Graphene oxide composited with different size of organic molecules for hydrogen isotopic water separation in membrane distillation

Abstract

Developing an efficient light water/tritiated water (H2O/HTO) separation process to meet environmental regulations is important in the nuclear energy field. The membrane distillation processes for the separation of H2O/D2O (deuteriated water), which is usually served as the laboratory model process for H2O/HTO separation, showed good separation performance with graphene oxide (GO)-based membranes. Here, the approach to enhance the H2O/D2O separation performance was explored through regulating interlayer spacing and physicochemical properties of membranes, for which two types of GO membranes were prepared and applied in air-gap membrane distillation: (i) small molecules of urea (UR) or ethanediamine (EDA) were cross-linked with GO platelets to obtain GO-framework (GOF) membranes designated as GO-UR or GO-EDA with varied interlayer spacing. The GO-EDA membrane with a permeation flux of 0.95 L·m−2·h−1 gave higher separation performance than the pristine GO membrane; (ii) macromolecules of hydrophilic polyvinyl alcohol (PVA) or hydrophobic polymethyl methacrylate (PMMA) were intercalated into GO laminates to adjust interlayer spacing and physicochemical properties of membranes. The resultant GO-PVA membrane exhibited a higher permeation flux of 0.94 L·m−2·h−1 and similar separation factor compared with the pristine GO membrane. Moreover, long-term process stability of H2O/D2O separation in membrane distillation was demonstrated using GO-EDA membrane for a 28-h process. Therefore, the results demonstrated that regulating interlayer spacing and physicochemical properties of membranes can provide a facile route to improve performance of GO-based membrane distillation processes for the separation of H2O/D2O, which may be applied to H2O/HTO separation process needed for the treatment of tritiated water in the nuclear energy field.