INTERNATIONAL NANO LETTERS (INL)
Year:2013 | Volume:3 | Issue:3|Papers Count:15

Sulfonic acid-functionalized ordered nanoporous sodium montmorillonite has been found to be a mild and efficient solid acid catalyst for the chemoselective protection of a variety of carbonyl compounds as oxathiolanes in good to excellent yields. The present method offers several advantages such as short reaction times, high yields, simple procedure and mild conditions. Also, the catalyst could be recycled and reused at least for five times without noticeably decreasing the catalytic activity.

In this article, using the Tauc model, the absorption spectrum fitting method was applied to estimate the optical band gap and width of the band tail of the CdSe nanostructural films that requires only the measurement of the absorbance spectrum, and no additional information such as the film thickness or reflectance spectra is needed. Samples are prepared by chemical bath deposition method. Fabricated nanostructural thin films are thick but are composed from nanoparticles.

Ex situ spectroscopic ellipsometry (SE) measurements have been employed to investigate the effect of liquid-phase hydrofluoric acid (HF) cleaning on Si<100>surfaces for microelectromechanical systems application. The hydrogen terminated (H-terminated) Si surface was realized as an equivalent dielectric layer, and SE measurements are performed. The SE analyses indicate that after a 20-s 100: 5 HF dip with rinse, the Si (100) surface was passivated by the hydrogen termination and remained chemically stable. Roughness of the HF-etched bare Si (100) surface was observed and analyzed by the ex-situ SE. Evidence for desorption of the H-terminated Si surface layer is studied using Fourier transform infrared spectroscopy and ellipsometry, and discussed. This piece of work explains the usage of an ex situ, non-destructive technique capable of showing state of passivation, the H-termination of Si<100>surfaces.

An amplitude-modulated laser, in the presence of a static magnetic field, interacts with an array of carbon nanotubes embedded on a metallic surface. The laser exerts a pondero motive force on the free electrons of carbon nanotubes at twice the modulation frequency that falls in the terahertz (THz) range. Each nanotube acts as an oscillatory electric dipole, producing THz radiations. The presence of magnetic field shifts the resonance condition and provides tunability. The THz radiation power increases with magnetic field strength.

This paper presents the structural, optical and photoluminescence properties of wet chemically synthesized ZnO: Pd2+ colloidal nanocrystals characterised by X-ray diffraction, scanning electron microscopy/energy-dispersive X-ray spectroscopy (EDS) and Fourier transform infrared spectroscopic techniques. Increase in lattice parameters from diffraction data indicates the incorporation of Pd2+ in the ZnO crystal lattice. A small amount of dopant favours the formation of stoichiometric ZnO nanoparticles; otherwise, non-stoichiometric nanocrystal formation was observed from the EDS data. The optical gap was found to decrease with the doping concentration, except for the small dopant level of 0.05% of Pd2+where an increase in the optical gap was observed. Intensities of characteristic luminescence bands for pure ZnO nanocrystals (357, 387 and 420 nm) were found to decrease with the increasing Pd2+ concentration, and two new bands centred at 528 and 581 nm for 0.5% Pd2+ concentration were observed.These results have been explained on the basis of change in the oxygen vacancy-related defects and/or formation of new trap states which in turn affect the luminescence properties of ZnO: Pd2+ nanocrystals, which are important in the realisation of visible light-emitting solid-state devices.

A green and efficient procedure for the preparation of bis (indolyl) methanes via the condensation of indoles with various carbonyl compounds in the presence of catalytic amount of nano silica gel under ultrasonic irradiation in good to excellent yields (83% to 94%) in solvent-free condition is described. Short reaction time, easy and quick isolation of the products, environmentally friendly procedure, excellent chemo selectivity, and excellent yields are the main advantages of this procedure. Native nanosilica gel was used as an inexpensive and readily available catalyst without any support of reagent or modification on it. The reaction is carried out in solvent-free condition in the absence of ultrasonic irradiation at 80oC, too. This methodology offers significant improvements for the synthesis of bis (indolyl) methane's with regard to the yield of products, simplicity in operation, and green aspects by avoiding toxic catalysts and solvents. Recovery and recycling of the silica nanoparticle catalyst were also described.

Electrical and photo response properties of a Al/porous silicon/crystalline silicon/Al structure (Al/PSi/Si/Al) are investigated under irradiation of Nd: YAG laser pulses. The effect of Nd-YAG laser irradiation on the morphological and structural properties of a porous silicon layer is also demonstrated. The porous Si layer is synthesized on a single crystalline p-type Si using electrochemical etching in aqueous hydrofluoric acid at a current density of 20 mA/cm2 for a 40-min etching time. The structure of the porous layer is investigated using atomic force microscopy and optical microscopy. The electrical properties and photo detector figures of merit (responsivity, detectivity, and carrier lifetime) are found to be dependent on the laser fluence.

Nanostructured copper oxide (CuO) thin films were prepared by spray pyrolysis technique. X-ray diffraction was used to investigate the structural properties. Surface morphology was studied using scanning electron microscopy.Microstructure was studied using a transmission electron microscope, and energy-dispersive X-ray analysis was used to determine the elemental composition of prepared nanostructured CuO thin film. Gas-sensing performance was conducted using static gas-sensing system, at different operating temperatures in the range of 200oC to 400oC for the gas concentration of 100 ppm. The maximum sensitivity (S=872) to H2S was found at the temperature of 250oC. Quick response (2 s) and fast recovery (5 s) are the main features of this film.

