Photocatalytic degradation of polycyclic aromatic hydrocarbons under visible light irradiation in water using TiO2/MgO nanocomposites

Abstract

An extensive class of pollutants found in soil, water, and bottom sediments are categorized as polycyclic aromatic hydrocarbons. A possible method of breaking down polycyclic aromatic hydrocarbons is thought to be the photochemical approach. The potential application of mesoporous nanocomposites on TiO₂/MgO as catalysts for the photooxidation of polycyclic aromatic hydrocarbons under the influence of visible light was assessed in this work. TiO₂/MgO nanocomposites were successfully obtained by the self-propagating high-temperature synthesis using methotitanic acid and magnesium nitrate as metal precursors. An important step in the synthesis was the conversion of the titanium precursor into a water-soluble form with the subsequent addition of glycine and citric acid at a carbon/nitrogen (C/N) molar ratio of 0.25. This synthesis via solutions allowed the target materials with major phases of magnesium metatitanate MgTiO₃, magnesium dititanate MgTi₂O₅, and magnesium titanate Mg₂TiO₄ to be obtained after heat treatment at 750 °C. Heterostructured mesoporous TiO₂/MgO powders with a specific surface area of 22.0–28.4 m²/g had an average diameter of the predominant pores of 10–30 nm. The greatest degree of photocatalytic oxidation of fluorene, pyrene, and benzpyrene (80, 68, and 53%, respectively) was obtained when it was combined with the TiO₂/MgTi₂O₅/MgTiO₃ nanocomposite under visible light irradiation. This study showed that mesoporous TiO₂/MgO nanocomposites could be used as photooxidation catalysts for polycyclic aromatic hydrocarbons. The maximum level of photocatalytic oxidation of polycyclic aromatic hydrocarbons in TiO₂/MgO nanocomposites occurred at pH 7 and a photocatalyst dose of 1 mg/L under the influence of normal solar radiation.