Study On Recycling Of Co,Mo₂C Co-Doped Biochar In Pollutant Removal And Nitrobenzene Reduction

Environmental problems caused by the vigorous development of economy are becoming more and more serious,especially water environment pollution,which is closely related to human production and life.As one of the most common pollutants,dyestuffs not only affect the ecological security,but also threaten human health.However,the traditional biological treatment is not effective in removing it,so it is urgent to develop a new process.Advanced oxidation processes（SR-AOPs）based on sulfate radicals(SO₄^·-)have been noted for being both efficient and clean.Active species during SR-AOPs are usually derived from the activation of Peroxymonosulfate（PMS）.Transition metals are effective activators of PMS,but they are prone to leaching of metal ions,agglomeration of nanoparticles and secondary pollution to the environment,so they usually need to be supported on other support to form heterogeneous catalysts.Biochar（BC）is a good nanoparticle carrier with a wide range of sources and low cost.Its excellent conductivity and abundant porous structure are conducive to electron transport and organic pollutant adsorption,respectively.In this paper,biochar is obtained by pyrolysis of waste biomass,and then it is combined with transition metal to obtain biochar based nanocomposite material,which is used to activate PMS.The failed composite catalyst is recycled for nitrobenzene reduction and finally tried to be used for PMS activation again.This strategy can realize the recycling and efficient utilization of catalysts in sewage treatment and chemical production.Specific research contents and results are as follows:1.Biochar co-doped with Co and Mo₂C is used to activate PMS to degrade methylene blue（MB）.Co has excellent PMS activation performance,and Mo stands out among non-precious metals due to its abundant reserves,unique properties and relative environmental friendliness.Therefore,in this study,Co and Mo were selected to doping biochar derived from Pusselgrass.The obtained Co,Mo₂C@BC,has excellent PMS activation ability,and the removal rate of MB can reach 99.36%in 15min.The synergistic effect between Co and Mo₂C was proved by changing the doping components,and Mo₂C was proved to be more conducive to the activation of PMS than other Mo species by changing the annealing temperature.The quenching results indicate that O₂^·-and ¹O₂ are the main active species.A series of characterization results show that Co is the main electron donor in the system,while Mo₂C completes electron transfer through its own three-valence cycle.2.Co,Mo₂C@BC recovery and reuse in nitrobenzene reduction.PMS activators are deactivated due to surface oxidation and active metal leaching in the reaction process,and generally need to be regenerated before reused.Different from the conventional practice,the materials used in the PMS activation process were directly reused as the catalyst for the reduction of nitrobenzene with hydrazine hydrate in this study,and the conversion rate of nitrobenzene could reach 96.74%in 20 minutes.Through a series of characterization methods,it is known that the excellent catalytic performance is due to the appearance of metal oxide species（CoO、MoO₂、MoO₃）and the increase of C=O in the material.The interfacial structure of metal oxides can dynamically stabilize the in-situ hydrogen species through the synergistic action of metal and acid-base sites to avoid its binding into gas spillover.3.Co,Mo₂C@BC regeneration and recycling.The catalyst deactivated after nitrobenzene reduction process was regenerated by heat treatment,and then used for PMS activation to complete the construction of closed-loop.The MB removal rate of the unregenerated catalyst was 19.38%in 15min,while the MB removal rate of the regenerated catalyst was 79.42%in 15min,and basically complete removal in 35min（removal rate 96.80%）.By analyzing the changes in the composition and properties of Co,Mo₂C@BC at each stage,it is found that the reduced components（such as Co,Mo₂C）are favorable to the oxidation process（electron transfer from catalyst to PMS）and unfavorable to the reduction process（electron transfer from hydrazine hydrate to catalyst）.Oxidation state components（such as CoO,MoO₂,MoO₃）favor the reduction process but not the oxidation process.