Preparation and characterization of N,O-carboxymethyl chitosan/Polysulfone composite nanofiltration membrane crosslinked with epichlorohydrin

N,O-carboxymethyl chitosan (NOCC) composite nanofiltration membranes crosslinked by ECH were developed using a method of coating and crosslinking, where an epichlorohydrin/ethanol 96.7% (0.067 M KOH) solution was used as the crosslinking agent. The structure and the morphology of the resulting membrane were characterized by attenuated total reflection infrared spectroscopy (ATR-IR) and environmental scanning electron microscopy (ESEM). The effects of preparation conditions on the rejection performance of the resulting composite membrane were also investigated. At 20 C and 0.40 MPa the rejections of the resulting membrane to Na2SO4 and NaCl solutions (1000 mg LÀ1) were 90.4% and 27.4%, respectively, and the permeate fluxes were 7.9, and 10.8 kg mÀ2 hÀ1, respectively. The rejections of this kind of NOCC/PSF composite NF membrane to the inorganic electrolyte solutions decreased in the order of Na2SO4, NaCl, MgSO4, and MgCl2.

Novel amphoteric composite NF membranes were prepared through a method of coating and crosslinking using NOCC, PSF UF membranes, and ECH as the active layer material, the base membranes, and the crosslinking agent, respectively. The results suggest that NOCC/PSF composite NF membranes with excellent rejection performance could be prepared under the following conditions: NOCC concentration 1.7 wt.%, curing time 1 h at 60 C, ECH/EtOH 96.7% (0.067 M KOH) concentration 3.0 wt.%, and crosslinking time 3 h at 50 C. The MWCO of the resulting NF membrane was %760 Da. At 20 C and 0.40 MPa the rejections to Na2SO4 and NaCl solutions (1000 mg LÀ1) were 90.4% and 27.4%, respectively, and the permeate fluxes were 7.9 and 10.8 kg mÀ2 hÀ1, respectively. The rejection of this kind of composite NF membrane to inorganic electrolyte solutions decreased in the order of Na2SO4, NaCl, MgSO4, and MgCl2. It can be concluded from the results that the amphoteric NOCC/PSF composite membrane showed similar rejection performance to negatively charged composite NF membranes. Additionally, the curve for the streaming potential also illustrates the negatively charged characteristics of the composite membrane. The resultant NOCC/PSF composite NF membrane with excellent rejection performance was characterized with ATR-IR and ESEM, respectively. The ATR-IR spectra revealed the crosslinking of hydroxyl groups and amino groups with ECH. The rejection properties of the developed composite membranes could be adjusted by changing the concentration of the casting solution of the active layer, the concentration of the crosslinking agent, the crosslinking time, the curing temperature, the addition of the low-molecular-weight organic additive, etc. It was found that PEG200 is a kind of excellent low-molecule-weight organic additive for NOCC/PSF composite NF membranes, and the rejection characteristic of the resultant membrane would be improved when the casting solution was added into PEG200 in the range of 5.0–30.0 wt.%.