CARBON NANOTUBE/NANOFIBER CONDUCTIVE COMPOSITE MEMBRANE AND PREPARATION METHOD THEREOF

Abstract

The present invention belongs to the technical field of membranes and provides a carbon nanotube/nanofiber conductive composite membrane and a preparation method thereof. The conductive membrane with a meshy pore structure intertwined by one-dimensional nano materials is constructed by taking one-dimensional nanofiber nonwovens prepared by electrospinning as a support layer and CNTs cross linked on the support layer as a separation layer. The membrane pore size of the composite membrane involved can be controlled from microfiltration to ultrafiltration, and membrane morphology includes flat membranes, hollow fiber membranes, and spiral-wound membranes. The main advantages and beneficial effects of the composite membrane involved are: simple preparation steps, better permeability and mechanical strength, good hydrophilicity and electrical conductivity, and easy mass production and application.

Claims

1. A carbon nanotube/nanofiber composite membrane, wherein the CNT/nanofiber composite separation membrane is divided into a support layer and a functional layer; nanofibers prepared by electrospinning are used as the support layer and CNTs are used as the separation layer; the CNTs are coated on the surfaces of the nanofibers; the CNTs are fixed by crosslinking agent 1 and crosslinking agent 2; the CNTs and nanofibers are both one-dimensional linear materials, which can be used to construct a separation membrane with three-dimensional meshy pore structure; and the interaction between the support layer and the separation layer is enhanced by interlacing linear materials to form a stable membrane structure.

2. The carbon nanotube/nanofiber composite membrane according to claim 1, wherein the crosslinking agent 1 and crosslinking agent 2 consist of polyacrylamide and succinic acid, or polyvinyl alcohol and glutaraldehyde, or polyvinyl alcohol and glutaric acid, or phenolic resin and oxalic acid.

3. The carbon nanotube/nanofiber composite membrane according to claim 1, wherein the morphology of the carbon nanotube/nanofiber composite membrane comprises flat membranes, hollow fiber membranes, and spiral-wound membranes.

4. A preparation method of the carbon nanotube/nanofiber composite membrane, comprising steps as follows: first step: preparation of nanofiber support layer (1) dissolving the spinning materials used as the support layer in corresponding solvent to form a spinning solution with a mass fraction of 10%-20%, and conducting electrospinning preparation; slowly injecting the spinning solution through a micro-injection pump; moving the droplets to a collector device under the electrostatic interaction and stretching into nanofibers; fitting the electrospinning voltage density to 1 kV/cm and the spinning distance to be in the range of 10 cm-20 cm; controlling the spinning time in the range of 4-20 h according to the concentration of spinning solution; and obtaining the corresponding nanofiber support layer from the collector device; wherein according to the different membrane shapes, the specific operations are as follows: flat membrane: a roller nanofiber collector or flat nanofiber collector is used to receive nanofibers prepared by electrospinning; and after the collection, the nanofibers are directly removed from the surface of the collector and set to hot-press forming flat support layer; hollow fiber membrane: a dynamic continuous filiform collector is used to receive nanofibers prepared by electrospinning; in the process of electrospinning, the continuous filiform collector is controlled to pass through a nanofiber receiving area at a fixed rate, and then the filiform collector is transferred to a heating chamber; the prepared nanofibers are heated to shrink stably according to the heat resistance of materials; the filiform collector is immersed in a 0.1 mol/L dilute acid solution or copper salt solution for 5-60 minutes; and then the hollow fiber support layer is obtained by pulling out filiform collector; spiral-wound membrane: a conductive spiral-wound hollow latticed collector is used as the nanofiber collector; after the collection, the nanofibers are set to hot-press together with the conductive spiral-wound hollow latticed collector; and then the non-woven nanofibers are fixed by glue sealing and then cooled to room temperature to obtain the spiral-wound membrane support layer. second step: preparation of CNTs functional layer by electrostatic spraying the CNTs acidified by mixed acids are dispersed in water to prepare a 5-10 mg/mL dispersion; the mixed acids are constituted by 95-98 wt. % concentrated sulfuric acid and 65-68 wt. % concentrated nitric acid with a volume ratio of 3:1; and then, the nanofiber support layer is electrostatically sprayed at a regulated voltage density of 1 kV/cm and a spinning distance in the range of 10-20 cm; third step: crosslinking of carbon nanotube/nanofiber conductive composite membrane the prepared composite membrane is taken off and immersed in the mixture of the cross-linking agent 1 and the cross-linking agent 2; 2M hydrochloric acid is added into the mixture solution to control pH to 2; and after taking the membrane out, the membrane is rinsed with deionized water and drilled and solidified at 60° C.

5. The carbon nanotube/nanofiber composite membrane according to claim 2, wherein the morphology of the carbon nanotube/nanofiber composite membrane comprises flat membranes, hollow fiber membranes, and spiral-wound membranes.

