Photothermal Janus PPy-SiO2@PAN/F-SiO2@PVDF-HFP membrane for high-efficient, low energy and stable desalination through solar membrane distillation

Currently, membrane distillation driven by solar energy (solar membrane distillation, SMD) is an effective method to address the high cost and high energy consumption problem of conventional seawater desalination. However, the complex preparation of photothermal membrane and low photothermal conversion efficiency limit the development of SMD. In this work, we fabricated a photothermal Janus membrane (PPy-SiO2@PAN/F-SiO2@PVDF-HFP) with asymmetric wettability (hydrophilic/superhydrophobic), and demonstrated that due to the high light absorption rate (∼96.48 %) of polypyrrole (PPy) coating (photothermal layer), hydrophilic SiO2@PAN nanofibers (serves as skeleton) and superhydrophobic F-SiO2@PVDF-HFP layer (provides channels for vapor escape), the photothermal Janus membrane achieves high water flux (∼44.4 kg m−2 h−1) and superior solar energy utilization efficiency (∼92.20 %) under 1 sun illumination when the temperature difference between the hot feed and cold side water (ΔT) is 60 °C; moreover, the membrane can maintain the high salt rejection rate of 99.99 % after working for 56 hrs. Both experimental and numerical simulation results reveal that the SMD process using photothermal membrane reduces the temperature polarization and increases the water flux (the greater light intensity leads to the generation of more water flux). Increasing ΔT is beneficial to enhance the solar energy conversion efficiency; however, it would also increase the temperature polarization and energy consumption. This work can provide important insights for the development of SMD technology with high water flux and low energy consumption.