Theoretical studies on the degradation mechanism of organochlorine pesticides in the presence of Si-OH in sepiolite

Nanofibers of sepiolite, a natural silicate belonging to the clay mineral family, are widely used in degrading toxic organic pollutants, air purification, and water pollutant adsorption. The role of Si-OH application in the degradation of organic pollutants, however, remains unclear. We performed density functional theory (DFT) calculations on organochlorine pesticides to gain insight into their degradation mechanism on the sepiolite surface. The results showed that organochlorine pesticides were preferentially adsorbed on Si and Si-OH sites. Meanwhile, the CCl bond could be effectively activated on the Si metal center. The search for the transition state showed that the reaction energy barrier of organochlorine pesticides at the Si-OH site was significantly lower than that at the Si site. In other words, the presence of hydroxyl effectively reduced the activation energy barrier, indicating that Si-OH was the main active site. This had a synergistic effect: the interaction between Si and the surface hydroxyl led to the degradation of organochlorine pesticides. We proposed a possible reaction mechanism that included adsorption, the forming and breaking of chemical bonds, and desorption.