Oxygen defects engineered CdS/Bi2O2.33 direct Z-Scheme heterojunction for highly sensitive photoelectrochemical assay of Hg2+

This work demonstrates that the photoelectrochemical response of the CdS/Bi2O2.33 direct Z-scheme heterojunction, synthesized by in situ deposition of CdS nanocrystals on the defect engineered Bi2O2.33, can be modulated by oxygen defect concentration. The appropriate oxygen defects not only increase the visible light absorption, provide active reaction sites to enhance PEC activity, but also promote the separation of carriers. The formation of CdS/Bi2O2.33 direct Z-scheme heterojunction further improves these properties by extending the visible light absorption and promoting separation and transport of carriers, but avoids the usage of noble metal nanoparticles as electron transfer mediators, thus has a low cost and easy fabrication technology. The CdS/Bi2O2.33 direct Z-scheme junction shows significantly improved photocurrent response as compared with those containing less oxygen defects, and is applied as a photoelectrochemical assay platform for Hg2+. The specific interaction between Hg2+ and the S2- in CdS significantly quenches the photocurrent response of the CdS/Bi2O2.33 due to the formation of HgS. The photocurrent decrease is linear to the concentration of Hg2+ in the range from 10(-11) to 10(-6) g/mL, with the limit of detection of 3.2 pg/mL. High accuracy and good reproducibility are realized in the real sample analysis of urine, river water, and sea water. The integration of oxygen defect engineering and direct Z-scheme electron transport principle provides a new avenue for fabricating high performance photoelectrochemical materials, which can be further combined with bio-recognition strategy for the ultrasensitive detection of biological molecules.