Co-existing TiO₂ nanoparticles influencing adsorption/ desorption of tetracycline on magnetically modified kaolin

Interaction of coexisting nanoparticles (NPs) and other pollutants may affect their behavior in the environment. In this study, we investigated the effects of TiO₂ NPs on the adsorption and desorption of tetracycline (TC) by magnetized kaolin (MK). The interactions among TC, TiO₂ NPs, and MK were then discussed through their morphology and characteristics by using scanning electron microscopy, X-ray energy dispersive spectrometry, Transmission electron microscope, X-ray diffraction, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy analyses. Results showed that TiO₂ NPs increased TC adsorption on MK by 2.02% and increased TC desorption by 45.26%, TC increased the maximum adsorption of TiO₂ on MK from 31.32 to 49.42 mg g^-1 and decreased the amount of stable adsorption state TiO₂ NPs on MK from 17.92 to 12.71 mg g^-1. The characterization results demonstrated that TC molecules combined on MK though hydrogen bonding, π-π bonding and hydrophobic interaction. The adsorption of TiO₂ NPs on MK can provide additional hydrogen-bonding sites for TC adsorption by increasing the number of hydroxyl groups. However, TC can decrease the electrostatic attraction sites for TiO₂ NPs adsorption on the MK surface. The complexation of TC and TiO₂ NPs weakened the electrical attraction between MK and TiO₂ NPs and decreased the amount of stable adsorption state TiO₂ NPs.