Design and synthesis of g-C3N4-doped Bi-MOF composites for high-efficient catalytic ozonation of 4-Nitrophenol: mechanism, effect parameters and degradation pathways analysis

4-Nitrophenol (4-NP), a toxic and persistent pollutant in chemical wastewater, presents significant challenges in degradation and mineralization. Conventional ozone-oxidation catalysts are hindered by low efficiency, mass transfer constraints and metal leaching, necessitating the development of stable and efficient catalysts. Herein, the Bi-MOF/g-C3N4/MS composite materials were prepared by the solvothermal method and an immersion-induced phase separation strategy. The resulting materials were characterized and applied for catalytic ozonation degradation of 4-NP. Under the specific experimental conditions of the O3 + BiCN100/MS system, the total organic carbon and chemical oxygen demand removal rates of 4-NP were observed to reach 71.2% and 83.7% within 20 min, respectively. These two parameters were improved by raising the initial pH, reducing 4-NP concentration and increasing the catalyst dosage. The abundant Lewis acid sites were regarded as the pivotal catalytic site of BiCN100/MS, which were conducive to the adsorption of O3 and the acceleration of the formation of reactive oxygen species (ROS). The electron paramagnetic resonance results demonstrated that the primary ROS engaged in the degradation reaction were 1O2, ·O2− and ⋅OH. Toxicity analysis revealed that the O3 + BiCN100/MS system exhibited an effective detoxification effect. Ultimately, the primary degradation pathway of 4-NP was proposed through liquid chromatography–mass spectroscopy (LC–MS) analyses at varying reaction times. Additionally, BiCN100/MS demonstrated excellent stability and reusability in actual waste water cyclic experiments.