Humidity capture and solar-driven water collection behaviors of alginate-g-PNIPAm-based hydrogel

Atmospheric water vapor, a ubiquitous and accessible clean water resource, is considered a promising freshwater alternative to alleviate water-deficient circumstances caused by nonnegligible pollution, climate change, and growing population. Sorption-based atmospheric water harvesting, which uses sorbents to capture vapor from the air and thermal energy to release absorbed water, has demonstrated great feasibility for moisture collection. In this work, a flexible hybrid photothermal vapor sorbent composed of hydrogel matrix of sodium alginate grafted-poly(N-isopropyl acrylamide) (Alg-g-PNIPAm), deliquescent salt calcium chloride (CaCl2), and photo-thermal detonation nanodiamond (DND) was rationally synthesized. The composite sorbent showed water sorption of 1.85 g/g in 30 h at 80 % relative humidity and 25 degrees C. The absorbed water could be released under simulated sunlight by the photothermal conversion of DND and structural transformation of graft copolymer Alg-g-PNIPAm. Moreover, the hydrogel sorbent showed excellent reusability without apparent capacity fading. The polysaccharide-based hydrogel sorbent with super-elasticity and low cost has broad application prospects in effectively collecting moisture in the atmosphere.