Cellulose-Based Photothermal Microspheres: A Sustainable Solution to Harvesting Freshwater Outdoor

Drinking water shortage is a global issue concerning fundamental human rights and well-being, and it drives people to seek freshwater from the ocean and industrial and municipal wastewater. Herein, we propose a sustainable solution based on the photothermal cellulose hydrogel microspheres and solar interfacial evaporation to harvest freshwater. The evaporation efficiency (1 sun, 2.70 kg m–2 h–1) is substantially improved because the intermediate water in the disposable cellulose hydrogel microspheres can reduce the vaporization enthalpy. The abundance of cellulose on earth also makes it possible for the large-scale production and application of cellulose-based microspheres. Furthermore, a simplified water-harvesting device that can generate 4.6 kg/m2 of water daily is easily assembled with the common materials in daily life and the photothermal cellulose hydrogel microspheres. Such a low-cost device could provide a practical solution to alleviate the scarcity of drinking water in impoverished territories worldwide, which fully conforms with the sustainable development goals.