Recent advances in photocatalytic plastic waste conversion: a review on renewable energy pathways

Abstract The escalating global crisis of plastic waste and the urgent demand for clean energy alternatives necessitate innovative, integrative solutions. Among emerging approaches, solar photoreforming stands out as a transformative dual-function technology that simultaneously degrades polymeric waste and produces hydrogen fuel. This review explores a cutting-edge strategy that synergistically integrates high-pressure torsion (HPT) a severe plastic deformation technique with defect-engineered brookite-phase titanium dioxide (TiO 2 ) nanoparticles to significantly elevate the solar-driven photoreforming performance of polypropylene (PP) waste. HPT introduces intense shear forces under compressive pressures (∼6 GPa), inducing substantial microstructural transformations in PP. These include the formation of high-density dislocations, amorphous domains, and interfacial defects, all of which enhance the polymer’s surface reactivity and its interaction with photocatalysts. Concurrently, brookite-phase TiO 2 , prized for its narrow band gap (∼3.1 eV), enhanced charge carrier separation, and high photoactivity, serves as an efficient photocatalyst. The strong interfacial coupling between the defect-rich PP surface and brookite TiO 2 nanoparticles facilitates rapid charge transfer, suppresses electron–hole recombination, and enhances radical generation. As a result, the integrated system exhibits a 2.4-fold improvement in hydrogen evolution, achieving production rates up to 580 μmol h −1 g −1 under solar irradiation. Moreover, the process enables selective oxidation of polymer fragments, yielding value-added chemicals such as formic acid and acetic acid with faradaic efficiencies exceeding 45 %. This review further elucidates the underlying mechanisms of defect-mediated catalysis, emphasizing the roles of nanoparticle phase composition, surface chemistry, and morphology. Collectively, this work establishes a promising and scalable pathway for circular plastic-to-fuel conversion, providing both environmental remediation and clean energy generation. The integration of mechanical defect engineering and nanostructured photocatalysis represents a pivotal advancement toward sustainable, high-efficiency solar photoreforming technologies.