Designing a multi-stage MoS2 fiber membrane for photothermal membrane distillation

Abstract

Among the various desalination technologies, membrane distillation (MD) stands out for its high salt rejection, low operating temperature and operating pressure. Photothermal membrane distillation (PMD) represents an innovative approach to membrane distillation (MD), wherein the process harnesses plentiful and renewable solar energy to achieve localized heating at the interface between the membrane and the feed solution. This is achieved by employing photothermal materials, eliminating the need for heating a substantial volume of the feed solution. This study has prepared membranes with micro/nano fiber interwoven structure based on polystyrene (PS) and polyvinylidene fluoride hexafluoropropylene copolymer (PVDF-HFP) by electrospinning technology, and constructed multi-stage MoS2 photothermal fiber membranes by hydrothermal growth process. The PS/PVDF-HFP micro/nano fiber membrane possesses a spacious pore structure and high porosity, serving as a robust framework that facilitates swift transport of water vapor. The MoS2 nanoflowers uniformly grown on the micro/nano fibers have both metal 1T and semiconductor 2H phases, which facilitate the absorption of sunlight, reaching an average absorbance of 90.9 % in the240-2600 nm wavelength range. Under 1 kW m−2 solar illumination, the surface temperature of the PS/PVDF-HFP/MoS2 membrane could be raised to 74.2 °C after 120 s. The permeate flux was stable at 1.21 ± 0.02 L m−2 h−1 within 20 h PMD. The membrane showcased a salt rejection rate of 99.96 % and achieved an energy efficiency of 72.08 %. This suggests that the multi-stage MoS2 photothermal fiber membrane, characterized by remarkable stability and high photothermal conversion efficiency, lays a solid foundation for advancing research in the field of PMD applications.