Synergistic Effect of Boron Doping and Porous Structures on Titanium Dioxide for Efficient Photocatalytic Nitrate Reduction to Nitrogen in Pure Water

Photocatalytic reduction of nitrate to N2 holds great significance for environmental governance. However, the selectivity of nitrate reduction to N2 is influenced by sacrificial agents and the kinds of cocatalysts (such as Pt and Ag). The presence of unconsumed sacrificial agents can aggravate environmental pollution, while noble metal-based cocatalysts increase application costs. Herein, the porous boron-doped TiO2 (B-TiO2) was successfully synthesized by using the sol–gel method with Amberlite IRA-900 as a template. The incorporation of 33% boron into TiO2 (33% B-TiO2) achieved a 100% nitrate (20 ppm) conversion rate and 94.5% N2 selectivity without the need for sacrificial agents and cocatalysts during the nitrate reduction process. The catalyst’s unique multistage porous structure not only enhances the light absorption ability but also significantly provides abundant surface adsorption sites. Additionally, theoretical studies show that boron doping effectively modulates the band structure of TiO2 and increases the electron density at the Ti surface active sites, both of which are essential for achieving a high nitrate reduction efficiency. This work emphasizes the synergistic effect between morphology control and electronic structure regulation in promoting the photocatalytic reduction of nitrate to nitrogen, providing valuable insights for the photocatalytic treatment of nitrate wastewater.