Fabrication and characterization of hydrophobic/hydrophilic dual-layer polyphenyl sulfone Janus membrane for application in direct contact membrane distillation

Abstract

In this study, single-layer (SL) and dual-layer (DL) polyphenyl sulfone (PPSU) flat sheet nanocomposite Janus membranes were fabricated via a combination of VIPS and NIPS techniques for direct contact membrane distillation (DCMD) for the first time. Hydrophobic silica nanoparticles (SiNP-B) were incorporated into the SL membranes and the top layer of the DL membranes, while hydrophilic silica nanoparticles (SiNP-L) were added into the down layer of the DL membranes. The effect of the SiNP-B concentration (1–5 wt%) and the top layer thickness (50 and 100 μm) on the morphology, mean pore size (MPS), thickness, porosity, surface roughness, water contact angle (WCA), liquid entry pressure, mechanical strength, and thermal conductivity were investigated. All of the membranes showed a finger-like structure surrounded by a sponge-like structure. The membranes were examined in the DCMD of a 35,000 ppm saline solution at different feed temperatures (50–70 °C) and flow rates (250–1000 mL/min). The DL membranes possessed higher fluxes than the SL membranes through increasing MPS and WCA. The DL membrane with a SiNP-B concentration of 2 wt% and a hydrophobic thickness of 50 μm (DL- 2,50) achieved the highest flux (42.68 ± 0.35 kg/m2h) and salt rejection (94.90 %) during 5 h. This membrane has an MPS of 0.22 ± 0.03 μm, a thickness of 201 ± 4 μm, and a porosity of 76 ± 2 %. It could be concluded the proper pore size distribution is the most important factor in achieving a successful DCMD operation.