Preparation Of β-cyclodextrin-modified Carbon Nanotubes And Its Application For Adsorption Of Heavy Metal Ions

With the rapid development of industry, the environmental pollution becomes more severe. More and more people concern about the harm of heavy mental pollution, which is the typical case of the environmental pollution. How to recover heavy metal and eliminate its damage effectively was the focus of many researchers. Carbon nanotubes as a kind of novel material has wide application prospect in the fields of electronic components, catalysis, hydrogen storage and so on. It’s potential application in pollutants absorption should be explored owing to its nano size and especial surface properties.In this paper, multi-walled carbon nanotubes (CNTs for short) produced by chemical vapor deposition (CVD) method was choosen as raw material to prepare two absorbents:oxidized carbon nanotubes (CNTs-ox) and β-cyclodextria-modified oxidized carbon nanotubes (CNTs-β-CD). Their micro-structure, BET surface area, Zeta potential and surface functional groups were characterized by SEM, TEM, BET, Zeta potential and FTIR, respectively. The prepared absorbents were used for the adsorption of Pb2+and Cu2+. Effect of several parameters, include pH value, time, metal ion concentration and temperature on the absorption process was investigated. Pseudo-second-order kinetics equation, Langumir adsorption isotherm model, Freundlich adsorption isotherm model and thermodynamic equation were used to fit and analyze the experiment results.In the process of preparation of the CNTs-ox, ultrasonic was employed to accelerate and improve the oxidation of concentrated nitric acid. The oxidation made CNTs have evident opening, larger specific surface area and more functional groups on surface. The equilibrium adsorption time of CNTs-ox was30min (While it was about90min for CNTs). The adsorption rate increased with increasing solution pH in a range of2.0-6.5. The absorption process was well related with pseudo-second-order kinetics model. The saturation absorptive capacity for Pb2+and Cu2+were98.57and31.60 mg·g-1, respectively. In a range of5-35℃, adsorption for Pb2+was endothermic reaction and adsorption for Cu2+was exothermic reaction.For the first time, CNTs-β-CD were prepared by linking P-CD molecules and CNTs-ox with non-covalent bond. Meanwhile, the prepared CNTs-β-CD were used for absorption of heavy metals. Comparing with the unmodifed CNTs-ox, the CNTs-β-CD material had a smaller specific surface area and a portion of the surface charge was shielded. The equilibrium adsorption time was15min and the solution pH had significant influence on absorption ability of CNTs-β-CD. The absorption process was well related with pseudo-second-order kinetics model. Under the concentration range from1.25mg·L"1to200mg·L-1, the maximum adsorptive capacity of Pb2+and Cu2+were114.17and88.00mg·g-1, respectively, which has increased16%and178%compared with CNTs-ox. In a range of5-35℃, both adsorption of Pb2+and Cu2+were endothermic reaction.Mechanism analysis of the two adsorbents indicated that the ion exchange reaction was included in all studied adsorption process. Simultaneously, a process of complex reaction was included in the adsorption of CNTs-β-CD for Pb2+and Cu2+...