Synthesis of One-Dimensional SiC Nanostructures from a Glassy Buckypaper

A simple and scalable synthetic strategy was developed for the fabrication of one-dimensional SiC nanostructuresnanorods and nanowires. Thin sheets of single-walled carbon nanotubes (SWNTs) were prepared by vacuum filtration and were washed repeatedly with sodium silicate (Na₂SiO₃) solution. The resulting “glassy buckypaper” was heated at 1300–1500 °C under Ar/H₂ to allow a solid state reaction between C and Si precursors to form a variety of SiC nanostructures. The morphology and crystal structures of SiC nanorods and nanowires were characterized using scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), energy-dispersive X-ray spectroscopy (EDX), electron diffraction (ED), and X-ray diffraction (XRD) techniques. Furthermore, electrical conductance measurements were performed on SiC nanorods, demonstrating their potential applications in high-temperature sensors and control systems

Photoinduced Charge Transfer and Acetone Sensitivity of Single-Walled Carbon Nanotube–Titanium Dioxide Hybrids

The unique physical and chemical properties of single-walled carbon nanotubes (SWNTs) make them ideal building blocks for the construction of hybrid nanostructures. In addition to increasing the material complexity and functionality, SWNTs can probe the interfacial processes in the hybrid system. In this work, SWNT–TiO₂ core/shell hybrid nanostructures were found to exhibit unique electrical behavior in response to UV illumination and acetone vapors. By experimental and theoretical studies of UV and acetone sensitivities of different SWNT–TiO₂ hybrid systems, we established a fundamental understanding on the interfacial charge transfer between photoexcited TiO₂ and SWNTs as well as the mechanism of acetone sensing. We further demonstrated a practical application of photoinduced acetone sensitivity by fabricating a microsized room temperature acetone sensor that showed fast, linear, and reversible detection of acetone vapors with concentrations in few parts per million range

Corking Carbon Nanotube Cups with Gold Nanoparticles

Nitrogen doping of carbon nanotubes during chemical vapor deposition synthesis can create unique stacked cup-shaped structures termed as nitrogen-doped carbon nanotube cups (NCNCs). These cups have semielliptical hollow cavities and elevated reactivity which could lead to various applications. In this work, by applying intense ultrasonication to the as-synthesized NCNCs, we demonstrated an effective mechanical method to isolate the individual cups with opened cavities from their stacks. The graphitic structures of the isolated cups and their inherent nitrogen functionalities were characterized by comprehensive microscopic and spectroscopic methods. In particular, we quantitatively determined the existence of amine functionalities on NCNCs and found that they were preferentially distributed at the open edges of the cups, providing localized reactive sites. Further, by thiolating the amine groups with 3-mercapto-propionic acid, we were able to effectively cork the isolated cups by gold nanoparticles with commensurate diameters. These cup-shaped carbon nanomaterials with controlled inner volumes and gold nanoparticle corks could find potential applications as nanoscale reaction containers or drug delivery vehicles

Rigid versus Flexible Ligands on Carbon Nanotubes for the Enhanced Sensitivity of Cobalt Ions

Carbon nanotubes have shown great promise in the fabrication of ultracompact and highly sensitive chemical and biological sensors. Additional chemical functionalization schemes can controllably improve selectivity of the carbon nanotube-based sensors; however, the exact transduction mechanism is still under debate. In this article we detail the synthesis and selective response of single-walled carbon nanotubes (SWNTs) functionalized with polyazomethine (PAM) polymer toward the application of a specific trace metal ion detector. The response of the polymer system was compared to shape persistent macrocycle (MAC) comprised of identical ion coordination ligands. While ion detection with rigid MAC/SWNT chemiresistor was comparable to bare SWNT, flexible PAM offers significant SWNT signal amplification, allowing for picomolar detection of Co²⁺ ions with both selectivity and a fast response. We hypothesized that rearrangement of the flexible PAM on the SWNT network is a sensing mechanism which allows for ultrasensitive detection of metal ions. The electron transfer and polymer rearrangement on the SWNT were studied by a combination of optical spectroscopy and electrical measurementsultimately allowing for a better understanding of fundamental mechanisms that prompt device response

Welding of Gold Nanoparticles on Graphitic Templates for Chemical Sensing

Controlled self-assembly of zero-dimensional gold nanoparticles and construction of complex gold nanostructures from these building blocks could significantly extend their applications in many fields. Carbon nanotubes are one of the most promising inorganic templates for this strategy because of their unique physical, chemical, and mechanical properties, which translate into numerous potential applications. Here we report the bottom-up synthesis of gold nanowires in aqueous solution through self-assembly of gold nanoparticles on single-walled carbon nanotubes followed by thermal-heating-induced nanowelding. We investigate the mechanism of this process by exploring different graphitic templates. The experimental work is assisted by computational studies that provide additional insight into the self-assembly and nanowelding mechanism. We also demonstrate the chemical sensitivity of the nanomaterial to parts-per-billion concentrations of hydrogen sulfide with potential applications in industrial safety and personal healthcare

