Green Chemistry Synthesis of Ag/ZnO (ashwater) Using Bark Ash Water and Mango Extract for Enhanced Photocatalytic Degradation of Rhodamine B

Abstract

Ag/ZnO (BAW) was synthesized via a green chemical precipitation method and evaluated as a visible-light photocatalyst for Rhodamine B (RhB) degradation. X-ray diffraction (XRD) analysis confirmed the coexistence of hexagonal wurtzite ZnO and metallic Ag phases, while energy-dispersive X-ray spectroscopy (EDX) verified the presence of Zn, O, and Ag. Scanning electron microscopy (SEM) revealed mixed rod-like and short tubular morphologies. UV–Vis diffuse reflectance spectroscopy demonstrated enhanced visible-light absorption of Ag/ZnO (BAW) compared with ZnO (BAW), and Tauc plot analysis showed a reduction in the optical band gap from 3.16 to 3.10 eV after Ag incorporation. Under visible-light irradiation, Ag/ZnO (BAW) achieved 99.69% RhB degradation within 120 min, compared with 89.51% for ZnO (BAW). The degradation followed a pseudo-first-order kinetic model, with Ag/ZnO (BAW) exhibiting an apparent rate constant of 0.0428 min⁻¹, approximately 2.6 times higher than that of ZnO (BAW) (0.0165 min⁻¹). The addition of 1,4-benzoquinone (BQ) markedly suppressed RhB degradation, suggesting the involvement of superoxide radicals (O₂⁻•) in the photocatalytic mechanism. However, the possible contributions of other reactive species cannot be excluded. The enhanced photocatalytic activity of Ag/ZnO (BAW) is associated with improved light absorption and enhanced photoinduced charge-carrier separation induced by Ag incorporation. These findings demonstrate the potential of Ag/ZnO (BAW) as an efficient and environmentally friendly photocatalyst for dye degradation under visible-light irradiation.