Preparation and Characterization of Chitosan Based Polymer Membranes for Water Purification Application

Abstract

For membranes to be competitive with conventional technology, a membrane process needs to operate with a high rate of flux, high degree of selectivity and high resistance to fouling. Chitosan is an excellent membrane material due to its good film forming nature, hydrophilicity, chemical stability and easy chemical modification. The membranes prepared from pure chitosan cannot offer sufficient mechanical stability for application in flow processes. To overcome this problem, techniques of polymer coating and blending have been employed by researchers. Blended chitosan membranes not only display superior mechanical properties but also they are benefited from the intrinsic advantages of each polymer involved in the blend.

Chitosan was blended with polysulfone to prepare PSf/CS ultrafiltration membranes. The chemical modification of chitosan has been carried out in the thesis, N-succinyl chitosan (NSCS) and N-propylphosphonyl chitosan (NPPCS) are the two derivatives prepared, among the two, NPPCS is the novel derivative synthesized. Further, these two derivatives were blended with polysulfone to prepare PSf/NSCS and PSf/NPPCS UF membranes. UF membranes were subjected to permeation, antifouling and heavy metal rejection study. Titanium dioxide nanotubes (TiO2NT) were synthesized and incorporated into PSf/CS blend to prepare PSf/CS/TiO2NT UF and NF membranes. PSf/Poly (isobutylene-alt-maleic anhydride) (PIAM) blend nanofiltration membranes were modified by changing coagulation bath with cross-linked chitosan solution. The nanofiltration membranes were subjected to salt rejection study.

The PSf/CS, PSf/NSCS and PSf/NPPCS UF membranes showed enhanced permeation and antifouling property compared to pristine PSf UF membrane. Even the UF process was efficient in the rejection of heavy metal ions effectively. Membranes showed a maximum of >90% rejection for Cu, Cd and Ni at very low pressure via polymer enhanced ultrafiltration (PEUF) process. All the nanofiltration membranes showed improved flux and antifouling properties. A maximum of 46 % NaCl rejection was observed in case of PSf/CS/TiO2 membrane with 8 % of nanotube content. Changing the coagulation bath with cross-linked chitosan solution emerged as a best technique to improve salt rejection property of PSf/PIAM membrane.