Tuning interlayer spacing of graphene oxide membrane to enhance its separation performance of hydrogen isotopic water in membrane distillation

Abstract

Separation of light water/tritiated water (H2O/HTO) is an important process in the nuclear energy sector to treat tritium-containing radioactive wastewater, for which H2O/D2O separation is usually used as a research model to minimize safety concerns. Recently Graphene oxide (GO)-based membrane distillation processes have demonstrated high separation factor, however, the permeation flux is low to affect the overall separation performance. In this study, the approach of tuning interlayer spacing and structure of GO membranes was explored to enhance the separation performance through two ways: (i) GO membrane was intercalated using cations (Na+, or Ca2+), or cationic surfactant-cetyltrimethylammonium bromide (CTAB) to vary interlayer spacing, and the resulting GO-Ca membrane gave the highest permeation flux of 0.87 kg·m−2·h−1 among the intercalated GO membranes with a separation factor of 4.6% to deliver higher separation performance than the pristine GO membrane; (ii) GO-framework (GOF) membrane was prepared by cross-linking GO nanosheets with cations (Ca2+, or Al3+) to prepare GOF@Ca and GOF@Al membrane, and GOF@Al membrane achieved a separation factor of 4.9% and a permeation flux of 0.9 kg·m−2·h−1, both higher than that of the pristine GO membrane. Furthermore, the up-to-date H2O/D2O separation data from different GO-based membrane distillation processes were summarized to understand the correlation between the permeation flux and the separation factor of processes. The results of this study suggested that tuning interlayer spacing and structure of GO membranes can be a good approach to enhance the overall separation performance by simultaneously improving permeation flux and separation factor for the separation of H2O/D2O, which can guide for future development of low-cost and efficient H2O/HTO separation processes needed in the nuclear energy field.