Showing papers in "Physica E-low-dimensional Systems & Nanostructures in 2015"

Density functional theory and molecular dynamics simulation study on corrosion inhibition performance of mild steel by mercapto-quinoline Schiff base corrosion inhibitor

Abstract: Corrosion inhibition mechanism of two mercapto-quinoline Schiff bases, eg., 3-((phenylimino)methyl)quinoline-2-thiol (PMQ) and 3-((5-methylthiazol-2-ylimino)methyl) quinoline-2-thiol (MMQT) on mild steel surface is investigated by quantum chemical calculation and molecular dynamics simulation. Quantum chemical parameters such as EHOMO, ELUMO, energy gap (ΔE), dipolemoment (µ), electronegativity (χ), global hardness (η) and fraction of electron transfers from the inhibitor molecule to the metallic atom surface (ΔN) have been studied to investigate their relative corrosion inhibition performance. Parameters like local reactive sites of the present molecule have been analyzed through Fukui indices. Moreover, adsorption behavior of the inhibitor molecules on Fe (1 1 0) surface have been analyzed using molecular dynamics simulation. The binding strength of the concerned inhibitor molecules on mild steel surface follows the order MMQT>PMQ, which is in good agreement with the experimentally determined inhibition efficiencies. In view of the above, our approach will be helpful for quick prediction of a potential inhibitor from a lot of similar inhibitors and subsequently in their rational designed synthesis for corrosion inhibition application following a wet chemical synthetic route.

Thermal radiation and slip effects on MHD stagnation point flow of nanofluid over a stretching sheet

Abstract: Present model is devoted for the stagnation point flow of nanofluid with magneto-hydrodynamics (MHD) and thermal radiation effects passed over a stretching sheet. Moreover, we have considered the combined effects of velocity and thermal slip. Condition of zero normal flux of nanoparticles at the wall for the stretched flow phenomena is yet to be explored in the literature. Convinced partial differential equations of the model are transformed into the system of coupled nonlinear differential equations and then solved numerically. Graphical results are plotted for velocity, temperature and nanoparticle concentration for various values of emerging parameters. Variation of stream lines, skin friction coefficient, local Nusselt and Sherwood number are displayed along with the effective parameters. Final conclusion has been drawn on the basis of both numerical and graphs results.

Broadband stripline ferromagnetic resonance spectroscopy of ferromagnetic films, multilayers and nanostructures

Abstract: This paper presents a comprehensive critical overview of fundamental and practical aspects of the modern stripline broadband ferromagnetic resonance (BFMR) spectroscopy largely employed for the characterisation of magnetic low-dimensional systems, such as thin ferro- and ferromagnetic, multiferroic and half-metallic films, multi-layers and nanostructures. These planar materials form the platform of the nascent fields of magnonics and spintronics. Experimental and theoretical results of research on these materials are summarised, along with systematic description of various phenomena associated with the peculiarities of the stripline BFMR, such as the geometry of stripline transducers, the orientation of the static magnetic field, the presence of microwave eddy currents, and the impacts of non-magnetic layers, interfaces and surfaces in the samples. Results from 240 articles, textbooks and technical reports are presented and many practical examples are discussed in detail. This review will be of interest to both general physical audience and specialists conducting research on various aspects of magnetisation dynamics and nanomagnetism.

Free vibration of nonlocal piezoelectric nanoplates under various boundary conditions

Abstract: This paper investigates the thermo-electro-mechanical vibration of the rectangular piezoelectric nanoplate under various boundary conditions based on the nonlocal theory and the Mindlin plate theory. It is assumed that the piezoelectric nanoplate is subjected to a biaxial force, an external electric voltage and a uniform temperature rise. The Hamilton's principle is employed to derive the governing equations and boundary conditions, which are then discretized by using the differential quadrature (DQ) method to determine the natural frequencies and mode shapes. The detailed parametric study is conducted to examine the effect of the nonlocal parameter, thermo-electro-mechanical loadings, boundary conditions, aspect ratio and side-to-thickness ratio on the vibration behaviors.

Study on blood flow containing nanoparticles through porous arteries in presence of magnetic field using analytical methods

Abstract: In this paper, flow analysis for a third grade non-Newtonian blood in porous arteries in presence of magnetic field is simulated analytically and numerically. Blood is considered as the third grade non-Newtonian fluid containing nanoparticles. Collocation Method (CM) and Optimal Homotopy Asymptotic Method (OHAM) are used to solve the Partial Differential Equation (PDE) governing equation which a good agreement between them was observed in the results. The influences of the some physical parameters such as Brownian motion parameter, pressure gradient and thermophoresis parameter, etc. on temperature, velocity and nanoparticles concentration profiles are considered. For instance, increasing the thermophoresis parameter (Nt) caused an increase in temperature values in whole domain and an increase in nanoparticles concentration near the inner wall.

