| Carbon nanotubes (CNTs) have unique morphologies and surface characteristics, such as high mechanical strength, large specific surface area, hollow and layered structures, high chemical and thermal stabilities. CNTs not only have great potential applications in electronics, field emission materials, catalysis, but also are of promising adsorption material in nanoscale science and technology. However, due to the formation of big bundles held strongly together, CNTs are difficult to disperse homogeneously in different solvents, which greatly limit their application. Therefore, surface modifications of CNTs have been studied to enhance the dispersion property and adsorption capacities.This dissertation focuses on the synthesis of modified carbon nanotubes adsorbents with good dispersion. Then the prepared adsorbents were applied for the adsorption and removal of organic Sudan dyes and inorganic heavy metal ions.(1) Modification and characterization of muti-walled carbon nanotubes (MWCNTs)Oxidation of MWCNTs using concentrate nitric acid could introduce hydroxyl groups, carboxyl groups and carbonyl groups to their surface. Then a silica layer was coated on oxidized MWCNTs (Ox-MWCNTs) with the aid of the cationic surfactant CTAB. Mesoporous structure was obtained by extracting CTAB via an ion-exchange procedure. Finally, APTES was grafted on the mesoporous silica coated MWCNTs (mSiO2@MWCNTs) by refluxing APTES and mSiO2@MWCNTs in toluene. The obtained material was marked as NN-mSiO2@MWCNTs. A number of advanced techniques, such as FTIR, TEM, N2adsorption-desorption and XRD, were used to characterize the structure and surface properties of prepared adsorbents. The results confirmed that the dispersibility of modified MWCNTs was obviously improved, and mesoporous SiO2layer was homogeneously coated on MWCNTs and APTES was successfully grafted on mSiO2@MWCNTs.(2) Adsorption and removal of Sudan â… , â…¡ by Ox-MWCNTsA simple adsorption procedure for the and adsorption removal of Sudan â… and â…¡ in n-hexane using oxidized multi-walled carbon nanotubes (Ox-MWCNTs) is presented in this paper. The effect of absorption conditions including absorption time, amount of adsorbent, initial concentration of Sudan â… and â…¡ were examined. Two isotherm models were used to describe the adsorption equilibrium, while three kinetic models were applied to evaluate the adsorption process. The adsorption process and equilibrium for Sudan â… and â…¡ were all proved to be fitted by the Langmuir model and second-order kinetic model. The Ox-MWCNTs possessed fast kinetics for Sudan â… and â…¡ from n-hexane solvent with each saturation time of <30min, and correspondingly the maximum adsorption capacities for Sudan â… and â…¡ were41.408mg/g and47.037mg/g, respectively.(3) Adsorption of heavy metals in aqueous solution by NN-mSiO2@MWCNTsThe comparative study of lead, nickel, copper and zinc ions adsorption from low concentration solution by different modified MWCNTs were carried out. The results indicated NN-mSiO2@MWCNTs could adsorb heavy metal ions with higher efficiency. In addition, Cu (â…¡) adsorption process was thoroughly studied from both kinetic and equilibrium points of view. Adsorption kinetics could be well described by pseudo-second-order kinetic equation and exhibited3-stage intraparticle diffusion mode. Adsorption isotherms fitted well with Langmuir model. The thermodynamic analysis revealed that the adsorption of Cu (â…¡) onto NN-mSiO2@MWCNTs was endothermic and spontaneous. We can state that NN-mSiO2@MWCNTs will be a very promising material for heavy metal adsorption from contaminated water and exhibit high adsorption capacity even at low concentration. |
PDF Full Text Request