Photothermal Mineralization of Polyolefin Microplastics via TiO₂ Hierarchical Porous Layer‐Based Semiwetting Air‐Plastic‐Solid Interfaces

Abstract Photo‐mineralization of microplastics under mild conditions has emerged as a promising solution to plastic waste disposal. However, the inadequate contact between oxygen, water‐insoluble polyolefin microplastics, and photocatalysts remains a critical issue. In this study, a TiO₂ hierarchical porous layer (TiO₂‐HPL) photocatalyst is presented to establish air‐plastic‐solid triphase interfaces for the photothermal mineralization of polyolefins. The wettability of the TiO₂‐HPL‐based triphase interface is finely controlled from plastophobic to plastophilic. High‐resolution imaging and finite element simulation demonstrate the significance of a semiwetting state in achieving multidirectional oxygen diffusion through the hierarchical pore structure while maintaining sufficient contact between the plastic phase and photocatalysts. For low‐density polyethylene, the TiO₂‐HPL achieves a photothermal mineralization rate of 5.63 mmol g⁻¹ h⁻¹ and a conversion of 26.3% after 20 h of continuous irradiation. Additionally, the triphase photocatalytic system with semiwetting gas‐plastic‐solid interfaces shows good universality for various polyolefin reagents and products, illustrating its potential in achieving efficient photothermal mineralization of non‐degradable microplastics.