In-situ Synthesis Of "Nuclear-Shell" Structure Metal@Carbon Nanocomposite And Characterization Of Their Performances

Bisphenols(BPs),as a typical endocrine disruptor(EDC),may have adverse effects on human health(such as disruption of hormone secretion,carcinogenicity,mutagenicity,etc.).As bisphenols are commonly used in the production of polycarbonate plastics and epoxy resins,their widespread use and high durability make them widely used in the wastewater of these chemical companies and influent water of wastewater treatment plants.The treatment of wastewater containing BPs has also become a focus of attention in recent years.In recent years,Advanced oxidation processes(AOPs)have become the main method for the treatment of wastewater containing BPs because of their high efficiency in the treatment of refractory organic pollutants.In AOPs,persulfate(PS)or persulfate monosulfate(PMS)can be activated to generate a variety of free radicals to degrade refractory organic pollutants in water.Catalysts based on transition metals and precious metals(e.g.Co,Cu,Ag,etc.)are effective PS activators,but low reserves and leaching toxicity are issues that cannot be ignored.Metals Fe and Mn have the advantages of large reserves and low environmental toxicity,which have attracted the attention of researchers in recent years.However,it is unavoidable that they are directly immersed in water for reaction and will cause toxicity to water bodies,and their catalytic activation Performance also has higher requirements on the pH of the water.In order to solve these problems,various metal-supported catalysts have been successively developed.Nano-carbon materials,including two-dimensional carbon materials(such as graphene)and three-dimensional carbon materials(such as carbon nanotubes),are commonly used as carriers to form metal/metal oxide@carbon nanocomposites with transition metals,which can not only achieve metal fixation,It can also play a synergistic catalytic role.However,the complex synthetic process of metal/metal oxide@carbon nanocomposites and the agglomeration of nano metal particles during the preparation process have greatly limited their practical use in the environment.Therefore,based on a large number of relevant domestic and foreign literature,aming at solving high cost,complex synthetic processes,and high leaching toxicity of the shortcomings of the catalysts used in the above AOPs applications,this paper synchronously synthesized "Core-shell" metal/metal oxide@carbon nanocomposite catalysts(Fe@CNs,MnO@CNs)for degradation of refractory organic pollutants(BPA and BPF)in the water environment,and in-depth study of the degradation pathways and Degradation mechanism.The main research contents of this article are as follows:1.Using a sodium alginate hydrogel as a template,a core-shell iron-carbon nanocomposite catalyst(Fe@CNs)was synthesized in one-step synthesis and used for BPA degradation.The effects of synthesis conditions(calcination temperature,Fe3+crosslinking concentration)on the structure,morphology and catalytic performance of the composite catalyst were studied.It was found that Sodium alginate can well fix and disperse Fe3+ well;Fe nanoparticles in the composite catalyst are wrapped by a "carbon shell" and a three-dimensional carbon network adhered to the outer layer,which can effectively protect the leaching of metallic Fe and promote electron transport.With the increase of calcination temperature,the specific surface area,average pore size and volume of the catalyst increase,which is conducive to the rapid progress of the catalytic reaction.The effect of Fe3+cross-linking concentration on the catalytic performance of the catalyst indicates that an appropriate increase in Fe3+ concentration can promote the catalytic BPA degradation.However,the high concentration of crosslinking agent leads to more Fe0 particles in the catalyst,which reduces the Fe3C ratio and fails to achieve a better catalytic degradation effect.Therefore,by selecting Fe3+ cross-linking concentration of 0.3 M and calcining temperature of 1100℃,a better catalyst can be obtained.The performance of Fe@CNs activated PS to degrade BPA under different reaction conditions was also studied.The higher reaction temperature is beneficial to PS activation to generate more free radicals to improve BPA degradation.And the Fe@CNs/PS system has a wide adaptation range to the initial pH value of the solution.In the pH range of 3-11,Fe metal leaching is very little,which effectively reduces the secondary pollution to the environment.In addition,the effects of coexisting anions and organics(Cl-,HCO3-,H2PO4-and HA)and different water matrices on the Fe@CNs/PS/BPA system show that the system has better catalytic degradation performance in practical applications.Quenching experiments and EPR spectroscopy were used to study the major free radicals that play a role in the reaction,and it was confirmed that several free radicals(including ·OH,SO4·-,O2·-and 1O2)jointly lead to the decomposition of BPA.The degradation of BPA mainly involves the hydroxylation,ketonization,oxidation and ring cleavage of BPA.Cyclic experiments show that the catalytic activity of Fe@CNs used can be recovered after thermal regeneration(1100℃).2.Using a sodium alginate hydrogel as a template,a core-shell iron-carbon nanocomposite catalyst(MnO@CNs)was synthesized in one-step synthesis and used for BPF degradation.The results show that MnO@CNs has better catalytic degradation effect than Fe@CNs.The three-dimensional carbon network structure composed of the"carbon shell" of the MnO@CNs catalyst and multilayer carbon nanosheets is conducive to the transfer of electrons during the reaction.We have also studied the effect of calcination temperature on the structure and performance of the catalyst,and the results show that high temperature is beneficial to the graphitization of the sample and the formation of Mn7C3.The performance of this composite catalyst to activate PS to degrade BPF is highly efficient and stable,and it has good adaptability in a wide pH range and high salt concentration solution.Several actual water samples(deionized water,tap water,and secondary treatment wastewater)were selected to investigate the catalytic degradation effect of the MnO@CNs/PS system in practical applications.The results show that the system also has high degradation performance of BPF in actual water body,and has a high removal rate of TOC.In addition,cyclic experiments show that the catalyst has good cycle stability and its catalytic performance is completely restored at 800℃.Quenching experiments confirmed that MnO@CNs activated PS produced a large amount of O2·-(dominant effect),which together with ·OH,SO4·-and 1O2 acted on BPF degradation.The changes in the relative proportions of Mn2+,Mn3+and Mn4+in the Mn 2p spectrum of fresh,used and regenerated MnO@CNs and the Mn-O bond in the O 1s spectrum indicate that the activation of PS is accompanied by the redox cycle of metal Mn,which confirms the contribution of Mn valence changes to free radical generation in the MnO@CNs/PS system.The degradation of BPF in the MnO@CNs/PS system mainly includes reactions such as hydroxylation,oxidation,and ring cracking.We propose a potential degradation pathway based on the degradation intermediates of BPF.