Polyelectrolyte complex nanofiltration membranes with low MWCO for pharmaceuticals removal

Abstract

Nanofiltration membranes have been popularly used in water reclamation to remove trace organic compounds. Nanofiltration membranes with low molecular weight cut-off (MWCO) and lower salt rejections are preferred to apply in water reclamation to avoid scaling. In the present work, polyelectrolyte complex nanofiltration membranes with lower MWCO were fabricated by electrostatic deposition of branched PEI on hydrolyzed PAN support, following glycerol treatment and thermal annealing. The performance of the membranes was evaluated by removing pharmaceuticals. At optimal conditions, a PEI/PANH membrane with MWCO around 200 Da was prepared. The membrane had a slightly positively charged surface in a nearly neutral environment. The rejections to neural solutes, such as PEG 200 and triclosan, were up to ∼ 90 %, and the rejections to the salts (NaCl, CaCl2, and MgSO4) were lower than 10 %, showing good organic selectivity toward salts. The crosslinking steps reversed the charge property of the membrane surface and narrowed the pores of the membrane. Consequently, both salt and organic rejections increased (higher than 80 % for the pharmaceuticals), and more increments were for salts. Incorporation of the cross-linker in the glycerol solution provided a facile method to crosslink the PEI/PAN membrane. These results demonstrate the feasibility of using the simple electrostatic deposition method to prepare low MWCO nanofiltration membranes for trace organic removals.