One-step hydrothermal synthesis of CQDs/TiO2/NH2-MIL-125 for efficient photocatalytic production of H2O2 under visible light

NH₂-MIL-125 and its derivatives are receiving more attention in various aspects of photocatalytic reactions, especially in the photocatalytic hydrogen peroxide (H₂O₂) production from water (H₂O) and oxygen (O₂), which is a promising and sustainable strategy. However, the generation of H₂O₂ from NH₂-MIL-125 is far from satisfactory due to rapid photo-generated carriers recombination and poor surface electron transfer. In the work, the composite photocatalyst CQDs/TiO₂/NH₂-MIL-125 (C/T/NM) was designed for the first time by one-step hydrothermal method. TiO₂ was in situ converted from partial NH₂-MIL-125 (NM) during the successful loaded of Carbon quantum dots (CQDs) by hydrothermal process. The results indicated the type Ⅱ heterojunction was successfully constructed between the NM and TiO₂ interface, which could promote the transmission of photo-generated electrons. In addition, the successful loaded of CQDs could effectively transfer and stored the photo-generated electrons to the photocatalyst surface to participate in the reaction, and further avoiding the recombination of photo-generated carriers. The C/T/NM composite photocatalyst achieved a H₂O₂ generation of 455 µmol/L for 5 hours under visible light without oxygen bubbling, which was 7.1 times superior to that of NM. The H₂O₂ generation rate reached 645.4 µM/(g·h), which was in priority in the reported literature under the same conditions. Finally, based on the active species capture experiments, energy band structure analysis and the photoelectrochemical measurements, a possible mechanism for the efficient H₂O₂ generation through C/T/NM had been proposed. This work provided new ideas for designing NH₂-MIL-125 based composite photocatalysts for the production of H₂O₂.