Enhancing the visible-light-catalytic activity of MIL-125(Ti)- based nanocomposites by adjusting the structure of the surface ligand: Mechanism and performance

Abstract

To further understand the structure impact of surface ligands on the performance of MIL-125(Ti), two molecules (TBPETC and TPETA) with different structures were designed to surface-modify MIL-125(Ti). The characterizations of powder X-ray diffractometry, Fourier transform infrared spectra, scanning electron microscope, transmission electron microscopy and energy-dispersive X-ray spectroscopy indicate the successful preparation of two novel nanocomposites, TBPETC@MIL-125(Ti) and TPETA@MIL-125(Ti). The photoelectrochemical properties of the materials were characterized by UV–visible spectroscopy, UV–visible diffuse reflectance spectra, photoluminescence spectroscopy and electrochemical impedance spectroscopy, respectively, which indicate both nanocomposites have lower bandgap energy and higher electronegativity than MIL-125(Ti). Under visible light irradiation, the removal percentage of tetracycline hydrochloride (TC) by TBPETC@MIL-125(Ti) and TPETA@MIL-125(Ti) were 91 % and 76 %. The active species capture experiments and HPLC-MS analysis indicated that O^2– and h⁺ were the predominate active substances and TC can be degraded into small molecules. In addition, the two nanocomposites showed good performance in practical applications, reusability and stability. All the results demonstrate that the effect of conjugate structures of the surface ligand on the properties of the nanocomposites is larger than that of functional groups, and TBPETC@MIL-125(Ti) is an effective material for degradation of TC under visible light in real environment.