| The treatment of groundwater contaminated with various types of chlorinated organic solvents(COSs)by synthesizing nanoparticles(NPs)composite has gained much attention due to their high specific surface area and higher catalytic activity.Natural zeolite was used as a support material for the synthesis of novel metallic and bimetallic nanocomposite materials that were used for the removal of contaminants like 1,1,1-trichloroethane(1,1,1-TCA)and trichloroethylene(TCE)in this study.COSs are extensively detected in contaminated soil and groundwater that pose long-term threats to human life and environment.In order to degrade COSs effeetively,a novel catalytic composite of natural zeolite supported nano zero valent iron(Z-nZVI)was synthesized in this study.The performance of Z-nZVI catalyzed sodium percarbonate(SPC)in a heterogeneous Fenton like system was investigated for the degradation of COSs such as 1,1,1-TCA and TCE.The surface characteristics and morphology of the Z-nZVI composite were tested using scanning electron microscopy(SEM)and transmission electron microscopy(TEM).Total pore volume,specific surface area and pore size of the natural zeolite and the Z-nZVI composite were measured using Brunauer Emmett Teller(BET)method.SEM and TEM analyses showed significant elimination of aggregation and well dispersion of iron NPs on the framework of natural zeolite.The BET N2 measurement analysis indicated that the surface area of the Z-nZVI composite was 72.3 m2 g-1,much larger than that of the natural zeolite(0.61 m2 g-1).For the contaminant analysis,the samples were extracted with n-hexane and analyzed through gas chromatograph.The degradation of 1,1,1-TCA and TCE in the Z-nZVI catalyzed percarbonate system were 48%and 39%respectively,while strong augmentation was observed up to 83%and 99%respectively by adding the reducing agent(RA),hydroxyl amine(NH2OH·HCl).Probe tests validated the presence of hydroxyl radicals(OH·)and superoxide radicals(O2-·)which were responsible for 1,1,1-TCA and TCE degradation,whereas both free radicals were strengthened with the addition of RA.In conclusion,the Z-nZVI/SPC oxidation with RA shows potential technique for degradation of groundwater contaminated by 1,1,1-TCA and TCE.The role of reactive oxygen species(ROSs)and effect of solution matrix have been investigated for the degradation of TCE.The Z-nZVI was used as an activator to catalyze SPC with or without RA.The probe tests confirmed the generation of OH·and O2-· in the Z-nZVI activated SPC system in absence of the RA.While,the presence of RA significantly increased the generation of OH· and O2-· radicals.Scavenger tests demonstrated that OH· was main ROSs responsible for TCE degradation,whereas O2-· also participated in the TCE degradation.From the solution matrix perspective,the experimental results confirmed the significant scavenging effects of Cl-(1.0,10.0,and 100 mM)and HCO3-(1.O and 10.0 mM),whereas the scavenging effects were fairly impeded at 100 mM concentration of HCO3-.On the other hand,a considerable decline in the scavenging effect was observed in the presence of RA in tested Cl-and HCO3-concentration ranges.In addition,negligible scavenging effects of NO3-and SO42-anions were found in all tested concentrations.The effect of initial solution pH on the catalytic activity indicated a significant increase in the TCE degradation in the presence of RA even at higher pH value of 9.The results indicated that the Z-nZVI activated SPC system in presence of RA can effectively degrade COSs but it is important to consider the intensive existence of anions in groundwater.The effect of solution matrix and pH was evaluated for the generation of ROSs in Z-nZVI-catalyzed SPC system for the degradation of 1,1,1-TCA in the absence and presence of RA.The degradation of 1,1,1-TCA was 49.5%and 95%in the absence and presence of RA.Probe tests confirmed the generation of major OH·and minor O2-·,and scavenger tests verified the key role of OH·and less of O2-· radicals.The 1,1,1-TCA degradation decreased significantly with the presence of Cl-and HCO3-,while NO3-and SO42-have negligible effect in absence of RA.Addition of RA significantly enhanced 1,1,1-TCA degradation by generating more OH· and