| Carbon nanotubes (CNTs), a kind of new nanomaterials with large surface area and unique pore structure, are widely applied in the studies of pollutants adsorption. It was proved that CNTs showed good adsorption effect to several contaminants, however, limited production scales and recycling technology limited it’s application in the respect of environmental pollution control. Consequently, improving adsorption capacity could accelerate it’s application process. In this dissertation, adsorption of predominant pollutants such as perfluorochemicals (PFCs) on CNTs under electrochemical assistance was explored. The electrodes based on CNTs were prepared as well as their ability of adsorption of typical pollutants were systemically investigated. The influence of chemicals structures and characteristics on adsorption were also discussed. The objective of this study is to realize effective removal of pollutants and expend the application of CNTs in the field of water pollution control. Correspondingly, several studies were conducted as follows:(1) Adsorption of perfluorooctanoic acid (PFOA), perfluorooctane sulfonate (PFOS), perfluorooctanesulfonamide (PFOSA),2,4-dichlorophenoxyacetic acid (2,4-D) and4-n-nonylphenol (4-NP) on oxidized CNTs was explored. It was found that the adsorption kinetics was fitted with pseudo-second-order model and the adsorption isotherm was well fitted with Freundlich model. Adsorption equilibrium coefficient Kt was ordered as4-NP> PFOSA> PFOS>2,4-D> PFOA. The adsorption capacity was found to be influenced by both the properties of organic pollutants and the oxygen contents of CNTs. Adsorption capacity was improved with increased hydrophobicity of chemicals, and decreased with increased oxygen contents of CNTs. Furthermore, the adsorption characters of five contaminants were affected by solution pH and solute pKa. The effect was weaken as the increasing of the oxygen contents. When the oxygen contents reached18%, the effect could be neglected.(2) Chemical vapor deposition (CVD) and electrophoretic deposition (EPD) were employed to fabricate MWNTs electrodes, separately. In the process of CVD, experimental conditions such as temperature program of the tube furnace, the ratio between carbon source and the catalyst and the inject volume need to be controlled strictly. According to this method, the surface area of obtained MWNTs<100m2/g, and the equilibrium adsorption capacity of100ug/L PFOS is168ug/g. By contrast, the advantages of EPD contain simple equipment, convenient operation and high efficiency. After sustaining for3min at a potential of160V, the MWNTs membrane with uniform and compact morphology was obtained in cathode, the electrochemical potential window of the electrode is in the range of±1.2V, surface electron transfer resistance is4.2Ω, and equilibrium adsorption capacity of PFOS reaches2.33mg/g.(3) Adsorptions of4-NP and phenanthrene (Phe) on MWNTs under electrochemical assistance were investigated. It was found that initial adsorption rate uo and maximum adsorption capacity qm of adsorption of4-NP on WNTs under electrochemical assistance could be improved. Obtained uo and qm were ordered as-0.6V> OC>0.6V> powder MWNTs. The value of uo at-0.6V was found to be1.5times of that for open circuit adsorption and7.9times of that for powder MWNTs adsorption. At-0.6V potential, uo of Phe adsorption on MWNTs was also improved, which is3.3times of open circuit adsorption and9times of powder MWNTs adsorption. However, the qm of Phe adsorption was not influenced.(4) Adsorptions of PFOA and PFOS on MWNTs under electrochemical assistance were investigated. It was found that adsorption kinetics of PFOA and PFOS on MWNTs under electrochemical assistance was well fitted with pseudo-second-order model, and the adsorption isotherm was well fitted with Langmuir model, υ0and qm at0.6V is higher than that at-0.6V and under open circuit conditions. Especially, compared with adsorption on powder MWNTs, uo and qm at0.6V improved dramatically, uo increased60-fold (PFOA) and41-fold (PFOS) and qm increased150-fold (PFOA) and94-fold (PFOS). Considering of the zeta potential of MWNTs, the point of zero charge and the potential of zero charge of electrode, these significant improvements were assumed to relate to enhanced electrostatic attraction. The adsorption capacities of PFOA and PFOS were also affected by solution pH and electrolyte concentration. Furthermore, the used MWNTs could be regenerated and reuses by cleaning with aqueous solution at90℃. The influence of structures and characteristics of pollutants on adsorption effect was explored. Adsorption on MWNTs under electrochemical assistance is suitable for effective removal of hydrophilic chemicals.In this work, PFOA and PFOS were removal effectively on CNTs under electrochemically assistant adsorption, which provides theoretical guidance for pollutants adsorption by CNTs, and also facilitates application and development of CNTs in the field of water pollution control. |
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