In or on, a study of the influence of the binding site for TiO₂ and MIL-101(Cr)

In this work, TiO₂ was formed in situ in the internal pores and on the surface of MIL-101(Cr). Density functional theory (DFT) calculations demonstrate that the difference in the binding sites of TiO₂ can be attributed to the different solvents used. The two composites were used to photodegrade methyl orange (MO), and the photocatalytic efficiency of TiO₂-in-MIL-101(Cr) (90.1% in 120 min) was much stronger than that of TiO₂-on-MIL-101(Cr) (14% in 120 min). This is the first work to study the influence of the binding site of TiO₂ and MIL-101(Cr). The results show that MIL-101(Cr) modification with TiO₂ can promote electron-hole separation, and TiO₂-in-MIL-101(Cr) has better performance. Interestingly, the two prepared composites have distinct electron transfer processes. For TiO₂-on-MIL-101(Cr), radical trapping and electron paramagnetic resonance (EPR) studies show that O₂˙^- is the main reactive oxygen species. Based on its band structure, it can be concluded that the electron transfer process of TiO₂-on-MIL-101(Cr) conforms to that of a type II heterojunction. However, for TiO₂-in-MIL-101(Cr), the EPR and DFT results show that ¹O₂ is the active substance that is formed from O₂ through energy transfer. Therefore, the influence of binding sites should be considered for the improvement of MOF materials.