Efficient photocatalytic degradation of organic pollutants by magnetically recoverable nitrogen-doped TiO2 nanocomposite photocatalysts under visible light irradiation

Preparation of novel nanocomposite particles (NCPs) with high visible-light-driven photocatalytic activity and possessing recovery potential after advanced oxidation process (AOP) is much desired. In this study, pure anatase phase titania (TiO₂) nanoparticles (NPs) as well as three types of NCPs including nitrogen-doped titania (TiO₂-N), titania-coated magnetic silica (Fe₃O₄ cluster@SiO₂@TiO₂ (FST)), and a novel magnetically recoverable TiO₂ nanocomposite photocatalyst containing nitrogen element (Fe₃O₄ cluster@SiO₂@TiO₂-N (FST-N)) were successfully synthesized via a sol–gel process. The photocatalysts were characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, field emission scanning electron microscopy (FE-SEM) with an energy-dispersive X-ray (EDX) spectroscopy analysis, X-ray photoelectron spectroscopy (XPS), UV–vis diffuse reflectance spectroscopy (DRS), and vibrating sample magnetometer (VSM). The photocatalytic activity of as-prepared samples was further investigated and compared with each other by degradation of phenol, as a model for the organic pollutants, in deionized (DI) water under visible light irradiation. The TiO₂-N (55 ± 1.5 %) and FST-N (46 ± 1.5 %) samples exhibited efficient photocatalytic activity in terms of phenol degradation under visible light irradiation, while undoped samples were almost inactive under same operating conditions. Moreover, the effects of key operational parameters, the optimum sample calcination temperature, and reusability of FST-N NCPs were evaluated. Under optimum conditions (calcination temperature of 400 °C and near-neutral reaction medium), the obtained results revealed efficient degradation of phenol for FST-N NCPs under visible light irradiation (46 ± 1.5 %), high yield magnetic separation and efficient reusability of FST-N NCPs (88.88 % of its initial value) over 10 times reuse.