Synthesis, characterization and visible light photocatalytic activity of Cr³⁺, Ce³⁺ and N co-doped TiO₂ for the degradation of humic acid

The synthesis, characterization and photocatalytic activity of Cr³⁺ and Ce³⁺ co-doped TiON (N-doped TiO₂) for the degradation of humic acid with exposure to visible light is reported. The synthesized bimetal (Cr³⁺ + Ce³⁺) modified TiON (Cr-Ce/TiON), with an evaluated bandgap of 2.1 eV, exhibited an enhanced spectral response in the visible region as compared to pure and Ce³⁺ doped TiON (Ce/TiON). The XRD analysis revealed the insertion of Cr³⁺ and Ce³⁺ in the crystal lattice along with Ti⁴⁺ and N that resulted in the formation of a strained TiON anatase structure with an average crystallite size of ∼10 nm. Raman analysis also supported the formation of stressed rigid structures after bimetal doping. HRTEM confirmed the homogeneous distribution of both the doped metallic components in the crystal lattice of TiON without the formation of surface oxides of either Cr³⁺ or Ce³⁺. Electron energy loss spectroscopy (EELS) analysis revealed no change in the oxidation of either Cr or Ce during the synthesis. The synthesized Cr-Ce/TiON catalyst exhibited appreciable photocatalytic activity for the degradation of humic acid on exposure to visible light. Additionally, a noticeable mineralization of carbon rich humic acid was also witnessed. The photocatalytic activity of the synthesized catalyst was compared with pristine and Ce³⁺ doped TiON.