Hydrothermal method for the production of reduced graphene oxide

Abstract: Reduced graphene oxide, RGO (also called chemically modified graphene, CMG) was synthesized by a simple hydrothermal method, with graphite oxide (GO), prepared by the modified Hummers method, served as the raw material. Structural and morphological studies indicate the degree of reduction is dependent on the temperature, which is also verified by Raman analysis. The variation in interlayer distance and the intensity ratio of the D to G Raman modes ( I D / I G ) indicates higher reaction temperature can accelerate the reduction of GO. The conductivity also varies with the degree of reduction, as verified by electrochemical analyzer. Moreover, the reaction process affects organic functional groups, the mechanism during the reaction process is discussed.

Structural, electrical and magnetic properties of (Fe, Co) co-doped SnO2 diluted magnetic semiconductor nanostructures

Abstract: Nanostructures (NSs) of basic composition Sn 1− x Fe x /2 Co x /2 O 2 with x =0.00, 0.04, 0.06, 0.08 and 0.1 were synthesized by citrate-gel route and characterized to understand their structural, electrical and magnetic properties. X-ray diffraction and Raman spectroscopy were used to confirm the formation of single phase rutile type tetragonal structure. The crystallite sizes calculated by using Williamson Hall were found to decrease with increasing doping level. In addition to the fundamental Raman peaks of rutile SnO 2 , the other three weak Raman peaks at about 505, 537 and 688 cm −1 were also observed. Field emission scanning electron microscopy studies showed the emergence of structural transformation. Electric properties such as dc electrical resistivity as a function of temperature and ac conductivity as a function of frequency were also studied. The variation of dielectric properties with frequency reveals that the dispersion is due to Maxwell–Wagner type of interfacial polarization in general. Hysteresis loops were clearly observed in M–H curves of Fe and Co co-doped SnO 2 NSs. However, pure SnO 2 nanoparticles (NPs) showed paramagnetic behaviour which vanished at higher values of magnetic field. The grain and grain boundary contribution in the conduction process is estimated through complex impedance plot fitted with non-linear least square (NLLS) approach which shows that the role of grain boundaries increases rapidly as compared to the grain volume with the increase of Fe and Co ions in to system.

Peristaltic transport of copper–water nanofluid saturating porous medium

Abstract: Prime goal of present study is to model the problem for peristaltic transport of copper–water nanofluid in an asymmetric channel. The fluid fills porous space. Analysis is carried out in the presence of mixed conviction, viscous dissipation and heat generation/absorption. Long wavelength and low Reynolds number approximations are utilized in problem formulation. Numerical computations are presented for the axial velocity, pressure gradient, streamlines, temperature and heat transfer rate at the boundary. Graphical analysis is carried out to examine the effects of sundry parameters on flow quantities of interest. Results revealed that the axial velocity of copper–water nanofluid decreases with an increase in the nanoparticle volume fraction. Copper nanoparticles prove effective coolant since they sufficiently reduce the fluid temperature and show increase in the heat transfer between the fluid and solid boundary. Moreover temperature of the fluid decreases by increasing the permeability of porous medium.

Ab initio studies of the interaction of formaldehyde with beryllium oxide nanotube

Abstract: The interaction of a formaldehyde molecule with a BeO nanotube was explored by means of density functional calculations. It was found that formaldehyde prefers to be adsorbed on a Be–O bond of the tube wall with the change of Gibbs free energy of 18.9 kcal/mol at 1 atm and 298 K. This adsorption process significantly shifts the lowest unoccupied molecular orbital of the tube to lower energies, thereby reducing the gap of the tube from 7.04 to 4.19 eV. It suggests that BeO nanotube may generate an electrical signal in the presence of formaldehyde molecule because of the conductance change. Also, we investigated the effect of humidity on this sensor.

Impurity position effect on optical properties of various quantum dots

Abstract: In this work, we have investigated the effect of impurity position on optical properties of a pyramid and a cone like quantum dot For this goal, we first obtain the energy levels and wave functions using finite element method (FEM) in the presence of impurity Then, we have studied the influence of impurity location on refractive index changes and absorption coefficients of the two quantum dots We found that there is a maximum value for total refractive index changes and absorption coefficients at a special impurity position Also, we have found that the refractive index changes and absorption coefficients of a cone like quantum dot are greater than a pyramid quantum dot in same volume and height According to the results, it is deduced that the impurity location plays an important and considerable role in the electronic and optical properties of a pyramid and a cone like quantum dot

Forced vibration analysis of functionally graded carbon nanotube-reinforced composite plates using a numerical strategy

Abstract: In this paper, the nonlinear forced vibration behavior of composite plates reinforced by carbon nanotubes is investigated by a numerical approach. The reinforcement is considered to be functionally graded (FG) in the thickness direction according to a micromechanical model. The first-order shear deformation theory and von Karman-type kinematic relations are employed. The governing equations and the corresponding boundary conditions are derived with the use of Hamilton's principle. The generalized differential quadrature (GDQ) method is utilized to achieve a discretized set of nonlinear governing equations. A Galerkin-based scheme is then applied to obtain a time-varying set of ordinary differential equations of Duffing-type. Subsequently, a time periodic discretization is done and the frequency response of plates is determined via the pseudo-arc length continuation method. Selected numerical results are given for the effects of different parameters on the nonlinear forced vibration characteristics of uniformly distributed carbon nanotube- and FG carbon nanotube-reinforced composite plates. It is found that with the increase of CNT volume fraction, the flexural stiffness of plate increases; and hence its natural frequency gets larger. Moreover, it is observed that the distribution type of CNTs significantly affects the vibrational behavior of plate. The results also show that when the mid-plane of plate is CNT-rich, the natural frequency takes its minimum value and the hardening-type response of plate is intensified.

