Characterization of TiO2 and an as-prepared TiO2/SiO2 composite and their photocatalytic performance for the reduction of low-concentration N-NO3- in water

Abstract

Excessive N-NO₃^- water pollution has become a widespread and serious problem that threatens human and ecosystem health. Here, a TiO₂/SiO₂ composite photocatalyst was prepared via the sol-gel/hydrothermal method. TiO₂ and TiO₂/SiO₂ were characterized by X-ray diffraction (XRD), UV-Vis differential reflectance spectroscopy (DRS), Fourier infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS). Afterward, the photocatalytic performance of TiO₂ and TiO₂/SiO₂ to reduce low nitrate concentrations (30 mgN L^-1) under UV light was evaluated and the effects of different factors on this process were investigated, after which the reaction conditions were optimized. Removal rates of up to 99.93% were achieved at a hole scavenger (formic acid) concentration of 0.6 mL L^-1, a CO₂ flow rate of 0.1 m³ h^-1, and a TiO₂ concentration of 0.9 g L^-1. In contrast, TiO₂/SiO₂ at a 1.4 g L^-1 concentration and a TiO₂ load rate of 40% achieved a removal rate of 83.48%, but with more than 98% of nitrogen generation rate. NO₂^- and NH₄⁺ were the minor products, whereas N₂ was the main product.

Keywords: Low-concentration N-NO3 −; Nitrogen conversion rate; Photocatalysis; Reduction reaction; TiO2; TiO2/SiO2.