In situ conversion of typical type-I MIL-125(Ti)/BiOBr into type-II heterostructure photocatalyst via MOF self-sacrifice: Photocatalytic mechanism and theoretical study

The type-I MIL-125(Ti)@BiOBr heterojunction was prepared by a foolproof wet chemical strategy. Since the self-doping of Ti3+ was introduced at the sacrifice of MOF, the type-I heterojunction was transformed into the type-II TiO2@BiOBr core-shell hollow heterojunction in situ. The self-doping of Ti3+ and the contact of the heterogeneous interface synergistically promote the photocatalytic activity of TiO2@BiOBr. The optimized Ti@BOB-3(m(MIL-125(Ti)): m(BiOBr) = 2:5) has a higher degradation rate (91%) for ciprofloxacin, and the first-order rate constant (0.02225 min(-1)) is pure 13.09 times of MIL-125(Ti) (0.0017 min(-1)) and 6.58 times of pure BiOBr (0.00338 min(-1)). UV-Vis diffuse reflection and photodegradation of antibiotics experiments show that type-II TiO2@BiOBr heterojunction has a broader range of light responses and better photocatalytic performance. The DFT calculation further studied the type-II heterojunction's energy band structure and forbidden band width (1.94 eV). Active species capture experiment and EPR spectrum analysis confirmed that h(+) and center dot O-2(-) are the main photoactive substances in the photodegradation process. This research is prospected to offer a cornerstone for the in-situ transformation design of different types of heterojunctions. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

The type-I MIL-125(Ti)@BiOBr heterojunction was prepared using a wet chemical method, and the introduction of self-doped Ti3+ transformed the heterojunction into a type-II TiO2@BiOBr core-shell hollow heterojunction in situ. The self-doping and heterogeneous interface contact of Ti3+ synergistically promote the photocatalytic activity. The optimized Ti@BOB-3(m(MIL-125(Ti)): m(BiOBr) = 2:5) exhibits higher degradation rate and first-order rate constant compared to MIL-125(Ti) and BiOBr alone. UV-Vis diffuse reflection and photodegradation experiments show that the type-II TiO2@BiOBr heterojunction has a broader light response range and better photocatalytic performance. DFT calculation further investigated the energy band structure and forbidden band width of the heterojunction. Active species capture experiment and EPR spectrum analysis confirmed the main photoactive substances in the photodegradation process. This research provides a foundation for the in-situ transformation design of different types of heterojunctions.