Direct visual evidence of S-scheme charge transfer: CeO2 quantum dots anchored on CdS nanosheets for synergistically enhanced photocatalysis.

Constructing S-scheme heterojunctions is a powerful strategy for photocatalytic remediation. Herein, CeO2 quantum dots (QDs) anchored on CdS nanosheets (CeO2/CdS) were fabricated via a microwave-assisted in-situ growth method. The optimized heterojunction exhibits a significantly enlarged specific surface area and demonstrates synergistically enhanced photocatalytic degradation of tetracycline (TC) and Rhodamine B (RhB), with rate constants 13 and 4.5 times higher than pristine CdS, respectively. Crucially, combined in-situ XPS, Kelvin probe force microscopy (KPFM) analyses and DFT calculation provide direct visualization of the interfacial charge transfer, unambiguously confirming the establishment of an internal electric field and the S-scheme electron transfer from CeO2 to CdS under light irradiation. This unique charge flow, further supported by photoelectrochemical and photoluminescence studies, efficiently separates powerful photogenerated carriers and boosts the generation of reactive radicals, as verified by EPR and trapping experiments. This work offers a multi-faceted methodological paradigm for unequivocally verifying the S-scheme mechanism in heterojunction photocatalysts.