions, respectively, as a function of simulation time per carbon nanoiube (20,0) for pristine (non-functionaiized) nanotubes, carbon nanotubes with one zwitterion at each end, and with two zwitterions at each end for a bulk concentration of 0.6 NaCI and a pressure drop of 208 Pa.
  • F!GS. 10A and 10B are graphs illustrating conductance of water and ions, respectively, as a function of simulation time per carbon nanoiube (26,0) for carbon nanotubes with two zwitterions at each end, with four zwitterions at each end, and with five zwitterions for each end fo a bulk concentration of 0.6 NaCI and a pressure drop of 208 MPa,
  • FSG. 1 1 is a graph illustrating water flux and salt rejection ratio as a function of carbon nanoiube concentraiton in the selective poiyamide layer of a non-limiting example of a nanocomposiie membrane of the invention.
  • F!GS. 12A and 12B are graphs illustrating conductance of water and ions, respectively, as a function of simulation time through carbon nanotubes functionalized with one or two zwitterions per tube end and with charges o the zwitterions turned on or off.
  • FSG. 13A-C are schematic diagrams iiiustrating configurations of zwitterions that are extended (unfolded) into the iiquid phase or folded inside the carbon nanotube for a (20,0) system with (A) one zwitterion or (B) two zwitterions per tube end and for a (26,0) system with (C) five zwitterions per tube end .
  • FIGS. 13D and 13E are PMF diagrams illustrating free energy as a function of carbon position along the z axis, wherein FIG. 13D is a PMF diagram for moving one zwitterion in a (20,0) carbon nanotube with one or two zwitterions per tube end, and FIG. 13E is a PMF diagram for moving one zwitterion in a (26,0) carbon nanotube with two or five zwitterions per tube end.
  • FIG, 14 is a table iiiustrating water and ion flow rate (number per ns per carbon nanotubule) and ion rejection ratio as a function of salt concentration for flow through a (20,0) carbon nanotubule having one zwitterion functional group at each end,
  • FIG. 15 is a graph illustrating salt rejection of NaCI feed concentration for a plain po!yarnide membrane and a non-limiting example of a nanocomposite membrane with 20 wt% carbon nanotubes.
  • FSGS. 16A and 16B are graphs illustrating conductance of water and ions, respectively, per carbon nanotube as a function of simulation time for pristine non-functiona!ized nanotubes, carbon nanotubes with one zwitterion at each end and with two zwitterions at each end for a bulk concentration of 0.6M KG! and a pressure drop of 208 MPa,
  • FIGS. 17A-C are graphs illustrating water flux and salt rejection for a pure polyamide membrane, 9wt% zwitterion-functiona Sized single-wailed nanotube/poiyamide nanocomposite membrane and a 20 wt% zwitterions- functionalized single-wal!ed nanotube/poiyamide nanocomposite membrane operated for a pressure drop of 530 pst,
  • FIGS. 18A-C are field emission scanning microscopy images of surface morphologies of a (FIG. 18A) PES support, (FIG. 18B) plain polyamide membrane, and (FIG. 18C) zwitterion-functiona Sized carbon nanotube/polyamide nanocomposite membrane.
  • FIG. 18D is a field emission scanning microscopy image of a cross- sectional view of a zwitterion-functionalized carbon nanotube/poiyarrtide nanocomposite membrane.
  • a method of the present invention may comprise a procedure or process for fabrication of a functionalized carbon nanotube nanocomposite membrane.
  • the method may comprise a carbon nanotube functiona!ization step, wherein carbon nanotubes are functionalized with zwitterions or other functional groups, a deposition step, wherein said functionalized carbon nanotubes are deposited on a membrane support, and a polymerization step, wherein a polymer matrix is deposited over the membrane support and/or carbon nanotubes to create a functionalized carbon nanotube nanocomposite membrane.
  • a product or products of the present invention may comprise functionalized carbon nanotube nanocomposite membranes fabricated by such a method.
  • the membranes of the present invention possess a number of potential advantages over the prior art, only some of which that are discussed herein, including high water fiux, excellent salt rejection, and resistance to biofouling.
  • the membranes of the present invention, and the method of their fabrication, may be particularly beneficial for use in desalination, water purification, and gas separation.
  • carbon nanotubes, nanotubes for use in nanocomposite membranes and for use in membrane fabrication methods of the invention may have a pore diameter of about 0.1 nm to about 60 nm, 0,1 nm to about 10 nm, such as from about 0.1 nm to about 3,0 nm, about 0.4 nm to about 2,5 nm, about 0.4 nm to about
  • Carbon nanotubes, nanotubes for us in nanocomposite membranes, and for use in membrane fabrication methods of the invention may have a pore diameter of about 1 A to about 100 A, about 2 A to about 30 A, about 5 A to about 25 A, about 10 A to about 20 A, about 10 A to about 18 A, about 10 A to about 16 A, about 10 A to about 14 A, about 10 A to about 12 A, about 12 A to about 20 A, about 14 A to about 24 A, about 16 A to about 22 A, about 12 A to about 18 A, about 14 A to about 16 A, about 15 A to about 19 A, about 11 A to about 15 A, and so on.
  • carbon nanotubes, nanotubes for use in nanocomposite membranes, and for use in membrane fabrication methods of the invention may have a length anywhere from about 0,1 pm to about 10 pm, about 0,1 pm to about 2,0 pm , about 0.5 pm to about 1.5 pm, about 0.7 pm to about 1.3 pm, about 0,8 pm to about 1.2 pm , about 0.9 pm to about 1 ,1 pm , about 0,5 pm to about 1.2 pm, about 0.9 pm to about 1,5 pm, about 0.8 pm to about 1.4 pm , about 0.7 pm to about 1.1 pm, and so on.
  • Such carbon nanotubes may have a length anywhere from about 20 A to about 100 A, about 30 A to about 50 A, about 35 A to about 45 A, about 36 A to about 44 A, about 37 A to about 43 A, about 38 A to about 42 A, about 40 A to about 44 A, about 41 A to about 43 A, about 39 A to about 42 A, about 41 A to about 45 A, about 40 A to about 42 A, about 42 A to about 44 A, and so on.
  • the length, diameter, and other properties of the carbon nanotubes may be chosen according to the particular filtering applications desired for the nanocomposite membrane. For example, for gas separations, smaller pore diameters which selectively allow specific gas molecules to pass through the nanocomposite membrane while excluding other gas molecules may be used, while for desalination applications, pore sizes which allow wate molecules to pass through the nanocomposite membrane while excluding salt ions may be used. Further, the length of the nanotubes may be chosen according to the thickness of the membrane desired.
  • the methods of the present invention may use a variety of types of carbon nanotubes, including multi-wailed carbon nanotubes (MVVNTs), double- walled carbon nanotubes (DWNTs), and single-walled carbon nanotubes (SWNTs).
  • MMVNTs multi-wailed carbon nanotubes
  • DWNTs double- walled carbon nanotubes
  • SWNTs single-walled carbon nanotubes
  • the carbon nanotubes may be synthesized through a variety of methods known in the art, including arc discharge, laser ablation, plasma torch, high pressure CO disproportion, and chemical vapor deposition (CVD), In a preferred embodiment, CVD is used to produce the carbon nanotubes.
  • SWNTs for use in methods of the invention may be of a variety of dimensions such as those disclosed herein.
