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

Intelligent materials with switchable wettability in response to external stimuli are highly desirable for sustainable water harvest from a humid atmosphere. Herein we present the design of a photothermal-responsive material for intelligent moisture capture and release based on marrying thermal-responsive poly(N-isopropylacrylamide) (PNIPAM) to reduced graphene oxide (RGO) with excellent photothermal property. The as-designed RGO/PNIPAM material could make itself as a heat source through efficiently converting sunlight into heat, driving the wettability change of thermal-responsive PNIPAM from hydrophilic to hydrophobic. Consequently, the RGO/PNIPAM achieves moisture capture with its hydrophilic PNIPAM chains below the low critical solution temperature (LCST) (<32 °C) and complete water release under sunlight illumination through switching the hydrophilicity into hydrophobicity of the PNIPAM. This intelligent photothermal-responsive behavior of RGO/PNIPAM matches nicely with the nature of typical day-and-night change of dry coastal areas, lighting up the practical prospect of RGO/PNIPAM for water harvest from a humid atmosphere. Moreover, the switchable wettability of RGO/PNIPAM is reversible, which endows it with good recyclability in moisture capture and release (e.g., >10 cycles). This study is interesting because it provides a paradigm in the design of intelligent materials for moisture harvest, which may shed light on the design and application of other high-performance stimuli-responsive materials.