Influence of polydopamine deposition conditions on pure water flux and foulant adhesion resistance of reverse osmosis, ultrafiltration, and microfiltration membranes

The influence of polydopamine (PDOPA) deposition and poly(ethylene glycol) (PEG) grafting on pure water flux and bovine serum albumin (BSA) adhesion of two polysulfone ultrafiltration (UF) membranes, a poly(vinylidene fluoride) microfiltration (MF) membrane, and a polyamide reverse osmosis (RO) membrane is reported. When modified with PDOPA, all membranes exhibited a systematic reduction in protein adhesion. For example, 90 min of PDOPA deposition led to at least 96% reduction in BSA adhesion to these membranes at neutral pH. BSA adhesion was further reduced by subsequent PEG grafting to PDOPA (PDOPA-g-PEG). The membranes' pure water flux values (i.e., with no foulants present) were influenced to different extents by PDOPA and PDOPA-g-PEG modifications. In the porous membranes (i.e., the UF and MF membranes), the pure water flux reduction due to these modifications correlated with membrane pore size, with the smallest flux reductions observed in the MF membrane (e.g., <1% flux reduction for all PDOPA modification times considered), which have the largest pores, and the largest flux reductions occurring in UF membranes (e.g., a 40% flux reduction after 90 min of PDOPA deposition), which have pore sizes on the order of the PDOPA deposition thickness. The RO membranes, which are essentially non-porous, exhibited a flux reduction of 25% after 90 min of PDOPA deposition.