Superwetting B₄C bilayer foam for high cost-performance solar water purification

Solar water evaporation holds great promising for future seawater desalination and wastewater purification via solar energy harvesting and efficient steam generation. While many performance advances have been achieved, up to now the low cost-performance remains a serious hindrance to practical applications. To overcome the limitations, herein we developed a boron carbide bilayer foam (BCBF) based solar evaporator to achieve a record high cost-effectiveness on seawater desalination and wastewater purification. Via integrating full-solar absorbing boron carbide into a porous PVA framework, the BCBF achieves a good hydrophilic wettability, heat-shielding and solar-thermal conversion to offer a high evaporation rate as high as 2.8 kg/m²/h with 93% solar evaporation efficiency under 1 sunlight radiation. Prepared in one step using commercially available low-cost raw materials, the BCBF evaporator is demonstrated to possess an ultra-high cost-effectiveness of 778 g/h/$, far beyond previously reported solar evaporation systems. Practical freshwater production from seawater and multiple wastewaters, with high stability under extreme conditions were also demonstrated. This work suggests a good performance and highly cost-effective solar evaporator for practical water purification.