Preparation of polysulfone support for higher-performance reverse osmosis membranes

We prepared a polysulfone (PSU) support by applying a coating of a PSU-N,N-dimethylformamide (DMF) solution on 91 µm thick nonwoven and then set it in water (the phase inversion process). The prepared PSU-substrate sheet was 280 mm wide and 10 m long. We then investigated the effects of the preparation conditions (i.e., the concentration of the PSU-DMF solution and the coating thickness) on the water permeability of the resulting PSU support. The thickness of the PSU layer increased almost linearly with the increase in the coating thickness, and the water permeability decreased monotonically with the increase in the PSU layer's thickness. A bubble point analysis revealed that the pore size dia. of the membranes was approx. 20–60 nm, depending on the PSU-DMF solution's concentration. Using these PSU membranes as the support, we prepared a reverse-osmosis (RO) membrane, the active layer of which consisted of aromatic polyamide (PA) that contained carbon nanotubes. The salt rejection rate 99.7% and water permeability at 0.56 L m−2 h−1 bar−1 were achieved at 5.5 MPa for a 3.2% NaCl solution with the RO membrane, the support of which was prepared from a 17.0% PSU-DMF solution.