Application of polysulfone/cyclodextrin mixed-matrix membranes in the removal of natural organic matter from water

Abstract

The removal of natural organic matter (NOM) by polysulfone/β-cyclodextrin polyurethane (PSf/β-CDPU) mixed matrix membranes (MMMs) was investigated in order to establish the effect of the addition of β-cyclodextrin polyurethane (β-CDPU) in polysulfone (PSf) membrane on the rejection of NOM (humic acid) and the fouling resistance of MMMs. It was found that the effective pore sizes and molecular-weight-cut-off (MWCO) of hand-cast PSf membranes were improved by β-CDPU addition due to its large pore size and its conical structure being capable of allowing easy passage of water molecules. An increase in pure water flux was achieved with increase in β-CDPU concentration in the PSf MMMs. Furthermore, the pure water flux of the hand-cast PSf membrane improved from 12 to 137l/m2h when the applied pressure was increased from 0.62 to 2.41MPa. The highest NOM removal efficiency achieved was 69% based on TOC measurements whereas a 76% NOM removal efficiency was attained as calculated from UV254 analysis. Fourier transform infrared (FT-IR) spectroscopy analyses confirmed the absence of OH and CH groups on all membranes after NOM rejection. This accounted for the increase in contact angle obtained after rejection tests. It is suggested that solution–diffusion mechanism is responsible for NOM filtration/rejection process. In addition, scanning electron microscopy (SEM) micrographs (after NOM rejection tests) revealed that the addition of β-CDPU in PSf resulted in improved antifouling properties based on the agglomeration of NOM on the membrane surfaces.