Photo-Tuned Cu/Cu2O/CdS/PPy Heterojunctions for Hg2+ Sensing in Seawater

Hg $^{\text {2+}}$ in seawater poses a threat to the ecological environment and human health, but the high salinity and complex composition of seawater make trace detection difficult. In this study, a Cu/Cu $_{{2}}\text{O}$ /CdS/PPy p-n junction foam was fabricated through layer-by-layer assembly. The influence of its photo-enhanced energy barriers upon electrochemical responses was investigated. The barrier was found to effectively provide the driving force for generating electrochemical response, and illumination further improved the sensing performance by expanding the tuning range of the height of the barriers. The photoelectric effect of the barrier enabled a highly sensitive response to Hg $^{\text {2+}}$ while resisting interference from seawater. The sensor demonstrated a low detection limit (1.29 nM) and a good recovery rate (98.9%–101.5%) when tested in actual seawater. This photo-enhanced barrier driving effect can be further utilized in developing other electrochemical sensors.