Balancing Photocatalytic and Photothermal Elements for Enhanced Solar Evaporation—A Review

Water is a critical resource underpinning natural, societal and economic development, and its importance will grow bigger in the next decades. Interfacial solar evaporators are a promising and cost-effective technology for the generation of freshwater from saline and polluted waters. Yet, although these devices effectively reject salts and non-volatile pollutants, the presence of volatile organic compounds in the water source may lead to low water quality of the distillate. This review addresses the introduction of photocatalytic materials in solar evaporator devices to improve water quality, highlighting in particular possible synergies and incompatibilities between the materials promoting these functionalities. The interactions of the photocatalyst with photothermal materials are described, along with an overview of the materials most commonly selected for both functionalities. A positive interaction clearly emerges, with the photothermal materials not only accelerating evaporation but also generally stimulating the photocatalytic degradation of VOCs. Limits to the implementation of such a combination are described, including those due to electrolyte content and salt accumulation, reaction rate and mass transfer. Finally, recommendations regarding testing conditions and future studies are presented.