Oxygen and Titanium Vacancies in a BiOBr/MXene-Ti3C2 Composite for Boosting Photocatalytic N-2 Fixation

Solar energy can be used as green energy by photocatalysis for the nitrogen fixation under the atmospheric conditions compared with the traditional energy- intensive industrial production of ammonia. However, the complex kinetics and high reaction barriers greatly hinder the development of the photocatalytic N-2 reduction reaction. Herein, a BiOBr/MXene-Ti3C2 composite catalyst is prepared by the simple electrostatic adsorption and self-assembly method. The as-prepared 10 wt % BiOBr/Ti3C2 exhibits the best performance for N-2 fixation to NH3 by photocatalysis. The evolution rate of NH3 is up to 234.6 mu mol center dot g(-1)center dot h(-1), which is approximately 48.8 times and 52.4 times higher than those of pure BiOBr and Ti3C2, respectively. It is found that the designed double vacancies of oxygen and titanium for BiOBr/ Ti3C2 composites, with the availability of localized electrons, have the ability to adsorb and activate N-2, which can be efficiently reduced to NH3 by the interfacial electrons transferred from the excited BiOBr/Ti3C2 composite. In addition, the results of in situ Fourier transform infrared show the generation of NxHy species by the continuous protonation processes. Moreover, titanium vacancy (V-Ti) induces a strong absorption energy for nitrogen atoms on the surface of BiOBr/Ti3C2 according to the density functional theory calculations. In particular, the P-electron feedback caused by V-Ti could effectively promote the weakening of the N.N triple bond and elongate the N-2 bond length by similar to 31.6%. This work might provide new insights into the synergistic effect of double defects and inspiration for the rational design of catalysts by defect engineering in the field of catalytic synthesis of ammonia.

Automated summary

In this research, a BiOBr/MXene-Ti3C2 composite catalyst was prepared for efficient nitrogen fixation to ammonia by photocatalysis. The designed double vacancies of oxygen and titanium in the composite exhibited enhanced N-2 reduction reaction efficiency. This work provides new insights into the rational design of catalysts for catalytic synthesis of ammonia.