An intelligent water production strategy: Controllable enhancement of evaporation rate through shape memory Janus foam

Abstract

Solar-driven interfacial evaporation is an eco-friendly and promising approach to address freshwater shortage. However, the intricate preparation process and low evaporation rate of evaporators limit its further practical applications. Herein, an ingenious design strategy is proposed for a shape memory Janus (SMJ) foam to controllably increase the evaporation rate. By sequentially adhering trans-1,4-Polyisoprene (TPI) and selectively modifying sodium alginate (SA) / AlCl₃ on PU substrate, a three-dimensional (3D) porous foam structure is conveniently constructed, which features a hydrophobic layer with efficient photothermal conversion and a superhydrophilic layer with sufficient water supply. Under varying light intensities, the evaporation rate of optimized SMJ foam exhibits a linear escalation through shape memory compression, specifically from 1.8 kg m⁻²h⁻¹ to 3.2 kg m⁻²h⁻¹ as the compression ratio increases from 0 to 80 % under one solar irradiation. Due to its large-pore porosity, the photothermal layer increases surface area density and gradually generates analogous vertical channels to enhance absorbance during compression, thereby improving the photothermal conversion effect and optimizing thermal management. Moreover, thanks to the Janus structure, the self-floating and salt-resisting properties of SMJ foam guarantee stable and efficient evaporation in complicated environments. This work introduces a novel strategy for promoting the evaporation rate, intelligence, and industrial application of solar-driven interfacial evaporators.