ZnO/g-C 3 N 4 photocatalyst activated by low-pressure ultraviolet for restoring the SWASV signals: A fast pretreatment method for electrochemically detecting Cd 2+ and Pb 2+ in soil extracts.

Soil organic matter (SOM) significantly impacts the detection accuracy of Cd ²⁺ and Pb ²⁺ using square wave anodic stripping voltammetry (SWASV) due to the complexation of SOM to heavy metal ions (HMIs), thereby attenuating SWASV signals. This study explored an effective pretreatment method that combined low-pressure ultraviolet (LPUV) photolysis with the ZnO/g-C ₃ N ₄ photocatalyst, activating the photocatalyst to generate highly oxidative •OH radicals and O ₂ ^•- radicals, which effectively disrupted this complexation, consequently restoring the electroactivity of HMIs and achieving high-fidelity SWASV signals. The parameters of the LPUV-ZnO/g-C ₃ N ₄ photocatalytic system were meticulously optimized, including the pH of photolysis, duration of photolysis, g-C ₃ N ₄ mass fraction, and concentration of the photocatalyst. Furthermore, the ZnO/g-C ₃ N ₄ photocatalyst was thoroughly characterized, with an in-depth investigation on the synergistic interaction between ZnO and g-C ₃ N ₄ and the mechanisms contributing to the restoration of SWASV signals. This synergistic interaction effectively separated charge carriers and reduced charge transfer resistance, enabling photogenerated electrons (e ^- ) from the conduction band of g-C ₃ N ₄ to be quickly transferred to the conduction band of ZnO, preventing the recombination of e ^- and hole (h ⁺ ) and generating more radicals to disrupt complexation and restore the SWASV signals. Finally, the analysis of HMIs in real soil extracts using the proposed pretreatment method demonstrated high detection accuracy of 94.9% for Cd ²⁺ and 99.8% for Pb ²⁺ , which validated the feasibility and effectiveness of the proposed method in environmental applications.
Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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