Study On The Removal Of Polychlorinated Biphenyls From Water By Nanoscale Zerovalent Iron Supported On Carbon Nanotube

Polychlorinated biphenyls?PCBs?are toxic to biological organisms and are persistent in environmental systems,and PCBs and related products were banned from production in the United States in 1979.However,PCBs in the environment still have negative impacts on human health by polluting ecosystems and food chains.The kinetic adsorption experiments of PCBs in aqueous solution was carried out by using carbon nanotubes?MWCNT?and powdered activated carbon?PAC?,and the equilibrium adsorption amount and removal rate of the two adsorbents were compared.By constructing the Langmuir and Freundlich isotherms,the best fit models were determined according to the adjustment factor of R².MWCNT was determined as the loaded material of nanoscale zero-valent iron?nZVI?by the different adsorption results of PCBs.The composites of nanoscale zerovalent iron supported on carbon nanotube?MWCNT-nZVI?were synthesized by liquid phase reduction method and characterized by SEM,TEM,BET and XRD.PCBs removal effects between different materials including nZVI,MWCNT and MWCNT-nZVI were compared.The removal effect of PCBs existed in the aqueous phase by MWCNT-nZVI was compared with MWCNT to explore removal and degradation laws of PCBs.The effects of different reaction conditions like MWCNT-nZVI dosage,temperature,initial pH values and initial PCBs concentrations on the removal of PCBs were evaluated and the reaction kinetic fitting of the experimental data was performed.The experimental results showed that the equilibrium adsorption capacity of MWCNT and PAC on PCBs was 152.32?g/g and 86.94?g/g,respectively.The removal rates of PCBs by MWCNT and PAC were 59.33%and 24.96%,respectively.The adsorption kinetics of MWCNT and PAC on PCBs were consistent with the pseudo-second-order kinetic model.The Freundlich model was suitable for the adsorption isotherm fitting process of MWCNT and PAC on PCBs.Scanning electron microscopy?SEM?and transmission electron microscopy?TEM?confirmed that MWCNT-nZVI material can significantly improve the dispersion of nZVI particles,and the images of structural identification indicated that nZVI particles was uniformly loaded on MWCNT and the oxidation and aggregation of nZVI particles was greatly minimized.N₂ adsorption-desorption isotherm curves showed characteristics of a highly ordered mesoporous structure of MWCNT-nZVI composite material.BET surface area was 61.77 m²/g and the nZVI particle size ranged from 20 to 80 nm.XRD images indicated that iron oxides were not formed in MWCNT-nZVI material.Experimental results indicated that the MWCNT-nZVI composites showed a PCBs removal rate of 71.98%,which was greater than that of MWCNT?63.84%?and nZVI?41.18%?under the same reaction conditions.The removal process followed the pseudo-first-order kinetic model.The process of PCBs removal by MWCNT-nZVI and MWCNT followed pseudo-first-order kinetics.Under the same reaction conditions,the removal efficiencies of PCBs by MWCNT-nZVI and MWCNT were 87.34%and 71.09%respectively after reaction.In addition,mass fraction of PCBs in solid phase were 27.00%and 71.00%,respectively.The physical adsorption of PCBs on MWCNT and their chemical dechlorination by nZVI on the MWCNT-nZVI could be simultaneously achieved.The effects of different reaction conditions like MWCNT-nZVI dosage,temperature,initial pH values and initial PCBs concentrations on the removal of PCBs were evaluated.The MWCNT-nZVI composites showed the best removal effect which was 93.99%on PCBs under the optimum conditions?the MWCNT-nZVI dosage was 1.6 g/L,the temperature was 25?,the initial pH value was 7.00,the initial PCBs concentration was1.4 mg/L?.