Chitosan based high performance filter with self-regenerating ability
A self-regenerating chitosan based filter medium for disinfecting and purifying organic pollutants and other pollutants in a gas or liquid is disclosed herein. Porosity and surface charge of said filter medium is manipulative/tunable by varying one or more of the following parameter(s): concentration of chitosan, crosslinking density, amount of copolymers and additives, freezing temperature, freezing profile, and/or types of crosslinker used. The present filter medium is capable of self-regenerating under exposure to ultra-violet light for sufficient time and removing over 90% of the pollutants from each influent flowing through the filter medium.
1. A method for preparing a self-regenerative gaseous and water pollutant filter membrane, said filter membrane being formed by a composition comprising chitosan derivatives or a mixture of chitosan derivatives and a polymer in a weight ratio from 1:1 to 3:1, a photocatalytic metal oxides being self-regenerative under exposure to light for a period of time, said filter membrane being prepared by selecting a specific weight ratio between said chitosan derivatives and said photocatalytic metal oxide, freezing said composition at a specific freezing temperature and profile from room temperature to from −10° C. to −55° C. at a freezing rate of about 1° C./min followed by air drying, and using a specific concentration of a crosslinker for cross-linking with the freeze-dried and air-dried composition for less than 20 minutes in order to result in a desired pore size, surface charge, at least two times of self-regenerating ability, and over 90% removal percentage of the organic pollutants from each influent flowing through said filter membrane.
2. The method of claim 1 , wherein said specific weight ratio between said chitosan derivatives and said photocatalytic metal oxide is from 1:2.78 to 1:3.8.
3. The method of claim 1 , wherein said composition comprises 0.27 g chitosan and 0.75 g TiO 2 in 15 mL water such that the self-regenerating ability of said filter membrane reaches eleven times.
4. The method of claim 1 , wherein said specific concentration of said crosslinker is from 0.0136M to 0.068M.
5. The method of claim 1 , wherein said polymer is selected from synthetic polymer or biopolymer.
6. The method of claim 5 , wherein said synthetic polymer is copolymer comprising polyvinyl alcohol, polyethylene glycol, and polyacrylic acid.
7. The method of claim 5 , wherein said biopolymer comprises cellulose, carrageenan, and alginate.
8. The method of claim 1 , wherein said photocatalytic metal oxide comprises titanium dioxide, zinc oxide, vanadium oxide, and manganese dioxide, which is in particle form with a particle size ranging from 10 nm to 10 μm.
9. The method of claim 1 , wherein said crosslinker comprises Trisodium citrate dihydrate, sodium hydroxide, tripolyphosphate (TPP), glyoxal, glutaraldehyde, polyethylene glycol, epichlorohydrin, N-hydroxysuccinimide, 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide, 1,4 butanediol diglycidyl ether, formaldehyde, genipin, and oxalic acid.
10. The method of claim 9 , wherein said chitosan is crosslinked by said crosslinker ranging from 0.0136M to 0.068M to result in a pore size of said filter membrane ranging from 100 nm to 100 μm.
11. The method of claim 10 , wherein said crosslinker is tripolyphosphate in a concentration of 0.5 wt % while the weight percentage of said chitosan is 2.5 wt % in said composition to be frozen.
12. The method of claim 1 , wherein said polymer is in a concentration from 0.24 wt % to 0.50 wt % in said composition.
13. The method of claim 1 , wherein said photocatalytic metal oxides is self-regenerated when said filter membrane is exposed to ultra-violet light for at least 3 hours.
14. The method of claim 1 , wherein the surface charge of said filter membrane is tuned to positive charge by introducing quaternary ammonium to said surface.
15. The method of claim 1 , wherein the surface charge of said filter membrane is tuned to negative charge by introducing 5-formyl-2-furansulfonic acid to said surface.
16. The method of claim 1 , wherein the surface charge of said filter membrane is neutralized by sodium hydroxide.
17. The method of claim 1 , wherein said method comprising the following steps:
(a) dissolving chitosan powder and said polymer into deionized water with acetic acid or providing a mixture of said chitosan derivatives and said polymer in a weight ratio from 1:1 to 3:1 followed by adding said photocatalytic metal oxide to form a mixture, and stirring the mixture for about an hour until homogeneous;
(b) freezing drying the homogeneous mixture obtained from (a) at about −55° C. for about 4 hours, followed by a two drying cycle treatment including a first drying cycle of −55° C. for about an hour and subsequently at −10° C. for about 12 hours, and a second drying cycle of about 40° C. for about an hour to obtain a scaffold;
(c) soaking the scaffold obtained from (b) into a crosslinking agent containing said crosslinker to crosslink the chitosan; and
(d) optionally tuning the surface charge of the filter membrane by treating the surface of the chitosan scaffold with an acid or an alkaline.
18. A chitosan-based filter medium prepared by the method of claim 1 .