| Atrazine(ATZ)has a strong disturbance to biological endocrine and is listed as a priority pollutant.Due to its long half-life,wide application range and other characteristics,it remains in the environment for a long time.ATZ is difficult to be removed effectively by the conventional water treatment processes,so it has become an urgent problem to effectively treat the ATZ polluted water.Advanced oxidation technology based on transition metal activated persulfate has been widely used for catalytic degradation of organic pollutants due to its high efficiency,simple operation and economic suitability.Among them,transition metal cobalt has the strongest catalytic activity upon peroxymonosulfate(PMS),but in the application practice,it will lead to the dissolution of Co2+ and secondary pollution.It is also prone to agglomeration,which can inhabit the activation performance.Biochar is well known with its stable structure,large specific surface area,abundant surface functional groups,cheap and easy access to raw materials,etc.It can be used as heavy metal adsorbent and persulfate catalyst in water treatment applications.However,biochar alone can not deal with the high concentration of organic wastewater corresponding with low recovery efficiency.Therefore,it is of practical significance to combine the two materials in order to degrade ATZ efficiently,give play to the advantages of Co and biochar catalysts,and solve the disadvantages of their application in water treatment.In this study,two biochar-Co3O4 composites(Co3O4/oak biochar(Co-OB)and Co3O4/firmiana platanifolia bark biochar(Co-FB)were prepared by improved hydrothermal impregnation.SEM,EDS,XRD,ATR-IR and other characterization methods were used to analyze the surface properties and the loading of Co3O4.The activation of PMS as well as the degradation of ATZ was analyzed by HPLC and ICP-MS.Different reaction parameters(additive amount of catalysts,reaction temperature,the PMS dosing amount)upon ATZ degradation was studied.The influence of humic acid(HA)and Cl-on ATZ degradation was examined.And the stability of two kinds of catalysts was assessed and compared.The main active free radicals in the degradation process were identified by HPLC and LC-MS.Mechanism of PMS activation was discussed,and the possible degradation pathway of ATZ was proposed.The following are the main results and conclusions of this study:1.Two kinds of Co3O4/oak biochar composites(Co-OB)and Co3O4/Firmiana bark biochar composites(Co-FB)were synthesized by hydrothermal impregnation and characterized by SEM,EDS,XRD,ATR-IR and BET.Comparative analysis shows that CoOB has large specific surface area and good pore structure,while Co-FB has more types of oxygen-containing functional groups and impurity metal salt(CaCO3).2.The Co-OB/PMS system can degrade 86.3%ATZ within 10 min when 20μmol/L ATZ was treated by 0.025 g/L Co-OB and 200 μmol/L PMS,which is 2.2 of the sum of Co3O4/PMS and OB/PMS system,and the apparent reaction rate constant(0.1919 min-1)is 58.1 times than that of Co3O4/PMS and 21.8 times than OB/PMS process.Under the same conditions,Co-FB/PMS system can degrade 86.3%ATZ,which is 2.3 of the sum of Co3O4/PMS and FB/PMS system,and the apparent reaction rate constant(0.1978 min-1)is 59.9 times than that of Co3O4/PMS and 21.5 times than FB/PMS process.The degradation effect of biochar-Co3O4/PMS on ATZ increased with increasing catalyst,PMS dosage and temperature.When the catalyst content and reaction temperature increased,Co-FB/PMS had higher degradation rate.The apparent reaction rate constant of Co-OB/PMS was positively correlated with the PMS concentration.The degradation effects of Co-OB/PMS and CoFB/PMS on ATZ were inhibited with the increase of Cl’ and HA concentrations.Comparatively speaking,the Co-FB/PMS system is more suitable for the low concentration(0～20 mM)of Cl-containing wastewater,while the Co-OB/PMS system is more suitable for the low concentration(0-2mg/L)of HA containing wastewater.The Co-OB has higher stability with a completely removal of ATZ in three-time cycling and the surface structure changes little after the reaction.3.The dominate active radicals in Co-OB and Co-FB activated PMS processes were·OH and SO4·-.Activation of PMS by biochar-Co3O4 is controlled by heterogeneous Co3O4.However,a large specific surface area can expose more Co3O4 active sites,which improves the catalytic performance of biochar-Co3O4.Six kinds of intermediate products were documented by LC-MS,and two possible degradation pathways:oxidation of alkyl side chain of ATZ and dichlorination-hydroxylation,were proposed. |
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