Method of preparation of conductive polymer/carbon nanotube composite nanofiltration membrane and the use thereof

Abstract

A method for preparation of conductive polymer/carbon nanotube (CNT) composite nanofiltration (NF) membrane and the use thereof. This conductive polymer/CNT composite NF membrane is obtained by polymerizing conductive polymer into a CNT membrane and then in-situ cross-linking with glutaraldehyde under acidic condition. The synthetic method for the conductive polymer/CNT composite NF membrane is simple and has no need of expensive equipment. The prepared membrane has controllable membrane structure and possesses superior electrical conductivity and electrochemical stability. The membrane can couple with electrochemistry for electrically assisted filtration. With the electrical assistance, the membrane can achieve improved ion rejection performance while retaining high permeability by enhancement of membrane surface charge density, which alleviates the permeability-selectivity trade-off. Furthermore, the electrically assisted NF membrane filtration can also enhance the removal for small molecular organic pollutants.

Claims

1. A method for preparing a conductive polymer/carbon nanotube (CNT) composite nanofiltration (NF) membrane, wherein, the method comprising the following steps: (1) CNTs are oxidized in mixed acid solution of 70 wt. % concentrated HNO.sub.3 and concentrated H.sub.2SO.sub.4 solution with 1:3 (v/v) at 40˜100° C. for 30˜120 min; then the mixed acid solution containing oxidized CNTs is diluted with ultrapure water and filtered; the oxidized CNTs are washed and dried; after that, the oxidized CNTs are re-dispersed to form a uniform aqueous dispersion and then vacuum-filtered onto a membrane support to yield CNT membranes; finally, the prepared CNT membrane is dried at 40˜80° C.; (2) soaking the prepared CNT membrane in a monomer solution of a corresponding conductive polymer for 10˜30 min and before draining off the monomer solution on the CNT membrane; afterwards, the CNT membrane is put into an initiator solution for initiating the polymerization of the monomer of the conductive polymer; after polymerizing at 0˜25° C. for 5˜30 min, the CNT membrane is taken out and continued to react for 4˜24 h under 0˜25° C. for completing chemical oxidative polymerization of the monomer of the conductive polymer; wherein the conductive polymer is selected from the group consisting of polyaniline, polypyrrole, polythiophene and derivatives thereof; the concentration of the conductive polymer is 0.01˜0.5 M; the initiator is selected from the group consisting of ammonium persulfate, potassium dichromate, potassium iodate, ferric chloride, ferric tetrachloride, hydrogen peroxide, aluminum trichloride, manganese dioxide and benzoyl peroxide; the molar concentration ratio of the initiator to the monomer of the corresponding conductive polymer is 1:0.5˜2; (3) the CNT membrane obtained from step (2) is fully immersed into a crosslinker solution prepared by mixing glutaraldehyde and concentrated HCl; after crosslinking for 10˜60 min, the CNT membrane is washed well with water and dried at room temperature to obtain the conductive polymer/CNT composite NF membrane; wherein the mass percentage of glutaraldehyde in the solution is 0.5˜5% and the molar concentration of HCl is 0.1˜2 M.

2. The preparation method according to claim 1, wherein, the monomer solution of the corresponding conductive polymer is mixed with polyelectrolyte; the polyelectrolyte is selected from the group consisting of polystyrolsulfon acid, polyacrylic acid, polyethyleneimine, poly(allylamine hydrochloride) and poly(diallyldimethylammonium chloride); the mass content of the polyelectrolyte in the solution is 0˜5%.

3. The preparation method according to claim 1, wherein, the CNTs are selected from the group consisting of single-walled CNTs, double-walled CNTs and multiwalled CNTs.

4. The preparation method according to claim 1, wherein, the membrane support used to form the CNT membrane in step (1) is made of one or more of polyacrylonitrile, polyvinylidene fluoride, non-sulfonated phenolphthalein polyaryl ether sulfone, polyethersulfone, bisphenol-A-polysulfone; the thickness of the CNT membrane is 0.05˜0.5 μm.

