A NiO film photocathode with a signal-weakening photoresponse for hexavalent chromium detection

Photoelectrochemical (PEC) sensors have the advantages of high sensitivity, low background noise, and fast response time, and are suitable for environmental monitoring, biomedical, and chemical industries. In this work, a photocathode whose photoresponses weaken with increasing concentration of the substance is proposed and used for Cr(VI) sensing, and a wide concentration range (0.04−16 µM) for Cr(VI) can be detected by just using one NiO film, with a sensing sensitivity of 0.69 lgC µAµM-1 cm-2 (where C is the concentration) and a low detection limit of 0.01 µM. The successful detection of Cr(VI) was achieved through the signal-weakening photoelectrochemical responses, as evidenced by the decrease in the photocathode signal with increasing Cr(VI) concentration. This can be attributed to the steric hindrance effect caused by the in-situ formation of Cr(OH)3 precipitates. Our proposed scheme can be successfully used for the monitoring of Cr(VI) in drinking water, as the world health organization requirement of 0.96 µM is included in the linear detection range.