Fouling resistant and performance tunable ultrafiltration membranes via surface graft polymerization induced by atmospheric pressure air plasma

Surface modification of polysulfone (PSf) surface, via acrylic acid (AA) surface graft polymerization, induced by atmospheric pressure Air plasma (Air APP) surface treatment, was explored for imparting UF membrane fouling resistance and tuning its performance. PSf surface activation with Air APP and subsequent tethering of PAA chains resulted in a higher degree of surface hydrophilicity relative to the use of He and He/O2 plasmas. Surface-nano-structed (SNS) PSf membranes with tethered PAA chains were of increased surface hydrophilicity and the polar component of the surface energy by 14% and 556%, respectively, and had a greater negative zeta potential (by 26% at pH >∼6) relative to the native-PSf membrane. Fouling filtration tests with bovine serum albumin (BSA) and sodium alginate demonstrated reduced fouling resistance, relative to the native-PSf membrane. Moreover, complete permeability recovery of the fouled SNS-PAA-PSf membrane was achieved, via simple water backwash, relative to 66%-81% permeability recovery for the native PSf membrane. Tethering the PSf UF surface with PAA chains was also enabled tuning of the membrane molecular weight cutoff (MWCO) and hydraulic permeability. It was shown that starting with the same PSf UF membrane a series of SNS-PAA-PSf membranes can be synthesized whereby performance tuning was achieved over a MWCO range of 5.5–11 kDa and a corresponding permeability range of 12.7–23.5 L·m−2·h−1·bar−1. The present approach of PSf UF membrane surface structuring with tethered PAA chains, employing Air APP for surface activation, was shown to be effective for UF membrane fouling reduction and performance tuning. Thus, the present study results suggest that there is merit in exploring its scalability given the utilization of air as a low cost plasma source gas.