Defect-Induced Near-Infrared Photoluminescence of Single-Walled Carbon Nanotubes Treated with Polyunsaturated Fatty Acids

Single-walled carbon nanotubes (SWCNTs) have been incorporated in many emerging applications in the biomedical field including chemical sensing, biological imaging, drug delivery, and photothermal therapy. To overcome inherent hydrophobicity and improve their biocompatibility, pristine SWCNTs are often coated with surfactants, polymers, DNA, proteins, or lipids. In this paper, we report the effect of polyunsaturated fatty acids (PUFAs) on SWCNT photoluminescence. A decrease in the SWCNT bandgap emission (E₁₁) and a new red-shifted emission (E₁₁^–) were observed in the presence of PUFAs. We attribute the change in SWCNT photoluminescence to the formation of oxygen-containing defects by lipid hydroperoxides through photo-oxidation. The observed changes in near-infrared emission of SWCNTs are important for understanding the interaction between SWCNTs and lipid biocorona. Our results also indicate that photoexcited SWCNTs can catalyze lipid peroxidation similarly to lipoxygenases

Electronic Detection of Bacteria Using Holey Reduced Graphene Oxide

Carbon nanomaterials have been widely explored for diverse biosensing applications including bacterial detection. However, covalent functionalization of these materials can lead to the destruction of attractive electronic properties. To this end, we utilized a new graphene derivative, holey reduced graphene oxide (hRGO), functionalized with Magainin I to produce a broad-spectrum bacterial probe. Unlike related carbon nanomaterials, hRGO retains the necessary electronic properties while providing the high percentage of available oxygen moieties required for effective covalent functionalization

Oxidative Unzipping of Stacked Nitrogen-Doped Carbon Nanotube Cups

We demonstrate a facile synthesis of different nanostructures by oxidative unzipping of stacked nitrogen-doped carbon nanotube cups (NCNCs). Depending on the initial number of stacked-cup segments, this method can yield graphene nanosheets (GNSs) or hybrid nanostructures comprised of graphene nanoribbons partially unzipped from a central nanotube core. Due to the stacked-cup structure of as-synthesized NCNCs, preventing complete exposure of graphitic planes, the unzipping mechanism is hindered, resulting in incomplete unzipping; however, individual, separated NCNCs are completely unzipped, yielding individual nitrogen-doped GNSs. Graphene-based materials have been employed as electrocatalysts for many important chemical reactions, and it has been proposed that increasing the reactive edges results in more efficient electrocatalysis. In this paper, we apply these graphene conjugates as electrocatalysts for the oxygen reduction reaction (ORR) to determine how the increase in reactive edges affects the electrocatalytic activity. This investigation introduces a new method for the improvement of ORR electrocatalysts by using nitrogen dopants more effectively, allowing for enhanced ORR performance with lower overall nitrogen content. Additionally, the GNSs were functionalized with gold nanoparticles (GNPs), resulting in a GNS/GNP hybrid, which shows efficient surface-enhanced Raman scattering and expands the scope of its application in advanced device fabrication and biosensing

Indium OxideSingle-Walled Carbon Nanotube Composite for Ethanol Sensing at Room Temperature

Utilizing a sol-gel synthesis, indium oxide is grown on the surface of oxidized single-walled carbon nanotubes (SWCNT) to form a hybrid material with high conductivity and sensitivity toward certain organic vapors. The room-temperature sensing of dilute ethanol and acetone vapors on the surface of indium oxide/SWCNT hybrid material is studied using electrical conductance experiments in a nonoxidizing environment. Through testing of variously calcinated materials, it was observed that the degree of annealing greatly affects the material’s response to acetone and ethanol, such that the intermediate calcination condition yields the best sensitivity. DFT simulations are used to study the interface between defective SWCNT and indium oxide, as well as the interaction between ethanol and acetone molecules with the indium oxide/SWCNT hybrid material

The Effect of Metal Catalyst on the Electrocatalytic Activity of Nitrogen-Doped Carbon Nanotubes

Nitrogen-doped and undoped carbon nanotubes (CNTs) were synthesized from ferrocene, nickelocene, and cobaltocene metal catalysts. Electrochemical testing for an oxygen reduction reaction (ORR) showed that nitrogen-doped CNTs synthesized from ferrocene had improved catalytic activity while nanotubes synthesized from nickelocene and cobaltocene, doped with a comparable amount of nitrogen and having similar stacked-cups structure as nitrogen doped CNTs from ferrocene, had a performance only slightly better than that of undoped CNTs. Ferrocene-based nitrogen-doped CNTs also demonstrated similar long-term stability and higher CO tolerance compared to Pt/C catalyst. Detailed ORR mechanisms were also studied and carbon nanomaterials showed different ORR processes as a result of the metal catalyst utilized in the chemical synthesis. Nitrogen-doped and undoped CNTs synthesized from nickelocene show a preferential 4-electron process as compared to materials synthesized from ferrocene and cobaltocene. We believe that the metal used in the growth process regulates the mechanism of oxygen reduction and can be used to develop improved nitrogen-doped carbon nanomaterials as nonprecious-metal catalysts for fuel cells