Influence of Particle Sizes of Zinc and Titanium Oxides on Their Activity in Metronidazole Photocatalytic Oxidative Degradation in Water

Mechanochemical (MCT) and ultrasonic (UST) treatments have been used to change the particle sizes of photoactive oxides ZnO and TiO₂ and their mixtures with inert oxides (MgO, Al₂O₃, and SiO₂). It is shown that MCT leads to a significant decrease in the size of particles, while UST either does not affect their size or leads to an insignificant increase in their size due to aggregation. It is established that a decrease in particle size is accompanied by an increase in the band gap. The dilution of photoactive oxides decreases the metronidazole oxidative destruction rate constant. The reaction rate constant, which refers to a unit mass of a photoactive oxide, and metronidazole conversion decrease for all samples when the size of photoactive oxide particles is decreased (in the range of 20-50 nm).