In-situ synthesis of efficient N-graphyne/Bi/BiOBr photocatalysts for contaminants removal and nitrogen fixation

Herein, a series of N-graphyne-Bi/BiOBr composites are fabricated via solvothermal method by using Bi(NO3)3·5 H2O, KBr, and nitrogen-doped graphyne as precursor materials in Ethylene glycol. The as-prepared ternary composites show flower-like three-dimensional microspheres self-assembled by nanosheets. N-graphyne contributes to in-situ formation of Bi0 on BiOBr microspheres. For photocatalytic removal of contaminants, the adsorption capacity of 1%-N-GY-Bi/BiOBr composite toward rhodamine B (RhB) is found to be 900.0 mg/g, which is 2.2 times higher than that of the pristine Bi/BiOBr photocatalyst. Moreover, compared to the Bi/BiOBr photocatalyst, the optimized 1%-N-GY-Bi/BiOBr composite revealed a 1.49 and 1.54-fold enhanced degradation performance for RhB and levofloxacin, respectively. Additionally, it is found that superoxide radical (·O2-) is the major active specie involved in the photocatalytic degradation process. The performance of the composites is also evaluated for nitrogen fixation. The NH3 production rate of the optimized ternary composite in water under UV–Vis light irradiation (i.e., 5.68 μmol·gcat−1·h−1) is 3.5 folds higher than that of the Bi/BiOBr. In addition, the stability of 1%-N-GY-Bi/BiOBr composite is also confirmed by the retention of 89.3% of RhB degradation performance and 88% NH3 production during N2 fixation after three catalytic cycles. Moreover, the mechanism is systematically explored by the results of photoluminescence spectra, photo-current, Tafel plots, electrochemical impedance, and Mott-Schottky curves, etc. In short, this study confirms that N-GY modification is an effective strategy for improving the photocatalytic performance of Bi/BiOBr.