Abstract: Harvesting clean water from seawater and wastewater based on solar-driven evaporators is emerging as one of the most promising way to alleviate the shortage of water resource today. However, it also faces a typical defect of massive deposition of salts and pollutants in the functional evaporator, which generally influences the cyclic evaporation performance of the device. To address this problem, a 3D Janus solar evaporator that with functions of solar desalination and wastewater purification was fabricated in this work by employing simple polyurethane foaming and surface impregnation techniques, which generally shows high-efficiency water evaporation and good performance on hindering the deposition of salt and pollution in the evaporator. To gain a standard matrix, a featured foam with 3D porous structure was first prepared by combining polyurethane foam and carbonized rice husk powders, in which the polyurethane frameworks can provide high strength and toughness while carbonized rice husk logically enables properties of high solar absorption and good hydrophilicity. Then, the hydrophobic polypyrrole was introduced in the upper layer of this foam matrix to construct a Janus solar evaporator with asymmetric wettability while the upper layer shows hydrophobicity and lower layer allows hydrophilicity. The featured structure ensures this evaporator sufficient water transmission in the lower layer and simultaneously endows a function on limiting the accumulation of salts and pollutants on evaporator surface, Ascribed to the as-mentioned points, the Janus evaporator has exhibited good evaporation performance and excellent anti-pollution properties, which demonstrates a maximum brine evaporation rate of 1.33 kg m-2 h-1 and wastewater evaporation rate of 1.29 kg m-2 h-1 under solar irradiation of 1 kW m-2, combining with good cycle stability. In addition, the introduction of organic polyurethane networks also endow the Janus evaporator with excellent structural stability, which can be fabricated and tailored to various sizes and shapes for large-scale application.

Key words: Carbonized rice husk, Polypyrrole, Janus structure, Solar-driven evaporator, Anti-pollution property