Turning waste into treasure: Carbonized walnut shell for solar-driven water evaporation

Waste walnut shell was selected and carbonized in different atmospheres to prepare excellent light-to-heat conversion materials for efficient solar-driven water evaporation. Carbonized walnut shell has a unique concave structure and rough surface, and its light absorption rate is higher than 88% in the full-spectrum range of 200–2500 nm. Moreover, under one-sun irradiation, carbonized walnut shell in a hydrogen/argon atmosphere mixture has better water evaporation performance (1.22 kg m-1h−1) and a higher η value (81.4%) than the carbonized walnut shell in an argon atmosphere. The main reason was due to its higher degree of graphitization and smaller surface pores, which are beneficial to light-to-heat conversion. Our work highlights the great potential of the waste biomass material (walnut shell) for realizing a highly effective solar energy-driven water evaporation.