Robust and Temperature‐Sensitive Hydrogels for High‐Efficiency Water Harvesting Under Low Solar Energy Radiation

Solar‐driven evaporation using hydrogels and photothermal materials is a promising freshwater harvesting technology. Clean water is generally collected through evaporation and subsequent condensation, which requires high energy input due to the inherent high vaporization enthalpy of water. Therefore, it is a great challenge to harvest fresh water efficiently under natural irradiation. Herein, a temperature‐sensitive polyacrylamide‐poly(N‐isopropylacrylamide) (A‐PNIPAm) gel is designed to pursue a high water collection rate under low energy input conditions, where the facile and reversible hydrophilic/hydrophobic transition in gels enables the quick acquisition of liquid water. A multifunctional hydrogel (ADS‐PNIPAm) is prepared using polydopamine and sodium alginate with excellent adsorption/filtration properties, which can remove pollutants and generate fresh water rapidly. Consequently, the water collection rate of the ADS‐PNIPAm hydrogel reaches up to 5.89 and 9.8 kg m−2 h−1 under 0.6 and 1 sun irradiation, respectively, which are superior to the previously reported values. Furthermore, ADS‐PNIPAm displays an excellent effect on purifying sewage, such as oils, algae, and dyes pollutants. ADS‐PNIPAm is a promising material for a rapid freshwater generation with solar irradiation only, which provides a new avenue to alleviate water source scarcity.