Insights into the interaction between cadmium/tetracycline and nano-TiO₂ on a zeolite surface

Titanium dioxide (TiO₂) nanoparticles interact with organic-inorganic pollutants in the environment, and these interactions affect their environmental behavior. The mechanisms of the interaction between TiO₂ and organic-inorganic pollutants on the surface of clay minerals are still unclear. In this work, isotherm adsorption was studied to explore the interactions between Cd²⁺/tetracycline (TC), TiO₂ nanoparticles, and a zeolite (Zeo). SEM, FT-IR, and XPS were also used to reveal the interaction mechanism between organic-inorganic pollutants and TiO₂ on their stability and mobility in the environment. Compared to the single systems, the adsorption of Cd²⁺ and TiO₂ in the Cd + TiO₂ composite system decreased by 3.43% and 9.90%, respectively; the TC and TiO₂ adsorption in the TC + TiO₂ composite system decreased by 14.39% and 45.47%, respectively. The antagonism between Cd²⁺ and TiO₂ was due to Cd²⁺ and TiO₂ competing for the electrostatic attraction (-OH) and hydrogen bonding sites (Si-O), and TC and TiO₂ competing for the hydrogen bonding sites (-OH and C = O) on Zeo. The presence of TiO₂ will increase the mobility of Cd²⁺ and TC on a clay surface, and this effect is more significant for organic pollutants TC. Compared with Cd²⁺, TC has a more significant boosting impact on the TiO₂ mobility.