O2-· radicals in presence of anions.The 1,1,1-TCA degradation was maximized in acidic range(pH=1-5)while,an inhibitive trend from neutral to basic(pH=7-9)was observed.On the contrary,a significant increase in 1,1,1-TCA degradation was observed with addition of RA in all pH values(pH=1-9).In conclusion,the anions and pH significantly influenced the generation and intensity of ROSs and 1,1,1-TCA was effectively degraded in Z-nZVI-catalyzed SPC system in the presence of RA.Further studies were conducted primarily focusing on the performance of 1,1,1-TCA and TCE degradation involving redox reactions in Z-nZVI-catalyzed-SPC system in aqueous solution with five different chelating agents(CAs)including oxalic acid(OA).citric acid monohydrate(CAM),glutamic acid(GA),ethylenediaminetetraacetic acid(EDTA),and L-ascorbic acid(ASC).The experimental results showed that the addition of OA achieved almost 100%degradation of 1,1,1-TCA and TCE.The addition of CAM and GA also significantly increased the contaminants degradation,while excessive addition of them inhibited the degradation.In contrast,EDTA and ASC showed negative impacts on 1,1,1-TCA and TCE degradation which might be due to the strong reactivity with iron and OH· scavenging characteristics.The efficiency with CAs addition on 1,1,1-TCA and TCE degradation decreased in the order of OA>CAM>GA>No CAs>EDTA>ASC.The extensive investigations using probe compound tests and scavenger tests revealed that both contaminants degraded primarily by OH· and O2-· in chelated Z-nZVI-catalyzed-SPC system.The significant improvement in 1,1,1-TCA and TCE degradation efficiency was accredited due to the(?)increase in concentration of Fe2+,(?)continuous generation of OH· radicals and maintenance of its quantity,ensuring more stability in the aqueous solution.Finally,the complete mineralization of 1,1,1-TCA and TCE in the OA chelated Z-nZVI-catalyzed-SPC system was confirmed without any chlorinated intermediate by-products detected,demonstrating a great potential of this technique in the application of groundwater remediation.Zeolite supported nano zero valent iron copper bimetallic composite(Z-nZVI-Cu)was synthesized using an ion exchange method.The morphology and physico-chemical properties of the Z-nZVI-Cu eomposite were determined using TEM,SEM,BET,EDS,XRD,and Fourier transform infrared spectroscopy(FTIR).The results showed that iron and copper nano particles were well dispersed on the zeolite sheet.The degradation efficiency of TCE achieved was more than 95%using Z-nZVI-Cu as a heterogeneous Fenton like catalyst.An efficient removal of total organic carbon(TOC)was promoted as compared to Z-nZVI and unsupported nano iron(nZVI).Electron spin resonance(ESR)detection confirmed the intensity of OH' in the system.While benzoic acid(BA),a probe indicator for the quantification of OH·,demonstrated the higher intensity of OH· in Z-nZVI-Cu as compared to Z-nZVI and nZVI.The less iron and copper leaching from Z-nZVI-Cu presented its higher stability and better catalytic activity,displaying its potential long term application for TCE degradation in contaminated groundwater.Zeolite supported nano iron-nickel bimetallic composite(Z-nZVI-Ni)was prepared using a liquid-phase reduction process.The corresponding surface morphologies and physico-chemical properties of the Z-nZVI-Ni composite were determined using SEM,TEMS,EDS,BET,FTIR,and wide angle X-ray diffractometry(WA-XRD).The results indicated high dispersion of iron and nickel nano particles on the zeolite sheet with an enhanced surface area.Complete destruction of TCE and efficient removal of TOC were observed by using Z-nZVI-Ni as a heterogeneous catalyst for a Fenton-like oxidation process employing SPC as an oxidant.The ESR of Z-nZVI-Ni verified the generation and intensity of OH·.The quantification of OH·elucidated by using p-chiorobenzoic acid,a probe indicator,confirmed the higher intensity of OH·.TCE transformation products were identified using gas chromatography-mass spectrometry(GC-MS).The slow iron and nickel leaching offered higher stability and better catalytic activity of Z-nZVI-Ni,demonstrating its prospective long term application in TCE contaminated groundwater remediation. |
PDF Full Text Request