Synergistic photoelectrochemical detection of Cd2+ with carbon-bismuth oxybromide composites: Mechanistic insights from DFT calculations

Abstract

The existences of hazardous heavy metals like cadmium (Cd) in water bodies necessitates rapid, accurate on-site detection strategies. Herein, a novel photoelectrochemical scheme for sensitive detection of Cd2+ was proposed based on the hybrid carbon-bismuth oxybromide materials (C/Bi4O5Br2 and CNTs/BiOBr). The effects of ultraviolet light (UV-light) illumination during the Cd2+ deposition and desorption stages were analyzed, revealing enhanced photocurrent responses and detection sensitivity compared with those non-illumiantion. The optimal sensitivity of 0.42079 μA/ppb (C/Bi4O5Br2 under both deposition and desorption stages) and 0.15634 μA/ppb (CNTs/BiOBr under desorption stage only) were observed with UV illumination within a Cd2+ range of 10–100 ppb. Density functional theory calculation elucidated that Cd2+ adsorption on the semiconductor surface reduced the badgaps of Bi4O5Br2 and BiOBr, which would benefit electron transfer and redox reactions. Additionally, the interaction between Cd and the semiconductor produced a Schottky barrier, which prolonged the lifetime of the photo-generated electron-hole pairs, where the electrons migrated on the semiconductor surface formed electron capture traps and induced band bending, therefore facilitated the electrons in the conduction band to react with Cd2+ deposited on the electrode surface. The study provides mechanistic insights into the photoelectrochemical processes in enhancng precise and sensitive on-site heavy metal ions detection.