The mechanism of catalytic degradation of secnidazole by semiconductor titanium dioxide: A density functional theory study

• The adsorption of secnidazole on (001) and (101) surfaces of TiO 2 was calculated and analyzed. • The reaction mechanism of the photocatalytic degradation of secnidazole in TiO 2 was investigated. • Hydrogen bond interaction exists when secnidazole is adsorbed on TiO 2 surfaces. • Degradation is mainly reflected in the C-N bond cleavage of imidazole ring. Photocatalytic degradation of nitroimidazole antibiotics is a very promising method. In this work, we not only employed density functional theory (DFT) calculations to investigate the degradation mechanism of secnidazole on the surfaces of anatase TiO 2 (101) and (001) but also explored the structural changes of secnidazole in the course of the degradation process. Specifically, we first optimized the adsorption configurations of secnidazole on different surfaces and analyzed the optimal adsorption sites, adsorption energies, and the most stable adsorption configurations. We found that secnidazole was adsorbed on the TiO 2 surfaces via hydrogen bonds. Meanwhile the C-N bond on the imidazole ring is weakened during the adsorption process, which facilitates the ring-opening reaction of the imidazole. Finally, we investigated two possible degradation pathways of secnidazole on different TiO 2 surfaces and obtained their reaction mechanisms, based on which we concluded that the degradation of secnidazole is more likely to take place on the (101) surface of anatase TiO 2 .