Photocatalytic degradation of 2,4-Dichlorophenoxyacetic acid by zero-valent Ag-modified zinc oxide composite

Photocatalytic degradation has emerged as a highly promising and effective approach for the removal of 2,4-Dichlorophenoxyacetic acid (2,4-D), a widely used herbicide. In this study, a one-step calcination method was developed to synthesize zinc oxide (ZnO) supported on Baizilian biochar (ABC) with simultaneous doping of silver (Ag). The ZnO/ABC catalyst incorporating 3% Ag nanoparticles exhibits the highest photocatalytic activity, achieving a 2,4-D degradation rate of 95.4% within 50 min, exhibiting a photocatalytic rate constant of 0.06462 ± 0.0004 min⁻¹, which is 3.21 and 1.80 times higher than that of pure ZnO and ZnO/ABC, respectively. Mechanistic investigations revealed that the incorporation of silver nanoparticles reduced the band gap energy of the 3% Ag-ZnO/ABC system, thereby enhancing the separation efficiency and utilization of photogenerated electrons and holes, leading to increased generation of •O₂⁻ responsible for organic pollutant degradation. Furthermore, based on the identification of intermediate products, two plausible degradation pathways were proposed.