State-of-the-Art Achievements and Challenges in Photochemical Conversion of Plastics to Chemicals and Composites

Plastics are low-cost materials characterized by their lightweight nature, ease of handling, and high mechanical strength, rendering them highly useful in daily life. Despite the advantages, the detrimental effects of plastics on the environment are rapidly increasing, which results in environmental damage and widespread pollution around the world. In this regard, incineration and disposal of waste plastics in landfills would generate tremendous amounts of microplastics that damage biodiversity. In contrast to thermocatalytic methods, photochemical conversion of plastics is considered promising and has garnered quite a bit of attention. This Review highlights the difficulties and current developments in the pretreatment methods and photocatalytic upcycling of different plastic polymers. To effectively interact with catalysts, pretreatment techniques are necessary to overcome the inherent chemical inertness and insolubility of plastics. The light-driven upcycling mechanisms of polyethylene (PE), polyethylene terephthalate (PET), polyurethane (PU), and polyamide (PA) are examined, and their interactions with various photocatalysts (organic, inorganic, hybrid, 2D materials, metal single atoms) are reviewed. Furthermore, we highlight the economic and environmental sustainability of photocatalytic plastic conversion. To achieve selective plastic conversion, heterogeneous photocatalysts are clarified with an emphasis on the mechanism of photoexcitation and redox reactions. Importantly, this Review presents a range of photocatalysts, and their design principles which could effectively convert different plastic wastes into hydrogen and other value-added chemicals without complete mineralization to CO₂. Hence, this photochemical approach is promising for mitigating greenhouse gas emissions. Such circumstances contribute to the reduction of pollution and are crucial for advancing a more circular economy. The main ideas and developments in the field of photocatalyst-based plastic upcycling showcase the importance of this technology for resource recovery and sustainable waste management policies. At the end, the limitations and the scope of future research directions are summarized.