Hydroxyl-functionalized TiO2@SiO2@Ni/nZVI nanocomposites fabrication, characterization and enhanced simultaneous visible light photocatalytic oxidation and adsorption of arsenite

In this study, salicylic acid-TiO 2 @SiO 2 @Ni/nZVI (SA-NFST) nanocomposites with rich hydroxyl groups were synthesized using in situ surface modified, co-precipitation, and sol-gel methods. A variety of techniques, including scanning electron microscopy (SEM), X-ray powder diffraction (XRD), vibrating sample magnetometer (VSM), transmission electron microscopy (TEM), the point of zero charge (PZC), UV–vis diffuse reflectance spectra (UV–vis), infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS), were used to characterize the properties of the nanoparticles. The results showed that the SA-NFST exhibited high visible light-harvesting efficiency, easily magnetic separation, rich hydroxyl groups and hydroxyl radicals, and larger surface area. The adsorption and photo-oxidation of arsenite by the new materials were explored in different experimental conditions, including pH, initial arsenite concentration, catalyst dosage, contact time, and coexisting anions (PO 4 3− , SiO 3 2− , CO 3 2− , and SO 4 2− ). The maximum adsorption capacities ( q m ) of As(III) onto SA-NFST calculated from Langmuir adsorption isotherm were 73.9 and 83.6 mg/g without and with visible light irradiation, respectively. >99.8% of As(III) (5.0 mg/L) was removed in the presence of 0.25 g/L SA-NFST nanoparticles (NPs) under 1.5 h visible light illumination. The residual concentration of As(III) (9.0 µg/L) was less than 10 µg/L, which is below the maximum allowable values in drinking water. As(III) removal may be due to the synergic combined effects of surface adsorption, photocatalytic oxidation under visible light illumination.