Simultaneous introduction of oxygen vacancies and hierarchical pores into titanium-based metal-organic framework for enhanced photocatalytic performance

Photo-generated radicals play an important role in photocatalytic reactions, yet numerous radicals undergo self-quenching before contact with the substrate because of their ultrafast lifetimes and limited diffusion distances, which decreases the utilization of free radicals and reduces the activity of photocatalysts. Herein, both hierarchical pores and oxygen vacancies (OVs) were successfully introduced into a titanium-based metal-organic framework (MOF), namely MIL-125-NH₂ (MIL for Materials of Institut Lavoisier), via a simple and controllable acid etching method. The generation of OVs increased the yield of photogenerated radicals, while the hierarchical pore structure conferred a pore enrichment effect, thus enhancing the utilization of photogenerated radicals. Owing to the synergistic effect of the hierarchical pores and OVs, the obtained single-crystal nanoreactor, H-MIL-125-NH₂-V_O, showed much higher catalytic activity for rhodamine (RhB) degradation than pristine MIL-125-NH₂. In fact, the rate constant for catalytic RhB degradation in H-MIL-125-NH₂-V_O was approximately eight times that of MIL-125-NH₂. This work highlights the significant contribution of both hierarchical pores and OVs to enhancing the photocatalytic performance of MOFs.