Description

DESCRIPTION OF THE DRAWINGS

[0036] FIG. 1 is the scanning electron microscope image of a support layer of a carbon nanotube/nanofiber conductive composite membrane; and

[0037] FIG. 2 is the scanning electron microscope image of a separation layer of a carbon nanotube/nanofiber conductive composite membrane.

DETAILED DESCRIPTION

[0038] Embodiments of the present invention will be described below in combination with the drawings, but the present invention is not limited to the following embodiments.

Embodiment 1. Preparation of CNTs/Polyacrylonitrile (PAN) Nanofiber Composite Flat Membranes

[0039] The First Step: Preparation of Nanofiber Matrix by Electrospinning

[0040] The polymer PAN used as a support layer is dissolved in N, N-dimethylformamide(DMF) to form a spinning solution with a mass fraction of 15%. The electrospinning voltage density is fit to around 1 kV/cm and the spinning distance is in the range of 10-20 cm. The spinning time is controlled at 10 h according to the concentration. The corresponding nanofiber matrix is obtained from the collector and set to hot-press at 150° C. to obtain a flat nanofiber support layer.

[0041] The Second Step: Preparation of CNTs Functional Layer by Electrostatic Spraying

[0042] The CNTs with diameter of 60-100 nm acidified by mixed acids are dispersed in water to prepare a 5 mg/mL dispersion. Then, then nanofiber matrix is electrostatically sprayed for 6 h at the controlled voltage density of around 1 kV/cm and the spinning distance in the range of 10-20 cm.

[0043] The Third Step: Crosslinking of CNTs/PAN Nanofiber Composite Membranes

[0044] The prepared composite membrane is taken off and immersed in the mixture of (0.2%)polyacrylamide and (1%)oxalic acid for 1 h. 2M hydrochloric acid is added into the mixture solution to control pH to be acidic. After taking the membrane out, the membrane is rinsed with deionized water and dried and solidified at 60° C.

[0045] Results: the support layer and the separation layer of the prepared CNTs/PAN nanofiber composite flat membranes both show a meshy interconnected hole structure. The pore size of the support layer is in the range of 1-2 μm and the pore size of the separation layer is around 300 nm. Because PAN has good thermal stability, which is convenient for shrinking nanofibers at higher temperatures CNTs/nanofiber composite membranes made of PAN materials show optimal mechanical strength and stability.

Embodiment 2. Preparation of CNTs/PAN Nanofiber Composite Hollow Fiber Membranes

[0046] The First Step: Preparation of Nanofiber Matrix by Electrospinning

[0047] The polymer PAN used as the matrix is dissolved in DMF to forma spinning solution with a mass fraction of 15%. The electrospinning voltage density is controlled to around 1 kV/cm and the spinning distance is in the range of 10 cm. A stainless steel wire collector is used as a receiving apparatus. The spinning time is controlled at 6 h according to the concentration. Then, the corresponding nanofiber hollow fiber support layer is obtained from the receiving apparatus.

[0048] The Second Step: Preparation of CNTs Functional Layer by Electrostatic Spraying

[0049] The 60-100 nm CNTs acidified by mixed acids are dispersed in water to prepare a 5-10 mg/mL dispersion. Then, then a no fiber matrix is electrostatically sprayed for 6 h at the controlled voltage density of around 1 kV/cm and the spinning distance in the range of 10-20 cm.

[0050] The Third Step: Crosslinking of CNTs/PAN Nanofiber Composite Membranes

[0051] The prepared composite membrane is taken off with the collector and immersed in the mixture of (0.2%)polyvinyl alcohol and (1%) glutaric acid for 1 h. 2M hydrochloric acid is added into the mixture solution to control pH to be acidic. After taking the membrane out, the membrane is rinsed with deionized water and dried and solidified at 60° C. Then, the composite membrane with collector is preoxidized at 250° C. in the oven. After pre oxidation, the composite membrane is immersed in the 1M copper sulfate solution for 10 min together with collector. The hollow fiber membrane can be pulled out from a filiform collector. The CNTs/PAN nanofiber conductive composite membrane is obtained after cleaning by deionized water and drying.

[0052] Results: the support layer and the separation layer of the prepared CNTs/PAN nanofiber composite flat membranes both show a meshy interconnected hole structure. The pore size of the support layer is in the range of 1-2 μm and the pore size of the separation layer is around 300 nm.

Embodiment 3. Preparation of CNTs/Polyvinylidene Fluoride(PVDF) Nanofiber Composite Flat Membranes

[0053] The First Step: Preparation of Nanofiber Support Layer by Electrospinning

[0054] The polymer PVDF used as the matrix is dissolved in the mixture of DMF and acetone (volume ratio 9:1) to form a spinning solution with a mass fraction of 18%. The electrospinning voltage density is fit to around 1 kV/cm and the spinning distance is in the range of 10 cm. The spinning time is controlled at 10 h according to the concentration. Then, the nanofibers are directly removed from the collector and set to hot-press at 80° C. to form a flat nanofiber matrix.

