A novel MIL-125(Ti)-based nanocomposite for enhanced adsorption and catalytic degradation of tetracycline hydrochloride: Synergetic mechanism of calcination and the nitrogen-containing reticulated surface layer.

A multi-nitrogen conjugated organic molecule (TPE-2Py) was selected to surface modify the calcined MIL-125(Ti) to prepare a nanocomposite (TPE-2Py@DSMIL-125(Ti)) for adsorption and photodegradation of organic pollutant (tetracycline hydrochloride) under visible light. A novel reticulated surface layer was formed on the nanocomposite, and the adsorption capacity of TPE-2Py@DSMIL-125(Ti) for tetracycline hydrochloride can reach 157.7 mg/g under neutral conditions, which is higher than that of most other reported materials. Kinetic and thermodynamic studies show that the adsorption is a spontaneous heat absorption process, dominated by chemisorption, in which electrostatic interaction, π-π conjugation and Ti-N covalent bonds played dominant roles. The photocatalytic study shows that the visible photo-degradation efficiency of TPE-2Py@DSMIL-125(Ti) for tetracycline hydrochloride can further reach 89.1% after adsorption. Mechanism studies reveal that •O and h play a major role in the degradation process, and the separation and transfer rate of photo-generated carriers increase, improving its visible photocatalytic performance. This study revealed the relationship between the adsorption/photocatalytic properties of the nanocomposite and the structure of the molecular as well as the calcination, providing a convenient strategy to regulate the removal efficiency of MOFs materials towards organic pollutants. Furthermore, TPE-2Py@DSMIL-125(Ti) exhibits good reusability and even better removal efficiency for tetracycline hydrochloride in real water samples, indicating its sustainable treatment of pollutants in contaminated water.