Effect of oxygenic groups on desalination performance improvement of graphene oxide-based membrane in membrane distillation

Graphene oxide (GO) based membranes show an advantage in desalination because of their unique water channels. Although influence of oxygenic groups of GO on water transport has become a focus of research, this is yet to be fully understood. In this work, the relative content of different oxygenic groups of GO was tuned by varying oxidation temperature (50, 60 and 70 degrees C). GO nanosheets were deposited on the permeate side of PVDF membrane in direct contact membrane distillation to enhance the desalination performance. The continuous GO layer enhanced flux by decreasing the vapor pressure at the permeate side. Salt rejection was improved from 99.2% of PVDF membrane to 99.9% of all the composite membranes. The deterioration of permeate quality caused by membrane wetting was avoided because the tiny solute in permeate was rejected by GO layer. Moreover, raising oxidation temperature resulted in GO that contains more epoxy groups, but less hydroxyl groups. GO oxidized at 70 degrees C provided the highest flux (17.80 kg m(-2) h(-1)) with enhancement proportion of 18.9% because it contains less hydroxyl groups but more epoxy groups. Therefore, the transformation of hydroxyl groups into epoxy groups of GO would be an effective approach for water flux enhancement of GO based membranes.