Engineering Surface Wettability to Alleviate Membrane Scaling in Photothermal Membrane Distillation

To address the growing demand for fresh water with a smaller carbon footprint, photothermal membrane distillation (PMD) has been proposed by combining membrane distillation with solar irradiation. Due to its low level of energy consumption and portability, PMD is becoming increasingly attractive for water production in off-grid areas. However, it still suffers from several challenges, including membrane scaling. To address this issue, we developed photothermal membranes with different wettabilities. #PCNT-2 with a hydrophobic surface was obtained by electrospinning a polyvinylidene fluoride (PVDF) nanofibrous substrate and a hydrophobic PVDF/carbon nanotube (CNT) surface layer. The surface was then modified by depositing a polydopamine (PDA) layer to make it hydrophilic (#PCNT-D). It was found that #PCNT-D exhibited the highest surface temperature under both dry and wet conditions and the highest evaporation rate due to its broad light absorption and high photothermal efficiency. PMD tests show that #PCNT-D with a hydrophilic surface possessed the best antiscaling performance under illumination. This can be attributed to it having the highest surface temperature and lowest mass transfer resistance, the highest salt solubility on a membrane surface, and the best heat transfer efficiency between the heated membrane surface and absorbed water in the PDA layer.