سال:1396 | دوره: | شماره: |تعداد مقالات:10

In the present investigation surface modification of silica nanoparticles by alumina was carried out by solgel process. Fourier transform infrared (FTIR) and X-ray fluorescence (XRF) confirmed the synthesis of silica and the surface modification as alumina is anchored to silica surface. Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) investigations observed that alumina doping affected significantly the morphology, particle size distribution and surface area of the synthesized nanoparticles. From N2 adsorption-desorption isotherms studies it was further noted that alumina doping improved the pore volumes of the synthesized silica nanoparticles and the synthesized silica alumina nanoparticles are mesoporous materials. The hydrophobicity test and thermal stability results confirmed the modification and conversion of silica to hydrophobic materials using alumina.

In this paper, we propose and evaluate a novel design of a lightly doped drain and source carbon nanotube field effect transistor (LDDS-CNTFET) with a negative differential resistance (NDR) characteristic, called negative differential resistance LDDS-CNTFET (NDR-LDDS-CNTFET). The device was simulated by using a non equilibrium Green’s function method. To achieve this phenomenon, we have created two quantum wells in the intrinsic channel by using two n-type regions. In the wells that are separated by a thin barrier, two resonance states are generated. On the other hand, the thickness of the barrier between the source and the well is variable depending on the energy level. Accordingly, with increasing gate-source voltage, the number of tunneling electrons and consequently drain-source current are varied. Furthermore, we have presented a structure with two n-type and three p-type regions in the channel that illustrates a larger NDR region. In this structure, the peak and valley of the drain-source current are shifted when compared with the previous structure. Finally, we investigated the effect of doping concentration on the NDR parameter.

First-principle calculations were carried out to investigate the adsorption of CO over Cun nanoclusters. The structural, spectroscopic and electronic properties like optimized geometries, HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital) energy levels, binding energy, adsorption energy, vibrational frequency and density of states (DOSs) of the pure Cun nanoclusters, and CunCO complexes in their ground state were thoroughly analyzed. The CO adsorbed on the Cun nanoclusters showed a stretch frequency at 1950-2052 cm-1, which was red-shifted relative to that of gas-phase CO (2143 cm-1). This red-shift was believed to arise from the charge transfer from the Cu metal d states to the CO antibonding 2p* level. The CO adsorption on the Cu nanoclusters was chemisorption in nature with the Cu-C bond length (adsorption height) in the range of 1.85-1.92 Å.

Density functional theory (DFT) based calculations have been performed to examine the relaxations of tautomers of 4-hydroxyl-6-methylpyridin-2(1H)-one (MPO), as a representative of pyridinone derivatives, at the fullerene (C60) surfaces. Optimized molecular properties including energies, dipole moments and atomic scale quadrupole coupling constants (CQ) have been evaluated to investigate the structural and electronic properties of the models. The structural configurations of tautomers show different relaxations at the C60 surface yielding different magnitudes of total and binding energies. Moreover, deformation of each tautomer due to relaxation at the C60 surface with respect to the initial singular structure has been examined. Complimentary parameters of energy gaps and dipole moments exhibit the effects of relaxations at the C60 surface for the MPO counterparts. Atomic scale CQ properties also indicate that the electronic properties of atoms show significant changes for tautomers and hybrid systems. As a final note, the tautomeric structures in singular and hybrid forms exhibit different electronic properties because of effects of interactions with C60, especially for the interaction regions.

Nowadays, green chemistry and its advantages are generating interest of researchers toward ecofriendly biosynthesis of the metallic nanoparticles. In this research, a rapid, simple and green method was developed for the synthesis of silver nanoparticles using aqueous extract of Prangos ferulaceae leaves. The synthesized silver nanoparticles were characterized by UV-Vis spectroscopy, scanning electron microscopy (SEM), dynamic light scattering (DLS), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) methods. The results of DLS, SEM, EDAX, XRD and UV-Vis techniques confirm the synthesis and formation of uniform and spherical shape of silver nanoparticles with average particles size around 10 nm. The aqueous extract of Prangos ferulaceae leaves was found to displays strong potential for the reduction of silver ions and producing of the silver nanoparticles via a very cost effective, clean, nontoxic, ecofriendly method which can be manufactured at a large scale.

