Agricultural straw waste-derived composite sorbents with photothermal properties for solar-powered atmospheric water harvesting

Solar-powered atmospheric water harvesting (AWH) technology shows great promise for solving water shortage problems for inland and arid regions. The development of low-cost and low-environmental impact sorbent materials with high water absorption and photothermal properties is critical for their large-scale application. Here, this work develops a high-performance hygroscopic salt-based composite sorbent for solar-powered AWH by taking agricultural waste straw as an example. The straw-based sorbent is facile to prepare, low-cost, environmentally friendly, and offers favorable adsorption and desorption properties. Specifically, high porosity, excellent hydrophilicity, and photothermal conversion properties can be integrally achieved by phytic acid-assisted one-step hydrothermal pretreatment of waste straw, thereby yielding a highly efficient straw/salt-based composite sorbent that can absorb water from the atmosphere over a broad humidity range and rapidly release it when exposed to sunlight. The prepared composite sorbent displays water adsorption from ~0.50 g g −1 to 1.29 g g −1 in the range of 30 % and 90 % relative humidity, exhibiting good capacity to obtain water from the atmosphere. Moreover, solar-driven evaporation desorption can be successfully achieved with an ~0.82 kg m −2  h −1 evaporation rate, double that of the original straw material, showing excellent solar-driven desorption efficiency. Furthermore, the composite sorbent demonstrates promising practical utilization by achieving ~0.81 g g −1 water adsorption and succeeding in condensing and harvesting 69 % of it in the outdoor test under natural conditions. This study provides an affordable solar-powered solution for atmospheric water harvesting together with promoting high-value utilization of agricultural waste.