The persistent nature and environmental toxicity of industrial dyes in wastewater necessitate the development of efficient and sustainable removal technologies, such as sonocatalysis. The sonocatalytic activity of the NiO nanoparticles (NPs) was studied for the degradation of Congo red dye (CR). NiO NPs were prepared via a green method. The obtained NiO NPs were characterized using XRD, BET, TEM, FESEM, EDX, and UV-Vis-DRS. The sonocatalytic efficiency of the NiO NPs was evaluated for the CR degradation. The results show that 95% of CR dye and 56% of total organic carbon (TOC) were removed within 30 min. Nevertheless, when a hydroxyl radical (•OH) scavenger t-butanol and hole (h+) scavenger (EDTA) were added it was observed that degradation efficiency reduced from 95% to 52% and 64% respectively, which revealed that •OH is the main oxidizing agents in this process. LC-MS analysis identified degradation products and enabled the proposal of a plausible sonocatalytic degradation pathway for Congo red dye. NiO NPs' reusability was evaluated using the same reaction conditions for five consecutive cycles. However, a slight loss of sonocatalytic efficiency was obtained, illustrating the stability and reusability of the nanoparticles.
