Mesoporous cobalt oxide nanoparticles synthesized by a sonochemical method in the presence of a deep eutectic solvent for oxidative sonophotocatalytic decomposition of caffeine

Herein, for the first time, we have prepared mesoporous Co3O4 nanoparticles (NPs) by the ultrasound-assisted method in the presence of deep eutectic solvent (DES) for sonophotocatalytic degradation of caffeine (CAF). The porosity, crystallinity, and morphology of the as-synthesized NPs were investigated by using BrunauerEmmett-Teller (BET), X-ray diffraction (XRD), and transmission electron microscopy (TEM) techniques. The as-prepared NPs were applied in sonophotocatalytic, photocatalytic, and sonocatalytic degradation of CAF in low energy and low-frequency ultrasound at neutral pH. The sonophotocatalytic process was the most effective in degrading CAF, reaching about 99.5 % in less than an hour with a pseudo-first-order rate constant of 0.0902 min-1. The photocatalytic and sonocatalytic processes degraded 83.4 % and 22.7 % of CAF, respectively, with lower rate constants of 0.0288 and 0.0049 min-1. Notably, the simultaneous application of UV light and ultrasound irradiation in a sonophotocatalytic decomposition process had a positive synergy effect of about 62.64 %. The commercial tablet was degraded by the optimum sonophotocatalytic process to prove the applicability of the catalyst. The reusability test of the NPs was examined, and after four consecutive uses, the NPs had negligible fading of their sonophotocatalytic performance. Due to the excellent sonophotocatalytic performance of the NPs, it is a suitable candidate for a broad range of environmental and remediation applications.