Nano-flakes Of Nickel-cobalt Bimetallic Oxide For Persulfate Activation To Degrade Organic Pollutant

Persulfate（PS）-based advanced oxidation technology has attracted wide interests in the field of wastewater treatment due to the advantages of high degradation efficiency,fast reaction rate,and adaption to wide p H range.Among many PS activation methods,transition metals related heterogeneous catalysts have high catalytic activity without energy input,hence exhibiting a promising application prospect.Compared to mono-metallic oxides,the catalytic activity and stability of poly-metallic oxides are significantly improved.Therefore,nano-fakes of nickel-cobalt bimetallic oxide（Ni-Co BO）catalysts are fabricated and applied to activate persulfate（PDS）to degrade organic pollutants.The performance of Ni-Co BO catalyst is optimized by regulating the pyrolysis temperature and the ratio of cobalt to nickel.The active species of the reaction are identified,the mechanisms of PDS activation for the degradation of organic pollutant bisphenol A（BPA）are analyzed,and the environmental adaptation of the catalyst is evaluated.The purpose of this research was to prepare a two-dimensional bimetallic oxide nano-fakes material with great activation performance for PDS and good environmental adaptability,providing a new idea for the development of PS activation heterogeneous catalyst.The main results are as follows:1.Ni-Co di-hydroxide precursor was synthesized by hydrothermal method,and Ni-Co BO catalyst was obtained by pyrolysis of the precursor.Scanning electron microscopy（SEM）results showed that the morphology of Ni-Co BO was regular hexagonal nano-flakes;Brunner-Emmet-Teller（BET）results showed that the material had a large specific surface area and the porous structure was dominated by mesopores.The results of inductively coupled plasma spectroscopy（ICP-OES）and X-ray photoelectron spectroscopy（XPS）showed that the prepared catalysts had different Ni/Co ratios.The X-ray diffraction（XRD）results showed that the crystal phase of the catalysts changed from Ni Co₂O₄ to Ni O with the increase in Ni/Co ratio.2.The effects of pyrolysis temperature（250,300,400,500^oC）and Ni-Co ratio（0.2:1,0.25:1,0.5:1,1:1,1.5:1,2:1,3:1,4:1,6:1）on the catalytic performance of Ni-Co BO were investigated.The results showed that the catalytic activity of the catalysts pyrolyzed at 250^oC was poor,mainly due to the incomplete decomposition of oleylamine in the precursor.The catalytic activity decreased with the increasing temperature over 300-500^oC.The optimized pyrolysis temperature was 300^oC,and BPA could be completely degraded within 20 min using the Ni-Co BO catalyst pyrolyzed at 300^oC.The catalytic activity firstly increased and then decreased with the increase in Ni/Co ratio.Ni:Co（1.5:1）showed the highest degradation efficiency to BPA,whose first-order kinetic reaction rate constant was 0.23 min^-1.3.The mechanisms of PDS activation by Ni:Co（1.5:1）for BPA degradation was investigated.Quenching experiment,electron paramagnetic resonance（EPR）and electrochemical analysis showed that Ni-Co BO mainly activated PDS via non-free radical pathway,that the catalysts combined with PDS to form surface-activated complex to degrade the pollutants by electrons attraction.4.The influence of environmental factors（temperature,p H,background ions,natural organic matter）on BPA degradation were studied,and the degradation efficiencies of different pollutants and packaging wastewater in Ni:Co（1.5:1）/PDS system were evaluated.The results showed that Ni:Co（1.5:1）had a good catalytic activity in the p H range of 5.5-9;The degradation rate of BPA was elevated by increasing the reaction temperature,and the activation energy of the reaction was determined to be 24.69 k J/mol;Cl^-and NO₃^-had insignificant effects on BPA degradation;Low concentration of HCO₃^-（1 m M）and humic acid barely influenced BPA degradation,but high concentration of HCO₃^-（over 5 m M）and humic acid slightly inhibited the degradation of BPA;Ni:Co（1.5:1）showed a high degradation efficiency to electron-rich pollutants（BPA,p-chlorophenol,phenol,etc.）.A good decolorization effect for actual packaging wastewater was obtained by using Ni-Co BO catalyst,realizing the complete decolorization and 28.28%of TOC removal after6 hours of reaction.5.The reusability and stability of Ni-Co BO catalysts were evaluated.The degradation efficiency of BPA decreased to 67.03%during the second cycle,mainly due to the coverage of active sites by degradation intermediates.The structure of the catalysts remained stable after reaction,and the catalytic activity could be recovered to 100%after facile thermal treatment.