Moisture-indicating cellulose aerogels for multiple atmospheric water harvesting cycles driven by solar energy

Abstract

Despite the boom in atmospheric water harvesting (AWH) techniques used to deal with the challenge of clean water shortage, few studies focus on hygroscopic materials that can indicate a moisture change in real time. Here, a moisture-indicating hygroscopic aerogel working in a broad range of relative humidities (RHs) and with fast sorption kinetics is designed for solar driven sorption-based AWH by integrating ethanolamine-decorated CoCl₂ (E-CoCl₂), microfibrillated cellulose (MFC) and LiCl-decorated polypyrrole (Cl-ppy). The specimen can visually indicate the sorption process in real time while harvesting moisture, achieving a flexible response to changes in environmental humidity and solar radiation. Fabricating an open, unordered, interconnected skeleton in E-CoCl₂ using MFC can effectively enhance its sorption kinetics and also prevent the leakage of liquefied salt solution. The specimen has water sorption capacities of 0.39–2.05 kg kg⁻¹ under RH 25–85% within 3.5 h and can quickly desorb within 1.5 h under 1 sun. An AWH device can conduct 3 sorption/desorption cycles within 9 h during one day outdoors and produces 2.81 kg_water kg_sorbent⁻¹. This strategy is a promising approach to enable sustainable water delivery without geographical and hydrological limitations, especially for the landlocked communities and arid areas.