Bimetal-based Biochar Composite Materials For Catalytic Oxidation Of Aqueous Refractory Organics

The traditional homogeneous oxidation reaction has the problems of narrow pH adaptation range,serious loss of metal ions and secondary pollution of the environment.In order to overcome these shortcomings,heterogeneous oxidation reactions have attracted much attention in recent years,and the design and investigation of heterogeneous catalysts with excellent performance has become a hot topic.Therefore,in this study,two Fe-Mo bimetallic biochar composites,nZVI/MoS₂-BC and Fe7.5/Mo1.0@BC700,were designed and prepared.They were applied to peroxymonosulfate oxidation system and Fenton oxidation system to degrade various organic pollutants,and their catalytic oxidation performance and mechanism were explored.（1）In this study,a composite catalyst of biochar modified with nZVI particles and MoS₂ nanosheets was synthesized by calcination and hydrothermal methods.Due to the synergistic effect of the bimetallic base,nZVI/MoS₂-BC exhibited better PMS activation performance.When the dosage of nZVI/MoS₂-BC was 0.10 g/L and the dosage of PMS was 0.325 m M,rhodamine B was efficiently degraded within 60 min,and the removal rate reached 100%.In the experiment of influencing factors,the suitable pH range of nZVI/MoS₂-BC peroxymonosulfate oxidation system was 3～9,and Cl^-could improve the degradation reaction rate of nZVI/MoS₂-BC activated PMS oxidation system.The interaction of Fe-Mo bimetallic based materials during the preparation process could improve the content of MoS₂ and dispersion of nZVI,increase the catalytic site of PMS activation and accelerate the electron transfer between substances in the reaction.The results of quenching test,EPR test and electrochemical test showed that there were non-radical pathways（surface electron transfer and ¹O₂）and radical pathways（SO₄·^-,·O₂^-and·OH）in the catalytic oxidation reaction.The recycling experiments of nZVI/MoS₂-BC and the degradation experiments of different types of pollutants proved that the catalyst had good reusability and universality.Compared with the single H₂O₂ or PMS oxidation system,the H₂O₂/PMS combined oxidation system significantly improved the pollutant removal efficiency and shorten the reaction time by changing the dosing interval and dosage ratio of two oxidants.According to the intermediates of rhodamine B,the degradation pathway of rhodamine B in nZVI/MoS₂-BC activated H₂O₂/PMS combined oxidation system was proposed.（2）On the basis of nZVI/MoS₂-BC materials,different series of catalysts were synthesized by changing the preparation conditions.Due to the different relative content of each component between Fe,Fe₃O₄,Fe S₂ and MoS₂,the catalytic performance would also show great differences.Among them,the Fenton system of Fe7.5/Mo1.0@BC700exhibited efficient catalytic oxidation ability.The influencing factors of the Fenton system of Fe7.5/Mo1.0@BC700 showed that the optimum dosage of H₂O₂ in 10 mg/L rhodamine B solution was 0.3 m M,the dosage of Fe7.5/Mo1.0@BC700 was 0.10 g/L,and the suitable pH range was 3～7.Cl^-and NO₃^-promoted the degradation of pollutants in the Fenton system of Fe7.5/Mo1.0@BC700,while the inhibition effects of CO₃^2-and HPO₄^2-were significant.By changing the number of H₂O₂ dosing times and the interval time of H₂O₂ dosing,it was found that the Fenton system of Fe7.5/Mo1.0@BC700enhanced the degradation ability of pollutants and the removal effect of TOC,and helped to slow down the decline of catalyst activity after recycling.The Fenton system of Fe7.5/Mo1.0@BC700 efficiently removed different types of refractory organics,indicating the universal adaptability of Fe7.5/Mo1.0@BC700.The results of quenching experiment and EPR test showed that there were·OH,·O₂^-and ¹O₂ in the Fenton system of Fe7.5/Mo1.0@BC700.Combined with XPS analysis and degradation experiment,the mechanism of H₂O₂ activation by Fe-Mo bimetallic synergy was proposed.The catalytic mechanism of H₂O₂ was mainly divided into two stages.The first stage was that Fe S₂was oxidized in water to form Fe SO₄,and the dissolved Fe（II）ions dominated the homogeneous Fenton reaction.The second stage was the process of deep degradation of pollutants by heterogeneous Fenton reaction on the surface of Fe7.5/Mo1.0@BC700.