Synthesis and characterization of ZnO nanowires by thermal oxidation of Zn thin films at various temperatures

In this research high-quality zinc oxide (ZnO) nanowires have been synthesized by thermal oxidation of metallic Zn thin films. Metallic Zn films with thicknesses of 250 nm have been deposited on a glass substrate by the PVD technique. The deposited zinc thin films were oxidized in air at various temperatures ranging between 450 °C to 650 °C. Surface morphology, structural and optical properties of the ZnO nanowires were examined by scanning electron microscope (SEM), X-ray diffraction (XRD), energy dispersive X-ray (EDX) and photoluminescence (PL) measurements. XRD analysis demonstrated that the ZnO nanowires has a wurtzite structure with orientation of (002), and the nanowires prepared at 600 °C has a better crystalline quality than samples prepared at other temperatures. SEM results indicate that by increasing the oxidation temperature, the dimensions of the ZnO nanowires increase. The optimum temperature for synthesizing high density, ZnO nanowires was determined to be 600 °C. EDX results revealed that only Zn and O are present in the samples, indicating a pure ZnO composition. The PL spectra of as-synthesized nanowires exhibited a strong UV emission and a relatively weak green emission.     

Activity Coefficient Determinations of KCl in the KCl + Formamide + Water Mixed Solvent System Based on Potentiometric Measurements at 298.2 K

In this work mean activity coefficient measurements for KCl in the KCl + formamide + water system, using the potentiometric method, are reported. The electromotive force measurements were performed on a galvanic cell of the type Ag | AgCl | KCl (m), formamide (w%), H₂O (1−w)% | K-ISE, in solvent mixtures containing w=(0,10,20,30, and 40)% mass percent of formamide over ionic strengths ranging from 0.0010 to 3.9578 mol⋅kg⁻¹. Modeling of the activity coefficients of this ternary system was based on an extended Debye–Hückel equation and the Pitzer ion-interaction model. The resulting values of the mean activity coefficients, the osmotic coefficients and the excess Gibbs energy, together with Pitzer ion-interaction parameters (β ⁽⁰⁾, β ⁽¹⁾ and C ^ϕ ) and Debye–Hückel parameters (a, c and d), are reported for the investigated system.     

Efficient simultaneous reverse Monte Carlo modeling of pair-distribution functions and extended x-ray-absorption fine structure spectra of crystalline disordered materials

An efficient implementation of simultaneous reverse Monte Carlo (RMC) modeling of pair distribution function (PDF) and EXAFS spectra is reported. This implementation is an extension of the technique established by Krayzman et al. [J. Appl. Cryst. 42, 867 (2009)] in the sense that it enables simultaneous real-space fitting of x-ray PDF with accurate treatment of Q-dependence of the scattering cross-sections and EXAFS with multiple photoelectron scattering included. The extension also allows for atom swaps during EXAFS fits thereby enabling modeling the effects of chemical disorder, such as migrating atoms and vacancies. Significant acceleration of EXAFS computation is achieved via discretization of effective path lengths and subsequent reduction of operation counts. The validity and accuracy of the approach is illustrated on small atomic clusters and on 5500-9000 atom models of bcc-Fe and α-Fe(2)O(3). The accuracy gains of combined simultaneous EXAFS and PDF fits are pointed out against PDF-only and EXAFS-only RMC fits. Our modeling approach may be widely used in PDF and EXAFS based investigations of disordered materials.     

A miniature gas analyzer made by integrating a chemoresistor with a microchannel

A microfluidic channel is integrated with a tin oxide-based generic gas sensor on a PMMA (polymethyl methacrylate) substrate to fabricate a miniature gas analyzer. The analyte gas diffuses along the air-filled channel to affect the sensor installed in a microcavity positioned at the end of the channel. Analyte diffusion rates, experimentally estimated based on the temporal responses received from the sensor, are connected to the analyte's interactions with the channel walls as well as its diffusivity in air. The analyte-related information is extracted from the recorded responses and used for analyte recognition. A single PMMA channel of 80 μm × 3 mm × 50 mm dimensions facilitates the correct classification of single component contaminants each introduced in a wide concentration range in air. The device is also shown to identify 15 ppm of 2-butanol in air contaminated with 1500 ppm of 1-butanol. The gas analyzer fabricated based on this concept is durable, inexpensive, handheld and suitable for a variety of applications.     

Regioselective Synthesis of Para‐Bromo Aromatic Compounds

Reaction of substituted benzene rings with N‐bromophthalimide, under neutral conditions, gave the corresponding bromo derivatives with a preference for the formation of the para bromo isomer over the ortho isomer. The simple work‐up procedure minimizes loss of product and the yields are good.     