  • a non-limiting example of a SWNT for use in nanocomposite membranes of the invention is a SWNT with an outer diameter of 1.5 nm and a length of 1 pm.
  • Another non-limiting example of a SWNT for use in nanocomposite membranes of the invention is a SWNT with a diameter of about 15.6 A and a length about 41.2 A
  • Another non-limiting example of a SWNT for use in nanocomposite membranes of the invention is a SWNT with a diameter of about 20.3 A and a length of about 43.3 A.
  • SWNTs for use in membrane fabrication have an outer diameter of about 0.5 nm to about 2.0 nm, and a length anywhere from about 0.1 pm to 10 pm, and any range in between such as those disclosed herein, indeed, any of the specific ranges disclosed above for length, pore size/diameter, and whether the structure is single waited, double walled, or multi-walled can be combined in any manner to obtain nanoiubes according to the invention.
  • the carbon nanoiubes can be functiona!ized with a variety of functional groups, inciuding but not limited to alkanes, alkenes, alkynes, phenyl groups, alkyl halides, amines, amides, alcohols, ethers, aldehydes, ketones, carboxyiic acids, ethers, esters, nitrates, nitrites, alkoxy groups, hydroxy! groups, amino groups, halo groups, earbonyi groups, benzyl groups, cyano group, siiyl groups, sulfonic acid groups, phosphoric acid groups, boronic acid groups, free radicals, and any combination thereof.
  • functional groups inciuding but not limited to alkanes, alkenes, alkynes, phenyl groups, alkyl halides, amines, amides, alcohols, ethers, aldehydes, ketones, carboxyiic acids, ethers, esters, n
  • the carbon nanotubes are functionalized with zwitterion functional groups.
  • Preferred are short zwitterion functional groups such as those with less than 18 carbon atoms, more preferably less than 18 carbon atoms, stiSi more preferably less than 14 carbon atoms, still more preferably less than 12 carbon atoms, stiil more preferably less than 10 carbon atoms, stilt more preferabl less than 8 carbon atoms, and most preferably less than 6 carbon atoms. Even more preferred are short zwitterion functional groups having 5 carbon atoms.
  • zwitterion functional groups with the structure: -COO-(CH2)3- ,' ⁇ CH3)2-(CH 2 )2COO " .
  • other structures may be substituted. Indeed, any functional group comprising from 1-20 carbon atoms can be used and including other atoms such as oxygen, nitrogen, sulfur, and/or halogens. These include zwitterion functional groups wherein the positive and negative charges are located at different locations.
  • SWNTs are obtained as starting materia! and then purified and functionalized with COOH groups by refluxing in sulfuric acid/nitric acid.
  • purity of the SWNTs may be greater than 95% ⁇ by TGA) and concentration of COOH groups in the SWNTs may be approximately 2-7 wt% (by titration).
  • concentration of COOH groups in the SWNTs may be approximately 2-7 wt% (by titration).
  • variations of this procedure and other methods of functionalization of SWNTs with COOH groups may be used.
  • the COOH groups in the SWNTs may serve as precursors for the addition of short zwitterion groups.
  • FIG.1 shows an exemplary embodiment of a series of chemical reactions for converting COOH groups to zwitterion groups.
  • the series of reactions produce a series of chemical modifications and may Include a thionyl chloride addition step, a 3-(dimethy!amino ⁇ propan-1-o! addition step, and a ⁇ -propiolactone addition step, !n particular, in the first step, COOH functionalized SWNTs may be reacted with thionyl chloride to change COOH groups into COC! groups (FIG 1 (A)).
  • purification and extraction methods may be utilized to purify the modified carbon nanotubes and to remove unreacted reagents. These purification and extraction methods may involve washing the carbon nanotubes in a suitable solvent, cenirifugation, filtration, and/or drying.
  • acyi chloride-functional ized SWNTs to zwitterion-functionaSized SWNTs
  • 100 mg of COCl SWNTs ⁇ 0.1 mmoi of COCI group may be added to a mixture of 1.2 ml 3-(dimethySamino)propan-1 ⁇ ol (10 mmoi) and 1 ,4 m! of triethyl amine (10 mmoi) in a 100 ml flask.
  • the reaction mixture may be stirred for 6 days at 100 RP and room temperature.
  • the SWNTs may then be washed with eihanol to remove ethylamine hydrochloride sa!t and dried under vacuum.
  • SWNTs may be reacted with B-propio!actone to form zwitterion-functionaiized SWNTs.
  • 100 mg of function a iized SWNTs may be added to 20 mi of dry tetrahydrofuran (THF) in a SO ml flask.
  • the reaction mixture may be stirred under nitrogen protection at room temperature for 5 hours.
  • SWNTs may be washed with dry THF and separated by centrifuging. They may be dried under vacuum to remove any washing so!vent.
  • the zwitterion functional group is circled red in FIG. 1 (C).
  • the amounts of reagents described herein are merely exemplary, and differing amounts and ratios may be substituted as appropriate as may be appreciated by a skilled artisan
  • Various embodiments of carbon nanotubes for use in methods for fabricating functiona!ized carbon nanotube nanocomposite membranes according to embodiments of the invention may include a range of a number of functional groups attached to carbon nanotubes.
  • various embodiments include carbon nanotubes with anywhere from 1 zwitterion to 20 zwiitenons attached at one or both ends.
  • Other embodiments include carbon nanotubes with 1 zwitterion to 10 zwiitenons attached at one or each end, or from 1 zwitterion to 5 zwitterions attached at one or each end, or foam 2 zwitterions to 6 zwitterions attached at one or each end, or from 1 zwitterion to 3 zwitterions attached at one or each end, o from 2 zwitterions to
  • the nanotubes can comprise 4, 5, 6, or 7 zwitterions attached at one end, or 4 zwitterions attached at each end or only at one end, or 4 zwitterions attached at one end and 5, 6, or 7 zwitterions attached at the other end, or 5 zwitterions attached at one end and 4, 6, or 7 zwitterions attached at the other end, or 6 zwitterions attached at one end and 4, 5, or 7 zwitterions attached at the other end, or 7 zwitterions attached at one end and 4, 5, or
  • the carbon nanotubes may be deposited on a membrane support.
  • a dispersion of the carbon nanotubes may be made.
  • the deposition of functiona!ized carbon nanotubes on a membrane support may include pretreatment of the membrane support with a surfactant and filtration of the dispersion through the support to deposit the carbon nanotubes.
  • the dispersion of carbon nanotubes may be made in a variety of solvents or surfactants. Use of various solvents or surfactants that allow fo efficient dispersion and alignment of the carbon nanotubes is contemplated. If a solvent is used, various concentrations of the carbon nanotubes in the solvent are contemplated. In certain embodiments of the invention, the solvent may be water. In other embodiments, other solvents that may be used for dispersion of the carbon nanotubes may be chosen from tetrahydrofuran (THF) 1 ,4-dioxane, acetone, acetonitrile dimethyifornamide, dimethySsulfoxide, or the like.
  • THF tetrahydrofuran
  • solvents more suitable for dispersion of the carbon nanotubes, depending on the type of chemical functional group that may be present on the carbon nanotubes.
