Towards Cleaner, Greener Future: Energy Efficient Sustainable Hydrogel Composites for Solar Driven Photothermal Water Evaporation and Purification

This comprehensive review presents hydrogel-based water evaporators for solar desalination and purification, focusing on ecological sustainability and mechanism-driven design. Unlike conventional Interfacial Solar-Driven Evaporation (ISDE) systems that prioritize photothermal conversion efficiency, this work emphasizes fundamental thermodynamic and lifecycle considerations for long-term sustainability. We propose a mechanism-driven framework using ecological hydrogel composites derived from renewable, biodegradable, and non-toxic precursors like cellulose, alginate, and starch. A key aspect is regulating water states within hydrogel matrices, particularly forming "intermediate water" that reduces vaporization enthalpy and enhances evaporation rates beyond bulk water limits. We correlate material properties like porosity, thermal conductivity, and optical absorption with thermodynamic parameters including latent heat, temperature gradient, and mass flux. The review also covers molecular hydration engineering, dynamic interfacial effects, and multifunctional systems using waste-derived photothermal materials like biochar. Challenges like fouling, salt accumulation, and scalability are evaluated. By bridging molecular insights with system-scale performance, this work shifts from material-centric to mechanism-oriented design, providing a sustainable roadmap for next-generation desalination technologies that minimize environmental risks.