A CuO/ZnO Heterostructure Interpenetrated with Hydrogel Network for Efficient Solar Water Evaporation

Solar-powered interfacial steam generation (ISSG) has been extensively researched and implemented due to its considerable potential for the cost-effective and environmentally sustainable production of purified water. However, the substantial energy requirements for phase change processes in water evaporation, along with the limited light absorption spectrum of photothermal materials seriously impede the further effective deployment of ISSG. Here, a sponge-like CuO/ZnO-PVA/PSS hydrogel (CZO-HH) was prepared by incorporating CuO/ZnO (CZO) heterojunction nanoparticles, known for their excellent photothermal properties, into poly(vinyl alcohol) (PVA) and polystyrene sulfonic acid (PSS) self-assembled interpenetrating double-network hydrogel. Surprisingly, the CZO-HH has identified a novel integration between the nonradiative relaxation effect in semiconductor photothermal materials and the unique structural properties of hydrogels. This synergistic function leads to a decrease in the enthalpy of evaporation by regulating the hydrogen bonding network of water, thereby achieving an enhanced evaporation rate. Moreover, the existence of the PVA/PSS hydrogel broadens the optical absorption spectrum of CZO heterojunction nanoparticles to encompass the full spectrum, while simultaneously enhancing their thermal management capability and the capabilities of the photothermal conversion. Consequently, the CZO-HH had been observed to achieve a maximum evaporation rate of 2.35 kg·m^-2·h^-1 and an energy efficiency of 95.28% under 1-sun irradiation. Furthermore, the CZO-PVA/PSS demonstrated the capacity for sustainable evaporation in wastewater and seawater desalination, and a significant number of -SO₃H groups within the PSS exhibited excellent self-cleaning performance, highlighting the potential for significant long-term practical applications. Therefore, this work reveals the importance of energy management and energy mass transfer in the process of solar energy utilization to enhance the efficiency of photothermal conversion and provides technical support for the next step of large-scale utilization of solar energy and promotion of seawater desalination.