Adsorption And Degradation Of3,3’,4,4’-Tetrachlorobiphenyl By Nano Materials

With the deep development of the researches on nanotechnology, the application of nanomaterials in environment has attracted great attentions, especially for the effective resolvement of some environmental problems, such as air pollution, sewage treatment, pesticide residues and urban garbage, which makes us more and more realize that nanometerial can be widely used in environmental problems. This paper focuses on the absorbability of nano-scale clay minerals on PCBs and the degradation of biphenyls by nano-iron and nano-silicon system.1.Adsorption of PCBs in soils and nano clay minerals were studied using the batch equilibration technique. Results showed that the adsorption of PCBs conformed to the Freundlich equation when the concentrations of PCBs were from0.25mg/L to5.0mg/L, and adsorption of PCBs in soils and nano clay minerals increased with increasing initial concentration. The adsorption capacity of soils for PCBs followed the order red soil> yellow brown soil> shajiang black soil. The contents of organic matter and clay in soil governed adsorption of PCBs, and the high chlorine of PCBs were easier to be absorbed by soils. The adsorption capacity of nano clay minerals for PCBs followed the order nano montmorillonite> nano SiO2> attapulgite. The adsorption ability of nano clay minerals for PCBs related to the surface area, diameter and layered structure of nano clay minerals. The molecular size of PCBs also affected the adsorption. Adding nano clay minerals to soil could improve the adsorption ability.2.The degradation kinetics of3,3’,4,4’-Tetrachlorobiphenyl(PCB77)by nano iron and silicon in aqueous solution were studied. PCB77could be dechlorinated by nano Fe0, Fe3O4and Si0, which followed with the pseudo first-order reaction kinetics, and the reaction rates(Kobs)were0.0177h-1,0.0038h-1and0.0045h-1, respectively. When the initial concentration of PCB77was5mg/L, the amount of nanomaterials was5g/L and pH was at4.5, the degradation efficiencies of nano Fe0to PCB77was the highest, and the residual rate of PCB77was19.83%after64h and the concentration of chlorion was50.3μmol/L with significant change of pH from4.5to5.26. Similarly, the degradation of PCB77by nano Fe0and Si0, Fe3O4and Si0composition followed the pseudo first-order reaction kinetics, and the reaction rates (Kobs) were0.0114h-1and0.004h-1respectively. The degradation efficiencies of nanometer-sized Fe0and Si0composition were better than nano Fe3O4and Si0combination, the residual rates of PCB77were34.91%and66.62%, and the concentrations of chlorion were40.07μmol/L and20.47μmol/L without the change of pH. The degradation efficiencies of nano Fe0and Fe3O4to PCB77decreased with increasing of initial pH, while the degradation efficiencies of nano Si0to PCB77increased with increasing of initial pH. The degradation efficiencies of nano Fe0and Si0, Fe3O4and Si0composition were not almost influenced by pH.3.6factors5levels orthogonal experiments are designed with the factors of pH value of reaction system buffer solution, the initial concentration of PCB77, nano Fe0dosage, nano Si0dosage, humic acid dosage and surfactant dosage. The results indicate that, with the condition of initial pH value of solution being4.5, the initial PCB77concentration of1mg/L, nano Fe0dosage of10g/L, humic acid dosage of0.25g/L, cyclodextrins dosage of1g/L, after two hours of reaction, the PCB77residue rate changes as35.2percent to the minimum, the hydrogen ion concentration changes into0.36×10-4mol/L to the maximum. However, Eh is not the one with the maximum variation. Initial pH value of nano materials degradation in PCB77reaction system remains the biggest influence PCB77concentration, followed by nano Fe0dosage. Initial pH value on the reaction system of hydrogen ion concentration, second is the surfactant dosage. PCB77reaction system in the initial concentration of the biggest influence Eh change, followed by nano Fe0dosage.Initial concentration PCB77for5mg/L, solution for6.8, initial pH value, nanometer reaction after64h Fe0dosage for10.0g/L, PCB77residue concentration, remain lowest rate is only29.3%.Nano Si0dosage for0.5g/L, PCB77residue concentration and retention rate lowest, only for67%. Nano Si0dosage of1.0g/L, namely the nano Si0/nano Fe0was1/10, PCB77residue concentration and retention rate lowest, only to22.2%.4. The degradation kinetics of PCB77by nano iron and silicon in soil were studied. The the initial concentration of PCB77was20μg/g, the dosage of nano Fe0was40mg/g, nano Si0was20mg/g and the amount of nanomaterials was60mg/g (nano Fe0was40mg/g, nano Si0was20mg/g), PCB77could be dechlorinated by nano Fe0and Si0in soil, which followed with the pseudo first-order reaction kinetics. When the soil was sterilized,the reaction rates(Kobs)were0.0057h-1,0.004h-1and0.0059h-1, and the residual rate of PCB77were68.2%,76.1%and63.6%after64h.The reaction rates(Kobs) were0.0081h-1,0.0067h-1and0.0083h-1and the residual rate of PCB77were53.2%,64.1%and51.7%after64h in non-sterilized soil. The degradation efficiencies of nano Fe0and Si0combination system were better than nano Fe0and Si0single system,when nano Si0/nano Fe0was1/10, the degradation efficiencies of nanometer-sized Fe0and Si0combination system to PCB77was the highest.