Facile Synthesis Of Alumina-decorated Multi-walled Carbon Nanotubes For Simultaneous Adsorption Of Cadmium Ion And Trichloroethylene

Groundwater pollution has become a critical environmental and economic issue in the worldwide. Heavy metal ions such as cadmium ion（Cd（Ⅱ） ion） are the main contaminant of groundwater and soils at the metal plating industry and the solid waste landfill site. Due to its nonbiodegradable nature, Cd（Ⅱ） ion can accumulate in the environment and enter the food chain, causing adverse effects to human health and ecological receptors and resulting in osteoporosis, anaemia and renal damage. Because of the improper storage and disposal of the spent solvents, groundwater contamination by chlorinated solvents（mainly trichloroethylene） at many industries and solid waste landfill sites has been discovered and can influence the human central nervous system, causing symptoms such as dizziness, headaches, confusion, euphoria, facial numbness, and weakness. Therefore, the US EPA recommends permissible limit in drinking water to be 5 ug/L for both Cd（Ⅱ） ion and TCE. It should be noted that there is a high possibility that Cd（Ⅱ） ion and TCE coexist in the environment, such as groundwater contamianted by the landfill leachate. Thus, this study is intending to find an effective approcach to remove the excess Cd（Ⅱ） ion and TCE from groundwater simultaneously.As a new type of nano-material, Carbon nanotubes（CNTs）, including single-wall（SWCNTs） and multi-wall（MWCNTs）, own unique mechanical, electrical and thermal properties. Unlike many adsorbents, CNTs possess different features that contribute to be considered by a good catalyst carrier, such as fibrous shape with high aspect ratio, large accessible external surface area, light mass density, easily modified surfaces and well developed mesopores. Therefore, the modification of carbon nanotubes on the surface of carbon nanotubes has become an important direction in the research of carbon nanotubes. These studies can obtain a new type of nano-composite based on carbon nanotubes, realizing the application of carbon nanotubes in such aspects as photo catalysis, environmental protection, drug loading and so on.Alumina-decorated multi-walled carbon nanotubes composite（Al₂O₃/MWCNTs） was prepared using chemical co-precipitation after multi-wall carbon nanotubes（MWNTs） were acidized by nitric concentrated nitric acid, hydrofluoric acid, concentrated nitric acid and concentrated sulfuric acid. In order to comprehensively grasp the various physical and chemical characteristics of the adsorbent, the MWCNTs, functionalized MWCNTs and Al₂O₃/MWCNTs obtained were characterized by the field emission scanning electron microscope（FESEM）, the transmission electron microscopy（TEM）, the BET specific surface areas, X-ray diffractometer, FTIR Spectrometer and Zeta potentials. Also the experiment studied the adsorption properties and underlying mechanisms of the adsorption of Cd（Ⅱ） ions and TCE by Al₂O₃/MWCNTs under various conditions adsorption. The adsorption kinetics, adsorption isotherm, effects of adsorbent dosage, stirring speed, pH and other groundwater constituents and on Al₂O₃/MWCNTs composite adsorption ability of Cd（Ⅱ） ions and TCE were discussed in detail.Alumina-decorated multi-walled carbon nanotubes were successfully synthesized and used as an effective adsorbent for simultaneous removal of TCE and Cd（Ⅱ） ion. The physicochemical analysis confirmed successful covalent linking of the functional groups on the Al₂O₃/MWCNTs and had more active adsorption sites than MWCNTs. The BET surface area of Al₂O₃/MWCNTs was much larger than MWCNTs. The Al₂O₃/MWCNTs exhibited excellent adsorption performance at neutral pH for both TCE and Cd（Ⅱ） ion. Both of the adsorption of TCE and Cd（Ⅱ） ion by Al₂O₃/MWCNTs were well fitted by the pseudo-second-order kinetic model and intraparticle diffusion model. Freundlich model was most appropriate to fit TCE adsorption, but for Cd（Ⅱ） ion, the Langmuir isotherm was more appropriate. Competitive adsorption experiments showed that the adsorption of TCE and Cd（Ⅱ） ion by Al₂O₃/MWCNTs had insignificant impacts on each other. The presence of Ca²⁺ reduced the equilibrium adsorption capacity of Cd（Ⅱ） ion, and slightly hindered the adsorption of TCE, while the presence of HA decreased the equilibrium adsorption capacity of TCE, but facilitated the adsorption of Cd（Ⅱ） ion. The adsorption mechanisms of Cd（Ⅱ） ion could be summarized as the electrostatic attraction, complexation and physical properties of Al₂O₃/MWCNTs, but for TCE, would be the physical properties of Al₂O₃/MWCNTs, hydrogen bond interactions and pore-filling theory. The simulated practical application indicated that Al₂O₃/MWCNTs exhibited good behavior in removing TCE and Cd（Ⅱ） ion.