Photo-enzyme synergistic catalysis by nitrogen-doped titanate nanotubes for efficient microplastic degradation: Acceleration of Ti valence cycle under visible light irradiation

Microplastics, as pervasive pollutants, pose severe threats to ecosystems and human health, necessitating efficient and sustainable degradation strategies. Nanozymes, mimicking natural enzymes, provide an innovative strategy for eliminating water contaminants, with light activation significantly boosting their catalytic efficiency through a simple, remotely adjustable process. However, the cooperative mechanism of the nanozyme-photocatalytic system is still poorly elucidated, highlighting the need for comprehensive investigations into its microplastic degradation efficacy and underlying mechanisms. Herein, we developed nitrogen-doped titanate nanotubes (NTNTs) with Ti-N coordination, achieving exceptional photo-enzyme synergistic catalysis for highly efficient microplastic decomposition. Nitrogen doping into TNTs broadens their light absorption spectrum, improves charge separation efficiency, and enhances photocatalytic activity. The Ti-N interaction induces electronic structure modifications that impart peroxidase-like (POD-like) property to NTNTs. First-principles calculations reveal that NTNTs exhibit enhanced POD-like activity by enabling exothermic adsorption of -O/-OH intermediates (up to −6.6 eV for −2OH) and reducing the energy barrier for hydroxyl (•OH) radical generation compared to endothermic TNTs, thereby accelerating H 2 O 2 activation kinetics. Furthermore, H 2 O 2 activation promotes Ti(III)/Ti(IV) cycling, significantly boosting •OH generation while creating an autocatalytic system that sustains reactive oxygen species production, thereby reinforcing the photo-enzyme synergistic mechanism. NTNTs-2 demonstrates superior photo-enzyme synergistic degradation of PE (15.19 % mass loss in 8 h), outperforming individual photocatalytic (2.49 %) and enzymatic (0.04 %) processes, with broader pH adaptability (4.7–12.3) and universal effectiveness across PP/PS/PVC microplastics, while SEM confirms progressive surface fragmentation enhancing catalytic accessibility. This study achieves a breakthrough in multifunctional catalyst design by synergizing photocatalytic and nanozyme mechanisms for environmental remediation.