| With the rapid development of industrialization and urbanization and the extensive use of herbicides,ever-growing organic compounds are released into the environment,resulting in water pollution.Some organic s are non-biodegradable and persistent,which pose a huge threat to human health and ecosystems.In recent years,advanced oxidation processes based on permonosulfate(PMS)has received widespread attention,but PMS needs to be activated to produce highly reactive species,which can degrade organic pollutants into low-toxic or harmless small molecule substances,carbon dioxide and water.There are many me thods for activating PMS.Among them,the method of activating PMS by metal or carbon catalysis has become a research hotspot at home and abroad due to its high efficiency and low cost.However,the metal activation method has the problems of metal dissolution and the carbocatalytic activation method has problems such as insufficient catalytic activity and unclear catalytic mechanism,which hinders the engineering application of such activation methods.Aim at the above problems,new catalytic PMS activation systems were constructed in this study,and the degradation performance characteristics of the new system for organic pollutants in wa ter were systematically studied and the degradation reaction mechanism was explored in depth.The results show that the new system constructed not only achieves the goals of high catalytic performance and low or no metal dissolution,but also the involved degradation reaction mechanism is clarified.The main contents and results are as follows:In Part 1,the efficiencies and mechanisms of atrazine degradation by ferrate(Fe(VI))/PMS system were investigated.The results showed that In comparison with Fe(VI)or PMS alone,Fe(VI)/PMS process significantly enhance d the degradation of atrazine,and its degradation efficiency was higher than that of Fe(VI)/persulfate or Fe(VI)/H2O2 system.Complete degradation of atrazine at an initial concentration of46.5?M could be achieved within 20 min at initial conditions of 6.0 m M Fe(VI),5.0m M PMS,p H 6.0 and 25°C.Moreover,Fe(VI)/PMS system could work effectively in a wide p H range(5-9).Dissolved organic matter concentration below 4.0mg/L was favorable for the degradation of atrazine.The results of electron spin resonance spectroscopy(ESR)and quenching experiments indicated that·OH and SO4·-were simultaneously produced during the Fe(VI)/PMS process,while SO4·-was the dominant radical responsible for atrazine degradation.The mechanisms of PMS activation were elucidated on the basis of the results of XRD and XPS.In addition,fourteen intermediates from atrazine degradation were identified by LC-MS,and consequently the degradation pathways were proposed.(Corresponding to Chapter 2of the article)Part 2 takes the perovskite oxide lanthanum ferrite(La Fe O 3)as an example to study the effects of support on the structure and performance of the catalyst.The results showed that the degradation efficiencies of acid orange II by PMS activation using supported La Fe O3 were in an order of La Fe O3/Al2O3(86.2%)>La Fe O3(70.8%)>La Fe O3/Ce O2(59.0%)>La Fe O3/Si O2(52.3%)>La Fe O3/Ti O2(32.2%).Moreover,compared with La Fe O3,the pseudo first-order rate constant of La Fe O3/Al2O3 was increased by 3.2 times.The enhancement was due to its large specific surface area,abundant chemisorbed surface-active oxygen,enhanced redox and electron transfer capabilities in La Fe O3/Al2O3.Degradation efficiency and iron ions leaching both decreased with the increase of p H.Data from ESR spectra and quenching experiments revealed that·OH and SO4·-were produced on the surface of La Fe O3/Al2O3,while SO4·-played a key role in degradation.Subsequently,the mechanism of PMS activation was proposed.In addition,La Fe O 3/Al2O3 showed great stability during five cycles.(Corresponding to Chapter 3 of the article)In Part 3,to address the problem of metal dissolution in the above studies,magnetic nitrogen-doped porous carbon(Co-N/C)was prepared by direct pyrolysis of ZIF-67 precursor and acid etching.The residual metal Co was integrated into the carbon layer,thereby achieving extremely low Co dissolution.Subsequently,the performance,intermediates,mechanism and toxicity of tetracycline degradation were thoroughly examined.Results indicated that Co-N/C could effectively activate PMS to degrade tetracycline from aqueous solutions and its performance was better than most reported catalysts.Integrated with quenching experiments,ESR spectra,chemical probes and premixing experiment,it was confirmed that singlet oxygen(1O2)played a vital role in the degradation of tetracycline.The effects of p H value(3-9),water components(dissolved organic matter,Cl-,SO42-and NO3-)and actual water matrix on the degradation could be negligible.Interestingly,although increasing the reaction temperature could accelerate the activation efficiency of PMS alone,the degradation of tetracycline in the Co-N/C-PMS system was more favorable at low temperatures.Based on three-dimensional fluorescence excitation-emission matrix spectroscopy and LC-MS technology,the degradation behavior of tetracycline was analyzed and a possible degradation pathway was deduced.At last,the microalgae Coelastrella sp.was used as an ecological indicator to assess the changes in toxicity during degradation.(Corresponding to Chapter 4 of the article)In Part 4,iron and nitrogen co-doped porous carbon(Fe-N/C)were delicately prepared by in-situ doping Fe into the zeolite imidazolate framework(ZIF-8)and calcination.The doped iron was highly dispersed in the carbon matrix without agglomerated iron particles,leading to the detection of no iron ions in the catalytic system.Moreover,Fe-N/C at an appropriate Fe doping(0.5-5.0%)possessed hierarchically porous architecture,rich structural defects,enhanced N-doping efficiency and conductivity.Compared with N/C,Fe-N/C retained the original polyhedral morphology and the particle size could be tuned by controlling Fe doping amount.When the Fe doping content was 1.0%,1.0%Fe-N/C exhibited the optimal catalytic activity for the degradation of bisphenol F.It pseudo first-order rate constant was 34.0 and 6.1 times that of N/C and benchmark catalyst Co3O4,respectively.More importantly,the 1.0%Fe-N/C-PMS system was not affected by p H and common water components,and had high selectivity for degradation of organic pollutants.The mechanism of PMS activation by 1.0%Fe-N/C was examined with chemical,electrochemical and physical analyses(chemical probes,solvent exchange,ESR spectra and quenching experiments).The results confirmed 1O2 was the primary reactive species responsible for the degradation.Therefore,the carbocatalyst prepared by in-situ metal doping not only obtained excellent degradation performance,but also avoided the dissolution of metal ions.(Corresponds to Chapter 5 of the article)Part 5 explored the structure-activity relationship of transition metals and co-doped carbon activators based on the research in Parts 3 and 4.In this study,a series of metals and nitrogen co-doped porous carbons(M-N/C,M=Fe,Co,Cu,and Mn)derived from in-situ metal-doped ZIF-8 were synthesized.The results showed that the activity of doped carbocatalysts for PMS was Fe-N/C>Co-N/C>N/C>Cu-N/C>Mn-N/C.In particular,compared with undoped N/C,doping with Fe and Co endowed the carbocatalysts with the enhancemen t of performance by 2.5-22.4 and1.5-19.5 folds for various contaminants,respectively.The improved catalytic performance may be attributed to smaller nano-size,increased volumes of mesopores and macropores,abundant structural defects and active N species.Further investigations demonstrated structural defects,graphite N and metal-Nx are the key catalytical active sites for 1O2-dominated non-radical pathway.Interestingly,although Fe-N/C had higher catalytic performance than Co-N/C in ultrapure water,the latter showed significant advantages in practical water applications.In addition,seven intermediates of sulfamethazine degradation were identified by LC-MS technology and possible degradation pathways were deduced.(Corresponds to Chapter 6 of the article)... |
PDF Full Text Request