NiO@Carbon quantum dots S-scheme heterojunction as a light-activated oxidase mimic for Cu2+ colorimetric detection

Light-activated oxidase mimics have a wide application prospect in environment, detection, medicine and other fields because of its stability, environmental friendliness and high activity. Here a S-scheme heterojunction formed by NiO nanosheets modified with carbon quantum dots (CQDs) is prepared as a light-activated oxidase mimic. The modification of CQDs expands the light absorption range of NiO, while NiO as a matrix improves the dispersion of CQDs. Moreover, at the contact interface a S-scheme heterojunction forms, accelerating the separation of photoexcited electrons and holes under the built-in electric field and band bending. The unique transfer of photoexcited carriers maintains high oxidation and reduction activity of NiO@CQDs, improving its photocatalytic activity. NiO@CQDs can oxidize o-phenylenediamine (OPD) to yellow under light, and when Cu2+ was present in the solution, this colorimetric reaction was inhibited. Therefore, NiO@CQDs could be used for colorimetric detection of Cu2+, with a wide linear range of detection (0–0.1 µM, 0.1–1 µM, 1–10 µM, 10–100 µM), low detection limit (0.024 μM), good selectivity and stability.