Construction of 2D/2D CaIn2S4/CeO2 Z-scheme heterojunction for highly efficient photocatalytic reduction of Cr(VI) under visible light

To mitigate the challenges of rapid charge carrier recombination and restricted visible light absorption inherent in single-semiconductor photocatalysts for Cr(VI) reduction, a 2D/2D Z-scheme CaIn 2 S 4 /CeO 2 heterojunction was engineered. The optimized materials exhibited Cr(VI) reduction rate constants that were 3.4-fold and 20.8-fold greater than those of pristine CaIn 2 S 4 and CeO 2 , respectively. Nevertheless, critical limitations are apparent. The efficacy of the Z-scheme mechanism, which depends on electron transfer and surface-generated •O 2 − species, becomes rate-limiting under elevated Cr(VI) concentrations, with efficiency decreasing from approximately 98% at 40 mg/L to ∼76% at 60 mg/L. Furthermore, the photocatalytic system displays pronounced pH sensitivity, with neutral and alkaline conditions substantially suppressing activity owing to the formation of CrO 4 2− and surface passivation. Cyclic durability assessments revealed a progressive deactivation trend, with reduction efficiency declining from 98% to 84% over four reaction cycles, indicative of material attrition or active site poisoning. In conclusion, while the CaIn 2 S 4 /CeO 2 heterojunction demonstrates high photocatalytic efficacy, its performance is contingent on specific operational parameters, and its advantages are not universally applicable across varying concentrations or pH regimes. This research, therefore, offers not only a high-performance photocatalyst but also a crucial cautionary perspective, emphasizing the necessity of balancing interfacial charge transfer efficiency with the availability of reactive oxygen species and the prevailing reaction environment.