State of the art in the photochemical degradation of (micro)plastics: from fundamental principles to catalysts and applications

Plastic, due to its low cost, light weight, and tunable mechanical strength, is one of the most commonly used materials in daily life. However, the massive production of plastics in the last century has resulted in an environmental crisis globally, clogging oceans and poisoning communities around the world. Furthermore, the traditional methods for handling plastic waste, such as incineration and landfill disposal, can easily result in the generation of excessive amounts of microplastics (MPs), which lead to severe environmental pollution and pose a great threat to living organisms. Photocatalytic conversion of plastics to light-weight hydrocarbons and recycling are considered to be promising strategies towards the mitigation of MPs and have attracted a great deal of attention in the last few decades. In this review, a few representative and frontier studies on photocatalysis are presented as green promising methods towards the degradation of (micro)plastics. Initially, we introduce the harmful nature of waste (micro)plastics and discuss the background of photocatalysis. Then, the mechanisms for the photocatalytic degradation of (micro)plastics are presented, followed by the classification of photocatalysts. Also, we highlight conventional inorganic semiconductor oxides (TiO2, ZnO, etc.) and organic-inorganic hybrid composites, including doped and surface-modified nanoparticles. To further improve the efficiency of photocatalytic degradation, several approaches related to reactants, photocatalysts, and reaction conditions are proposed. Finally, based on current photocatalyst-mediated (micro)plastic degradation techniques, we provide some existing limitations and a perspective towards future research directions. This review systematically summarizes the efforts devoted to the photocatalysis of plastic and progress made in the degradation rate.