Study On Performance And Mechanism Of Efficient Fenton-like Reactions Induced By Dual Reaction Centers For Refractory Organics Removal In Water

The circulation of active sites is the key factor affecting the catalytic reaction rate in Fenton-like reaction based on H2O2 and PMS activation.The electrons required for the reduction of active sites on the catalyst mainly depend on the oxidation of H2O2 and PMS.This reaction is very slow,producing superoxide radicals and peroxide species with weak oxidation capacity,which limits the degradation rate of pollutants and the effective utilization of H2O2 and PMS.Therefore,solving the electron supply problem of active sites is the key to break through the above limiting factors.The essence of Fenton-like oxidation is the electrons transfer from pollutants to H2O2/PMS on active sited via catalyst mediating.By framing the electron-deficient/rich dual-reaction-center on the catalyst,we realized the directional transmission of electrons from the pollutant→dual-reaction-center→H2O2/PMS,utilizing the electrons of the pollutant to drive high-efficiency H2O2/PMS activation and pollutant conversion and degradation.At the same time,the construction of dual-reaction-center was also successfully applied to the photo-Fenton system,which promoted the separation of photogenerated carriers and the activation of PMS.1.Surface oxygen vacancy(VO)-rich ZnFe0.8Co0.4O2.4 nanoparticles were prepared and characterized,which exhibited high activity and stability for refractory pollutant degradation with PMS activation.It was found that PMS([O3S-OⅠ-OⅡ-H]-)could be adsorbed and trapped by the surface oxygen vacancies in the form of OⅠ-VO or OⅡ-VO during the reaction.Different electron transfer pathways from Vo to different O sites of PMS was realized in the solid-liquid interface based on the generation of ·OH,SO4·or H2 from PMS reduction.Pollutants were predominantly adsorbed at metal Co sites in which their electrons were captured by metal species and then transferred to the surface oxygen vacancies,achieving efficient recycling of electrons in the aqueous suspensions.This system achieved a dual-pathway degradation of pollutants and electron transfer from pollutants to PMS to produce free radicals and H2,essentially changing the traditional concepts of pollutants removal and providing a sustainable strategy for pollutant utilization during water purification.2.To achieve high efficiency and low consumption for water treatment in the Fenton reaction,we use the surface oxygen vacancies(VO)as the electron temporary residences to construct a dual-reaction-center(RDC)Fenton-like catalyst with abundant surface electron-rich/poor areas consisting of Vo-rich Co-ZnO microparticles(Vo-CoZnO MPs).The lattice-doping of Co into ZnO wurtzite results in the formation of VO with unpaired electrons(electron-rich VO)and electron-deficient Co3+ sites according to the structural and electronic characterizations.Both experimental and theoretical calculations prove that the electron-rich VOS are responsible for the capture and reduction of H2O2 to generate hydroxyl radicals,which quickly degrades pollutants,while a large amount of pollutants are adsorbed at the electron-deficient Co3+ sites and act as electron donors for the system,accompanied by their own oxidative degradation.The electrons obtained from the pollutants in the electron-deficient sites are transferred to the VO through the internal bond bridge to achieve the balance of electron gain/loss.Through this process,pollutants are efficiently converted and degraded by multiple pathways in a wide range of pH(4.5-9.5).This discovery provides a sustainable strategy for pollutant utilization,which shows new implications for solving the troublesome issues of the Fenton reaction and for developing novel environmental remediation technologies.3.A novel strategy by coating Cu-F complex on the surface of zinc oxide to drive photocatalytic pollutant degradation and accelerated PMS activation under visible light was practiced.Multiple pollutants could be degraded rapidly by the Cu-F complex coated zinc oxide(CuF-ZnO)with visible light irradiation.The surface Cu-F complex was accountable for the enhanced photoresponse of CuF-ZnO.A very unique photocatalytic mechanism involving photoinduced hole(h+)injection from the photoexcited Cu-F complex to the valence band of ZnO was revealed by a series of detection of photogenerated reactive oxygen species,electrochemical properties and DFT calculation of the materials.The photoexcited ligand to metal charge transfer(LMCT)from F to Cu in Cu-F complex leaded to the formation of unstable Cu+ and F0 under visible light.The former could use organics as electron acceptor to form organic radical and the latter with high oxidability induced to inject to the valence band of ZnO.The ·OH generating from the oxidation of H2O by the h+ on the valence band of ZnO played the key role in pollutant remove.PMS served as the better electron acceptor for photoexcited Cu+in Cu-F complex which prevent the recombination of photogenerated carriers,meanwhile,the LMCT from F ligand to Cu promoted the electronic loop of Cu site thus accelerated the activation of PMS.This study provided a peculiar sight of enhancing photocatalysis in water treatment.4.Orbital interaction involving metal cation-π is an important form for electron transfer regulation.To accelerate the interfacial electron transfer of peroxymonosulfate(PMS)activation for water treatment,we report a new strategy through bonding atomically dispersed cobalt with nanospheric C-based graphene-like structures(SACoNGs)to form metal cation-π structure,driving rapid and directional transfer of the electrons of pollutants to PMS on the catalyst surface.The catalyst SACo-NGs is synthesized by an enhanced hydrothermal-sintering method and the formation of metal cation-π structure is demonstrated by X-ray absorption fine structure(EXAFS),X-ray photoelectron spectroscopy(XPS),electron paramagnetic resonance spectroscopy(EPR)and Raman spectroscopy.It is found that Co-π structures(Co2+-N-Cπ play a key role for the efficient activation of PMS,which results in pollutants being greatly removed in a few minutes.During the reaction,pollutants can donate electrons for the system through π-π interaction accompanying by the direct oxidative degradation of pollutants.The obtained electrons are quickly transferred to the atomically dispersed cobalt sites through the formed cation-π structure,which promotes the activation of PMS.This is a successful practice in the field of PMS activation using cation-π structure to accelerate electron transfer and achieve rapid degradation of pollutants.