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.