  • a hydrophobic functional group has been added to the carbon nanotubes, it may be more desirable to disperse the carbon nanotubes in a non-polar solvent such as diethylether, hexane, benzene, toluene, chloroform, ethyl acetate, dichloromethane or the like.
  • the membrane support may be made of a variety of materials, including po!yfluoroethyiene (PTFE) and polyviny!idene fluoride (PVDF), or hydrophi!ic materials, such as polypropylene, poiyethersulfone (PES), and nylon,
  • PTFE po!yfluoroethyiene
  • PVDF polyviny!idene fluoride
  • hydrophi!ic materials such as polypropylene, poiyethersulfone (PES), and nylon
  • the surfactant may be an anionic surfactant such as sulfate, sulfonate, and phosphate esters, Including but not limited to sodium dodecylsulfonate, sodium dodecyibenzenesulfonate, ammonium tauryi sulfate, sodium laureth sulfate, alkyl benzene sulfonate, and the like.
  • anionic surfactant such as sulfate, sulfonate, and phosphate esters, Including but not limited to sodium dodecylsulfonate, sodium dodecyibenzenesulfonate, ammonium tauryi sulfate, sodium laureth sulfate, alkyl benzene sulfonate, and the like.
  • the dispersion may be filtered avoirough the membrane support through high-pressure filtration or vacuum filtration, or at ambient pressure, atmospheric pressure, or no pressure.
  • a fixed amount of zwitterion-functionaiized SWNTs may be sonicated in deionized water, in a volume, for example, of 40 mi, to create a carbon nanotube solution
  • Poiyethersulfone (PES) membrane supports may be pretreated by soaking in a surfactant solution.
  • a surfactant solution of sodium dodecyibenzenesulfonate at a concentration of 0,5% (w/v) may be used.
  • the surfactant treatment may be of various lengths of time, ranging from 1 hour, to several hours, up to 1 day or even up to 1 week,
  • the membrane supports are pretreated for two days.
  • surfactant pretreatments may make the membrane support more hydrophilic and also at the same time open the pores of the support enabling to filter the carbon nanotube dispersion through it using an apparatus shown in FIG. 2A, which shows a Miilipore filtration cell.
  • the length of time of pretreatment may be adjusted according to the strength and concentration of surfactant used, in another embodiment, after soaking in the surfactant solution, the PES support may b stored in deionized water to remove any excess of surfactant.
  • the PES support may be stored in water for at least four hours up to and including 72 hours, for example. In a preferred embodiment, the PES support is stored in water for one day.
  • the SWNTs may then deposited on the membrane support using various techniques, such as high-pressure or vacuum filtration method, or gravity, wherein the support acts as a fitter paper and the carbon nanotubes are filtered out of the solution and aligned on the support.
  • the membrane support may be fitted at the bottom of the filtration cell, and filled with carbon nanotube dispersion and pressurized using an inert gas such as nitrogen at high pressure (at least 40 PSI feed gas tank pressure).
  • the dispersion inside the filtration ceil may be stirred at a very low RPM (for example, around 50). The stirring helps in forming a uniform layer of SWNTs on top of the PES support as shown in FIG. 2B, which shows the polyethersulfone (PES) support membrane with functionaiized carbon nanotubes deposited using the high-pressure filtration technique described here.
  • the carbon nanotubes may be deposited by other filtration techniques such as vacuum filtration.
  • zwitterion-functionalized carbon nanotube nanocomposite membranes of the invention may be fabricated with zwitterion- functionalized carbon nanotubes at weight percentages in the polymer layer ranging from about 0.1 wt% to about 99.9 wt%, 10 wi% to about 90 wt%, 40 wt% to about 80 wt%, 60 wt% to about 70 wt%, such as from about 1 wt% to about 50 wt%, 1 wt% to about 20 wt%, 2 wt% to about 20 wt%, or from about 5 wt% to about 30 wt%, 10 wt% to about 30 wt%, 15 wt% to about 25 wt%, or from about 16 wt% to about 24 wt%, 18 wt% to about 26 wt%, 18 wt% to about 25 wt%, 15 wt% to about 23 wt%, 19 wt%
  • the particular concentration of carbon nanotubes may be selected based on various factors including the functional groups attached to the carbon nanotubes, dimensions of the carbon nanotubes, and the number of functional groups attached. Any combination of one or more of these features, especially combinations of the particular dimensions provided in this specification for these features, can be used to obtain a desired nanotube according to the invention.
  • Non-limiting examples of proportions of zwitterion- functionalized carbon nanotubes making up a composite membrane include 9 wt% and 20 wt% of the polymer matrix, in embodiments, the polymer matrix comprises polymer and nanotubes to provide a matrix.
  • a polymerization step wherein a polymer matrix is deposited over the membrane support and deposited functionalized carbon nanotubes to create a functionalized carbon nanotube nanocomposite membrane, may be included to complete fabrication.
  • a polymerization step wherein a polymer matrix is deposited over the membrane support and deposited functionalized carbon nanotubes to create a functionalized carbon nanotube nanocomposite membrane, may be included to complete fabrication.
  • Preferred is the interfacia! polymerization procedure described below.
  • intrafacial polymerization may occur through contact of an organic solution comprising an acid chloride with an aqueous solution comprising a diamine.
  • the organic solution comprises trimesoy! chloride (TMC) and the aqueous solution comprises phenyiene diamine (IVIPD).
  • the organic solution and aqueous solution are introduced on different sides of the support.
  • the membrane support is a PES support comprising a poiysulfone side and a pofyester side
  • the organic solution may be introduced on the poiysulfone side of the support and the aqueous solution may be introduced on the polyester side of the support.
  • the organic solution may be introduced on the polyester side of the support and the aqueous solution may be introduced on the poiysulfone side of the support.
  • the aqueous solution contains a surfactant and the organic solution contains a non-polar solvent.
  • the organic solution and the aqueous solution may be briefly introduced to the membrane support as described above, and then removed.
  • the membrane support may then be cured at high temperature and then washed to remove excess solution.
  • the support after filtering the carbon nanotube dispersion through the PES support, the support may be dried in a vacuum oven ⁇ for example, for one hour). It may then be soaked in 0.5 % (w/v) surfactant solution (for example, for one day).
  • aqueous and an organic solution may be prepared.
  • the aqueous solution and the organic solution contain m-phenylene diamine (MPD) and trimesoyt chloride (TMC), respectively.
  • the MPD solution contains surfactant aiong with the MPD,
  • the concentration of surfactant may be 0.2 % (w/v) and the concentration of MPD may be 2 % (w/v) in water.
  • the concentration of TMC may be 0.5 % (w/v) in hexane or similar organic solvent. However, differing concentrations within this genera!
  • the PES support with the deposited carbon nanotu es may be placed between two circular PTFE frames, holding together using a metal clamp.
  • the interfaciai polymerization method followed here is different from the one generally described in the art.
  • This method of interfaciai polymerization may be referred to herein as 'Back and Front' interfaciai polymerization method.
  • the polyester side of the PES support may be briefly soaked with MPD (for example, 1 min).
  • the MPD solution may be drained and the support dried for a minute, cleaning the excess MPD solution using a Kim wipe or other suitable absorbent material.
  • the TMC solution may be briefly introduced (for example, 2 minutes) on the polysulfone side of the support, using a syringe, pipet, or other suitable transfer means and then may be drained. Polymerization will occur relatively quickly (within minutes).