5. The preparation method according to claim 3, wherein, the membrane support used to form the CNT membrane in step (1) is made of one or more of polyacrylonitrile, polyvinylidene fluoride, non-sulfonated phenolphthalein polyaryl ether sulfone, polyethersulfone, bisphenol-A-polysulfone; the thickness of the CNT membrane is 0.05˜0.5 μm.

Description

DETAILED DESCRIPTION

(1) The following describes the specific embodiments of the present invention in combination with technical solutions.

(2) Three specific examples are to further illustrate the present invention in detail, but the scope of the present invention is not limited thereto.

Example 1

(3) (1) CNTs are oxidized in mixed acid solution of 70 wt. % concentrated HNO.sub.3 and concentrated H.sub.2SO.sub.4 solution (⅓, v/v) at 60° C. for 60 min. Then the obtained dispersion is diluted with ultrapure water and filtered. The resulting oxidized CNTs are washed to neutral pH and dried. After that, the oxidized CNTs are re-dispersed in ultrapure water to form a uniform aqueous dispersion (0.5 mg mL.sup.−1) with ultrasonication. Then 10 mL CNT dispersion is vacuum-filtered onto a polyvinylidene fluoride membrane support to yield CNT membrane, and the membrane is dried at 60° C. The prepared CNT membrane is soaked in 0.1 M aniline solution with 1.0 wt. % polyacrylic acid for 10 min before draining off the excess solution. Afterwards, the membrane is put into 0.1 M ammonium persulfate solution for initiating the polymerization of aniline. After polymerizing at 4° C. for 10 min, the membrane is taken out and continued to react for 6 h under 4° C. and then dried at room temperature. Finally, the composite membrane is fully immersed into a crosslinker solution containing 1.0 wt. % glutaraldehyde and 0.5 M HCl. After the crosslinking for 30 min, the membrane is washed well with water and dried at room temperature to obtain a polyaniline/CNT composite NF membrane.

(4) (2) The prepared NF membrane is sealed in a membrane module and then installed onto a membrane filtration setup. The membrane serves as the work electrode and a titanium mesh is used as the counter electrode. The distance between the work electrode and the counter electrode is 2 mm. A DC stabilized power supply is used to provide voltage by titanium wires. A feed solution of 5 mM Na.sub.2SO.sub.4 is filtered for 30 min at a transmembrane pressure of 2 bar before collecting the permeate sample. Without the electrical assistance, the NF membrane exhibits a permeance of 14.0 Lm.sup.−2 h.sup.−1 bar.sup.−1 and a rejection rate of 81.6% for Na.sub.2SO.sub.4. Adjusting the DC stabilized power supply and setting the voltage to 2.5 V (the membrane electrode is applied with negative bias), the electrically assisted NF membrane exhibits a permeance of 13.7 L m.sup.−2 h.sup.−1 bar.sup.−1 and a rejection rate of 93.0% for Na.sub.2SO.sub.4 after the pre-filtration for 30 min.

Example 2

(5) (1) CNTs are oxidized in mixed acid solution of 70 wt. % concentrated HNO.sub.3 and concentrated H.sub.2SO.sub.4 solution (⅓, v/v) at 80° C. for 30 min. Then the obtained dispersion is diluted with ultrapure water and filtered. The resulting oxidized CNTs are washed to neutral pH and dried. After that, the oxidized CNTs are re-dispersed in ultrapure water to form a uniform aqueous dispersion (0.5 mg mL.sup.−1) with ultrasonication. Then 15 mL CNT dispersion is vacuum-filtered onto a polyethersulfone membrane support to yield CNT membrane, and the membrane is dried at 80° C. The prepared CNT membrane is soaked in 0.15 M pyrrole solution with 1.5 wt. % polyacrylic acid for 20 min before draining off the excess solution. Afterwards, the membrane is put into 0.1 M hydrogen peroxide solution for initiating the polymerization of pyrrole. After polymerizing at 0° C. for 15 min, the membrane is taken out and continued to react for 12 h under 0° C. and then dried at room temperature. Finally, the composite membrane is fully immersed into a crosslinker solution containing 2.0 wt. % glutaraldehyde and 1 M HCl. After the crosslinking for 20 min, the membrane is washed well with water and dried at room temperature to obtain a polypyrrole/CNT composite NF membrane.

