pH-Controllable regeneration and visible-light photocatalytic redox of carbon and nitrogen co-doped Zn3Nb2O8 towards degradation of multiple contaminants

Abstract

The visible light photocatalytic activity and stability of bare Zn₃Nb₂O₈ and carbon doped Zn₃Nb₂O₈ (C–Zn₃Nb₂O₈) were enhanced with nitrogen and carbon co-doped Zn₃Nb₂O₈ (N/C–Zn₃Nb₂O₈) for the oxidative and reductive degradation of pH-sensitive substrates, such as Cr(VI), Cu(II), methyl orange, and tetracycline hydrochloride. Compared to pure Zn₃Nb₂O₈, the band structure of N/C–Zn₃Nb₂O₈ was optimized with the conduction band at −0.37 eV and the valence band at 1.61 eV due to the co-doping of nitrogen and carbon, which could stimulate the formation of ˙OH and ˙O₂⁻ radicals. Moreover, the N/C–Zn₃Nb₂O₈ catalyst was highly improved by the synergistic effect of carbon and nitrogen dopants on the visible light absorption, the charge conductivity, and the electron–hole pair separation. In addition, the N/C–Zn₃Nb₂O₈ catalyst with a negatively charged surface and layered structure can selectively adsorb and degrade some pH-sensitive pollutants, thus achieving high photocatalytic activity in visible light irradiation and stable recyclability by designing a regeneration test and controlling the pH range.