Sonophotocatalytic degradation of malachite green in aqueous solution using six competitive metal oxides as a benchmark

A comparison study examines six different metal oxides (CuO, ZnO, Fe₃O₄, Co₃O₄, NiO, and α-MnO₂) for the degradation of malachite green dye using four distinct processes. These processes are as follows: sonocatalysis (US/metal oxide), sonocatalysis under ultra-violet irradiation (US/metal oxide/UV), sonocatalysis in the presence of hydrogen peroxide (US/metal oxide/H₂O₂), and a combination of all these processes (US/metal oxide/UV/H₂O₂). The effective operating parameters, such as the dosage of metal oxide nanoparticles (MONPs), the type of the process, and the metal oxides' efficiency order, were studied. At the same reaction conditions, the sonophotocatalytic is the best process for all six MOsNPs, CuO was the better metal oxide than other MOsNPs, and at the sonocatalysis process, ZnO was the best metal oxide in other processes. It was found that the metal oxide order for sonocatalytic process is CuO > α-MnO₂ ≥ ZnO > NiO ≥ Fe₃O₄ ≥ Co₃O₄ within 15-45 min. The order of (US/metal oxide/UV) process is ZnO ≥ NiO ≥ α-MnO₂ > Fe₃O₄ ≥ CuO _≥ Co₃O₄ within 5-40 min. The order of (US/ MOsNPs/ H₂O₂) process is ZnO ≥ CuO ≥ α-MnO₂ ≥ NiO > Co₃O₄ > Fe₃O₄ within 5-20 min. The maximum removal efficiency order of the sonophotocatalytic process is ZnO ≥ CuO > α-MnO₂ > NiO > Fe₃O₄ ≥ Co₃O₄ within 2-8 min. The four processes degradation efficiency was in the order US/MOsNPs ˂ US/MOsNPs/UV ˂ US/MOsNPs/H₂O₂ ˂ (UV/Ultrasonic/MOsNPs/H₂O₂). Complete degradation of MG was obtained at 0.05 g/L MONPs and 1 mM of H₂O₂ using 296 W/L ultrasonic power and 15 W ultra-violet lamp (UV-C) within a reaction time of 8 min according to the MOsNPs type at the same sonophotocatalytic/H₂O₂ reaction conditions. The US/metal oxide/UV/H₂O₂ process is inexpensive, highly reusable, and efficient for degrading dyes in colored wastewater.