Excellent solar-driven interface evaporation by an oil repellence Janus photothermal membrane for oily wastewater treatment

Solar-driven interface evaporation (SDIE) is considered to be a crucial solution for the global water shortage due to its ability to directly produce fresh water with minimal carbon footprint. However, efficient evaporation processes have typically only been achieved in simple systems, and the removal of oil and ions from complex oily seawater to produce clean water remains a serious challenge. In this study, we developed a novel asymmetric superhydrophilic/amphiphobic Janus photothermal membrane (F@CMPsHM-CHM). It employed a hydrogel composite film composed of CMPsHM as a substrate and was created by simple and direct single-side 1H,1H,2H,2H-Perfluorodecyltrichlorosilane/candle soot (PFDTCS/CS) particle spraying. The lower layer of the membrane serves multiple functions such as water supply, insulation and support, while the top PFDTCS/CS coating provides liquid repellency (with a water contact angle of >150° and an oil contact of >120°) and photothermal capability. The membrane's micro/nano composite structure enables it to absorb up to 97 % of light across the entire solar spectrum, and it can achieve an evaporation rate of 1.67 kg m-2h−1 in pure water evaporation. Also, it can achieve an evaporation rate of 1.4 kg m-2h−1 in oil–water emulsion evaporation under 1 kW m−2 solar irradiation. Importantly, the membrane demonstrates long-term stable evaporation for 6 h and ion removal in complex oil/salt dual systems emulsion. With its scalable manufacturing process, excellent flexibility, unique asymmetrical microstructure, and high and stable evaporation performance in a variety of environments, our strategy provides new solutions for efficient SDIE in real-world complex environments, thereby expanding the applications of photothermal materials.