Pulsed electrodeposition of CdS on ZnO nanorods for highly sensitive photoelectrochemical sensing of copper (II) ions

Pulsed electrodeposition was adopted to decorate one-dimensional (1D) ZnO nanorods with CdS nanocrystals. The synthesized 1D ZnO-CdS hybrid photoelectrode was employed in the construction of a dynamic photoelectrochemical (PEC) sensing system. The surface analysis showed that CdS nanocrystals in the size of ca. 10 nm were deposited and homogeneously distributed on ZnO nanorods with the interface of high quality. Under visible light illumination, the ZnO-CdS hybrid photoelectrode achieved an anodic photocurrent density of 5.8 mA cm⁻² at 0.3 V vs. Ag/AgCl (1 M KCl), owing to the extended absorption in the visible light region, enlarged active interfaces, and efficient separation of photogenerated charge carriers. By the interaction of Cu²⁺ ions with CdS nanocrystals via the formation of Cu_xS, the ZnO-CdS hybrid photoelectrode was developed as a PEC sensor for the detection of Cu²⁺ ions. A fast parasitic photocurrent response to the addition of Cu²⁺ ions was observed in the sensing test. The photocurrent density of the developed sensor was linearly declined with increasing the concentration of Cu²⁺ ions from 0.01–1 μM and 1–1000 μM at a logarithm scale. Moreover, it exhibits a limit of detection (3σ/S) of 3 nM with high selectivity and good reproducibility