Study On Degradation Of Organic Pollutants By Iron-Doped Soybean Straw Biochar Activated By Persulfate

Environmental pollution is divided into water,soil and air pollution,which are closely related to human health and survival.With the development and research of nature,human beings have synthesized a large number of organic pollutants(organic synthetic dyes,antibiotics,pesticides and petroleum hydrocarbons,etc.).These organic pollutants will spread widely in the natural ecosystem with human labor.At present,various organic pollutants have posed a potential threat to human health.Advanced oxidation technology(AOP)based on sulfate radical(·SO4-)has been widely studied because of its strong water and soil remediation ability.However,the preparation conditions of persulfate(PDS)catalyst have always been controversial,such as the preparation scheme lacks system design and theoretical guidance,the valence state of metal ions loaded on the carrier is impure,and the application scope of the catalyst is limited.Aiming at the above problems,this paper is improved through the following three tasks.Firstly,high-carbon and low-nitrogen soybean straw was selected as the carrier of catalyst,and nano-Fe2O3 was selected as the source of metal ions.The co-heating conditions of high-carbon and low-nitrogen soybean straw and nanoiron oxide were obtained by single factor experiment,orthogonal experiment and response surface method,and an efficient persulfate(PDS)catalyst(nZVI-BC)was obtained.nZVI-BC can effectively activate sodium persulfate(PDS)and degrade four synthetic dyes:methyl orange(MO),orange-yellow II,amino black 10B(AB10B)and rhodamine B(RhB).Under the optimum pyrolysis conditions,the total organic carbon(TOC)removal rate of the four dyes reached 63.0%,61.1%,41.1 and 89.8%,and the final degradation rate could reach 100%.It is found that nZVI-BC is rich in multivalent iron ions(Fe0,Fe2+,Fe3+,C0.09Fe1.91).This study provides the design ideas and theoretical guidance for the production of efficient catalysts,as well as an effective treatment scheme for synthetic printing and dyeing wastewater.Secondly,a series of bio char-supported nano-zero-valent iron catalysts(nZVI-BC400-1100)were prepared at different co-pyrolysis temperatures(4001100℃).Oxytetracycline(OTC)in antibiotics was selected as the model pollutant for degradation of nZVI-BC400-1100/PDS system.The results of show that different co-pyrolysis temperatures have great influence on the maximum N2 adsorption capacity and nano-zero-valent iron(nZVI)content of nZVI-BC400-1100.The catalyst nZVI-BC1000 generated at the pyrolysis temperature of 1000℃ showed high activation performance for persulfate(PDS),and the degradation rate of OTC in water reached 99.54%.The results of N2 adsorption/desorption,XRD,XPS and FT-IR analysis show that the strong catalytic activity of nZVI-BC1000 for PDS depends on the high content of nZVI in nZVI-BC1000.The content of nZVI can be increased by increasing the co-pyrolysis temperature,and the oxidation and degradation ability of nZVI-BC1000/PDS system for OTC can be enhanced.·SO4-,·OH,and 1O2 are the main active species in nZVI-BC1000/PDS system.The high content of nZVI makes nZVI-BC1000 catalyze PDS to form more ·SO4-.This study provides scientific guidance for the formation of high-content nZVI and the optimization of catalysts in advanced oxidation technology.Thirdly,in order to overcome the problem of limited application range of catalyst,PDS was activated by high-content nano zero-valent iron-based biochar(nZVI-BC 1000),and the degradation ability of nZVI-BC1000/PDS system in soil system was studied.The pesticides atrazine and petroleum phenanthrene were selected as the main model pollutants.The effects of water-soil ratio,initial pH,humic acid,inorganic anions(Cl-,SiO32-,NO3-)on nZVI-BC1000/PDS system were studied.The results show that Cl-,SiO32-,and NO3-have a strong inhibitory effect on nZVI-BC1000/PDS system.The water-soil ratio can promote the nZVIBC1000/PDS system.The initial pH and humic acid not only promoted but also inhibited the nZVI-BC1000/PDS system.This provides important reference value for the development of high-content nZVI catalyst and its application in soil remediation.Finally,the preparation principle of catalyst(nZVI-BC)is:the reaction of carbon reducing iron oxide under the condition of high temperature and limited oxygen.Organic synthetic dyes,oxytetracycline,atrazine and phenanthrene are oxidized and degraded by active species(·SO4-,·OH,and 1O2)through hydrogen extraction,electron transfer and addition reaction.Ultimately,large molecules are converted into small molecules and CO2.