Preparation of polysulfone nanofiltration membranes by UV-assisted grafting polymerization for water softening

The rising demand for high quality water heightens the need to soften hard and very hard water. In this study, flat sheet polysulfone ultrafiltration membranes were prepared by phase inversion and modified by UV-induced polymerization of acrylic acid in order to prepare nanofiltration membranes for water desalination. Polyethylene glycol of different molecular weights mainly in the range of 1500–4000 Da were used in the casting solution and acrylic acid was polymerized on the membrane surface. In this way, a manipulated membrane was prepared with higher pore size and higher surface charge density for improved water softening. The results show that by increasing irradiation time and monomer concentration in the photografting process, pure water flux declines and salt rejection increases. For a membrane photografted for 180 min with acrylic acid solution (6 wt.%) and PEG-4000 as additive, the rejection of Na2SO4, MgSO4, NaCl and CaCl2 follows a decreasing in order of 100%, 77.9%, 49.9% and 35.9% respectively. The RMS roughness of the prepared membrane is 1.65 nm, which is well in the nanofiltration roughness range. Featuring a large pore size and high surface charge density, the developed nanofiltration membranes show a promising capability for water desalination.