Waste-Extracted Zn and Ag Co-Doped Spent Catalyst-Extracted V2O5 for Photocatalytic Degradation of Congo Red Dye: Effect of Metal-Nonmetal Co-Doping

The current study applies the eco-friendly principle of “wastes treat wastes”. By swift methods, a composite photocatalyst was prepared from waste-extracted oxides, namely V2O5, Ag, and ZnO. The metal–lixiviant complexes were used as metal precursors, where the lixiviants act as auto-templates and increase the compatibility between the mixed metallic species, and their controlled thermal removal generates pores. The tri-constitute composite catalyst was doped with nitrogen. The constitution, surface composition, and optical properties of the doped catalysts were investigated by XRD, SEM, TEM, BET surface analysis, XPS, diffuse reflectance, and PL spectra. The as-prepared catalysts were employed in the photodegradation of Congo red dye (CR) under visible irradiation at ambient temperature. The degree of Ag dispersion had a significant effect on the bandgap, as did metal and metal-nonmetal co-doping. The efficiency of dye removal changes dramatically with time up to 120 min, after which it begins to decrease. According to the pH effect, the normal pH of Congo red dye (6.12) is optimal. At a catalyst dose of 1 g L−1 and an irradiation period of 120 min, photodegradation efficiency reached 89.9% and 83.4% over [Ag0.05 ZnO0.05 V2O5(0.90)] and [Ag0.05 ZnO0.05 V2O5(0.90)]N, respectively. The kinetic study depicted the significant role of mass transfer in the reaction rate. The obtained rate constants were 0.995 mole L−1 S−1 and 0.998 mole L−1 S−1 for [Ag0.05 ZnO0.05 V2O5(0.90)] and [Ag0.05 ZnO0.05 V2O5(0.90)]N, respectively.