Adsorptive-photocatalytic removal of oxytetracycline by mesoporous silicates immobilized N-doped TiO2 nanoparticles: A comparative study on effect of support

Abstract

Two typical mesoporous silicates HMS and KIL-2 modified by N element doped TiO2 (N–TiO2) nanoparticles were successfully synthesized via a two-step method containing neutralization and immobilization. The materials were used in the adsorptive-photocatalytic removal of oxytetracycline contaminant in model wastewater, during which the effect of the support for N–TiO2 was comparatively studied. Neutralization of the N–TiO2 sol was crucial to obtain highly dispersed N–TiO2 nanoparticles and maintain the original porous structure of the supports. HMS support showed a confinement effect on the small sized N–TiO2 nanoparticles by its channels, while KIL-2 support obtained more dispersive and smaller N–TiO2 particles almost in a quantum dots scale. Specially, the N–TiO2 content showed a remarkable regulation effect on the pore size of KIL-2, easily matching with the OTC adsorption. The optimal materials also obtained the improvement in the electrons transport ability and the separation of e−-h+ pairs. In comparison, HMS loading N–TiO2 exhibited larger adsorption capacity for OTC removal, while KIL-2 loading N–TiO2 exhibited higher photocatalytic efficiency for OTC removal, and they both achieved significant final removal of OTC. They also showed good recyclability after regeneration treatment. A mechanism study revealed that the HMS and KIL-2 supports respectively achieved surface adsorption and intergranular pores adsorption for OTC. The •OH and the h+ acted as the major active species contributed to the photocatalytic degradation of OTC.