Enhancing solar-driven atmospheric water harvesting by a bilayer macroporous hydrogel

The adsorption-based atmospheric water harvesting technique has shown great potential in providing clean water. An ideal device for atmospheric water harvesting should enable the massive and quick release of water after it is rapidly absorbed by the moisture adsorbent. At present, however, the moisture adsorbent still experiences issues such as a slow water absorption rate, hampered adsorption–desorption kinetics, and a low total water yield. In this paper, a bilayer moisture adsorbent (BMA), which glues a hydrophilic macroporous layer for rapid water adsorption and a carbonized sunlight-absorbing layer for both water harvesting and desorption acceleration, is introduced. Further evidence suggests that it is the stable, fluffy, and rough porous structure of the BMA that helps to harvest atmospheric water efficiently. The fully carbonized BMA exhibits a water absorption capacity of up to 396% at a relative humidity of 90%, which is 20% higher than a monolayer sample. More importantly, the desorption efficiency of the half-carbonized BMA reaches 98% under 1 sun illumination. These results jointly demonstrate that the BMA can play the dual role of absorbing moisture and light, allowing for rapid atmospheric water harvesting, massive water storage, and efficient desorption under the light.