NiO nanoparticles with superior sonophotocatalytic performance in organic pollutant degradation

Herein, NiO nanoparticles were prepared by a facile solvothermal route. The as-synthesized nanoparticles were characterized using XRD, BET, TEM, HRTEM. The BET measurements prove the mesoporous nature of the NPs, having good specific surface area and pore volume. The synthesized NiO NPs were used for the first time in dye decomposition using methylene blue (MB) as a model pollutant in low frequency and low energy ultrasound at pH = 7 and room temperature in presence of UV light and H2O2 as an oxidant. The change of the pollutant concentration was estimated by UV-VIS spectrophotometry. Dye degradation performance investigated for sonocatalysis, photocatalysis, and sonophotocatalysis processes. The data showed that the decomposition performance was in the following order: sonophotocatalysis > photocatalysis > sonocatalysis. After about 30 min of dual (Sono + UV) irradiation in the presence of NiO NPs more than 90% of the pollutant degraded, achieving a rate constant of about 0.089 min(-1). Sonophotocatalytic performance was compared with sonocatalysis and photocatalysis processes carried out in the same conditions. Interestingly, the combination of ultrasound and UV light irradiation in a sonophotocatalytic degradation process led to about 33% synergy effect, proving a positive synergy between the sonocatalytic and photocatalytic processes. Reusability data exhibited the excellent stability of sonophotocatalysts within four consecutive runs with negligible fading in their sonophotocatalytic performance. This feature improves the reusability potential of the sonophotocatalysts to be applied in the industrial directions. The obtained results proved that the performance of the sonophotocatalytic process was severely affected by the addition of different kinds of trapping agents, therefore based on these results the mechanism of the sonophotocatalysis was discussed. Finally, the presently combined system paved the way toward excellent efficiency and it could pose a good strategy, in terms of environmental impact and energy cost, in comparison to conventional sonophotocatalytic systems. (C) 2021 Elsevier B.V. All rights reserved.