[0055] The Second Step: Preparation of CNTs Functional Layer by Electrostatic Spraying

[0056] The 10-20 nm CNTs acidified by mixed acids are dispersed in water to prepare a 5-10 mg/mL dispersion. Then, then nanofiber matrix is electrostatically sprayed for 6 h at the controlled voltage density of around 1 kV/cm and the spinning distance in the range of 10-20 cm.

[0057] The Third Step: Crosslinking of CNTs/PVDF Nanofiber Composite Membranes

[0058] The prepared composite membrane is taken off and immersed in the ethanol solution with (0.2%)phenolic resin for 1 h. Then, oxalic acid is added into the mixture solution to control pH to be acidic. After taking the membrane out, the membrane is rinsed with ethanol and dried and solidified at 60° C.

[0059] Results: the support layer and the separation layer of prepared CNTs/PVDF nanofiber composite flat membranes both show a meshy interconnected hole structure. The pore size of the support layer is in the range of 400-600 nm and the pore size of the separation layer is around 70 nm.

Embodiment 4. Preparation of CNTs/Aluminium Oxide (AO) Nanofiber Composite Flat Membranes

[0060] The First Step: Preparation of Nanofiber Support Layer by Electrospinning

[0061] The formic acid and the acetic acid are added to high-purity water at a mass ratio of 1:1, and then a certain amount of Al powder is added into the mixture solution with heating and stirring until Al powder is completely dissolved. A glass fiber membrane is used to filter the above solution to remove the residue. The solution is prepared into Al gels with a mass fraction of about 10% and a certain amount of polyvinylpyrrolidone is added to increase the viscosity of the solution. The electrospinning voltage density is fit to around 1 kV/cm and the spinning distance is in the range of 10 cm. The spinning time is controlled at 10 h according to the concentration. Then, the nanofibers are directly removed from the collector and calcined at 800° C. The Al.sub.2O.sub.3 nanofiber matrix is obtained after preserving the temperature for 2 h.

[0062] The Second Step: Preparation of CNTs Functional Layer by Electrostatic Spraying

[0063] The 60-100 nm CNTs acidified by mixed acids are dispersed in water to prepare a 5-10 mg/mL dispersion. Then, the voltage density is fit to around 1 kV/cm. The Al.sub.2O.sub.3 nanofiber substrate after calcination is fixed on the receiving apparatus and the spinning distance is in the range of 10-20 cm to electrostatically spray then nanofiber matrix for 6 h.

[0064] The Third Step: Crosslinking of CNTs/Nanofiber Composite Membrane

[0065] The prepared composite membrane is taken off and immersed in the ethanol solution with (0.2%)phenolic resin for 1 h. Then, oxalic acid is added into the mixture solution to control pH to be acidic. After taking the membrane out, the membrane is rinsed with ethanol and dried and solidified at 60° C.

[0066] Results: the support layer and the separation layer of prepared CNTs/AO nanofiber composite flat membranes both show a network-like interconnected hole structure. The pore size of the support layer is in the range of 300-500 nm and the pore size of the composite membrane is around 100 nm.

Embodiment 5. Preparation of CNTs/PAN Nanofiber Composite Spiral-Wound Membrane

[0067] The First Step: Preparation of Nanofiber Matrix by Electrospinning

[0068] The polymer PAN used as the matrix is dissolved in DMF to form a spinning solution with a mass fraction of 15%. The electrospinning voltage density is fit to around 1 kV/cm and the spinning distance is in the range of 10-20 cm. The spinning time is controlled at 10 h according to the concentration. The spiral-wound stainless steelreseau is used as a collector. After the spinning, the non-woven membrane is fixed by gluing and hot pressing, and then cooled to room temperature to obtain the corresponding spiral-wound nanofiber support layer.

[0069] The Second Step: Preparation of CNTs Functional Layer by Electrostatic Spraying

[0070] The 60-100 nm CNTs acidified by mixed acids are dispersed in water to prepare a 5 mg/mL dispersion. Then, then nanofiber matrix is electrostatically sprayed for 6 h at the controlled voltage density of around 1 kV/cm and the spinning distance in the range of 10-20 cm.

[0071] The Third Step: Crosslinking of CNTs/PAN Nanofiber Composite Membranes

[0072] The prepared composite membrane is taken off and immersed in the mixture of (0.2%)polyacrylamide and (1%)oxalic acid for 1 h. 2M hydrochloric acid is added into the mixture solution to control pH to be acidic. After taking the membrane out, the membrane is rinsed with deionized water and dried and solidified at 60° C.

[0073] Results: the prepared CNTs/PAN nanofiber composite spiral-wound membrane shows a meshy interconnected hole structure. The pore size of the composite membrane is around 300 nm.