Use of nanoporous Na+-montmorillonite sulfonic acid (SANM) as an eco-benign, efficient and reusable solid acid catalyst for the one-pot synthesis of 14-aryl-14-H-dibenzo[a,j]xanthenes and 1,8-dioxo-dodecahydroxanthene derivatives

Nanoporous Na⁺-montmorillonite sulfonic acid was found to be an efficient and green catalyst for the synthesis of various 14-aryl-14H-dibenzo[a,j]xanthenes and 1,8-dioxo-dodecahydroxanthene derivatives by the reaction of aldehydes with 2-naphthol and 1,3-cyclohexanedione, respectively. This novel synthetic method has the advantages of high yields, short reaction times and recyclability of the catalyst, simplicity and easy workup compared to the conventional methods reported in the literature.     

“Grafting through” approach for synthesis of polystyrene/silica aerogel nanocomposites by in situ reversible addition-fragmentation chain transfer polymerization

Aerogel/polystyrene nanocomposites with mixed free and aerogel-attached polystyrene chains were synthesized using reversible addition-fragmentation chain transfer (RAFT) polymerization. 3-methacryloxypropyldimethylchlorosilane containing a double bond, which could be incorporated into polystyrene chains by a “grafting through” approach, was used as an aerogel modifier. Kinetics of RAFT polymerization of styrene in the presence of modified silica aerogel was studied by monitoring conversion and molar mass values. To further study, attached polymers were detached and their molecular characteristics were compared to free chains. According to results, the presence of silica aerogel particles has a sensible influence on polymerization kinetic and more aerogels result in decreased polymerization rate and conversion. The dispersity (Ð) of polymer chains increased by the addition of silica aerogel. In the case of aerogel-attached polystyrene chains, number-averaged molar mass values were slightly lower than that of free chains. Also, thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC) techniques were used to observe the effect of loading on thermal properties of synthesized nanocomposites.     

Elimination of autofluorescence background from fluorescence tissue images by use of time-gated detection and the AzaDiOxaTriAngulenium (ADOTA) fluorophore

Sample autofluorescence (fluorescence of inherent components of tissue and fixative-induced fluorescence) is a significant problem in direct imaging of molecular processes in biological samples. A large variety of naturally occurring fluorescent components in tissue results in broad emission that overlaps the emission of typical fluorescent dyes used for tissue labeling. In addition, autofluorescence is characterized by complex fluorescence intensity decay composed of multiple components whose lifetimes range from sub-nanoseconds to a few nanoseconds. For these reasons, the real fluorescence signal of the probe is difficult to separate from the unwanted autofluorescence. Here we present a method for reducing the autofluorescence problem by utilizing an azadioxatriangulenium (ADOTA) dye with a fluorescence lifetime of approximately 15 ns, much longer than those of most of the components of autofluorescence. A probe with such a long lifetime enables us to use time-gated intensity imaging to separate the signal of the targeting dye from the autofluorescence. We have shown experimentally that by discarding photons detected within the first 20 ns of the excitation pulse, the signal-to-background ratio is improved fivefold. This time-gating eliminates over 96 % of autofluorescence. Analysis using a variable time-gate may enable quantitative determination of the bound probe without the contributions from the background.     

Synthesis of 2‐Aryl‐5‐oxo‐4‐[2‐(phenylmethylidene)hydrazino]‐2,5‐dihydro‐1H‐pyrrole‐3‐carboxylates by the Reaction between Hydrazones,Acetylenedicarboxylates, and 1‐Aryl‐N,N′‐bis(arylmethylidene)methanediamines

An efficient approach for the preparation of functionalized 2‐aryl‐2,5‐dihydro‐5‐oxo‐4‐[2‐(phenylmethylidene)hydrazino]‐1H‐pyrroles is described. The four‐component reaction between aldehydes, NH₂NH₂?H₂O, dialkyl acetylenedicarboxylates, and 1‐aryl‐N,N′‐bis(arylmethylidene)methanediamines proceeds in EtOH under reflux in good‐to‐excellent yields (Scheme 1). The structures of 4 were corroborated spectroscopically (IR, ¹H‐ and ¹³C‐NMR, and EI‐MS, and, in the case of 4f , by X‐ray crystallography). A plausible mechanism for this type of reaction is proposed (Scheme 2).     

Physical and Rheological Characteristics of Emulsion Model Structures Containing Iranian Tragacanth Gum and Oleic Acid

The physical and rheological properties of oil in water model emulsion systems containing Iranian tragacanth gum (TG) (0.5, 1 g/100 ml emulsions), whey protein isolate (WPI) (2, 4 g/100 ml emulsions), and oleic acid (5, 10 ml/100 ml emulsions) were investigated for droplet-size distribution, creaming index, and rheological properties of emulsions. The shear-thinning behavior of all dispersions was modeled using power law, Cross, and Ellis models. The power law model described the flow behavior of dispersions for its lowest standard error (0.29) and highest determination coefficient (R²) (0.99). Rheological investigation showed that both loss (G″) and storage (G′) modules increased as gum and oil content increased. Delta degree was 0.1 and increased as frequency increased, indicating that liquid-like viscose behavior dominated solid-like elastic behavior. Droplet-size distribution was measured by light scattering and microscopic observations revealed a flocculated system. Gum, WPI, and oil contents decreased the emulsion creaming index with gum concentration having the greatest effect.