Bioinspired photothermal sponge for simultaneous solar-driven evaporation and solar-assisted wastewater purification

Abstract

Solar-driven evaporation (SDE) garners widespread attention for solving the freshwater shortage. However, most designed photothermal evaporators lack consideration of contaminants in bottom bulk water which seriously reduces their credibility in practical application. Inspired by the bump structure of Rafflesia arnoldii and truss building, a photothermal evaporator with secondary structure was constructed by embedding biochar loaded with UiO-66-NH2 (C@MOF) into chitosan/bamboo fibers (CS/BFs) matrix for simultaneous freshwater generation and dye adsorption. Due to the efficient light utilization, CS/BFs/C@MOF sponge exhibits an energy conversion efficiency of 86.84% under 1 sun illumination. In addition, CS/BFs/C@MOF sponge possesses the maximum adsorption capacities of 105.48 mg g−1 for methylene blue (MB) and 60.57 mg g−1 for methyl orange (MO). Importantly, the dye adsorption process on CS/BFs/C@MOF is essentially an endothermic reaction, which is more effective in sunlight. The good dye adsorption capacity allows CS/BFs/C@MOF to confine most contaminants to the bottom region during long time working in dye solution, ensuring an efficient SDE process. In outdoor practical application, a single evaporator can extract 6.72 kg m−2 purified water from 50 mg/L of simulated dye wastewater one day with a contaminant removal efficiency of 85.14%. This work achieves a good integration of separation and purification strategies through solar energy and offers a promising solution for solar-driven in-depth water treatment.