  • the TFN membrane prepared may be cured in air-circu Sated oven briefly at high temperature (for exampie, at 68°C for 5 min). The membrane may be washed in Dl water to remove excess MPD, and then stored in wafer for at least one day before testing for either gas separation or desalination.
  • the interfaciai polymerization could be carried out by briefly soaking the front side with MPD solution (for example, for about 2 min).
  • the excess solution from the impregnated membrane may then be removed using a glass roller or other suitable means.
  • the membrane may be placed back to the PTFE frame and the TMC solution may be introduced on the front side of the support using a syringe or pipet.
  • the TMC solution may be drained very slowly after a brief period (for example, 90 seconds) and the following procedures were identical to that mentioned previously.
  • the 'Back and Front (B-F)' intrafacial polymerization (IP) method is particularly advantageous over prior art intrafacial polymerization methods, where both the MPD and the TMC solutions are introduced on the polysuifone side of the membrane followed in making desalination membranes, intrafacial poiymerization methods previously described in the art result in a loose polyamide layer formed on the top of the SWNTs. This layer was washed away while testing the membranes for desalination.
  • the Back and Front intrafacial poiymerization method described herein in forming poSyamide embedding the functionalized carbon nanotubes over the PES support, the polyamide formed adhered to the polysuifone thereby forming an excellent integral membrane.
  • various embodiments of methods of fabricating functionalized carbon nanotube nanocomposite membranes according to the invention include use of a range of materials for forming the polymer of the nanocomposite. While polyamide is preferred, particularly according to the intrafacial polymerization methods described herein, other polymers commonly used in desalination membranes may be substituted in the methods disclosed herein, inciuding polyurea, polyimide, poiycarbonate, poSymethaerylate, poiysuiphone, other thermoplastic polymers, or ceilu!ostc polymers (e.g. , cellulose acetate (CA) and celiuiose triacetate (CIA)). Various methods of polymerization of these materials are known in the art.
  • CA cellulose acetate
  • CIA celiuiose triacetate
  • FIG. 3A represents a PES ultrafiltration membrane, composed of a thin PES layer covered on a nonwoven polyester web, soaked in a surfactant solution to clean the pores and increase hydrophilicity. The membrane was then sandwiched by two PTFE holders.
  • FIG. 38 represents zwitterion-functionalized carbon nanotubes, deposited on the pretreated PES membrane, through vacuum filtration.
  • FIG..
  • FIG. 3C represents inter acial polymerization of polyamide earned out between semi-aligned functionalized carbon nanotubes at which aqueous solution of MPD comes in contact with the non-aqueous solution of IMC.
  • FIG. 3D shows a photograph of the top of the functionalized carbon nanotube nanocomposite membran that is exposed to the feed.
  • Embodiments of the invention include methods of fabricating functionalized carbon nanotube nanocomposite membranes scaled up to industrialized scales for industrial membrane manufacture. For example, some of the individual steps may be carried out in industrial reactors wherein raw material or materials enter a reactor to produce a product
  • the product may be an intermediate product that is subsequently feed to a second downstream reactor, which is fed additional raw materia! or materials to produce a second intermediate product, which is then fed to a third downstream reactor, which is fed additional raw material or materials to produce a third intermediate product, and so on.
  • intermediate products may be fed on a conveyor to different stations where individual fabrication steps occur, either through automation, human assistance, or a combination of both.
  • interracial polymerization of poiy amide is carried out by industrial sprayers that apply the MPD and TSvlC solutions to a PES membrane that has previously been applied zwitterion-functionalized carbon nanotubes at an upstream processing station.
  • Scaling of the fabrication steps disclosed herein to an industrial scale is within the capabilities of a skilled chemical engineer or industrial chemist,
  • the present invention also provides various embodiments of functionalized carbon nanotube nanocomposite membranes, including those fabricated by the methods described herein.
  • the functionalized carbon nanotube nanocomposite membranes may comprise any component at any specification in any range disclosed above, such as with respect to the types of carbon nanotubes, carbon nanotube length and pore diameter, functional group type, structure, length, number, and position, type of polymer, and weight percentage of the carbon nanotubes in the polymer layer,
  • nanocomposite membranes After the nanocomposite membranes are formed, they may be used as is for filtration or further modified. It is contemplated that additional modifications may be made to the nanocomposite membranes to confer additional properties. For example, additional layers of polymers may be added to the nanocomposite membranes in order to modify their permeability. It is contemplated that chemical modifications may be made to the carbon nanotubes, polymer, or membrane support to change the properties of the membrane.
  • the nanocomposite membranes of the invention exhibit excellent properties for filtration applications Including high water flux, excellent salt rejection, resistance to biofouling, and high gas permeability and selectivity.
  • the functionalized carbon nanotube nanocomposite membranes of the invention have a variety of applications, only some of which are discussed herein. They may be used as membranes in desalinization plants for reverse-osmosis filtration of salt water, and are durable enough for use in conjunction with high pressure pumps. Since the membranes of the invention are resistant to biofouling, this obviates the use of blocides and biofouiing inhibitors in desalination plants that employ them.
  • the membranes may be used for other water filtering and purification applications, such as removal or harmful waterborne pathogens such as Cryptosporidium and Giardia as well as toxins such as perch iorate, and may be used fo water purification at utilities, at households, or campsites, in addition, the membranes of the invention can be used to separate various gases in mixtures that result from industrial processes, such as chemical plants, oil refineries, gasification plants, etc. Additional applications that are contemplated include the use in respirators, drug delivery channels for drug delivery, chemical sensing, and protein purification. Additional, non-limiting descriptions of some of the properties and advantages of the nanocomposite membranes according to the invention will be provided in the Examples below.
  • FIG. 4 shows results of gas permeabilities of nanocomposite membranes according to the invention that have differing amounts of zwittenon-functionalized carbon nanotubes in comparison to a pure polyamide membrane.
  • Gas permeabilities of all the gases tested increased with increase in the concentration of the carbon nanoiubes without affecting the selectivity.
  • the permeability increased by a factor of 1 1 (H 2 ), 19 (H 2 ), 33 ( ⁇ 1 ⁇ 4), 20 (CH 4 ) and 37 (CO2) compared to the pure polyamide membrane.
  • the functional group in the carbon nanotubes also affected (increased) the gas permeabilities, but not the selectivities.
  • COOH functionalized carbon nanotube membrane showed higher permeabilities compared to the zwitterion-functionalized carbon nanotube membrane. This is in accordance with the sorption results obtained for the COOH and zwitterion-functionalized carbon nanotubes.
  • thin nanocomposite membranes may be fabricated whose gas separation performance (high permeability and selectivity) transcends Robeson upper bound, and consequently make these membranes economically attractive for gas separation operations in a chemical plant.
  • FIGS. 5A and 5B show results obtained from a reverse osmosis testing of zwitterion-functionalized carbon nanotube nanocomposite membranes with 0.25 mg of carbon nanotube.
  • the table in FIG. 5A compares the water flux (unit in GFD) and salt rejection (unit in %) within three consecutive testing days. At 530 psi, there is no significant drop in the salt rejection rate after three days of testing. Testing verified that the membrane is durable and stable against the surface fouling by salt water.
