Photo-Reduction of Cr (VI) on the novel hetero-System BaCr2O4/TiO2 under solar light irradiation

BaCr2O4, synthesized via coprecipitation, was characterized both physically and photoelectrochemically. With a band gap (E-g) of 1.48 eV, close to the optimal value for photoelectrochemical devices, BaCr2O4 exhibits activity in the visible spectrum. The material demonstrates a flat band potential of -0.25 V vs. SCE, enabling the photoelectrochemical reduction of chromate (Cr(VI)) to Cr3+ on the novel heterojunction system BaCr2O4/TiO2 (P25). Electrons from the conduction band of BaCr2O4 (-1.43 V vs. SCE), excited by sunlight, are injected into the conduction band of TiO2 (-0.78 V vs. SCE) and subsequently transferred to Cr(VI) species adsorbed on the TiO2 surface. Under optimal conditions (25 degrees C, pH similar to 4, [C2H2O4] = 10(-5) mol/L, BaCr2O4/TiO2 ratio = 1:1, dose = 1 mg/mL), a Cr(VI) concentration of 30 mg/L was completely reduced to the less toxic Cr3+ within 120 min. The addition of oxalic acid (C2H2O4) as a complexing agent was essential to prevent the photocorrosion of BaCr2O4, enhance electron-hole (e(-)/h(+)) separation, and improve photoactivity. Notably, the reduction of Cr(VI) in the presence of oxalic acid did not occur at room temperature without irradiation, underscoring the necessity of light activation.