Modified Carbon-based Catalyst Activated PMS To Degrade Emerging Contaminants Such As Bisphenol A

Emerging contaminants(ECs)are frequently detected in water environment,posing a threat to ecological environment and human health.Due to their low concentrations and biological toxicity,traditional wastewater treatment processes struggle to completely remove them.Advanced oxidation technology based on peroxymonosulfate(PMS)boasts strong oxidizing active species,a wide pH adaptation range,low transportation and storage costs,and has demonstrated great potential in the removal of emerging contaminants.Transition metalbased catalysts exhibit high efficiency in activating PMS,but their use poses environmental risks due to the potential for metal ion leaching.Carbon-based catalysts are widely used as substitutes for transition metal-based catalysts due to their lower cost and superior environmental benefits.However,the structure-activity relationship between the active site and oxidation pathway of carbon-based catalysts is still controversial.Carbon-based catalysts have low catalytic activity,poor stability and difficult to recovery.These limitations impede the development and application of highly active carbon-based catalysts.To solve these problems,two types of modified carbon-based catalysts were prepared by doping and structure modification.Using bisphenol A(BPA)as a representative of ECs,the properties of the catalysts for activating PMS were systematically investigated;the structure-activity relationship between the active sites and oxidation pathways of different catalysts was analyzed,and the practical application potential of the modified carbon-based catalysts was investigated.The main research results are as follows:(1)Dopamine-derived iron-nitrogen co-doped carbon-based complex catalysts(DH@Fe3C-X)were synthesized by carbonization using dopamine and Fe3O4 as precursors.The DH@Fe3C-7(carbonization at 700℃)exhibits the best crystal structure of Fe3C,the highest nitrogen doping content,and can completely remove BPA within 40 min.Metal and nitrogen doping polarize the charge distribution of the original carbon material,giving it higher catalytic activity,promoting Fe2+/Fe3+cycling,providing electrons for PMS decomposition to produce oxidation species(SO4·-,·OH,and 1O2).The uneven charge distribution of DH@Fe3C7 allows it to accept electrons from PMS and BPA,facilitate the generation of Fe(Ⅳ)species,and degrade BPA through electron transfer pathways.The DH@Fe3C-7/PMS system is applicable in a pH range of 3.0～11.0 and exhibits low interference from anions(Cl-,SO42-,NO3-,HCO3-)and humic acid.About 72%BPA removal capacity was maintained after 5 cycles,and iron dissolution was less than 0.25wt%of catalyst mass.In river water substrate,DH@Fe3C7/PMS system can also remove 80%BPA within 40min,which have good application prospects.(2)The above work found that dopamine can be used as an optimal precursor for the synthesis of in situ nitrogen-doped carbon(PDA-C).However,its catalytic activity remains low and the problem of metal ion dissolution still exists.Therefore,the structure of PDA-C was modified by template etching,and in situ nitrogen-doped hollow carbon spheres DNC-X were synthesized successfully.The hollow structure of DNC-X provides a larger surface area and exposes more active sites,facilitating the contact between pollutants and active sites,thereby enhancing its adsorption and catalytic activities.DNC-9 has high nitrogen doping content(7.37%),high degree of graphitization(ID/IG=0.9957),and large specific surface area(103.6703 m2/g).Its contaminant removal performance is comparable to that of some transition metal-based catalysts.DNC-9 can adsorb about 20%BPA and remove 100%BPA within 15 min,while also demonstrating efficient degradation in a wide pH range(3.0～9.0).DNC-9/PMS system mainly relies on non-free radical pathway(1O2 and electron transfer)to degrade BPA,and graphite nitrogen as the main active site can promote the decomposition of PMS to produce 1O2.The hybrid carbon skeleton(C=C/C-C)exhibits a high electron transfer rate,which,combined with the adsorbed PMS,leads to the formation of a highly active metastable complex DNC-9-PMS*.This complex effectively degraded BPA through the electron transfer pathway.(3)DNC-9 has the advantages of high catalytic activity and no secondary pollution to the environment.Therefore,the application potential of DNC-9/PMS system is further studied.DNC-9/PMS system demonstrates excellent tolerance towards various anions(Cl-,SO42-,NO3-,HCO3-,CO32-)and humic acids at different concentrations.After four cycles,the catalytic activity of DNC-9 decreased to 46%,but DNC-9 could still completely degrade BPA within 15 min after thermal regeneration treatment.DNC-9/PMS system is almost unaffected by river water matrix,and can be used for practical chemical wastewater treatment where many pollutants coexist.The column test results show that the removal rate of BPA can exceed 80%at a flow rate of 15 mL/h and a catalyst dosage of 10 mg.In conclusion,this paper prepared two kinds of highly active carbon-based catalysts through doping and structural modification to activate PMS to efficiently remove ECs from water environment.The mechanism of action and application potential of these catalysts in the catalytic degradation process have been discussed in detail,providing basis and theoretical support for the development of carbon-based catalyst activation PMS technology.