Construction of Ca-CuFeO₂/TiO₂(B) p–n Heterojunctions with Efficient Visible Light-Driven Photocatalysis

Ca-CuFeO2/TiO2(B) heterojunctions were constructed to improve the photocatalytic reduction efficiency of Cr(VI). The results suggest that Ca doping gives rise to the phase transition of 3R to 2H, increased surface area, and improved charge transfer ability of CuFeO2. Covering CuFeO2 with TiO2(B) effectively inhibits the partial oxidization of Cu1+ to Cu2+. The schematic energy band diagram and carrier density distributions for Ca-CFO/TiO2 heterojunctions were theoretically simulated using AMPS software. It suggests that photogenerated electrons in the CuFeO2 conduction band adjacent to the depletion region drift into TiO2(B) due to the presence of a built-in electric field to directly participate in the reducing process of Cr(VI) on the TiO2 surface. Photogenerated holes in CuFeO2 can hardly drift or diffuse into TiO2(B) due to the presence of an energy barrier in the valence band and will diffuse to the uncovered CuFeO2 surface and be captured by formic acid to generate reactive CO2·– free radicals to effectively reduce Cr(VI). The maximum photocatalytic efficiency using 5%Ca-CuFeO2/TiO2 (3:1) was 100% in 40 min. The study results can provide a new avenue for the efficient treatment of Cr(VI)-containing wastewater with Ca-CuFeO2/TiO2(B) p–n heterojunctions owing to the advantages of high efficiency, environmental friendliness, sustainability, and low energy consumption.