(6) (2) The prepared NF membrane is sealed in a membrane module and then installed onto a membrane filtration setup. The membrane serves as the work electrode and a titanium mesh is used as the counter electrode. The distance between the work electrode and the counter electrode is 1 mm. A DC stabilized power supply is used to provide voltage by titanium wires. A feed solution of 5 mM NaCl is filtered for 30 min at a transmembrane pressure of 2 bar before collecting the permeate sample. Without the electrical assistance, the NF membrane exhibits a permeance of 12.4 L m.sup.−2 h.sup.−1 bar.sup.−1 and a rejection rate of 59.6% for NaCl. Adjusting the DC stabilized power supply and setting the voltage to 2.5 V (the membrane electrode is applied with negative bias), the electrically assisted NF membrane exhibits a permeance of 11.2 Lm.sup.−2 h.sup.−1 bar.sup.−1 and a rejection rate of 85.3% for NaCl after the pre-filtration for 30 min.

Example 3

(7) (1) CNTs are oxidized in mixed acid solution of 70 wt. % concentrated HNO.sub.3 and concentrated H.sub.2SO.sub.4 solution (⅓, v/v) at 60° C. for 90 min. Then the dispersion is diluted with ultrapure water and filtered. The resulting oxidized CNTs are washed to neutral pH and dried. After that, the oxidized CNTs are re-dispersed in ultrapure water to form a uniform aqueous dispersion (0.5 mg mL.sup.−1) with ultrasonication. Then 15 mL CNT dispersion is vacuum-filtered onto a polyethersulfone membrane support to yield CNT membrane, and the membrane is dried at 80° C. The prepared CNT membrane is soaked in 0.15 M 3-methylthiophene solution with 1.5 wt. % poly(allylamine hydrochloride) for 10 min before draining off the excess solution. Afterwards, the membrane is put into 0.2 M ferric chloride solution for initiating the polymerization of 3-methylthiophene. After polymerizing at 20° C. for 30 min, the membrane is taken out and continued to react for 24 h under 20° C. and then dried at room temperature. Finally, the composite membrane is fully immersed into a crosslinker solution containing 2.5 wt. % glutaraldehyde and 1 M HCl. After the crosslinking for 30 min, the membrane is washed well with water and dried at room temperature to obtain a poly(3-methylthiophene)/CNT composite NF membrane.

(8) (2) The prepared NF membrane is sealed in a membrane module and then installed onto a membrane filtration setup. The membrane serves as the work electrode and a titanium mesh is used as the counter electrode. The distance between the work electrode and the counter electrode is 5 mm.

(9) A DC stabilized power supply is used to provide voltage by titanium wires. A feed solution of 10 mg L.sup.−1 bisphenol A is filtered for 30 min at a transmembrane pressure of 2 bar before collecting the permeate sample. Without the electrical assistance, the NF membrane exhibits a permeance of 8.7 L m.sup.−2 h.sup.−1 bar.sup.−1 and a rejection rate of 48.6% for bisphenol A. Adjusting the DC stabilized power supply and setting the voltage to 2.0 V (the membrane electrode is applied with positive bias), the electrically assisted NF membrane exhibits a permeance of 8.5 Lm.sup.−2 h.sup.−1 bar.sup.−1 and a rejection rate of 98.8% for bisphenol A after the pre-filtration for 30 min.

(10) The foregoing descriptions are merely specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions within the technical scope disclosed in the present invention, which are readily conceived of by a person skilled in the art, should be covered by the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.