  • reverse osmosis membranes consisting of neat polyamide coating of similar thickness (without carbon nanotubes) on the same support had much lower water flux (0 - 7 GFD) and lower rejection rates (less than 57%),
  • Simulations were carried out using standard molecular dynamics techniques and tested potential models to model the effects of water and ion transport through functionalized SVVNT membranes.
  • Two different types of nanotubes were used in the simulations in order to identify effects due to the diameter of the SWNTS,
  • the tubes used were (17,0), having diameters of 1 ,33 nm, and (20,0) SWNTs, having diameters of 1.56 nm.
  • the diameter of the (20,0) SWNTs are very close to the average diameter of the nanotubes used in the experiments.
  • the model membrane was constructed by embedding the nanotubes between a pair of graphene sheets that prevented water and ions from flowing through the space between the nanotubes.
  • FIGS. 7 A and 78 illustrate a computer simulation of the flux of salt ions through a pristine single- wailed carbon nanotube membrane and a singie-wailed carbon nanotube functionalized with two zwitterions on the end of each nanotube.
  • the zwitterions effectiveiy block the sait flux under identical conditions of operation according to the predictions from the simulations.
  • the zwitterions are effective gatekeeper moieties that turn an unseSective membrane into a highly selective membrane suitable for desalination.
  • Water Flux and ion Rejection Molecular simulations clearly show that zwitterion-funcfionalized carbon nanotubes reject ions, while allowing an acceptable flux of water.
  • FiG Another embodiment of a simulation ceil for single- wailed carbon nanotube membranes is shown in FiG, 8, which depicts a simulation ce!! containing a membrane composed of four carbon nanotubes embedded between two graphene sheets with saltwater on either side of the membrane, wherein each end of the tube is functionalized with two zwitterionic groups, in FIG.
  • the carbons of the carbon nanotubes and graphene sheets are shown as cyan lines.
  • Water molecules are shown as red and white sticks, ⁇ and Na + ions are shown as green and blue spheres, respectively, and the atoms of the zwitterions are shown as space filling models, cyan for C, red for O, white for H, and magenta for N,
  • each end of each tube was functionalized with 0, 1, or 2 zwitierion groups.
  • the diameter of each tube is about 15 A, which is similar to the average diameter of the carbon nanotubes used in experiments.
  • the conductance of water and ions for NaCl solutions was calculated at a pressure drop of 208 MPa foundedough pristine and functiona Sized carbon nanotubes. This large pressure drop was used in order to improve the sampling statistics in the simulations, because the time scales accessible in simulations were only on the order of 10s of nanoseconds.
  • extrapolation to lower pressure drops can be made since the flux of water has been shown to be a linear function of the pressure drop for both nanotubes (Corry, 2008) and for graphene nanopores (Cohen- Tanugi and Grossman, 2012).
  • FIGS. 9A and 9B The conductance of water and ions through (20,0) carbon nanotubes as a function of simulation time is shown in FIGS. 9A and 9B, respectively.
  • Error bars show the standard deviation based on four independent simulations. The linear increase in conductance with time indicates that the simulations are at steady state.
  • FIGS. 9A and 9B The conductance of water and ions per carbon nanotube (20,0) for pristine (non-functionalized) nanotubes (black line with solid square), carbon nanotubes with one zwitterion (1 Zl) at
  • nanotubes for example, carbon nanotubes can be configured in a manner to provide for the flow of water through the nanotubes at a rate ranging for example between 0 and 2,000 water molecules per nanotube per ns, such as from about 50 to 1 ,000 water molecules per nanotube pe ns, such as from about 150 to 750 water molecules per nanotube per ns, or from about 200 to about 800 water molecules per nanotube pe ns, such as from about 300 to 500 water molecules per nanotube per ns, and so on.
  • a rate ranging for example between 0 and 2,000 water molecules per nanotube per ns, such as from about 50 to 1 ,000 water molecules per nanotube pe ns, such as from about 150 to 750 water molecules per nanotube per ns, or from about 200 to about 800 water molecules per nanotube pe ns, such as from about 300 to 500 water molecules per nanotube per ns, and so on.
  • the nanotubes such as carbon nanotubes
  • the nanotubes can be configured in a manner to provide for an ion rejection ratio of between 0 and 100%, such as from about 10-90%, or from 20-80%, or from 30-70%, or from about 40-80%, such as about 50%.
  • FIGS, 16A and 16B show conductance of (FIG. 16A) water and (FiG. 16B) ions per carbon nanotube for pristine (non-functionalized) nanotubes (biack line with solid square), carbon nanotubes with one zwitterion (1 Zi) at each end (blue line with empty triangle), and with two zwitterions (2 ZI) at each end (red Sine with solid circle) for a bulk concentration of 0.6 M KCi and a pressure drop of 208 MPa. Error bars show the standard deviation based on four independent simulations.
  • the diameter distribution of carbon nanotubes used in experiments ranges from 10 to 20 A, with an average diameter of 15 A- NanoLab inc. 179 Bear Hill Road, Waitham, MA 02451 ("NanoLab").
  • One or two zwitterion groups on one or both ends should be adequate to block all ion transport in carbon nanotubes having diameters less than 15 ⁇ (vide supra).
  • FIG. 11 shows water flux (solid) and salt rejection ratio (hatched) as a function of CNT concentration in the selective PA layer of the nanocomposite membrane.
  • concentrations of zwitterion-functionalized CNTs Z-CNTs
  • Z-CNTs zwitterion-functionalized CNTs
  • EC-CNTs end- capped CNTs
  • concentration of NaCI is 1000 ppm.
  • Pressure of 530 psi was applied for each membrane test. Error bars were computed from the standard deviations of the fluxes over a three day period.
  • FIGS. 17A-C Adding 0.25 mg carbon nanotubes to the polyamide membrane resulted in the water flux increasing more than two-fold, from 6.8 GFD (gallons per square foot per day) to 14.0 GFD, while the rejection of Na + increased by approximately 1% from 97.6% to 98.5%.
  • increasing the amount of carbon nanotubes to 0.75 mg the water flux increased by about a factor of four (to 28.5 GFD) over the plain polyamide membrane and the ion rejection ratio also increased to 98.6%.
  • FIG. 1 1 also shows that a significant increase in flux was achieved when 20 wt% closed-ended carbon nanotubes were incorporated into the polyamide matrix. However, this increase in water fiux was accompanied by a drop in salt rejection down to 93%, which is Sower than the salt rejection of the neat polyamide membrane.
  • the carbon nanotubes are entirely embedded within the polyamide membrane and are not completely aligned within the polyamide. This means that there is considerable room for improvement in the synthesis of the composite membrane.
  • An ideai membrane wouSd have carbon nanotubes perfectly aiigned with the direction of fluid flow and would perco!ate completely through the membrane, so that no fluid would have to permeate through the polymer.
  • the tested membranes provide a proof that functionalized carbon nanotubes can enhance both water flux and salt rejection.
  • the zwitterionic functional groups are attached not only at the pore entrance of the carbon nanotubes, but also along the wall of SWNTs, they can reject salt ions by size exclusion and Donnan exclusion at the entrance as well as snside the nanochannels. It is thus possible that water molecules travel both inside the SWNTs and around them in the nanochannels. For functionalized carbon nanotubes, both of the paths could be blocked by the zwitterionic groups, which offer good water/ions selectivity.
