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 [email protected](mMIL-125(Ti): mBiOBr = 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 •O2- 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.