Characterization of TiO 2 and an as-prepared TiO 2 /SiO 2 composite and their photocatalytic performance for the reduction of low-concentration N-NO 3 − in water

Excessive N-NO 3 − water pollution has become a widespread and serious problem that threatens human and ecosystem health. Here, a TiO 2 /SiO 2 composite photocatalyst was prepared via the sol–gel/hydrothermal method. TiO 2 and TiO 2 /SiO 2 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 TiO 2 and TiO 2 /SiO 2 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 CO 2 flow rate of 0.1 m 3 h −1 , and a TiO 2 concentration of 0.9 g L −1 . In contrast, TiO 2 /SiO 2 at a 1.4 g L −1 concentration and a TiO 2 load rate of 40% achieved a removal rate of 83.48%, but with more than 98% of nitrogen generation rate. NO 2 − and NH 4 + were the minor products, whereas N 2 was the main product.