Improved membrane structures for seawater desalination by studying the influence of sublayers

This study describes the influence of polyethersulfone (PES) sublayers on the performance of polyamide (PA) reverse osmosis membranes. Asymmetric polymeric sublayers were synthesized by using the DIPS technique (Diffusion Induced Phase Separation). Sublayers are optimized mainly with respect to hydrophilicity, permeability and rejection potential by adjusting synthesis procedures. Parameters that were found to have an influence are the type of solvent (DMF and NMP were used), the air humidity, processing time, and concentrations of polymer. By carefully controlling these parameters, it was possible to prepare a range of sublayers with different characteristics, in the ultrafiltration–nanofiltration area. To visualize membrane surface characteristics, both scanning electron microscopy (SEM) and atomic force microscopy (AFM) measurements were performed. In addition, titanium (TiO2) nanoparticles were assembled with polyethersulfone (PES) membranes at ultralow concentrations of nanoparticles to characterize TiO2/PES composite membranes and evaluate their permeate flux and solute rejection. Subsequently, a polyamide top layer was added by interfacial polymerization using typical reagents both in the aqueous and in the organic phase. The membrane performance was evaluated in terms of flux and salt rejection. Experimental design was performed in order to obtain the importance of some experimental variables during the polymerisation process. It was found that depending on the type of sublayer used in the procedure, a different membrane performance could be obtained.