Carbon Nitride Homojunction Induced by Metal Salts-Based Deep Eutectic Solvents for Portable and Self-Powered Detection of Lead Ions

Reasonable design of semiconductors is crucial for improving the sensitivity of self-powered photoelectrochemical (PEC) sensors. In this study, metal salt-based deep eutectic solvents (DES(CC-V)) were self-assembled on molten salt-assisted carbon nitride via hydrogen bonding, forming a DES(CC-V)/KCN homojunction. The DES(CC-V)/KCN homojunction exhibits a negative conduction band position and facilitates directional electron transfer and separation. The modification with DES(CC-V) increases the oxygen active sites and the hydroxyl amount, enhancing hydrophilicity. The synergistic effect of electron transport, active sites, and hydrophilicity promotes the photocatalytic oxygen reduction reaction, thus amplifying the open circuit potential and power density of the self-powered system. A self-powered sensing showcased high sensitivity, stability, and applicability for lead ions in a water environment and achieved portable monitoring via a multimeter device with a limit of detection (0.4 ng L–1). This research proposes a novel green synthesis strategy of metal salt-DES modified carbon nitride to form a homojunction and enrich surface functionalization.