The preparation of nanocomposite materials from carbon nanotubes (CNTs) and metal or metal oxide nanoparticles has important implications to the development of advanced catalytic and sensory materials. This paper reports findings of an investigation of the preparation of nanoparticle-coated carbon nanotube composite materials. Our approach involves molecularly mediated assembly of monolayer-capped nanoparticles on multiwalled CNTs via a combination of hydrophobic and hydrogen-bonding interactions between the capping/mediating shell and the CNT surface. The advantage of this route is that it does not require tedious surface modification of CNTs. We have demonstrated its simplicity and effectiveness for assembling alkanethiolate-capped gold nanoparticles of 2-5 nm core sizes onto CNTs with controllable coverage and spatially isolated character. The loading and distribution of the nanoparticles on CNTs depend on the relative concentrations of gold nanoparticles, CNTs, and mediating or linking agents. The composite nanomaterials can be dispersed in organic solvent, and the capping/linking shells can be removed by thermal treatment to produce controllable nanocrystals on the CNT surfaces. The nanocomposite materials are characterized using transmission electron microscopy and Fourier transform infrared spectroscopy techniques. The results will be discussed in terms of developing advanced catalytic and sensory nanomaterials.

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Thin films derived from nanocrystal cores and functionalized linkers provide a large surface area-to-volume ratio and three-dimensional ligand framework. This paper describes the results of an investigation of the interfacial mass flux and binding properties of such thin films using an electrochemical quartz crystal nanobalance technique. The hydrogen-bonding assembly from gold nanocrystals and 11-mercaptoundecanoic acid was studied as a model system. The results reveal four distinctive mass response characteristics upon pH tuning or metal ion binding. First, the protonation-deprotonation characteristic of the carboxylic acid groups in the nanostructured framework is dependent on particle core size and film thickness. Second, the pHtunable cationic redox reaction across the electrode|film|electrolyte interface is accompanied by a large cationic electrolyte mass flux. Third, the spontaneous complexation to copper ions by the nanostructured carboxylate framework is reflected by a mass increase of the film. Fourth, the redox reaction of copper loaded in the nanostructured film is accompanied by fluxes of electrolyte cations across the electrode|film|electrolyte interface which compensate electrostatically the fixed negative charges. On the basis of the mass change detected in the presence of a series of electrolyte cations, a linear relationship was determined between the mass increase and the atomic mass of the cation, and a concurrent flux of solvent molecules was also revealed. Implications of the findings to the delineation of the design parameters of the nanostructured ligand framework for controlled release and environmental monitoring or removal of metals are also discussed.

This paper reports the result of a study of organic-inorganic network assembles as chemically sensitive interfacial materials. Core-shell gold nanoparticles of a 5 nm size and organic linkers such as 1,9-nonanedithiol and 1,5-pentadithiol are utilized as building blocks for constructing network assembles on planar substrates. To explore the responsive properties of such materials to volatile organic compounds, we utilized interdigitated microelectrodes as transducer. The responses at these nanostructured interfaces are demonstrated to be dependent on the chain length of the linking molecules. The difference of molecular interactions at the nanostructured interface has a significant impact to the response profile and sensitivity. The implications of the findings to the delineation of design parameters for constructing organic-inorganic network assemblies as chemically-sensitive interfacial materials are also discussed.