Preparation, characterization and application of Nd-TiO₂ photocatalyst for the reduction of Cr(VI) under UV light illumination

A novel photocatalyst, titanium dioxide (TiO₂) doped with neodymium (Nd), was prepared by the sol-gel method and used for the photocatalytic reduction of Cr(VI) under UV illumination, in order to determine its photocatalytic properties. A series of Nd³⁺-TiO₂ catalysts prepared with different Nd³⁺ dosages were characterized by XRD, Raman spectroscopy, SEM, EDX, TEM, EDS and XPS spectroscopy. In the experiments, formic acid was used as a hole scavenger to enhance the photocatalytic reduction reaction. The experiments demonstrated that Cr(VI) was effectively reduced in aqueous Nd³⁺-TiO₂ suspension by more than 95% within 60 min, while the pH of the solution increased from 3.1 to 3.35 due to the consumption of formic acid. The experimental results indicate that the presence of Nd³⁺ in TiO₂ catalysts substantially enhances the photocatalytic reaction of chromium(VI) reduction. It was found that the optimal dosage of 1-3 wt% Nd³⁺ in TiO₂ achieved the fastest reaction of Cr(VI) reduction under the experimental conditions. The neodymium ions deposited on the TiO₂ surface behave as sites at which electrons accumulate. The improved separation of electrons and holes on the modified TiO₂ surface allows more efficient channeling of the charge carriers into useful reduction and oxidation reactions rather than recombination reactions. The presence of sacrificial electron donors such as formic acid enhances the photocatalytic reduction of Cr(VI). The Cr(VI) adsorbed on the surface of the TiO₂ particles was observed to be almost completely photoreduced to Cr(III).