Abstract

Solar-driven membrane distillation (SMD) with local heating of photothermal membranes has shown great potential in the field of seawater desalination due to its low energy consumption, low cost and high efficiency in freshwater production performance. However, the current photothermal membranes with solely hydrophobic property have limitations such as pore blockage, intolerance to oil contamination and short service life that seriously hinder their further implementations in industrial application. In this work, an innovative separable Janus superhydrophilic/superhydrophobic nanofiber membrane (PPy@PVA-PVDF/F-SiO2-PVDF) is proposed for SMD, which consists of a superhydrophilic/underwater-oleophobic PPy@PVA-PVDF membrane with photothermal effect (local heating and prevention of oil contamination) and a superhydrophobic F-SiO2-PVDF membrane with high porosity (separates seawater and provides water vapor passage). The optimized Janus photothermal membrane achieves high water flux (4.17 kg m-2h−1), solar energy utilization efficiency (77.33 %), and fresh water generation (salt interception rate of 99.9 %) under 3 sun intensity. In addition, Janus bilayer membrane are stable in silicone oil/salt water emulsions for 30 hrs (only 2hrs for a single hydrophobic membrane). The unique separable structure design of Janus bilayer membrane enables the upper photothermal superhydrophilic and the lower hydrophobic layers to be replaced and maintained independently, thereby prolonging the service life of the membranes and reducing the post-maintenance costs of SMD. The separable photothermal Janus bilayer membrane in this study provides an innovative solution for low-cost, efficient and sustainable freshwater production, with promising applications in the treatment of oil-contaminated seawater.

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