Photoelectrochemical detection of Cd2+ based on in situ electrodeposition of CdS on ZnO nanorods

A novel and simple photoelectrochemical method was developed for the selective detection of Cd2+. CdS, a semiconductor, was obtained by electrodepositing Cd2+ solution containing S2O32- and EDTA, and ITO glass covered with ZnO nanorod arrays, synthesized by a hydrothermal process, was used as the photoelectrochemical sensing matrix. Compared with ZnO, CdS is a narrow band semiconductor and could be easily stimulated by light irradiation. Based on the principle that CdS could enhance the charge separation of ZnO nanorods, the detection of Cd2+ was achieved. SEM images of the CdS/ZnO electrode showed that different amounts of CdS were obtained when the electrodepositions were operated in solutions containing different concentrations of Cd2+, and on account of the different concentrations of Cd2+, different photocurrent intensities were obtained. A good linear relationship between the photocurrent intensity and Cd2+ concentration was achieved from 0.01 mM to 5 mM with a detection limit of 3.3 mu M. The analysis of Cd2+ in a water sample using the proposed method also gave satisfactory results. Therefore, this work provides a novel methodology for Cd2+ analysis, which has potential application in environmental monitoring and analysis.