CuS Nanosheet-Coated PVA Sponge for Desalination and Wastewater Purification

Interfacial solar steam generation (ISSG) utilizing polymeric hybrid evaporators has emerged as a promising strategy for sustainable freshwater production from seawater and wastewater, addressing one of the most pressing global challenges: the freshwater crisis. Despite significant progress, practical deployment is hindered by the lack of compact, low-cost, and portable ISSG systems that combine high evaporation efficiency with salt-resistance and antimicrobial performance. In this study, a straightforward solar light-induced deposition technique was employed to uniformly coat CuS nanosheets onto a commercial poly(vinyl alcohol) (PVA) sponge, creating a three-dimensional (3D) CuS nanosheet-coated PVA sponge (CuS@PVA) solar evaporator. By optimizing the viscosity of the coating suspension, a homogeneous distribution of the photoactive layer was achieved throughout the sponge architecture without clogging its microporous structure. The resulting 3D CuS@PVA solar evaporator exhibited a significantly reduced water evaporation enthalpy (1833.07 kJ kg–1) compared to pure water (2422.16 kJ kg–1 at 33.5 °C), attributed to synergistic hydrogen bonding interactions among water molecules, PVA hydroxyl groups, and the CuS nanosheet interfaces. This structural design led to an impressive evaporation rate of 3.18 kg m–2 h–1 and a solar-to-vapor conversion efficiency of 162% under 1 sun irradiation. Long-term outdoor testing confirmed robust antisalt fouling behavior, with no visible salt accumulation after sustained exposure to seawater (2.34 kg m–2 evaporated in 1 h). A spontaneous ion-gradient-driven exchange mechanism within the porous matrix supports continuous desalination without clogging. Furthermore, the system demonstrated superior sewage purification capabilities alongside antibacterial properties, paving the way for practical real-world implementation. Altogether, the low-cost, recyclable, and multifunctional CuS@PVA evaporator presents a highly scalable pathway toward decentralized, sustainable freshwater production in remote or resource-limited settings.