| Emerging contaminants(ECs)are constantly detected in surface water and groundwater,posing a threat to the ecological environment and human health.However,traditional sewage treatment technologies can’t effectively remove such ECs.In this paper,in order to efficiently degrade ECs in water,green and ecological magnetic nanoparticles were chosen as catalysts,and advanced oxidation technology based on permonosulfate(PMS)was carried out.Aiming at the key scientific issue of the low Fe2+/Fe3+ cycling efficiency of magnetic nanoparticles in the advanced oxidation processes,we innovatively proposed a strategy to modify magnetic nanoparticles using electron-rich materials(metal sulfides and carbon materials),and constructed a series of composites.The degradation efficiency of ECs was systematically investigated,and the structure-activity relationships of the catalysts in enhancing the degradation of ECs were elucidated.The main researches are as follows:(1)Metal sulfides such as MoS2 have strong reducibility,which can promote the metal ions cycle of magnetic nanoparticles and improve the catalytic activity.Firstly,the core-shell Fe3O4@MoS2 composite was constructed by modifying Fe3O4 nanoparticles with electron-rich MoS2,and the performance in activating PMS to degrade sulfonamide(SA)was evaluated.It was found that when Fe3O4 was modified with MoS2,the degradation efficiency of SA increased by 4 times and the rate constant increased by 86 times.Fe3O4@MoS2-3/PMS system exhibited high degradation efficiency(100%/5 min),fast degradation rate(1.3225 min-1),high mineralization(57.1%/15 min)and wide pH application range(3.0～9.0);It could quickly and completely degrade different types of pollutants such as pharmaceuticals and personal care products(SA,sulfadiazine and chloroxylenol),endocrine disruptors(bisphenol A and bisphenol S)and phenols(phenol and 2,4-dichlorophenol).Mechanistic studies showed that MoS2 acts as a co-catalytic role,and Mo4+ surf.accelerates the Fe2+/Fe3+cycle and improves the catalytic activity.Anions(Cl-,NO3-,SO42-)and natural organic matter(humic acid,HA)had weak interference on the catalytic activity.Real surface water had no significant effect on the catalytic performance.Fe3O4@MoS2 exhibited excellent practical application prospects.(2)Based on the consideration that the active center of WS2 is more reducible than that of MoS2.Subsequently,electron-rich sulfurized WO3(S-WO3)composed of WS2 and WO3 was synthesized,and Fe3O4/S-WO3 composite was constructed to explore the removal efficiency of chloroxylenol(PCMX)by activating PMS.It was found that the degradation efficiency of PCMX was increased by up to 16 times when Fe3O4 and S-WO3 were combined.80-Fe3O4/SWO3/PMS system achieved efficient decomposition of PMS(100%/5 min)and rapid degradation of PCMX(1.0982 min-1).The catalyst utilization efficiency reached 0.3506 mmol·g-1·min-1,which was higher than that of most iron-based heterogeneous catalysts.The system achieved high mineralization(45.4%/10 min),and the catalytic activity was not affected in the pH range from 3.0 to 9.0.The degradation efficiency of most pollutants such as pharmaceuticals and personal care products,endocrine disruptors and phenols was above 90%.The mechanism study showed that WS2 in S-WO3 plays a co-catalytic role,and active W4+surf.promotes Fe2+/Fe3+ cycle and improves catalytic activity.(3)Both MoS2 and S-WO3 have reduced metal active centers,while Co3S4 has both reduction ability and excellent PMS activation ability.In this paper,core-shell Fe3O4@Co3S4 composites with dual catalytic centers were constructed by using electron-rich Co3S4 to modify Fe3O4 nanoparticles.The efficiency of sulfadiazine(SDZ)degradation was investigated.Fe3O4@Co3S4-3/PMS system achieved complete PMS decomposition and 96.2%removal SDZ efficiency within 3 min;TOC removal efficiency of SDZ reached 55.7%within 30 min.The catalytic activity of the system was not affected in the initial pH range of 3.0～10.0.Fe3O4@Co3S4-3 exhibited good stability,the removal efficiency of SDZ could still reached 81.2%after 3 cycles reaction.The highest cobalt ion dissolution concentration only accounted for 1.65wt%of the catalyst mass.Both Co2+ surf.and Fe2+ surf.are active metal centers for PMS activation,and Co2+ surf.of Co3S4 accelerates the Fe2+/Fe3+ cycle and further improves the catalytic activity.(4)On the basis of the above work on metal sulfides and the consideration of alleviating metal leaching,the activation of PMS by carbon materials modified magnetic nanoparticles was also carried out.The mesoporous Fe3O4/GO composites were successfully constructed by insitu growth and encapsulation of Fe3O4 nanoparticles on electron-rich graphene nanosheets.The physicochemical properties of Fe3O4/GO composites and their SA removal performance were studied.It was found that Fe3O4/GO had excellent adsorption-oxidation activity.After Fe3O4 was modified,the SA removal efficiency in 0.4-Fe3O4/GO/PMS system increased by about 2.9 times,and the degradation rate constant increased by about 27.7 times.The adsorption efficiency was positively correlated with the pore volume,and the degradation rate constants were positively correlated with the surface areas.Cyclic experiments showed that the Fe3O4/GO/PMS system is an interfacial reaction,and the oxidation process takes place on the surface of the catalyst.Graphene encapsulation enables extremely low dissolution of iron ions(<0.00325wt%).The mechanism study showed that Fe3O4 and Fe-O-C bond are double reaction centers,and GO mainly plays a synergistic catalytic role.The SP2 hybrid C=C bond improves the electron transport efficiency,accelerates the Fe2+/Fe3+cycle and improves the reaction efficiency.(5)From an economic point of view,cheap and easily available biochar was used as modifier instead of graphene.Fe3O4 particles were in situ grown on chitosan and calcined to prepare Fe3C/C composites.The physicochemical properties of Fe3C/C composites and the removal efficiency of SA were studied.It was found that the Fe3C/C-3/PMS system could remove 80%of SA,and the degradation process was divided into two stages:fast and slow.The calcination temperature profoundly affected the carbon defect degree and nitrogen species of the catalyst.The activity of the fast/slow degradation stages were proportional to the defect degree of Fe3C/C-3 and the content of pyrrolic nitrogen,respectively.The activity of Fe3C/C3/PMS system was not affected in the pH range from 3.0 to 10.0.The mineralization reached 54.3%.Mechanism analysis showed that Fe2+ surf.was the main active site for PMS activation to generate HO· and SO4·-.Nitrogen-doped biochar accelerates electron transfer and promote the Fe2+/Fe3+cycle.The C=C bond,C=N bond and C=O groups of biochar also participate in the activation of PMS.Anions such as Cl-and SO42-and HA had no effect on the catalytic activity of Fe3C/C-3.Fe3C/C-3 still remained about 80%of its catalytic capacity after 5 cycles reaction.The coating effect of carbon layer greatly reduced the metal dissolution,and the maximum iron leaching mass was only 0.09wt%of the catalyst mass.The packed column experiment proved that Fe3C/C-3 can treat pollutants continuously for a long time,showing a good application prospect.In conclusion,from the perspective of promoting Fe2+/Fe3+ cycle efficiency and alleviating metal ion leaching,this paper applied electron-rich metal sulfides and carbon materials to modify magnetic nanoparticles to efficiently remove ECs in water via PMS activation.It is expected to provide theoretical and technical support for improving PMS based advanced oxidation technology through the modification strategies of using electron-rich materials. |
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