Nickel-impregnated ZnO catalysts: a promising catalyst for efficient methylene blue dye degradation via photocatalysis and sonocatalysis.

This research used the wet impregnation method to prepare visible light-induced nickel-impregnated zinc oxide (Ni/ZnO) photocatalysts. The synthesized catalysts were tested for methylene blue (MB) degradation in aqueous media. The photocatalyst's structure, morphology, and composition were confirmed using EDX, SEM, and XRD analyses. The Ni/ZnO exhibited a high specific surface area of 192.88 m²/g and a mesoporous structure with an average pore size of 110.02 Å, as determined by BET analysis. The effect of different parameters such as the pH of the dye solution, catalyst dose, the concentration of dye, and the impact of oxidizing agent and radical scavenger on the photodegradation efficiency of catalyst for MB in aqueous media was investigated. The photocatalysis and sonophotocatalysis led to 75% and 98% degradation of 20 mg L^-1 of MB in 60 min at pH 9 using 0.1 g L^-1 of catalyst. The photocatalyst was found reactive upto five runs. The number of degraded molecules was 2.34E-06 mol and 3.06E-06 mol for photocatalysis and sonophotocatalysis, respectively. It was found that the degradation efficiency increased in the presence of H₂O₂ while decreasing with the increase of dye concentration and radical scavenger. The sonophotocatalytic degradation of methylene blue, demonstrating enhanced kinetics over photocatalysis alone, followed both pseudo-first-order and pseudo-second-order models. The photocatalysis reaction rate (r) was 7.82E-03 mmol g^-1 min^-1 with a quantum yield of 1.86E-06 mol/photon and a space-time yield of 1.86E-07 mol/photon/mg. In contrast, the reaction rate for sonophotocatalysis was 1.02E-02 mmol g^-1 min^-1 with a quantum yield of 2.43E-06 mol/photon and a space-time yield of 2.43E-07 mol/photon/mg. The results revealed that Ni/ZnO can be an effective catalyst for degrading toxic MB and MB like other dyes.