Peroxymonosulfate Activation By Nitrogen/Sulfur Doped Porous Carbon Materials For Degradation Of Organic Pollutants

Water pollution is a worldwide problem that poses a serious threat to human health and the environment.It is caused by the arbitrary discharge of toxic and non-biodegradable pollutants from agriculture,industry and human activities.Contaminated water may contain persistent organic pollutants that are difficult to be eliminated,such as azo dyes,endocrine disruptors,and antibiotics.Advanced oxidation processes（AOPs）can oxidize refractory organics into low-toxicity or non-toxic small molecules,among which activated peroxymonosulfate（PMS）-based AOPs are widely used due to their relatively low cost and high reactivity.Carbon based catalyst for activating persulfate has good application prospects due to the advantages of low cost,abundance,easy availability,no secondary pollution,and good stability.In order to improve the performance of carbon-based catalysts,the strategy of non-metallic heteroatom doping is usually employed.But the current doping process has the problems such as uneven distribution of heteroatoms,low element content,and complex process.In this study,we attempt to prepare the in-situ sulfur-doped hierarchical porous carbon materials by direct pyrolysis of sodium lignosulfonate,and explored the co-carbonization reaction of trisodium citrate and thiourea to achieve nitrogen-sulfur co-doping of porous carbon materials.In addition,the performance and mechanism of the prepared catalyst to activate PMS were investigated.First,in situ sulfur-doped hierarchical porous carbon material（SHPC-T）was prepared by direct carbonization of sodium lignosulfonate at 700℃-900℃.The catalytic performance of SHPC-T was evaluated by activating PMS to degrade bisphenol A（BPA）.SHPC-800 prepared at 800℃ showed the best catalytic performance.The removal rate of BPA in 5 min reached more than 98%,and it was suitable for a wide pH range（pH 3-9）.The excellent performance of SHPC-800 is closely related to its high specific surface area(1215.5 m²g^-1),uniformly distributed pore structure and the highest sulfur doping content（4.54%）.The hierarchical porous structure and high specific surface junction are favorable for the adsorption and exposure of catalyst active sites,and the high sulfur doping content provides more active sites.Singlet oxygen（¹O₂）was determined to be the dominant active species,and thiophene sulfur was identified as the catalytic site.SHPC-800/PMS system can also effectively degrade various organic pollutants,which possess the potential in the application of the treatment of organic waste water.Second,nitrogen-sulfur co-doped porous carbon（NSPC）was synthesized by freeze-drying the solution of trisodium citrate and thiourea followed by the co-carbonization process.Compared with pristine porous carbon（PC）and nitrogen-doped porous carbon（NPC）,NSPC exhibited the best catalytic activity for PMS,and BPA was completely degraded within 12 min.The excellent catalytic activity of NSPC is closely related to its structural composition,and the largest specific surface area(906.8 m²g^-1)and higher nitrogen doping content（8.52%）,which are beneficial to the adsorption of BPA and the activation of PMS.And additionally doped sulfur will increase the nitrogen doping amount,thus providing more active sites for PMS activation,and achieving the synergistic effect of nitrogen and sulfur co-doping.The quenching experiments showed that singlet oxygen（¹O₂）was the main active species,indicating that the degradation of BPA mainly followed a non-radical oxidation pathway.This study provides a greener and facile route to design high-performance carbon catalysts for environmental remediation.In summary,both in-situ doped sulfur hierarchical porous carbon and exogenously doped nitrogen-sulfur doped porous carbon catalysts have the advantages of facile synthesis,high activity and high stability,and can be used in AOPs technologies for activating PMS.The designed catalyst has good application prospects in the field of organic wastewater treatment.