Asymmetric nanotube containing membranes
This invention relates to heterogenous pore polymer nanotube membranes useful in filtration, such as reverse osmosis desalination, nanofiltration, ultrafiltration and gas separation.
1. A water filtration method, comprising passing water through a membrane to filter the water, wherein the membrane comprises an asymmetric porous polymer and terminating on one side in a skin, with open-ended nanotubes embedded in said skin and protruding through opposite surfaces of said skin to provide fluid communication through each of said nanotubes through said membrane, and said skin forming a substantially impermeable barrier around said nanotubes, said membrane having pores increasing in diameter with increasing distance from said skin.
2. The method of claim 1 , wherein said membrane terminates on the opposite side from said skin in a porous non-woven substrate.
3. The method of claim 1 wherein the polymer is selected from the group consisting of poly(1,4-phenylene ether-ether-sulfone), poly(1-hexadecene-sulfone), poly(1-tetradecene-sulfone), poly(oxy-1,4-phenylenesulfonyl-1,4-phenylene), poly(oxy-1,4-phenylenesulfonyl-1,4-phenylene), poly(oxy-1,4-phenylenesulfonyl-1,4-phenylene), poly(oxy-1,4-phenylenesulfonyl-1,4-phenylene), poly[1-[4-(3-carboxy-4-hydroxyphenylazo)benzenesulfonamido]-1,2-ethanediyl, polyphenylsulfone and polysulfone.
4. The method of claim 1 wherein the polymer is polysulfone.
5. The method of claim 1 wherein the nanotubes are single walled carbon nanotubes.
6. The method of claim 1 wherein the skin has a minimum thickness of one-fifth of the average nanotube length.
7. The method of claim 1 wherein the average length of the nanotubes is from 300 nm to 2000 nm.
8. The method of claim 1 wherein the nanotubes have inner diameters from 0.4 nm to 20 nm.
9. The method of claim 1 , wherein the filtration method comprises a reverse osmosis desalination method, a nanofiltration method or an ultrafiltration method.
10. The method of claim 1 , wherein the step of passing water through the membrane comprises passing the water through said nanotubes from one side of the membrane to an opposite side of the membrane such that the skin forms the substantially impermeable barrier to the water around said nanotubes.