Fabrication of GO modified PVDF membrane for dissolved organic matter removal: Removal mechanism and antifouling property

In this study, graphene oxide (GO) layers were successfully grafted onto a polyvinylidene fluoride (PVDF) membrane using chemical activated treatment and layer-by-layer assembly method. The physicochemical properties of GO modified membranes were analyzed by Fourier-transform infrared spectroscopy, field-emission scanning electron microscopy, zeta potential, and water contact angle measurements. Our results showed that GO layers resulted in a decrease in pore size, an increase in the negative surface charge and hydrophilicity of the modified membrane. Thus, much higher removal rates of proteins, humic acids and fulvic acids were observed for GO modified membranes due to the enhanced size exclusion. Notably, the higher rejection of the smaller molecular weight (MW) organics in the range of 50-500 Da was also obtained for the GO modified membrane, which was attributed to the size exclusion of GO layers' surface and adsorption effect of GO layers. The foulant desorbed from fouled membrane before and after physical rinsing illustrated that, the hydrophilic and proteins with large MW were the major foulants resulting in irreversible fouling for both pristine and GO modified membranes. The pristine membrane exhibited severe irreversible fouling caused by pore blocking. However, GO modified membrane displayed the efficient antifouling performance. The foulants were more prone to forming a loose cake layer on the surface and prevented membrane pore blocking due to the negative charge and stronger hydrophilicity of GO layers, which resulted in a lower irreversible fouling ratio during the filtration of DOM solution. Therefore, GO modified membranes exhibited the higher rejections of foulants with large MW and small MW and better antifouling property in comparison of pristine membrane.