  • end-capped carbon nanotubes induce voids in the poiyamide membrane while the zwitterion-functionalized carbon nanotubes do not. This is based on the following differences between the end-capped and zwitterion-functionalized carbon nanotubes: 1) The end-capped carbon nanotubes are about a factor of five longer than the zwitterion- functionalized tubes, the former being as long as 5 pm, while the latter are about 1 pm in length (NanoLab). it is reasonable to assume that these very long carbon nanotubes will disrupt the poiyamide membrane structure to a much larger degree than the shorter carbon nanotubes.
  • each zwitterion-functionaiized carbon nanotube will have about 6.4*10 3 zwitterions or an average of about one zwiiterion for every 30 carbon atoms on the carbon nanotube (see Appendix below). This means that most of the zwitterions will be bound to and distributed along the sidewalls of the carbon nanotubes because the ends can only accommodate a small number of functional groups. For example, a (20,0) carbon nanofube could have a maximum of 20 zwitterions on each end.
  • FIGS. 12A and 12B show conductance of (FIG. 12A) water and (FIG. 12B) ions through carbon nanotubes functionalized with one or two zwitterions per tube end and with charges on the zwitterions turned on or off.
  • each tube is 15.6 A, corresponding to carbon nanotube (20,0).
  • the pressure drop was 208 Pa in each case. Error bars show the standard deviation based on four independent simulations.
  • the conductance of both water and ions increased by about 30% in the 1 zwitterion system when the charges were turned off.
  • the ion rejection remained at 100% whe the zwitterion charges were turned off, whereas the water conductance increased by about 35%, which is a modest increase given that the drop in water flux from unfunctionaiized to functionalized with 2 zwitterions is about one order of magnitude. This indicates that steric hindrance is the dominant mechanism for reducing the ion and water flux.
  • the molecular simulations described in this specification probe the details of the steric hindrance due to the zwitterions. Unlike short functional groups, such as carboxylic acids, the zwitterions used in the experiments and simulations described herein are very flexible and can adopt a large number of different conformations. This flexibility is manifested in the simulations by noting that zwitterions, which are initially placed into the solution with their molecular chains in an extended (unfolded) configuration away from the tube pores, tend to fold during the course of the simulation so that they are at least partially folded inside the tube. The configuration of the zwittenon has a profound effect on the flux of wafer and ions.
  • FIG. 13D shows the computed potential of mean force (PfvlF) for the change of free energy for a zwitterion functional group as it moves from a configuration where it is folded inside the nanotube (folded) and to a configuration where it is extended outside the nanotube into the solution phase (unfolded).
  • PfvlF mean force
  • FIG. 13A-C show configurations of zwitterions that are extended (unfolded) into the liquid phase or folded inside the carbon nanotube for the (20,0) system with (FIG. 13A) one (1 Zf) or (FIG. 138) two zwitterions (2 Zls) per tube end and for the (26,0) system with (FIG. 13G) five zwitterions (5 Zis) per tube end
  • FIG, 13D shows the PMF diagram of moving one zwitterion group from inside (folded) to outside (unfolded) of the carbon nanotube. F!G.
  • FIG. 13D shows PMF for moving one zwitterion in a (20,0) carbon nanotube having one (red) or two (blue) zwitterions per tube end.
  • FIG. 13E shows the PMF for moving one zwitterion in a (26,0) carbon nanotube having two (green) or five (black) zwitterions per tube end.
  • the carbons on the carbon nanotube and zwitterion groups are shown as cyan.
  • Oxygen , nitrogen and hydrogen are shown as red, purple and white.
  • the tube end positions are represented as vertical dash lines in D.
  • FIGS. 13D-E St can be seen from FIGS. 13D-E that the free energy favors the folded configurations for all systems studied.
  • the zwitterions tend to block tube entrances to reduce the effective pore size when they are folded inside the tubes, which is consistent with observations shown in FIGS. 12A and 12B that steric effects dominate over electrostatics.
  • the foided configuration is about 2.9 kcal/mol more favorable than the unfolded configuration for a single zwitterion, and about 2.3 kcal/mol more favorable for having the second zwitterion folded inside the carbon nanotube when there are two zwitterions per tube end.
  • the folded configuration is about 1.6 kcal/mol more favorabie than the unfolded configuration for the (26,0) carbon nanotube system with two zwitterions (FIG. 3E).
  • FIG. 14 shows water and ion flow rate (number per ns per carbon nanotube) and ion rejection ratio as a function of salt concentration for flow through a (20,0) carbon nanotube having one zwitterion functional group at each end.
  • FIG. 15 shows salt rejection as a function of NaCI feed concentration in plain PA (black curve with open circle) and a nanocomposite with 20 wt % carbon nanotubes (orange curve with solid circle). Feed pressure was 530 psi.
  • the graph of FIG. 15 shows an increase in the salt rejection ratio with ion concentration for both the plain poiyamide membrane and the nanocomposite membrane with 20 wt% carbon nanotubes.
  • concentration observed for the nanocomposite membrane in FIG. 15 can be attributed to the poiyamide component rather than the zwitterion-functionaiized carbon nanotubes. This agrees with the molecular simulations described herein, showing no effect of concentration on the rejection ratio (FIG. 14).
  • each tube were functionalized with 0, 1 , or 2 zwitterionic groups for the (20,0) system and 2, 4, or 5 zwitterions for the (26,0) system.
  • the carbon nanotubes were embedded in two graphene sheets to form a membrane.
  • the membrane was immersed into a water box containing NaCS or KCS with periodic boundary conditions along three dimensions.
  • the sizes of the simulation boxes were 54.1 A * 55.38 A ⁇ 114 A for the (20,0) carbon nanotubes and 68.9 A x 68.2 A * 95,3 A for the (26,0) system.
  • the nominal concentration of salt in seawater of 0.6 was used for most of the calculations. Selected calculations were also performed for a concentration of 0,3 M.
  • the temperature of the system was controlled by a Nose-Hoover thermostat with a damping parameter equal to 100, All calculations were performed with the LAMMPS package (See Plimpton, S., Fast parallel algorithms for short range molecular dynamics, J. Comp. Phys,, 117 » 1-19 (1995),) using a time step of 1fs.
  • a pressure drop was introduced to generate the flux through the membrane using the method developed by Zhu ef a/. See Zhu, F. Q,; Tajkhorshid, E.; Schulten, K. s Pressure-induced water transport in membrane channels studied by molecular dynamics, Biophys. J., 83, 154-160. (2002).
  • a one dimensional spring potential was applied along tube axis direction to each sampled zwitterion group.
  • the spring force constant k z was equal to 1 kcal/mol/A 2 .
  • the spring force constant k 2 ' was equal to 1 kcal/mol/A 2 .
  • a larger spring force constant k z ⁇ 3 kcal/mol/A 2 was applied in order to improve sampling.
  • the sampling time for each window was 500 ps with the first 100 ps discarded for equilibration.
  • the convergence of the PMF calculations was checked by comparing PMF taking sampling times of 200, 300 or 400 ps for each window. Results from these shorter sampling times are in good quantitative agreement with the 500 ps sampling. Details of the WHAM method are given in the Appendix below.
