Multi-walled Carbon Nanotubes Modified With Nanoparticles And Their Properties

As an emerging class of materials, carbon nanotubes (CNTs) have attracted considerable attention over the past decade because of their unique optical, electronic, mechanical and chemical properties. To optimize their performance for potential applications, great efforts have been made to functionalize CNTs with other compounds, such as organic, inorganic, and biological species. The surface functionalization of CNTs permits the fabrication of novel one-dimensional hybrid materials. This thesis mainly studied the modification of nanoparticles on the sidewall of carbon nanotubes. The nanocomposites were characterized and their photoluminescence properties, optical limiting properties or magnetic properties were also determined and discussed. The contents of this thesis include four chapters.In chapter 1, the advanced development in the research of modifying carbon nanotubes with nanoparticles was summarized. The research envisagement for the whole thesis was also proposed.In chapter 2, Multi-walled carbon nanotubes (MWCNTs) were coated with rare earth (RE = Eu3+, Tb3+) complex layers by a simple in-situ synthetic method via noncovalently functionalized MWCNTs with sodium dodecyl sulfate. This facile method could be extended to prepare other CNT/RE complex nanocomposites. Extensive characterizations of the produced nanocomposites have been performed using scanning electron microscopy (SEM), FT-IR spectra, X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The photoluminescence properties of the RE-complex modified MWCNTs were also investigated. Under the excitation of UV light, these samples exhibit characteristic emission of Eu3+ or Tb3+ ions. The presence of MWCNT framework does not quench the lanthanide-centered luminescence originating from the characteristic electronic transitions within the 4f shell of the RE ions. Furthermore, the existence of nanotube framework can improve the stability of RE complex under UV irradiation and elongate the fluorescence lifetime of the RE complex.By a solvent-thermal-assisted in-situ synthetic method, MWCNTs can also be easily coated with europium(III)-dibenzoylmethane-1, 10-phenanthroline or terbium(III)-acetylacetone-1,10-phenanthroline complex layers via noncovalently functionalized MWCNTs with sodium dodecyl sulfate. The obtained nanocomposites have been well characterized by a variety of microscopy and spectroscopic techniques. The heat treatment temperature had an important effect on the composition and photoluminescence (PL) properties of the nanocomposites. At low temperature, the PL intensity of the nanocomposites increased with the increase of reaction temperature. When the temperature was increased to 100 oC, the europium(III) nanocomposite showed the best luminescence. On the other hand, the MWCNTs coated with terbium(III) complex showed the best luminescence at 60 oC. In a further increase of reaction temperature, the PL intensity decreased markedly due to the decomposition of Eu(III)-complex and Tb(III)-complex on the sidewall of MWCNTs.In chapter 3, a metal sulfide such as ZnS, CdS, Ag2S or PbS was coated on the sidewall of MWCNTs by an in situ wet chemical synthesis approach via non-covalent functionalization of MWCNTs with polyelectrolyte (polyelthylenemine or poly(diallyldimethylammonium chloride)) without causing a significant electronic and structural modification of the carbon nanotubes. We also tried a solvent-thermal-assisted in-situ synthetic method. Extensive characterizations of the fabricated nanocomposites showed that the coating layers were composed of metal sulfide nanoparticles with mean size of less than 10 nm. The optical limiting property measurements for some metal-sulfide-coated MWCNTs were carried out by the open-aperture z-scan technique. The results demonstrate that the samples suspended in water showed optical limiting behavior better than that of purified MWCNTs. The content of metal sulfide in the composites may be an important factor that affects the OL properties of the composites. In chapter 4, nickel or copper metal nanoparticles were coated on the sidewall of MWCNTs by an in situ wet chemical synthesis approach via non-covalent functionalization of MWCNTs with polyelectrolyte (polyelthylenemine or poly(sodium-p-styrenesulfonate)). Extensive characterizations of the fabricated nanocomposites have been performed. The results show that CNTs were well modified with the metal nanoparticles and their mean sizes were less than 10 nm. The magnetic properties of the composites were investigated. The magnetic data reveal that Ni-nanoparticle modified MWCNTs exhibit favorable magnetic properties at low temperature.