Photoreforming Hydrogen From Polystyrene, Low‐Density Polyethylene, and High‐Density Polyethylene Microplastics via UV‐Driven Photolysis and TiO ₂ ‐Based Photocatalysis

This study investigated UV‐induced photolysis and photocatalysis in the presence of TiO 2 (Evonik P25) as methods for producing hydrogen from polystyrene (PS), low‐density polyethylene (LDPE), and high‐density polyethylene (HDPE) microplastics. Photolysis showed a strong dependence of reactivity on polymer structure, especially the one‐type LDPE microplastics, exhibiting the highest hydrogen production, while PS showed the lowest activity due to the stability of its aromatic backbone. Although thermodynamic analysis showed the lower Gibbs energy of decomposition for polyethylenes than for PS, all processes remained nonspontaneous. Photocatalysis selectively increased hydrogen production only in PS, where there was an increase of approximately 44% compared with photolysis, which is attributed to favorable polymer–photocatalyst interactions and more efficient charge transfer at the interface. In contrast for polyethylene microplastics, the presence of TiO 2 led to a decrease in hydrogen yields, likely due to limited contact between the microplastics and the photocatalyst and radiation shielding by floating particles. Mixing proved to be a key operating parameter that significantly increases hydrogen production by improving particle dispersion and light distribution. Overall, the results show that the efficiency of microplastic photoreforming is governed by polymer chemistry, morphology, and system hydrodynamics under UV irradiation.