Superhydrophobic composite graphene oxide membrane coated with fluorinated silica nanoparticles for hydrogen isotopic water separation in membrane distillation

Abstract

Due to the laminar structure constructed by two-dimensional nanosheets, nanochannels are formed in the graphene oxide membrane (GOM), including capillaries formed by two closely spaced graphene sheets and nanopores in the nanosheets. These nanochannels have strong molecular sieving properties that can be tuned by various methods and applied in molecules separation. Such membranes are often used for the separation of different molecules or ions, but are rarely used for the isotope separation. In this work, superhydrophobic modification of the GOM was achieved by introducing layers of fluorinated silica nanoparticles on the membrane surface, combining the fluoro-containing resin to enhance the adhesion and decrease the surface energy. Using light/heavy water as a model, the hydrogen isotopic separating performance of this composite membrane was evaluated in an air gap membrane distillation (AGMD) apparatus. It was shown that the superhydrophobic coating of the membrane can effectively prevent the liquid water penetrating into the membrane, thus providing a pure vapor process in the membrane. Meanwhile, when compared to pure GOM and commercial polymeric membranes, the resultant membranes acquired superior isotopic selectivity in membrane distillation. The best performing membrane contains three layers of nanoparticles, of which the outermost surface was treated with 40 μL (heptadecafluoro-1, 1, 2, 2-tetrahydrodecyl) trimethoxysilane (17-FTMS) and 10 μL methyltrimethoxysilane (MTMOS). A mean separation factor value of 1.151 and a permeation flux of 0.036 kg m−2 h−1 were obtained. In addition, continuous test for up to 90 h showed a stable performance of the composite membrane, without compromising the selectivity and flux of the membrane. This study not only demonstrates the potential of superhydrophobic composite GOM for hydrogen isotopic sieving in membrane distillation, but also provides a facile and generic method for superhydrophobic modification of the hydrophilic membrane.