Construction of Ag NPs/CQDs/(La0.2Ce0.2Gd0.2Zr0.2Fe0.05)O2 high-entropy oxide heterostructures: Synergistic enhancement for photocatalytic degradation performance

High-entropy oxides (HEOs) are promising photocatalysts because of their compositional flexibility, defect-rich structures, and high structural stability. However, inefficient visible-light utilization and rapid charge-carrier recombination limit their photocatalytic performance. This study aimed to enhance the photocatalytic activity of fluorite-structured (La 0.2 Ce 0.2 Gd 0.2 Zr 0.2 Fe 0.05 )O 2 by constructing a ternary heterostructure comprising silver nanoparticles (Ag NPs), carbon quantum dots (CQDs), and HEO. The HEO was prepared by a sol–gel method, modified with CQDs, and subsequently decorated with Ag NPs by in situ photodeposition. The optimized ACH-2 composite removed 89.73% of tetracycline hydrochloride (TCH) within 120 min under visible-light irradiation and exhibited an apparent rate constant of 0.0176 min −1 , compared with 0.0072 min −1 for pristine HEO. The enhanced activity was accompanied by a broader optical response, lower interfacial charge-transfer resistance, a higher photocurrent response, and weaker steady-state photoluminescence. CQDs contributed to light utilization and interfacial charge transfer, whereas the Ag/HEO contact promoted directional electron migration and inhibited electron–hole recombination. Reactive-species experiments identified •O− 2 and h + as the predominant species involved in TCH degradation. The composite also maintained useful activity during repeated operation. These results demonstrate that cooperative CQD/Ag surface modification is an effective strategy for regulating light harvesting and interfacial charge transfer in HEO photocatalysts.