  • ion rejection ratio was calculated from simulations using: R(%) - (1 - - ⁇ - x 1 ⁇ 2 ⁇ x100,
  • Carbon anotube FunciionaSization Carboxylate functionalized carbon nanotubes of outer diameter 15 A and length 1 pm were purchased from Nano Lab Inc. (Waltham, MA). (NanoLab). The COOH-functtonailzed carbon nanotubes were produced by chemical vapor deposition (CVD). Concentration of -COOH groups in the carbon nanotubes was approximately 2-7 wt% (as determined by titration). The functionalized carbon nanotubes were reacted with thionyl chloride (SOCb) at 65°C for 38 hours and the -COOH groups were replaced by GOG! groups.
  • SOCb thionyl chloride
  • acylated carbon nanotubes were then esterificated using 3 ⁇ dimethylamino-1 ⁇ propanol, ⁇ CHsVN-CsNe-QH, This was followed by a ring-opening reaction of lactone, in which ⁇ -propioSactone was opened to form an acid group and attached to the tertiary amine on the functional group.
  • FIGS. 3A-3C Functionalaiized carbon nanotube nano- composite membranes. Briefly, the fabrication process was divided into three steps, as shown schematically in FIGS. 3A-3C.
  • the PES support was pretreated by soaking in 0.5 wt% SDBS solution to open the pores and to increase the hydrophi!icity.
  • Field emission scanning electron microscopy (FESEM) was used to examine the surface of the support, as shown in FIG. 18A and described in the Appendix below.
  • the support was sandwiched between two round Poly ⁇ tetrafSuoroethyiene) (PTFE) holders. Afterwards, a predetermined amount of functionaiized carbon nanotubes was poured on the support.
  • PTFE Poly ⁇ tetrafSuoroethyiene
  • the third step in the membrane fabrication process was interfacial polymerization of polyamide.
  • the support with semi-aligned carbon nanotubes was wetted in turn with 2 wt% PD (with 0.2 wt% of SDBS) and 0.5% (w/v) TMC solutions before polymerization.
  • the polyamide apparently completely covers the carbon nanotubes, as can be inferred by comparing the FESEM images for the plane polyamide and the carbon nanotube/polyamide membrane surfaces in FIGS. 18B and C.
  • the partial alignment of the carbon nanotubes within the polyamide layer can be observed from the FESEM image of the cross section of the carbon nanotube/polyamide membrane shown in FIG. 18D. Details of the fabrication procedure are given in the Appendix below.
  • End-capped carbon nanotube nano-composite membranes were purchased from NanoLab Inc. (NanoLab) and used as received without any further purification. They were produced by CVD method, with diameter of 15 A and length of 1 to 5 pm. Unlike the zwitterionic functionaiized SWNTs, end-capped SWNTs required the presence of surfactant in the solution to maintain a well-dispersed phase. In this case, 10 mg of SBDS was added into 40ml of de-ionized water to create a 0.025 wt% SBDS soSutson.
  • end-capped SWNTs were deposited and semi-aligned on a pretreated membrane support by filtration, foliowed with an interfacial polymerization of the polyamtde carried out on the carbon nanotubes-attached support. After 5 min of oven curing, the fresh nanocomposite membrane was washed thoroughly with Dl water, submersed in fresh Dl water and stored in a laboratory refrigerator at 4 °C.
  • Membrane Characterization Pressure-driven experiments were carried out on a laboratory-scale cross-flow membrane test unit, capable of pressures from 25 to 1000 pss.
  • This test unit is comprised of a membrane cell (GE SepaTM CF SI Cell), high pressure pump (Hydra-ceil pump, Warner Engineering), back-pressure regulator (US Paraplate ⁇ , bypass valve (Swageiock), feed water reservoir (Nalgene), operated in closed loop mode with retentate being circulated into the feed water reservoir.
  • the concentration analysis of the sodium cation present in the permeant was measured by a sodium ion-selective electrode (Thermo Scientific; 881 1 BNWP, MA),
  • the sodium ion electrode was calibrated using a standard sodium solution with concentration of 1000 ⁇ 5 ppm Na +'
  • the atomic absorption spectrophotometer (AAS) was also calibrated using standard solutions, which contained 5, 10, 15 and 20 ppm of the specific cations, respectively.
  • concentrations of cations in the feed, C f , and the permeant, C p were measured and the salt rejection ratio (in percent) was calculated from:
  • IP interfacia! polymerization
  • Different publications report different recipes in terms of the concentration of monomers, contact time, air-drying time, curing temperature, etc. See Ghosh, A. .; Hoek, E.M.V., Impacts of support membrane structure and chemistry on polyamide- po!ysu!fone interfacia! composite membranes, J. Membr. Sci., 336, 140-148 (2009). Saha, N. K.; Joshi, S. V., Performance evaluation of thin film composite polyamide nanofi!tration membrane with variation in monomer type. J. Membr.
  • FIGS. 3A-3C A schematic of a recommended fabrication procedure is shown In FIGS. 3A-3C.
  • the poSyethersulfone (PES) membrane support was first pretreated by soaking in a 0.5 wt% sodium dodecy!benzenesu!fonate (SDBS) solution (FIG. 3A) for two days to increase the hydrophiticity and to open the pores of the support.
  • SDBS sodium dodecy!benzenesu!fonate
  • the support was then soaked in deionized (DI) water for one day to remove any excess surfactants. This soaking pretreatment guaranteed that there was no SBDS solution left in the pores. The absence of this step may introduce air bubbles underneath the later polyamide layer.
  • the support was then sandwiched in between two round PoSy(tefrafSuoroethylene) (PTFE) holders. Before being poured on the top of the membrane support, a predetermined weight of zwitterion-functionalized carbon nanotubes was dispersed in 40 ml of deionized (Df) water by sonicatton. During the sonication step, the carbon nanotube solution was heated by the sonicator horn and therefore required cooling to room temperature. As shown in FIG.
  • the functionalized carbon nanotubes were deposited and semi- aligned on the membrane support using high-vacuum filtration (Kim, Jinschek, Chen, Shoii, and Marland, 2007)
  • the support and carbon nanotubes were then dried for an hour in a vacuum oven. This insured that at! water was removed from the nanotubes before the interfaciai polymerization took place.
  • An alternative way to filter the carbon nanotube solution was to use a solvent- resistant stirred eel! (XFUF04701 ; !Vliliipore, MA).
  • This apparatus utilized a deadend filtration method, in which the support was held at the bottom of the celi and the carbon nanotubes solution was stored within the cell above the support.
  • the ce!S was pressurized up to 6 bar with inert gas on the top of the solution. Under this relatively high pressure the carbon nanotube solution also filtered through the support leaving the carbon nanotube behind.
  • intrafacial polymerization was subsequently carried out on the carbon nanotube covered support by wetting the fabrication side (with carbon nanotubes) with an aqueous diamine solution containing 2 wt% PD and 0.2 wt% of SDBS at ambient temperature for 2 min and then the membrane was unciamped and immediately placed on a glass plate. A glass roller was rolled over the membrane once to remove all the excess MPD solution.
  • the membrane was then sandwiched again into the holder and wetted by a n-hexane solution containing 0,5% (w/v) T C for 90 seconds.
  • the resulting poiyamide thin film nanocomposite membrane was subsequently heat cured at 68°C for 5 min. After the membrane had cooled down, it was washed thoroughly with Dl water, submersed in fresh DS water and stored in a laboratory refrigerator at 4°C.
