Study On Electrokinetic Remediation Of Cr(?)-contaminated Soil And Degradation Of Tetracycline By PMS Activated Based On Polypyrrole

With the continuous development of industry,the pollution of heavy metal and organics is becoming increasingly prominent.Based on the current pollution situation of hexavalent chromium(Cr(?))in soil and tetracycline in water,this study explores an economic and effective method of treatment.Polypyrrole is a conductive polymer with low density,large specific surface area,loose porosity and lots of positive charges,so it is a potential material for removing heavy metals and organics.In this study,pyrrole(Py)was oxidized and polymerized on linen to synthesize a polypyrrole-linen composite material(PPy-LF),which was used as an auxiliary electrode in electrokinetic remediation of Cr(?)-contaminated soil.A new electrokinetic remediation system containing main-auxiliary electrodes(EKR-PPy)was explored.This study confirms that the feasibility of using PPy-LF as auxiliary electrode and the migration behavior and removal mechanism of Cr(?)in EKR.Carbonized polypyrrole(CPPy)was prepared by carbonizing polypyrrole(PPy)at high temperature,which was used to activate permonosulfate(PMS)to degrade tetracycline in water.The catalytic activity of PMS and the mechanism for tetracycline degration were investigated.PPy-LF(PPy-LF-1,PPy-LF-2,PPy-LF-3 and PPy-LF-4)was synthesized based on the different concentration ratios of C(CTAB):C(SDBS)and its morphology analysis,infrared characterization and Cr(?)adsorption performance were studied.PPy-LF,the largest Cr(?)adsorption capacity and good electrochemical performance,was selected as auxiliary electrodes for subsequent soil electrokinetic remediation.It was found that the Cr(?)adsorption capacity by PPy-LF-3 reached 95.69 mg/g and the removal rate reached 93.I%within 30 minutes.The main-auxiliary electrodes system was constructed and the graphite rod was used as mian electrode and PPy-LF was used as auxiliary electrode.Five EKR experiments lasting 72 h were carried out in order to explore the Cr(?)removal mechanism of the new EKR system.In the presence of the PPy,the distribution of electric field along the ion migration direction and electric current were all improved.Comparing EK1(EKR,1V/cm)and EK2(EKR+PPy,1 V/cm),the potential difference between the two auxiliary electrodes increased from 9.37 V to 21.46 V,the current increased from 26 mA to 62 mA and Cr(?)concentration around the auxiliary electrode decreased.The changes of these parameters promoted the migration and removal of Cr(?).The proportion of Cr(?)migrated into the anode compartment were 20.60%and 11.27%in the presence and absence of PPy auxiliary electrodes,respectively.The maximum removal efficiency of Cr(VI)in soil was 91.7%.The combination of PPy auxiliary electrode and EKR(EKR-PPy)has a positive effect on the removal of Cr(VI).It can not only accelerate the migration of Cr ions by affecting the the electric field distribution,but also adsorb and reduce Cr(VI).PPy was prepared through in-situ chemical oxidative polymerization.We developed a novel nitrogen-doped carbonaceous catalyst by carbonization of PPy,which was used as a catalyst for PMS activation to achieve high degradation efficiency for tetracycline.Comparing the catalytic activity of four carbonized polypyrroles and the results indicated that CPPy-3(C(CTAB):C(SDBS)was 3:1)showed the best catalytic performance.The effects of catalyst dosage,PMS concentration,initial pH and reaction temperature on the catalyst activity were investigated in detail.When the PMS concentration was 1 g/L,the CPPy-3 concentration was 0.1 g/L and the reaction time was 10 mimutes,the degradation efficiency was 92%.The catalyst system(CPPy-3/PMS)can effectively remove tetracycline in the wide pH range of 2-9.The effects of inorganic anions in water on the degradation of tetracycline by CPPy-3/PMS were investigated.It can be seen that the inorganic anions had a little impact on tetracycline degradation,which was beneficial to the practical application.Scanning electron microscopy(SEM),Fourier infrared spectroscopy(FTIR),X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS)and Raman spectroscopy(Raman)were used to explore the surface morphology,structure and chemical composition of material.The results show that nitrogen-doped carbon-based material was successfully synthesized and graphite N is the main active site.The types of reactive species in the catalytic process were detected with scavenging tests.Based on the experimental results and theoretical knowledge,the mechanism of tetracycline degradation in CPPy/PMS was analyzed.The CPPy activated PMS through a non-radical path and CPPy acts as an electronic intermediate.The electrons on the organic pollutants were transferred to the PMS through CPPy,resulting in the decomposition of the PMS and the degradation of the pollutants.