Sn4+ and S2− co-doped N–TiO2−x nanoparticles for efficient and photocatalytic removal of contaminants

Abstract

N–TiO_2−x nanoparticles (NPs) were selected as a basic construction unit because there are many Ti³⁺ and O vacancies on its surface. When S²⁻ and Sn⁴⁺ are co-doped into the N–TiO_2−x lattice, the O²⁻ and Ti⁴⁺ atoms can be replaced, respectively. The formation of dopant energy levels from Sn⁴⁺ and S²⁻ in Sn⁴⁺/S²⁻/N–TiO_2−x causes an obvious red shift to the visible light region. The recombination rate of the e⁻/h⁺ pairs was significantly reduced due to the fast migration and separation of the electrons as a result of the energy level doping from Sn⁴⁺ and S²⁻ and the formation of electron traps with Sn⁴⁺. The N–TiO_2−x NP band gap was significantly narrowed from 3.07 eV to 0.77 eV upon co-doping with Sn⁴⁺ and S²⁻, resulting in the superior photocatalytic activity of the Sn⁴⁺/S²⁻/N–TiO_2−x NPs. The photocatalytic reduction rate of Cr(VI) increased by 11.6 times and the photodegradation rate of doxycycline hydrochloride (DH) achieved about 5.7 times that of the original N–TiO_2−x NPs. This study provided a simple approach to preparing metal and non-metal co-doped N–TiO_2−x NPs, which could greatly improve the removal efficiency of contaminants via their synergistic effect.