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

Abstract

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.