Metallic Nanoparticles in Heterogeneous Catalysis

Catalysis Letters - Heterogeneous catalysis is a chemical process achieved at solid–gas or solid–liquid interfaces. Many factors including the particle size, shape and metal-support...     

Spatially resolved near-infrared excited Raman spectroscopy of nanocrystalline diamond films

Scanning Raman spectroscopic measurements were performed on nanocrystalline diamond thin films with 0.5 μm lateral steps and excitation spot limited to 1 μm in diameter using 488 nm and 785 nm excitation wavelengths. The comparison of the spectra measured with different excitation energies showed that in contrast to the well-known five bands in the 488 nm excited Raman spectra of nanocrystalline diamond a number of narrow peaks appears in the spectra when using near-infrared excitation. The intensity and position of the latter vary when moving the excitation spot along the sample. The detailed analysis of the sequences showed that the 785 nm excited Raman spectroscopy allows the detection and identification of the Raman peaks arising from individual diamond crystallites of the nanocrystalline diamond films.     

Synthesis and photocatalytic performance of titanium dioxide nanofibers and the fabrication of flexible composite films from nanofibers

Titanium dioxide nanofibers were synthesized and applied in flexible composite films that are easy to handle and recycle after use. The nanofibers were obtained in a multi-step procedure. First, sodium titanate nanofibers were prepared from TiO2 nanoparticles through the alkali hydrothermal method. In the next step, sodium hydrogen titanate nanofibers were made by washing the sodium titanate nanofibers in HCl solution. Finally, the sodium hydrogen titanate nanofibers were transformed to TiO2 anatase nanofibers by calcination in air. The photocatalytic activity of TiO2 anatase nanofibers were evaluated and compared to a TiO2 nanoparticle catalyst by decomposing methyl orange dye in aqueous solutions. The achieved reaction rate constant of TiO2 anatase nanofibers was comparable to that of Degussa P25. Paper-like flexible composite films were prepared by co-filtrating aqueous dispersions of TiO2 catalyst materials and cellulose. The composite films made from the nanofibers exhibit better mechanical integrity than those of the nanoparticle-cellulose composites.     

Comparison of Nanoscaled Palladium Catalysts Supported on Various Carbon Allotropes

Today there is a need for inexpensive and reliable catalysts due to the increasing demand for ??green?? catalytic processes of high conversion and selectivity. We now report on the performance of palladium nanoparticles supported on various carbon allotropes in the model reaction of cyclohexene hydrogenation. Palladium catalysts supported on pristine and oxidatively functionalized multiwalled carbon nanotubes and activated carbon were synthesized and characterized by transmission electron microscopy, X-ray diffraction, temperature programmed desorption and nitrogen adsorption measurements. Catalyst based on multiwalled carbon nanotube proved to be more active and less prone to deactivation than the activated carbon supported one. This finding could be interpreted on the basis of morphological differences between the supports.     

Moderate anisotropy in the electrical conductivity of bulk MWCNT/epoxy composites

Bulk aligned multi-walled carbon nanotube films and their epoxy composites were prepared and their DC and AC conductivity studied. Nanotube films of up to 2 mm thickness were grown by catalytic chemical vapor deposition. Composites of nanotubes were made by infiltrating the films with a commercial epoxy. DC electrical resistivities in the axial direction of as-grown and purified films were found to be ∼1.2 Ωmm and ∼3.4 Ωmm, respectively. For the transverse direction the resistivity values were higher only with a factor of ∼2. In the case of composites, anisotropy is more pronounced showing more than an order of magnitude higher resistivity in the transverse direction (∼71.4 Ωmm) as compared to the axial value (∼4.2 Ωmm). AC behavior of the films investigated between 1 MHz and 3 GHz shows the presence of inductive and capacitive components at frequencies above ∼100 MHz. The moderate anisotropy for both DC and AC electrical properties are explained on the basis of the films’ structure combined with percolation theory and equivalent circuit models.     

A Novel Catalyst Type Containing Noble Metal Nanoparticles Supported on Mesoporous Carbon: Synthesis,Characterization and Catalytic Properties

We report on a method for the controlled synthesis of a new type of high specific surface area mesoporous carbons denoted as the CMH family. By using mixtures of colloidal silica particles as templates it was possible to synthesize samples exhibiting 1,630 m² g⁻¹ specific surface area and 4.37 cm³ g⁻¹ pore volume. CMH materials exhibit high thermal stability in oxygen and can be used as catalyst supports. This function was demonstrated by synthesizing Pt/CMH and Rh/CMH catalysts and testing them in the hydrogenation of cyclohexene. We have found Pt/CMH to be more stable and easier to regenerate than Rh/CMH.     

Thermal stripping of supramolecular structures: C60 nanorods

The investigated ionic C60 derivative self-assembles into nanorods. When the functional side groups are removed by heating the nanorods to 623 K, they retain their shape. Utilization of lithographic markers allows the study of identical nanostructures before and after heat treatment by dynamic mode atomic force microscopy. Various independent techniques, including Raman spectroscopy and mass spectroscopy demonstrate that the shape-preserving mechanism is a thermal-stripping process, stabilizing the original supramolecular morphology. The latter implies two coherent sub-processes: detachment of the side groups and oligopolymerization running in parallel, eventually yielding rod-shaped C60 polymers. Synthesizing fullerenic polymers in this way can lead to several applications.     

Determination of the diameter distribution of single-wall carbon nanotubes from the Raman G-band using an artificial neural network

A novel, artificial neural network-based method is now available for obtaining the mean diameter of single wall carbon nanotube (SWCNT) samples from the diameter dispersive features of their Raman G-band. The method is demonstrated here for six different diameter SWCNT samples and 14 different excitation wavelengths. With an adequately large pool of standard nanotube samples, the suggested method is a useful complementary technique for SWCNT diameter analysis as it is capable of rapid diameter evaluation without prior knowledge of the relevant phonon dispersion relations.     

Cu–Fe Incorporated Graphene-Oxide Nanocomposite as Highly Efficient Catalyst in the Degradation of Dichlorodiphenyltrichloroethane (DDT) from Aqueous Solution

Topics in Catalysis - Fe/graphene oxide and Cu–Fe/graphene oxide nanocomposite were synthesized by the atomic implantation method to study the photocatalytic degradation of...     

Lightweight porous silica foams with extreme-low dielectric permittivity and loss for future 6G wireless communication technologies

In the next generation wireless communication systems operating at near terahertz frequencies, dielectric substrates with the lowest possible permittivity and loss factor are becoming essential. In this work, highly porous (98.9% ± 0.1%) and lightweight silica foams (0.025 ± 0.005 g/cm3), that have extremely low relative permittivity (εr = 1.018 ± 0.003 at 300 GHz) and corresponding loss factor (tan δ< 3 × 10?4 at 300 GHz) are synthetized by a template-assisted sol-gel method. After dip-coating the slabs of foams with a thin film of cellulose nanofibers, sufficiently smooth surfaces are obtained, on which it is convenient to deposit electrically conductive planar thin films of metals important for applications in electronics and telecommunication devices. Here, micropatterns of Ag thin films are sputtered on the substrates through a shadow mask to demonstrate double split-ring resonator metamaterial structures as radio frequency filters operating in the sub-THz band.