Synthesis of single-walled carbon nanotubes using binary (Fe, Co, Ni) alloy nanoparticles prepared in situ by the reduction of oxide solid solutions

Passing a H2–CH4 mixture over oxide spinels containing two transition elements as in Mg0.8MyM'zAl2O4 (M, M' = Fe, Co or Ni, y + z = 0.2) at 1070°C produces small alloy nanoparticles which enable the formation of carbon nanotubes. Surface area measurements are found to be useful for assessing the yield and quality of the nanotubes. Good-quality single-walled nanotubes (SWNTs) have been obtained in high yields with the FeCo alloy nanoparticles, as evidenced by transmission electron microscope images and surface area measurements. The diameter of the SWNTs is in the 0.8–5 nm range, and the multiwalled nanotubes, found occasionally, possess very few graphite layers

An investigation of carbon nanotubes obtained from the decomposition of methane over reduced Mg1− xM xAl2O4 spinel catalysts

Carbon nanotubes produced by the treatment of Mg1−xMxAl2O4 (M = Fe, Co, or Ni; x = 0.1, 0.2, 0.3, or 0.4) spinels with an H2–CH4 mixture at 1070 °C have been investigated systematically. The grains of the oxide-metal composite particles are uniformly covered by a weblike network of carbon nanotube bundles, several tens of micrometers long, made up of single-wall nanotubes with a diameter close to 4 nm. Only the smallest metal particles (<5 nm) are involved in the formation of the nanotubes. A macroscopic characterization method involving surface area measurements and chemical analysis has been developed in order to compare the different nanotube specimens. An increase in the transition metal content of the catalyst yields more carbon nanotubes (up to a metal content of 10.0 wt% or x = 0.3), but causes a decrease in carbon quality. The best compromise is to use 6.7 wt% of metal (x = 0.2) in the catalyst. Co gives superior results with respect to both the quantity and quality of the nanotubes. In the case of Fe, the quality is notably hampered by the formation of Fe3C particles

Silk and its composites for humidity and gas sensing applications

Silk fibroin (SF) is a natural protein largely used in the textile industry with applications in bio-medicine, catalysis as well as in sensing materials. SF is a fiber material which is bio-compatible, biodegradable, and possesses high tensile strength. The incorporation of nanosized particles into SF allows the development of a variety of composites with tailored properties and functions. Silk and its composites are being explored for a wide range of sensing applications like strain, proximity, humidity, glucose, pH and hazardous/toxic gases. Most studies aim at improving the mechanical strength of SF by preparing hybrids with metal-based nanoparticles, polymers and 2D materials. Studies have been conducted by introducing semiconducting metal oxides into SF to tailor its properties like conductivity for use as a gas sensing material, where SF acts as a conductive path as well as a substrate for the incorporated nanoparticles. We have reviewed gas and humidity sensing properties of silk, silk with 0D (i.e., metal oxide), 2D (e.g., graphene, MXenes) composites. The nanostructured metal oxides are generally used in sensing applications, which use its semiconducting properties to show variation in the measured properties (e.g., resistivity, impedance) due to analyte gas adsorption on its surface. For example, vanadium oxides (i.e., V2O5) have been shown as candidates for sensing nitrogen containing gases and doped vanadium oxides for sensing CO gas. In this review article we provide latest and important results in the gas and humidity sensing of SF and its composites

Synthesis of inorganic nanotubes

Nanotubes constitute an exciting class of one-dimensional nanomaterials of which carbon nanotubes are recognized widely as materials of importance. The possibility of having inorganic nanotubes was recognized early in the 1990s, accompanied by the report of nanotubes of MoS<SUB>2</SUB> and WS<SUB>2</SUB>. Since then, nanotubes of several inorganic materials have been prepared and characterized. While nanotubes of metal chalcogenides and oxides form a high proportion of the inorganic nanotubes investigated hither to, nanotubes of many other materials have also been prepared and characterized. Several synthetic strategies including both physical and chemical methods have been employed, of which the use of templates, precursors, and hydro- or solvothermal methods are prominent. In this article, we shall present a brief account of the present status of the synthesis of nanotubes of elemental materials as well as binary and complex metal oxides, chalcogenides, pnictides and carbides

Studies on effect of temperature on carbonization of silk (Bombyx mori) and its application as proximity sensor

Silk, a pyroprotein with its unique micro-structural features comprises of soft amorphous Image 1 regions containing compact Image 2-sheet crystals resulting in its potent characteristics. Annealing in inert atmosphere causes carbonization followed by graphitization of these stable Image 2-sheet-rich silk fibroins (SFs). Here we carry out systematic studies of annealed silk fibroin (Bombyx mori) in the temperature range of 200-1200°C by various analytical techniques. Herein the structural changes in SFs at different annealing temperature have been discussed using Raman, FTIR, XPS, XAES, SEM, XRD characterization techniques. Notably XPS and XAES studies were executed to examine the influence of sp2/sp3 ratio and the presence of hetero-atom on D-parameter value in silk Image 2-sheet material on gradual increase in annealing temperature. The mechanical properties of SFs were measured using UTM. The application of carbonized silk fibroins (CSF) as a proximity sensor is also investigated and proposed as a probable active material

Binding of DNA Nucleobases and Nucleosides with Graphene

Interaction of two different samples of graphene with DNA nucleobases and nucleosides is investigated by isothermal titration calorimetry. The relative interaction energies of the nucleobases decrease in the order guanine (G) &gt; adenine (A) &gt; cytosine (C) &gt; thy mine (T) in aqueous solutions, although the positions of C and T seem to be interchangeable. The same trend is found with the nucleosides. Interaction energies of the A-T and G-C pairs are somewhere between those of the constituent bases. Theoretical calculations including van der Wools interaction and solvation energies give the trend G &gt; A similar to T &gt; C. The magnitudes of the interaction energies of the nucleobases with graphene are similar to those found with single-walled carbon nonotubes

Binding of DNA nucleobases and nucleosides with graphene

Interaction of two different samples of graphene with DNA nucleobases and nucleosides is investigated by isothermal titration calorimetry. The relative interaction energies of the nucleobases decrease in the order guanine (G)>adenine (A)>cytosine (C)>thymine (T) in aqueous solutions, although the positions of C and T seem to be interchangeable. The same trend is found with the nucleosides. Interaction energies of the A-T and G-C pairs are somewhere between those of the constituent bases. Theoretical calculations including van der Waals interaction and solvation energies give the trend G>A~T>C. The magnitudes of the interaction energies of the nucleobases with graphene are similar to those found with single-walled carbon nanotubes