Rb 2 Ti 1.95 Yb 0.05 (PO 4 ) 3 crystals with langbeinite-type structure were grown by high-temperature solution method. The chemical composition and electronic structure were analyzed using inductive coupled plasma atomic emission spectroscopy (ICP-AES) and X-ray photoelectron spectroscopy (XPS). The deconvolution of Ti 2p 3/2 photoemission line reveals two peaks at 459.3 eV and 458.1 eV, indicating titanium existence in two valence states: Ti 4+ (459.3 eV) and Ti 3+ (458.1 eV). The reduced BE difference ΔBE (O 1s-Ti 2p 3/2 ) shows stronger ionicity of Ti–O bonds in Rb 2 Ti 1.95 Yb 0.05 (PO 4 ) 3 compared with RbTiOPO 4 . Additionally, UV absorption, specific heat, and second harmonic generation (SHG) efficiency were studied. The UV absorption edge of the Rb 2 Ti 1.95 Yb 0.05 (PO 4 ) 3 crystal was observed at 368 nm. The SHG intensity of Rb 2 Ti 1.95 Yb 0.05 (PO 4 ) 3 is 5–6 times greater than that of KDP crystal when the particle size is between 38 and 74 μm.
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.
The band gap width has always been the main reason for the low photocatalytic performance of TiO 2 semiconductors. “Band gap engineering” is often used to change the band gap width of TiO 2 . On this basis, the impurity band gap was induced below the TiO 2 conduction band by regulating N element. What's interesting was that N element adjusted the valence state of adjacent Ti element and caused the generation of oxygen vacancy . This is due to the extraction of neutral oxygen atoms, resulting in electron transfer to the Ti cation band structure . The 300-N-T catalyst exhibited the best photocatalytic hydrogen production performance under visible light, which was 307.65 μmol/(g·h) and was 61.53 times higher than that of anatase. And the concentration of Ti 3+ defects and oxygen vacancy reduced with decreasing of N content in TiO 2 . According to Kubelke Munk formula, the band gap of 300-N-T photocatalyst was narrowed to 2.73 eV, which indicated that there are impurity energy levels near the CB and VB of TiO 2 material. The Ti 3+ ions as the active site of the photocatalytic reaction was confirmed by instantaneous photocurrent response and EIS characteristic. This study revealed the structure-activity relationship between the content of N element, Ti 3+ ions and oxygen vacancy in TiO 2 materials, as well as the decisive process of defect induced visible light catalysis.
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