Enhancing the selectivity of hydrogen isotopic water in membrane distillation by using graphene oxide

Abstract

Isotopes of hydrogen are playing an increasingly important role in applications such as controllable nuclear fusion and other nuclear processes, yet directly separating isotopic water from its mixture is still energy-intensive and largely limited by the moderate separation factor values. In this study, Graphene oxide (GO) and reduced graphene oxide (rGO) nanosheets, combining optimized hydrophobicity by grafting perfluoroalkylsilanes (PFAS), have been used for improving the selectivity of isotopic water in membrane distillation. By utilizing heavy/light water mixture as a model, permeation flux and isotopic selectivity of the membranes are systematically evaluated. The graphene oxide membranes, particularly for the rGO grafted by PFAS, exhibit enhanced selectivity with an increased isotopic separation factor, as compared with that of commercial membranes, which is probably due to the efficient synergy between unimpeded nanochannels and near-super hydrophobic surface. A maximum mean separation factor value of 1.067, combined with a permeation flux of 0.47 kg m−2 h−1 have been achieved for the grafted rGO -membrane reduced at 750 °C. Furthermore, our study demonstrates utilizing two-dimensional materials, like GO and rGO, can be an effective avenue for promoting the isotopic selectivity in membrane distillation, based on increasing hydrophobic water vapor channels with higher selectivity.