UV–vis and photoluminescence spectra of the hydrothermally synthesized crystalline lithium metasilicate (Li2SiO3) and lithium disilicate (Li2Si2O5) nanomaterial’s are studied. The intensity of the bands in the emission spectra increases with increasing reaction time in both compounds. The electronic band structure along with density of states calculated by the density functional theory (DFT) method indicates that Li2SiO3 and Li2Si2O5 have an indirect energy band gap of 4.575 and 4.776 eV respectively. The optical properties, including the dielectric, absorption, reflectivity, and energy loss spectra of the compounds, are calculated by DFT method and analyzed based on the electronic structures.

Nanocrystalline cobalt ferrite powder has been synthesised by citrate precursor and co-precipitation methods. Structural characterization of the samples has been carried out using powder X-ray diffraction, Fourier transform infrared spectroscopy (FT-IR) and field emission scanning electron microscope (FE-SEM). Distribution of cations among the two interstitial sites (tetrahedral and octahedral sites) has been estimated by analysing the powder X-ray diffraction patterns by employing Rietveld refinement technique, and the results reveal the existence of samples as a mixed type spinel with cubic structure. It is observed that the distribution of cations and structural parameters are strongly dependent on synthesis method and annealing temperature. The vibrational modes of the octahedral and tetrahedral metal complex in the sample have been examined using FT-IR in the wave number range of 390 to 750 cm-1, and it shows an absorption band within this range, which confirms the spinel structure of the sample. The existence of constituents in the sample, i.e., Co, Fe and O has been authenticated using energy dispersive spectrum with the help of a FE-SEM.

Forced convective heat transfer from a vertical circular tube conveying deionized (DI) water or very dilute Ag-DI water nanofluids (less than 0.02% volume fraction) in a cross flow of air has been investigated experimentally. Some experiments have been performed in a wind tunnel and heat transfer characteristics such as thermal conductance, effectiveness, and external Nusselt number has been measured at different air speeds, liquid flow rates, and nanoparticle concentrations. The cross flow of air over the tube and the liquid flow in the tube were turbulent in all cases. The experimental results have been compared and it has been found that suspending Ag nanoparticles in the base fluid increases thermal conductance, external Nusselt number, and effectiveness. Furthermore, by increasing the external Reynolds number, the external Nusselt number, effectiveness, and thermal conductance increase. Also, by increasing internal Reynolds number, the thermal conductance and external Nusselt number enhance while the effectiveness decreases.

Nanocomposite ZnO-TiO2 powders of varying ZnO/TiO2 molar ratios have been prepared from their salt/compound by heating at 600°C and 900°C and characterized using scanning electron microscope and X-ray diffraction techniques. The nanosized powders can decolorize/degrade brilliant golden yellow (BGY), an azo dye extensively used in textile industries, in water under solar irradiation. The effects of various parameters such as photocatalyst loading, molar ratio of ZnO/TiO2, pH of the solution, initial dye concentration, and irradiation time on the photodecolorization have been investigated. ZnO-TiO2 nanocomposite (6 g/L) in the molar ratio of 1:1 or 3:1, prepared at 900°C, can efficiently decolorize about 98% of 20 mg/L BGY at pH of about 7 by 2-h illumination in sunlight. The initial dye decolorization follows pseudo-first-order kinetics. Finally, trial experiments were done using real textile wastewater to find out the effectiveness of the photo catalysts to a more complex system.

In this work, transparent heterojunction between zinc oxide (ZnO) and poly (N-vinyl carbazole) (PVK) was fabricated by solution processing techniques such as spin-coating and dip-coating techniques; then, its performance was studied using current (I) -voltage (V) measurement at room temperature. Before fabricating the heterojunction, initially, the growth characteristics of both thin films were independently optimized on a well-cleaned glass substrate, then its structural properties, optical properties, and surface topography were characterized using an Xray diffractometer, UV-VIS-NIR spectrophotometer, and atomic force microscope, respectively. The structural analysis confirms the existence of a PVK thin film in amorphous nature and ZnO thin film in hexagonal crystal structure. The transparent nature of the heterojunction was found to be more than 85% in the visible and NIR regions with the absorption onset in the ultraviolet region. The observed experimental results explored the possibilities of fabricating ZnO/PVK transparent heterojunction by solution-based routes on a transparent fluorine-doped tin oxide substrate for transparent electronics applications.

Natural flaky graphite in Shandong, China was purified by H2O2, a new patent method to produce graphite without sulfur and used as precursor to prepare exfoliated graphite through microwave irradiated expansion with some chemicals (such as hydrogen peroxide, nitric acid, and acetic acid). With the centrifugation process, graphene was synthesized by using an efficient and simple method under ultrasonic and microwave irradiation at the room temperature. Natural graphite and exfoliated graphite were characterized by X-ray diffraction and scanning electronic microscopy, and the resultant graphene was investigated and confirmed by atomic force microscopy, Raman micro-spectrometer, etc. Natural graphite in Shandong, China, consisted of mainly hexagonal (2H) and a little rhombohedral structure (3R), was beneficial for the synthesis of graphene. Graphene-like nanosheets about 1 to 3 nm, around three to five carbon layers can be synthesized efficiently by microwave and ultrasonic irradiation with natural graphite.

Herein, the interaction of hydrogen sulfide with inside and outside single-wall carbon nanotube of (5, 0) and (5, 5) is investigated using density functional theory at B3LYP/6-31G* level of theory in the gaseous phase by Gaussian 09. The adsorption energies, thermodynamic properties, highest occupied molecular orbital, lowest unoccupied molecular orbital, energy gaps, and partial charges of the interacting atoms are also studied during two kinds of rotation of hydrogen sulfide (H2S) molecules as vertical and horizontal to the main axes of the nanotube. For these systems, the binding energy of H2S-single-wall carbon nanotubes is low and the process is thermodynamically near-simultaneous.