A contactless 3D Janus evaporator with superhydrophobic core and superhydrophilic shell for efficient desalination and water purification

Solar interfacial evaporation is a low-cost strategy for desalination and water purification. However, for most evaporators, the coplanar configuration of light absorption and water evaporation results in a confined evaporation surface and salt deposition problems. Here, a contactless 3D Janus evaporator (Ag-NSP@BFP) with a core/shell structure is designed by wrapping Ag nanoparticles (Ag-NPs) decorated nickel sponge (Ag-NSP) using bamboo fiber paper (BFP). The superhydrophobic Ag-NSP core (absorber) achieves highly efficient light absorption and photothermal conversion. Meanwhile, the superhydrophilic BFP shell not only provides a larger evaporation area (side surfaces as evaporation surfaces) but also forms a 2D water channel to ensure sufficient water supply. Furthermore, polystyrene foam (EPS) isolates photothermal material from bulk water, minimizing heat transmission losses dramatically. The 3D Janus evaporator increases the evaporation area and harvests energy from the ambient environment, achieving an evaporation rate of up to 2.77 kg m−2h−1 and an energy conversion efficiency of 105.2 %. Moreover, the Janus structure effectively inhibits salt accumulation on the photothermal surface and exhibits a good purification effect on wastewater containing dyes and heavy metal ions. Thus, combining a 3D evaporator with Janus structure to achieve efficient salt-resistant evaporation provides a new design idea for stable seawater desalination and wastewater purification.