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Adsorption of Copper (II) on Functionalized Carbon Nanotubes (CNT): A study of adsorption mechanisms and comparative analysis with Graphene Nanoplatelets (GNP) and Granular Activated Carbon (GAC) F-400

Rosenzweig, Shirley Ferreira

Abstract Details

2013, PhD, University of Cincinnati, Engineering and Applied Science: Environmental Engineering.
CNT are known to have a high-mass transfer capacity for fast-flow rates at low pressure systems which make them desirable for water ultrafiltration. USEPA established regulating limits when copper levels exceed 1.3 mg/L. Copper contamination depends on corrosion reactions, stagnation of water and age of copper pipes, acidity and temperature of the water. In many cases, the pH drops after leaving the distribution systems, which can cause disruption of passivation films and pitting of copper pipes with metal precipitation or dissolution in the household water stream. CNT surface is usually chemically modified to improve desired properties, such as colloidal stability, surface charge and purity. Alcohol (OH) and acid (COOH) network forces formed within functionalized CNT bundles can define their aggregate state and adsorption mechanisms. The adsorption kinetic suggested a two-step process: electrostatic attraction of Cu(II) to oxygen-negatively- charged CNT surface causing deprotonation followed by chemisorption. The adsorption rate was dependent on the concentration of Cu(II) and amount of reactive functional groups on the surface. The adsorption capacity was improved after treating COOH-CNT with alkaline solution, by deprotonating the surface groups and reducing the strong COOH network forces. There is a significant decrease in adsorption capacity of COOH-CNT in the presence of Cl-, but it did not affect OH-CNT. SEM/EDS images showed adsorption of Cl- to pristine-CNT due to its positively charged walls. Extensive washing experiments evaluate the amount of residual impurities leached from CNT, followed by thermodynamic analysis simulations identifying possible CNT near-surface chemistry affecting copper adsorption. In this dissertation, a systematic correlation method was developed to identify chemisorption mechanisms on CNT using converted FTIR absorbance curves of as-received and hybrid CNT (with adsorbed copper) and pure reagent grade CuO and Cu(OH)2. The results identified new peaks on the spectra for Cu(II) chemisorbed on CNT surface, and showed that Cu(II) target acidic functional groups on CNT surface during adsorption. In order to evaluate the effectiveness of CNT in continuous filtering application, a fixed-bed column experiment was performed using a refillable column. OH-CNT break-point occurred later than F-400, confirming OH-CNT better adsorptive capacity. F-400 rate of desorption was longer with residual Cu(II) still leaching into water after 3 days. This experiment confirmed Cu(II) chemisorption mechanisms on OH-CNT surface, a desirable property if the adsorption application requires minimum or no Cu(II) leaching into continuous water flow after saturation. Finally, systematic adsorption experiments with different nanomaterials were carried out to compare the influence of physical-chemical properties and their interactions. Experimental data followed the Freundlich model, indicating the highest adsorptive capacity for OH-CNT. In a RSM analysis, the best subsets of properties to predict qe in order of significant contribution were: inner-diameter, bulk density, pHpzc, tube-length, mesopore volume and outer-diameter. GNP showed poor adsorptive capacity associated to stacked-nanoplatelets, but good colloidal stability due to high-functionalized surface. Good adsorption results of pristine-single-wall CNT indicated that short- tube/small-diameter values were more sensitive to adsorption than functionalized surface. Ball milling changed CNT aggregate shape and released more residual impurities, but had little effect on the adsorption capacity.
George Sorial, Ph.D. (Committee Chair)
E Sahle-Demissie, Ph.D. (Committee Member)
Dionysios Dionysiou, Ph.D. (Committee Member)
Margaret Kupferle, Ph.D. P.E. (Committee Member)
253 p.

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Citations

  • Rosenzweig, S. F. (2013). Adsorption of Copper (II) on Functionalized Carbon Nanotubes (CNT): A study of adsorption mechanisms and comparative analysis with Graphene Nanoplatelets (GNP) and Granular Activated Carbon (GAC) F-400 [Doctoral dissertation, University of Cincinnati]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1368026548

    APA Style (7th edition)

  • Rosenzweig, Shirley. Adsorption of Copper (II) on Functionalized Carbon Nanotubes (CNT): A study of adsorption mechanisms and comparative analysis with Graphene Nanoplatelets (GNP) and Granular Activated Carbon (GAC) F-400. 2013. University of Cincinnati, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ucin1368026548.

    MLA Style (8th edition)

  • Rosenzweig, Shirley. "Adsorption of Copper (II) on Functionalized Carbon Nanotubes (CNT): A study of adsorption mechanisms and comparative analysis with Graphene Nanoplatelets (GNP) and Granular Activated Carbon (GAC) F-400." Doctoral dissertation, University of Cincinnati, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1368026548

    Chicago Manual of Style (17th edition)