New method of synthesis of sulfonated polyethersulfone (SPES) and effect of pH on synthetic gray water filtration performance by negatively charged SPES/PS UF membranes

All polymeric membrane-based water purification systems suffer serious membrane fouling problem due to protein adsorption and bacteria attachment. Increasing the negative surface charge density of the membrane will increase its hydrophilicity; this would hinder the colloidal and bacteria attachments. This can be achieved through inclusion of sulfonated group () as part of the moiety of the polymer that made up of the membrane. In this work, a new method of synthesis of sulfonated polyethersulfone (SPES) is reported. In this method, concentrated sulfuric acid was used as the solvent for polyethersulfone (PES) and also as the source of SO3(g) when the PES/H2SO4 solution was heated to 90°C. The degree of sulfonation of the polyethersulfone polymer was assessed by ATR-FTIR spectra and ion-exchange capacity determination. Nine polysulfone membranes, containing various amounts of SPES, were fabricated via phase inversion process with a continuous membrane casting machine. The membranes were also characterized using techniques such as SEM, AFM, water permeability, water content, molecular-weight-cut-off, and the negative surface charge. Effects of pH of the synthetic gray water feed (with common domestic wastewater composition, excepting microbiological components) on membrane fouling were evaluated for all nine SPES/PS membranes.