Carbon nanotube immobilized super-absorbing membranes
Carbon nanotube (CNT) immobilized membranes for harvesting pure water from air include CNTs incorporated into a layer of super-absorbing polymer. The super-absorbing polymer may be cast over a porous substrate. The super-absorbing polymer binds strongly to water and generates water clusters while the CNTs are operable to interrupt the specific water-polymer and water-water interactions to generate more free water which permeates more easily through the membrane. Methods of forming the CNT immobilized membranes are provided. The CNT immobilized membranes disclosed herein exhibit improved water vapor extraction efficiency, water vapor removal and mass transfer coefficient.
1. A polymeric membrane comprising a porous substrate and a layer disposed on a surface of the porous substrate, the layer comprising a plurality of carbon nanotubes immobilized in a super-absorbent polymer.
2. The polymeric membrane according to claim 1 wherein the porous substrate comprises a porous polymeric material.
3. The polymeric membrane according to claim 2 wherein the porous substrate is selected from the group consisting of cellulose acetate, cellulose ester, polysulfone, polyether sulfone, polyacrilonitrile, polyamide, polyimide, polyethylene, polypropylene, polytetrafluoroethylene, polyvinylidene fluoride and polyvinylchloride.
4. The polymeric membrane according to claim 1 wherein the porous substrate comprises polypropylene.
5. The polymeric membrane according to claim 1 wherein the porous substrate comprises hollow fiber polypropylene.
6. The polymeric membrane according to claim 1 wherein at least one of the plurality of carbon nanotubes is single walled.
7. The polymeric membrane according to claim 1 wherein at least one of the plurality of carbon nanotubes is multi-walled.
8. The polymeric membrane according to claim 1 wherein at least one of the plurality of carbon nanotubes is carboxylated.
9. The polymeric membrane according to claim 1 wherein the super-absorbent polymer is selected from the group consisting of cross-linked poly(acrylamide-co-acrylic acid) and salts thereof and cross-linked sodium polyacrylate.
10. The polymeric membrane according to claim 1 wherein the super-absorbent polymer is poly(acrylamide-co-acrylic acid).
11. A method of making a carbon nanotube- immobilized membrane comprising the steps of dispersing a plurality of carbon nanotubes in water to form a carbon nanotube dispersion, dissolving a super-absorbent polymer in water to form a super-absorbent copolymer solution, adding the super-absorbent copolymer solution to the carbon nanotube dispersion to form a super-absorbent polymer-carbon nanotube mixture, applying the super-absorbent polymer-carbon nanotube mixture to a surface of a porous substrate and drying the super-absorbent polymer-carbon nanotube mixture.
12. The method according to claim 11 further comprising carboxylating at least one of the plurality of carbon nanotubes.
13. The method according to claim 11 further comprising pre-treating the porous substrate prior to the step of applying the super-absorbent polymer-carbon nanotube mixture thereto to enhance adhesion between the porous substrate and the super-absorbent polymer-carbon nanotube mixture.
14. The method according to claim 13 wherein the porous substrate comprises polypropylene and the step of pre-treating comprises hydrophilization.
15. The method according to claim 14 wherein the hydrophilization step comprises applying chromic acid to the porous substrate.