The Study Of Co-N-MoO₂ And Fe@CO/NC Modified Graphite Felt Cathode For Electro-fenton Removing Of EDTA-Ni

Ethylenediaminetetraacetcic acid?EDTA?is widely used as a powerful chelating agent in the electroplating industry.Due to strong chelating between EDTA and toxic nickel ions,EDTA-Ni complexes exhibit poor biodegradable performance and high persistence over a wide range of environment.At present,the removal of nickel ions from chelating wastewater by conventional chemical precipitation technologies,including direct neutralization precipitat io n and sulfide precipitation is very difficult.Therefore,it needs to explore an efficient treatment technology of EDTA-Ni complexes.Electro-Fenton process have attracted great attention due to the in-situ generation of H₂O₂ at cathode.But the selection and modification of the cathod ic material can directly affect the removal efficiency of EDTA-Ni in the electro-Fenton system.It was found that the metal/nitrogen-doped matrix material could regulate and enhance the electrochemical active sites of the catalyst,and nitrogen-doped metal core-shell carbon materials could directly obtained from the metal-organic framework-derivative which was prepared by calcination under nitrogen atmosphere.The obtained composite material not only maintains the original framework structure but also has excellent oxygen reduction reaction?ORR?performance.In this study,MoO₂ and ZIF-67 were used as precursors to prepare Co-N-MoO₂ and Fe@Co/NC for modified graphite felt cathodes.Two kinds of cathodic electro-Fenton system of modified graphite felt were constructed.The influence of heteroatoms on the basic properties of composite catalysts and the degradation of EDTA-Ni were studied.The mechanism of this system was analyzed combining experimental data.It provided data support and theoretical basis for the treatment of EDTA-Ni,and paved the way for electro-Fenton system to practical applications.In this experiment,a non-precious metal ion Co/N-doped MoO₂ nanowire?Co-N-MoO₂?was prepared through a pyrolysis reaction with cobalt acetate and dicyandiamide precursors,and coated on a graphite felt cathode.The prepared catalysts were characterized by XRD,XPS and SEM.It was proved that the Co/N-doped caused the distortion of the MoO₂ crystal lattice,which brought more active sites and oxygen vacancies.Electrochemical analysis showed that Co-N-MoO₂ had good ORR performance,low reduction potential?-0.157V vs.Ag/AgCl?,higher electrochemical active area(EASA:3.917 mC·cm^-2).Under pH=3,the highest ring current was more than 35 times of that pure phase MoO₂.The results of the electro-Fenton system showed that the removal efficiency of EDTA-Ni reached 70.2%after 120 min reaction at pH=3,which was higher than that of the bare controlled group.The free radical quenching experiment clarified that the main function of the electro-Fenton system was hydroxyl radicals?·OH?,highly reactive·OH could degrade and mineralize EDTA-Ni to small organic molecules.Although the modification of cathode can effectively improved the removal efficiency of EDTA-Ni in electro-Fenton process,the addition of ferrous ions may cause subsequent irons mud treatment and the limitation of applied pH.To address these issues,ZIF-67 was chosen as a template,and metal-nitrogen-carbon composites?Fe@Co/NC?with different iron doped amounts?0%,2.5%,5%,10%?were prepared by means of pre-synthetic metal doping in this study.The change of morphology and valence of the element after doping were characterized by SEM,XRD,XPS,and the electrochemical properties were analyzed by electrochemic a l analysis.The Fe@Co/NC/GF electrodes were prepared by brushing.The electrodes were first applied to the cathode in electro-Fenton process.Based on the idea of H₂O₂ and heterogeneous Fenton reagents,Fe@Co/NC/GF-electron Fenton system were constructed.Simula te wastewater EDTA-Ni was set as the target pollutant,and the degradation effects of differe nt iron doped amounts were studied.Batch experiments were conducted to investigate the effect of application current,pH value,electrolyte concentration and other factors on the degradation of EDTA-Ni,and the stability of the electrode material was discussed.The main mechanism of EDTA-Ni degradation of electro-Fenton system was elucidated through radical screening experiments.The results showed that 5%Fe@Co/NC had the highest content of pyridine nitrogen?2.42%?and graphite nitrogen?3.23%?,which effectively improved the oxygen reduction performance of the catalyst.The degradation of EDTA-Ni has reached 98%by 5%Fe@Co/NC/GF in electro-Fenton system at pH 3,the electrolyte concentration of 0.1 M,and application current of 40 mA.Furthermore,this system effectively broadened the pH response range.Stability experiments showed that 5%Fe@Co/NC/GF could be used as a cathode and has good stability.