Effect of oxygen vacancies on the photocatalytic activity of flower-like BiOBr microspheres towards NO oxidation and CO2 reduction

The presence of defects on semiconductor photocatalysts can change the electronic band structure and improve the catalytic activity. However, the synthesis of photocatalysts with defects is a challenging task, and the role of defects is still unclear. This work reports flower-like BiOBr microspheres prepared by a facile hydrothermal process in the presence of glycerol (GL), which induces the creation of oxygen vacancies (OVs). The obtained samples are denoted as BrGLx, where x is the amount of glycerol (0–150 mL) in the total (160 mL) volume of glycerol/water mixture. The photocatalytic performance of BrGLx photocatalysts is reported for NO oxidation and CO2 reduction. Comparing the pristine BiOBr sample (BrGL0) with the BrGL150 material, the NO removal rate increases from 10.6% to 48.2%, and the CH4 generation rate improves from 0 to 7.1 μmol·g−1·h−1, respectively, maintaining the same level of CO production. Combining the results of reaction kinetics, reactive oxygen species identification and in situ Fourier-transform infrared spectroscopy, the improved photoreactivity of BiOBr with OVs is attributed to the combined effects of enhanced substrate adsorption, enlarged light-response range and increased charge separation/migration. This work not only demonstrates the effect of OVs on the structure and photocatalytic performance/selectivity of BrGLx photocatalysts towards NO and CO2 conversion, but also provides new insights to tune and evaluate OVs.