Ultra-robust vertically aligned three-dimensional (3D) Janus hollow fiber membranes for interfacial solar-driven steam generation with salt-resistant and multi-media purification

The emerging solar-driven steam generation technology is considered as one of the most promising strategies for purifying seawater and wastewater, while it is still challenging to achieve superior evaporation rate, salt-resistant property and multi-media evaporation applications at the same time. Herein, an ultra-robust Janus PP hollow fiber membrane (PP HFM) with capillary-driven siphon and photothermal properties was fabricated. Dopamine (DA), (3-aminopropyl) triethoxy-silane (KH550), TiO 2 nanoparticles were immobilized on the inner surface of PP HFMs for turning from a common hydrophobic state to a hydrophilic state. An outer surface with hydrophobicity is constructed by chemical vapor deposition polymerization (CVDP) of polypyrrole (PPy). The fabricated PP-PDA/KH550/TiO 2 -PPy HFMs showed an asymmetric wettability (inner and outer water contact angle of 0° and 95°), mechanical strength of 1.2 GPa, and light absorption of 95%. Importantly, the low heat loss through decreasing contact area with water enabled vertically aligned HFMs with a superior solar evaporation rate of 3.65 kg/(m 2 ·h), and a high photothermal conversion efficiency of 229.13% under one-sun irradiation. Furthermore, the Janus PP HFMs showed a superior salt-resistance without salt crystals even in 20 wt% high salinity condition, rejections of ion (<10 ppm salt ions), oil (>99%), and dye (>99%), and excellent stability. The Janus PP HFMs evaporator provide a new paradigm   for low heat loss, high evaporation rate, salt-resistant and multi-media purification.