| Carbon nanotubes (CNTs), with unique morphologies and surface characteristics not only have great potential applications in electronics, field emission materials, catalysis, but also are of potential in hydrogen storage or wastewater treatment. This dissertation focuses on the investigation of adsorption of cadmium, iron, nickel, copper, and zinc ions from low concentration solution on the CNTs and coal-derived micro-size carbon fibers (CCFs). The effects of the adsorption time, temperature, pH value, and ion concentration on adsorption were investigated. A number of advanced techniques such as SEM, TEM, adsorption of nitrogen, FTIR, XPS, and potentiometric titration were used to characterize the structure and surface chemistry of adsorbents. The relationship between the surface properties of adsorbents and the adsorption capacity was analyzed. The kinetics and thermodynamics of adsorption were also studied.The comparative study of cadmium adsorption on different CNTs was carried out. Oxidation could significantly increase the cadmium adsorption capacity of the CNTs obtained from chemical vapor deposition (CVD) method. Both Langmuir and Freundlich models showed good agreement with the experimental data. The exponential relationship was found between the capacity of adsorbents for cadmium ions and their surface pH values, while the linear dependence was observed between the amounts adsorbed at certain pH on the number of groups dissociated at that pH. When the adsorption was analyzed based on the unit surface area of the adsorbents, the adsorption amounts were found to be comparable with those obtained on activated carbons.The adsorption of Fe (â…¡) and Fe (â…¢) ions using the oxidized CNTs obtained from CVD method was also studied. The results showed that the adsorption of Fe (â…¢) is more pH dependent than that of Fe (â…¡). The uptakes of Fe (â…¢) at the same equilibrium concentration were higher than those of Fe (â…¡). The study of kinetics showed that the pseudo-second-order kinetic adsorption model is suitable for describing the adsorption of Fe (â…¡) and Fe (â…¢) ions on the CNTs. The study of thermodynamics revealed that the adsorption process of Fe (â…¡) and Fe (â…¢) ions on the oxidized CNTs was spontaneous, endothermic and with an increase in entropy.The competitive adsorption of nickel, copper, zinc and cadmium ions from aqueous solutions was studied in single, binary, ternary and quaternary systems with the oxidized CNTs as an adsorbent. The uptakes in the single and binary systems at the same equilibrium concentration varied in the following order: Cu2+(aq) > Ni2+(aq) > Cd2+(aq) > Zn2+(aq). This order agreed with that of oxidation ability of ions based on the standard electrode potential. For the binary, ternary and quaternary system, the isotherms of the copper ions followed the Langmuir model while for the isotherms of other ions, a decrease in the amount adsorbed was observed at certain concentration. For the ternary and quaternary system, except copper ions, the order in the amount adsorbed was following: Cd2+(aq) > Zn2+(aq) > Ni2+(aq). This particular behavior can be related to the complex redox properties and ion exchange processes.CCFs were also used to remove cadmium ions from the aqueous solution. Oxidation introduced a large quantity of functional groups which caused a remarkable increase in adsorption capacity. If compared based on the unit weight and the unit surface area, the adsorption ability of oxidized CCFs was higher than that of activated carbon, bagasse fly ash and carbon nanotubes reported in literature. The kinetic study showed that the adsorption followed the pseudo-second order kinetic adsorption model. Both Langmuir and Freundlich models described the adsorption isotherms well at pH<7.00, while the surface precipitation model showed good agreement with the experiment data when deposition occurred.
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