Photothermal-Responsive Sponge with Switchable Wettability for Intelligent and Sustainable Moisture Capture and Release

Intelligent materials with switchable wettability inresponse toexternal stimuli are highly desirable for sustainable water harvestfrom a humid atmosphere. Herein we present the design of a photothermal-responsivematerial for intelligent moisture capture and release based on marryingthermal-responsive poly(N-isopropyl-acrylamide)(PNIPAM) to reduced graphene oxide (RGO) with excellent photothermalproperty. The as-designed RGO/PNIPAM material could make itself asa heat source through efficiently converting sunlight into heat, drivingthe wettability change of thermal-responsive PNIPAM from hydrophilicto hydrophobic. Consequently, the RGO/PNIPAM achieves moisture capturewith its hydrophilic PNIPAM chains below the low critical solutiontemperature (LCST) (<32 & DEG;C) and complete water release undersunlight illumination through switching the hydrophilicity into hydrophobicityof the PNIPAM. This intelligent photothermal-responsive behavior ofRGO/PNIPAM matches nicely with the nature of typical day-and-nightchange of dry coastal areas, lighting up the practical prospect ofRGO/PNIPAM for water harvest from a humid atmosphere. Moreover, theswitchable wettability of RGO/PNIPAM is reversible, which endows itwith good recyclability in moisture capture and release (e.g., >10cycles). This study is interesting because it provides a paradigmin the design of intelligent materials for moisture harvest, whichmay shed light on the design and application of other high-performancestimuli-responsive materials.