Theoretical study of the electronic structure, and nonlinear optical properties (NLO) analysis of 12-crown-4 were done using Density Functional Theory (DFT) evaluations at the B3LYP/6-311G (d, p) level of theory. The optimized structure is nonlinear compound as indicated from the dihedral angles were presented. The calculated EHOMO and ELUMO energies of 12-Crown-4 (12CN4) can be used to explain the charge transfer in 12-Crown-4 (12CN4) and to calculated the global properties; the chemical hardness (h), softness (S) and electronegativity (χ). The NLO parameters: static dipole moment (m), polarizability (a), anisotropy polarizability (Da) and first order hyperpolarizability (btot) of the 12-Crown-4 (12CN4) have been calculated at the same level of theory. The molecular electrostatic potential (MEP) and electrostatic potential (ESP) for the title molecule were investigated and analyzed. Also the electronic absorption spectra were measured in ethanol and water solvents and the assignment of the observed bands has been discussed by timedependent density functional theory (TD-DFT) calculations. The correspondences between calculated and experimental transitions energies are satisfactory. From the experimental conductance measurements, the association thermodynamic parameters (KA, ΔGA, ΔHA and DSA) and complex formation thermodynamic parameters (Kf, DGf, DHf and DSf) for nano-CuSO4 in presence of 12-crown-4 (12CN4) as chelating agent in 10% ethanol – water solvents at different temperatures (298.15, 303.15, 308.15 and 313.15K) were applied and calculated.

Template synthesis is a powerful method for the preparation of nanoscale materials with specific size and shape. Cadmium oxide (CdO) nanoparticles were prepared by using sodium dodecyl sulfate (SDS), Cd(OAc)2.2H2O and sodium hydroxide as starting materials. The sample was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM). The XRD pattern proves that the final product has cubic phase and the particle size diameter of the nanoparticles are 36.4 nm. The SEM was used for direct visualization of the size and shape of the nanoparticles. The morphology of the CdO was found nanospherical. Antibiotics are a major class of drugs included in the designation of emerging contaminants, representing a high risk to natural ecosystems. We studied the degradation of Sulfathiazole antibiotic by nanosized CdO under ultraviolet irradiation. Various experimental parameters such as initial Sulfathiazole (STZ) concentrations, initial CdO concentration and initial pH were investigated. According to the results this method can be good performance in removal of Sulfathiazole.

ZnO thin film of 80 nm thickness was deposited by the sol-gel spin coating method on SiO2/Si substrate and subsequently post-annealed at 500oC with a flow of oxygen for 60 min. Crystallographic structure of the sample was characterized by X-ray diffraction (XRD) method while a field emission scanning electron microscope (FESEM) was used to investigate the surface physical morphology and chemical composition. The sensitivity of the sample was tested to acetic acid vapor with different concentrations (20 ppm, 40 ppm, and 80 ppm) in the temperature range of 200-400oC. The results showed that the ZnO thin film can be introduced as an acetic acid vapor sensor with a good reliability and detection limit of 20 ppm at the operating temperature of 320oC.

Recently, the demands for the production of many different types of plastic wastes are greatly growing that subsequently, lead to the serious challenges in environmental considerations. Since, these materials are rarely resolved by microorganisms, hence, their recycling to the useful materials is crucial. In the present study, we used a solution electrospinning technique to synthesize nano/microfibers. SEM and FTIR analyses were performed for characterization of the prepared samples. The investigations obviously confirmed the formation of nano/microfibers of polyethylene terephthalate (PET), polystyrene (PS) and polycarbonate (PC) from the related waste plastics. To investigate the effect of various operational parameters of electrospinning method, the effect of the used needle diameter and voltage difference was taken into consideration.

Amitriptyline hydrochloride is a highly permeable active pharmaceutical ingredient (API). The function of these drugs is to block the reuptake of the neurotransmitters, norepinephrine and serotonin in the central nervous system. The nano-sized Amitriptyline (AT) imprinted polymer particles were synthesized successfully. The nanoparticles were characterized by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and thermal gravimetric (TG) methods. AT-imprinted polymer was prepared using suspension polymerization in silicon oil with AT as template, Methacrylic acid (MAA) as functional monomer and ethylene glycol dimethacrylate (EGDMA) as cross-linker. As illustrated in SEM images, it is possible to obtain real nano-sized molecular imprinted polymer particles (around 80 nm) with approximately spherical shapes, through the methods and techniques presented and discussed in this study. Thermal analyzes indicated that, an abrupt weight loss for nano-sized MIP was observed at 310oC. This mass loss can be attributed to the loss of nano-sized MIP chain degradation.