  • the thickness and diameter of the interfaciai poiyamide layer (FIG. 3D) was approximately 500 nm and 3.7 cm, respectively.
  • FIG. 18D The cross-sectional view of the Z-carbon nanotubes/poiyamide membrane, also taken by FESESV1, is shown in FIG. 18D.
  • the neat PES support (FIG. 1SA) has a relatively smooth and porous surface with pore sizes ranging approximately from 6 to 20 nm.
  • a thin poiyamide skin layer with ridge- valley shape was formed on the top of the PES substrate (FIG. 18B) and acted as a barrier layer in separating salt ions from water.
  • FIG. 18C For the Z-carbon nanotubes/poiyamide nanocomposite membrane (FIG. 18C), it can be seen that all the nanotubes were covered by interfaciaily polymerized poiyamide.
  • FIG. 18D shows that nanotubes are embedded in poiyamide with semi-aligned orientation (examples indicated by arrows),
  • This membrane would have a density of 1.86x1 ⁇ 13 carbon nanotube/cm 2 . Assuming a linear flux of water with pressure drop (Corry, 2008) a flux of 1.75 water molecules per carbon nanotube per ns can be obtained. Converting to units of gallons per square foot per day gives a flux of about 20,000 GFD at a pressure drop of 530 psi,
  • n c ; (Aiexiadis et a/., 2008).
  • the number of atoms per unit eel! is 80.
  • the length of the carbon nanoiubes used in experiments is around 1000 nm, so that the number of C atoms in one carbon nanotube is
  • x 1000nm 1.88x10 atoms/carbon nanotube.
  • 77- 18 typical carbon nanotube be x.
  • x is calculated as— -— - i.88;rtO s
  • the number of zwittenons is estimated to be 6400 x
  • the sampling was started by using a one dimensional spring with a force constant of 1 kcai/mo!/A 2 .
  • the sampling process tasted for 500 ps.
  • the initial 100 ps was discarded and oniy the last 400 ps was used for the WHAM analysis.

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Inorganic Chemistry (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Nanotechnology (AREA)
  • Dispersion Chemistry (AREA)
  • Carbon And Carbon Compounds (AREA)
  • Separation Using Semi-Permeable Membranes (AREA)

Abstract

L'invention concerne une membrane nanocomposite de nanotubes de carbone fonctionnalisés et ses procédés de fabrication. Les membranes nanocomposites sont fabriquées en nanotubes de carbone fonctionnalisés déposés sur un support de membrane qui est recouvert par une matrice polymère telle que du polyamide. Les nanotubes de carbone peuvent être fonctionnalisés par divers groupes fonctionnels, tels que des groupes fonctionnels zwittérioniques courts. Des procédés de fonctionnalisation des nanotubes de carbone, de dépôt des nanotubes de carbone sur un support de membrane et de polymérisation interfaciale du polyamide sont également décrits. Les procédés de l'invention peuvent être réalisés à un niveau industriel et fournissent des membranes présentant un transport d'eau et un rejet de sel élevés, et une résistance aux bio-incrustations, qui peuvent être particulièrement utiles dans des applications de dessalement.
PCT/US2013/040744 2012-05-11 2013-05-13 Membranes nanocomposites de nanotubes de carbone fonctionnalisés et leurs procédés de fabrication Ceased WO2013170249A1 (fr)

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CN104028126A (zh) * 2014-05-16 2014-09-10 浙江大学 磺酸型两性聚电解质纳米粒子杂化聚酰胺纳滤膜的制备方法
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US10392272B2 (en) 2015-02-27 2019-08-27 Ut-Battelle, Llc Modulation of ion transport in a liquid by application of an electric potential on a mesoporous carbon membrane
KR102058631B1 (ko) 2018-05-11 2019-12-23 한국수자원공사 1d 구조의 나노물질을 증착한 역삼투용 나노복합막의 제조방법 및 이에 따라 제조된 역삼투용 나노복합막
JP2020531260A (ja) * 2017-08-21 2020-11-05 オハイオ・ステート・イノヴェーション・ファウンデーション ガス分離用膜
CN113893708A (zh) * 2021-09-24 2022-01-07 南京南开伊沃环境研究院有限公司 一种陶瓷基负载碳纳米管复合膜制备方法
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CN103785309B (zh) * 2013-12-20 2015-11-18 三达膜科技（厦门）有限公司 一种聚醚砜/聚甲基丙烯酸甲酯合金平板超滤膜及其制备方法
CN103785309A (zh) * 2013-12-20 2014-05-14 三达膜科技（厦门）有限公司 一种聚醚砜/聚甲基丙烯酸甲酯合金平板超滤膜及其制备方法
US20150224450A1 (en) * 2014-02-13 2015-08-13 The Regents Of The University Of California Electrically conducting reverse osmosis membranes
US9802163B2 (en) * 2014-02-13 2017-10-31 The Regents Of The University Of California Electrically conducting reverse osmosis membranes
CN104028126A (zh) * 2014-05-16 2014-09-10 浙江大学 磺酸型两性聚电解质纳米粒子杂化聚酰胺纳滤膜的制备方法
US10392272B2 (en) 2015-02-27 2019-08-27 Ut-Battelle, Llc Modulation of ion transport in a liquid by application of an electric potential on a mesoporous carbon membrane
US10559755B2 (en) 2016-04-07 2020-02-11 International Business Machines Corporation Heterogeneous nanostructures for hierarchal assembly
US9806265B1 (en) 2016-04-07 2017-10-31 International Business Machines Corporation Heterogeneous nanostructures for hierarchal assembly
US20190176096A1 (en) * 2016-08-25 2019-06-13 Zhejiang University All-Carbon Film Based On Activated Carbon And Preparation Method And Use Thereof
JP2020531260A (ja) * 2017-08-21 2020-11-05 オハイオ・ステート・イノヴェーション・ファウンデーション ガス分離用膜
EP3672708A4 (fr) * 2017-08-21 2021-04-28 Ohio State Innovation Foundation Membrane de séparation de gaz
JP7271508B2 (ja) 2017-08-21 2023-05-11 オハイオ・ステート・イノヴェーション・ファウンデーション ガス分離用膜
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KR102058631B1 (ko) 2018-05-11 2019-12-23 한국수자원공사 1d 구조의 나노물질을 증착한 역삼투용 나노복합막의 제조방법 및 이에 따라 제조된 역삼투용 나노복합막
EP4146376A4 (fr) * 2020-05-04 2024-03-13 Atom H20, LLC Membrane à base de nanotubes de carbone et ses procédés de fabrication
CN113893708A (zh) * 2021-09-24 2022-01-07 南京南开伊沃环境研究院有限公司 一种陶瓷基负载碳纳米管复合膜制备方法
CN114713042A (zh) * 2022-04-20 2022-07-08 杭州水处理技术研究开发中心有限公司 一种高分辨率和水通量的纳滤膜及其制备方法
CN114713042B (zh) * 2022-04-20 2023-05-12 杭州水处理技术研究开发中心有限公司 一种高分辨率和水通量的纳滤膜及其制备方法
CN116851007A (zh) * 2023-07-11 2023-10-10 山东交通学院 基于碳纳米管-硫化铟锌纳米片复合材料的制备与磁场辅助光催化应用
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