Triphase Photocatalysis: Beyond Conventional Diphase Photocatalytic Reactions

Poor light absorption, recombination of photogenerated charges, low surface area, and insufficient catalytically active sites are the most studied conventional bottlenecks of photocatalysis processes, which hinder the efficiency of photocatalytic materials. However, there are other less studied factors such as solubility and diffusion of reactants in the reaction system, which are also responsible for sluggish kinetics and can alter the reaction selectivity. The conventional diphase photocatalytic reactions at the liquid-solid interface suffer from poor solubility and slow transport of the reactants in a reaction medium. The emerging triphase photocatalysis, which occurs at the gas-liquid-solid interface and liquid-liquid-solid interface has shown the potential of addressing these less-studied issues and achieved better performance than the diphase photocatalytic reactions. This review article mainly focuses on the understanding of the mechanism and basic difference between diphase and triphase photocatalysis along with the requirements for triphase photocatalysis. Several examples of triphase photocatalytic reactions including CO₂ reduction, N₂ fixation, H₂O₂ production, and organic pollutant degradation are discussed in detail in this review. Finally, a summary and future directions in this field are provided to guide the researchers to design remarkable triphase photocatalytic systems with excellent efficiencies.