Heterogeneous photocatalytic materials for sustainable formation of high-value chemicals in green solvents

The most investigated materials used as heterogeneous photocatalysts for the formation of high-value chemicals under mild experimental conditions are presented in this survey. Only papers reporting reactions carried out in harmless solvents such as water, the green solvent par excellence, are reported. Metal oxides have been used often, but carbon-based materials such as carbon nitride and graphene, metal nanoparticles, sulphides and selenides also have received a great attention mainly due to their good performances both in partial oxidations and reductions. The results presented indicate that an appropriate choice of the photocatalytic material is the main problem to be faced to efficiently perform the desired photocatalytic synthesis. Moreover, the highly specific nature of the interaction between the surface of the photocatalyst and the molecules involved in the process must be carefully considered in order to maximize conversion and selectivity and to make these processes green and sustainable competitive alternatives to traditional synthetic methods. Many structural and physicochemical parameters can be tailored such as the initial pH in the case of liquid-solid systems, concentration of reagent(s), induction of defects in the photocatalyst, crystallinity, addition of loading or dopant species to tune the opto-electronic features of semiconductors, and specific surface area.