Functionalized Multiwall Carbon Nanotube/Gold Nanoparticle Composites

Abstract

Multiwall carbon nanotubes (MWCNTs) were chemically oxidized in a mixture of sulfuric acid and nitric acid (3:1) while being ultrasonicated. The effect of oxidative ultrasonication at room temperature on development of functional groups on the carbon nanotubes was investigated. The dispersability and the carboxylic acid group concentration of functionalized MWCNTs (fMWNTs) varied with reaction time. The concentration of carboxylic acid groups on fMWNTs increased from 4 x 10(-4) mol/g of fMWNTs to 1.1 x 10(-3) mol/g by doubling the treatment period from 4 to 8 h. The colloidal stability of aqueous fMWCNTs dispersions was enhanced through elongated oxidation. fMWCNTs that were reacted longer than 4 h did not precipitate in aqueous media for at least 24 h. The layer-by-layer self-assembly of polyelectrolytes on fMWCNTs was characterized by zeta potential measurements. The zeta potential of fMWCNTs changed from negative charge to positive charge when cationic polyelectrolytes were self-assembled on their surface. With addition of anionic polyelectrolytes, cationic polyelectrolyte coated fMWCNTs showed the expected charge reversal as expected for multilayer self-assembly. Complex formation of positively charged gold nanoparticles and negatively charged fMWCNTs was achieved with and without polyelectrolyte coatings by electrostatic interaction. The complex formation was characterized by high-resolution transmission electron microscopy and energy-dispersive X-ray spectroscopy. The here found complex formation of positively charged colloidal gold and defect sites on fMWNTs indicates the location of functional groups on carbon nanotubes. It is suggested that positively charged colloids such as gold nanoparticles could be used for detection of defect sites on carbon nanotubes.

Carbon Nanotube and Gold‐Based Materials: A Symbiosis

“…[39] Positively charged AuNPs were anchored on negatively charged fMWNTs prepared by the layer-by-layer selfassembly technique using polyelectrolytes. Positively charged AuNPs were also attached onto raw fMWNTs, because of the negatively charged carboxylic acid groups produced by the chemical oxidation process during ultrasonication, followed by deprotonation on immersion in water.…”

Carbon Nanotubes Supported Metal Nanoparticles for the Applications in Proton Exchange Membrane Fuel Cells (PEMFCs)

“…By choosing different kinds of polyelectrolytes the surface of the CNT can be also negatively charged in order to the deposit of positively charged NPs. The electrostatic approach has been used to build mixed Au/MWCNT layers using the LBL (layer-by-layer) methodology (Kim & Sigmund, 2004). In the work, the acid-functionalized MWCNTs were first covered with a layer of a positively charged polymer [PDDA, poly(diallyldimethylammonium chloride)] and then with a layer of a negatively charged polymer [PSS,].…”

Purification, Functionalization, and Bioconjugation of Carbon Nanotubes

“…Resuspend the collected solids in 1.8 L of water with 20 mL of Triton X-100 surfactant, and adjust the mixture to pH 10 with sodium hydroxide. (36)(37)(38)(39)(40). This section describes some key protocols for the preparation of thiolated CNTs, and the self-assembly of gold and other metallic nanoparticles onto such thiol-modified CNTs.…”