| Nitrobenzene(NB)belongs to typical refarctory organic pollutant with high toxcity.The strong passivation of nitro makes the treatment of NB more difficult.Among various treamen technologies,persulfate advanced oxidation technology has become the best choic,and the construction of heterogeneous supported persulfate catalysts with high efficiency and no pollution is the focus of the research.Based on the unique channel structure of three-dimensional(3D)graphene and the catalytic reinforcement of nitrogen doping,in this study,a a series of Co3O4/nitrogen-doped 3D graphene(Co3O4/N-GN)were prepared by hydrothermal method using cobalt nitrate as precursor of active components through changing different conditions,which include nitrogen source,the mass ratio of nitrogen source to graphite oxide,the concentration of precursor,hydrothermal reaction temperature and time.Moreover,various modern analytical techniques were used to characterize the catalysts.Furthermore,through comparative experimental studies,the optimum preparation conditions were determined.Combining kinetic analysis,thermodynamic analysis and the kinetic results of free radical competition inhibition,the catalytic properties of the catalytic materials prepared under the optimal conditions were investigated in detail,and the activation mechanism was discussed.In addition,according to the complex characteristics of the actual wastewater water quality,the effects of various influencing factors on the performance of the catalytic oxidation system were investigated in detail,and the degradation pathways of nitrobenzene were analyzed to further verify the feasibility of the catalytic oxidation method.Specific conclusions were obtained as follows:(1)The catalysts prepared using acrylamide as the nitrogen source,and the mass ratio of acrylamide to graphite oxide was 10%,the concentration of the precursor was 15%,the hydrothermal temperature was 180?,and the hydrothermal time was 12h,had the best catalytic activity.The characterization results showed that nitrogen doping could regulate the size of Co3O4 nanoparticles,and form Co-N-C bond and various structural nitrogens.The pseudo-second order kinetic constant k and Ea for the degradation of nitrobenzene wastewater by Co3O4/3D N-GN/PMS were 0.0118 L/(mg-min),16.223 kJ/mol,respectively.In this oxidation system,SO4-·,·OH and singlet oxygen(1O2)existed together,compared with·OH and SO4-·,1O2 played a leading role.The formation of Co-N-C bonds can contribute to the stability of Co3O4,inhibit the dissolution of Co ion,and improve its catalytic stability.The results showed that SO4-·,·OH and singlet oxygen(1O2)existed together,compared with·OH and SO4-·,1O2played a leading role.The effective activation of Co3O4/3D N-GN for PMS was mainly attributed to the anchoring effect of Co-N-C bond on the active components and the catalytic synergy of structural nitrogen in the nitrogen-doped 3D grapheme carrier.Compared with pyrrolic and graphite nitrogen,pyridine nitrogen has a pair of lone pair electron pairs that are not involved in conjugation,which is more conducive to anchore active component and paly a synergistic catalytic role.Moreover,because the electronegativity of nitrogen is stronger than that of carbon,adjacent carbon existed in the form of C+,which is easier to absorb negatively charged HSO5-,further promoting its activation to produce reactive oxygen species.The formation of Co-N-C bond could still inhibit the dissolution of cobalt ion and improved its stability.The removal efficiency of nitrobenzene was above 78%in seven consecutive reutiliazation.(2)when the dosage of Co3O4/3D N-GN catalyst was 3600 mg/L,the dosage of PMS was 2.0 g/L,and pH=6,the catalytic oxidation system had the best effect on nitrobenzene degradation,and the removal efficiency of nitrobenzene and CODcr reached 84.23%and 80.27%,respectively.H2PO4-had a certain promoting effect on the removal of nitrobenzene.HCO3-could inhibit the degradation of nitrobenzene to some extent.The effect of NO3-on the degradation of nitrobenzene was not obvious.The inhibiton of Cl-on the degradation of nitrobenzene was more obvious and increased with the increase of concentration;By means of the synergistic oxidation of SO4-·,·OH and 102,nitrobenzene can be first transformed into nitrophenols,which would then be converted into bisphenols and quinones in sequence,and finally be mineralized stable end product,namely CO2 and H2O,through open-ring reaction,thus effectively avoiding the production of byproduct. |
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