Mechanistic insights into the visible light photocatalytic activity of g-C₃N₄/Bi₂O₂CO₃–Bi₄O₇ composites for rhodamine B degradation and hexavalent chromium reduction

The two-dimensional layered structure of g-C₃N₄ (GCN) has drawn a lot of attention in the field of photocatalysis due to its good thermochemical stability, large surface area, and environmental friendliness. A wide bandgap of GCN restricts its absorption to UV light and a limited portion of visible light; therefore, its bandgap engineering by coupling it with a suitable semiconductor can offer the utilization of a wider spectrum of incident light and a lower electron-hole recombination rate. In this study, GCN is coupled with mixed-phase Bi₂O₂CO₃-Bi₄O₇ (BO) in different weight percentages (wt%) to find the optimal loading of BO for maximum photocatalytic degradation. The XRD analysis confirms the preparation of GCN, BO, and g-C₃N₄/Bi₂O₂CO₃-Bi₄O₇ composites. The g-C₃N₄/Bi₂O₂CO₃-Bi₄O₇ composite with 24 wt% of BO (CN/BO-24) demonstrates 92.3% rhodamine B (RhB) dye degradation in 25 min under visible light irradiation, which is considerably higher compared with the corresponding % degradation realized with pristine GCN (73.4%) and BO (9.4%). The improved performance of the composite with optimal loading of BO is attributed to the reduced recombination rate of photo-generated electrons and holes, as confirmed by photoluminescence analysis, and utilization of a wider spectrum of incident light. Photo-degradation experiments performed with different scavengers reveal that peroxide radicals and holes play a decisive role in the degradation of RhB using the best composite sample (CN/BO-24). The potential of the CN/BO-24 ternary composite for the photoreduction of Cr(vi) is also explored. The fabricated composite holds promising potential in water treatment and environmental remediation.