Fabrication of a novel octadecylamine functionalized graphene oxide/PVDF dual-layer flat sheet membrane for desalination via air gap membrane distillation

Abstract

In the present research, a novel dual-layer membrane was prepared by coating a very smooth layer of octadecylamine functionalized graphene oxide (GO-ODA) on the surface of polyvinylidene fluoride membrane. The GO and GO-ODA were characterized by XRD, TGA and FE-SEM and pure PVDF (unmodified) and dual-layer (modified) membranes were also characterized by contact angle, pore size distribution, liquid entry pressure (LEP), FT-IR, SEM, AFM, and ATR-FTIR. Modified membranes in comparison with unmodified membrane showed a superior performance in terms of surface roughness, hydrophobicity, water flux and NaCl rejection. In air gap membrane distillation (AGMD) experiments using a 3.5wt% NaCl solution as feed at 80°C, unmodified, M1 (low GO-ODA loading), and M2 (high GO-ODA loading) modified membranes showed water fluxes of 18.2, 13.8, and 16.7kg/m2·h and salt rejections of 88.5%, 96.3%, and 98.3%, respectively. This improvement in membrane performance was attributed to the existence of GO-ODA on the top layer of modified membranes that formed interconnected nano-channels with high surface area for high NaCl rejection and fast flow of water. Furthermore, GO-ODA with high hydrophobicity and low thermal conductivity on the surface of modified membranes contributed to reduce pore wetting, temperature polarization and heat diffusion across the membrane.