Photothermal conversion and utilization in solar-driven interfacial water evaporation

Global water scarcity and increasing energy demand have created an urgent need for sustainable and energy-efficient freshwater-production technologies. Solar-driven interfacial evaporation (SIE) localizes solar absorption, heat generation, and vaporization near the water–air interface, thereby reducing ineffective bulk-water heating. However, SIE performance is determined not only by the amount of solar radiation absorbed but also by how the absorbed photon energy is converted into heat, transported to interfacial water, and ultimately translated into vapor and collected freshwater. This review therefore establishes a mechanism-to-device-to-water framework linking microscopic photothermal conversion with system-level energy utilization. The heat-generation mechanisms of major photothermal material classes are discussed, including localized surface plasmon resonance in metallic nanomaterials, carrier thermalization and nonradiative recombination in semiconductors, electronic excitation and phonon-mediated dissipation in carbon materials, excited-state nonradiative relaxation in organic molecules and conductive polymers, and free-carrier absorption and electronic–phononic dissipation in MXenes. Developments in COFs, MOFs, and hybrid photothermal systems are also examined. Beyond material-level conversion, the review analyzes how solar absorptance, mid-infrared thermal emittance, heat localization, water supply, vapor diffusion, salt management, and multiscale architecture collectively govern evaporation. An energy-flow framework is introduced to distinguish solar absorptance, intrinsic light-to-heat conversion efficiency, solar-to-vapor efficiency, and water-collection efficiency, while addressing environmental heat uptake, dark-evaporation correction, and evaporation-enthalpy interpretation. The integration of evaporation, condensation, freshwater collection, and all-day operation through radiative cooling or auxiliary Joule heating is further considered. Finally, standardized testing, cost, long-term stability, scalability, and system-level water productivity are identified as key requirements for translating advances in photothermal conversion into reliable freshwater-production technologies.