Experimental and computational studies of naphthyridine derivatives as corrosion inhibitor for N80 steel in 15% hydrochloric acid

Abstract: The inhibition effect of three naphthyridine derivatives namely 2-amino-4-(4-methoxyphenyl)-1,8-naphthyridine-3-carbonitrile (ANC-1), 2-amino-4-(4-methylphenyl)-1,8-naphthyridine-3-carbonitrile (ANC-2) and 2-amino-4-(3-nitrophenyl)-1,8-naphthyridine-3-carbonitrile (ANC-3) as corrosion inhibitors for N80 steel in 15% HCl by using gravimetric, electrochemical techniques (EIS and potentiodynamic polarization), SEM, EDX and quantum chemical calculation. The order of inhibition efficiency is ANC-1>ANC-2>ANC-3. Potentiodynamic polarization reveals that these inhibitors are mixed type with predominant cathodic control. Studied inhibitors obey the Langmuir adsorption isotherm. The quantum calculation is in good agreement with experimental results.

Peristaltic transport of magneto-nanoparticles submerged in water: Model for drug delivery system

Abstract: Recent development in biomedical engineering has enabled the use of the magnetic nanoparticles in modern drug delivery systems with great utility Nanofluids composed of magnetic nanoparticles have the characteristics to be manipulated by external magnetic field and are used to guide the particles up the bloodstream to a tumor with magnets In this study we examine the mixed convective peristaltic transport of copper–water nanofluid under the influence of constant applied magnetic field Nanofluid is considered in an asymmetric channel Aside from the effect of applied magnetic field on the mechanics of nanofluid, its side effects ie the Ohmic heating and Hall effects are also taken into consideration Heat transfer analysis is performed in presence of viscous dissipation and heat generation/absorption Mathematical modeling is carried out using the lubrication analysis Resulting system of equations is numerically solved Impact of embedded parameters on the velocity, pressure gradient, streamlines and temperature of nanofluid is examined Effects of applied magnetic field in presence and absence of Hall effects are studied and compared Results depict that addition of copper nanoparticles reduces the velocity and temperature of fluid Heat transfer rate at the boundary enhances by increasing the nanoparticles volume fraction Increase in the strength of applied magnetic field tends to decrease/increase the velocity/temperature of nanofluid Further presence of Hall effects reduces the variations brought in the state of fluid when strength of applied magnetic field is increased

MHD squeezed flow of water functionalized metallic nanoparticles over a sensor surface

Abstract: Present study is devoted to analyze the magnetohydrodynamics (MHD) squeezed flow of nanofluid over a sensor surface. Modeling of the problem is based on the geometry and the interaction of three different kinds of metallic nanoparticles namely: copper (Cu), alumina (Al2O3) and titanium dioxide (TiO2) with the homogeneous mixture of base fluid (water). The self-similar numerical solutions are presented for the reduced form of the system of coupled ordinary differential equations. The effects of nanoparticles volume friction, permeable velocity and squeezing parameter for the flow and heat transfer within the boundary layer are presented through graphs. Comparison among the solvent are constructed for both skin friction and Nusselt number. Flow behavior of the working nanofluid according to the present geometry has analyzed through Stream lines. Conclusion is drawn on the basis of entire investigation and it is found that in squeezing flow phenomena Cu–water gives the better heat transfer performance as compare with the rest of mixtures.

F−, Cl−, Li+ and Na+ adsorption on AlN nanotube surface: A DFT study

Abstract: Adsorption of two anions (F − and Cl − ) and two cations (Li + and Na + ) on the surface of aluminum nitride nanotubes (AlNNTs) is investigated by density functional theory. The reactions are site-selective, so that the cations and anions prefer to be adsorbed atop the N and Al atoms of the tube surface, respectively. The adsorption energies of anions (−4.46 eV for F − and −1.12 eV for Cl − ) are much higher than those of cations (about −0.17 eV for Li + and −0.12 eV for Na + ) which can be explained using frontier molecular orbital theory. It was found that the adsorption of anions may facilitate the electron emission from the AlNNT surface by reducing the work function due to the charge transfer occurs from the anions to the tube. It has been predicted that in contrast to the cations the adsorption of anions also obviously increases the electrical conductivity of AlNNT.

Nitric oxide adsorption on non-stoichiometric boron nitride fullerene: Structural stability, physicochemistry and drug delivery perspectives

Abstract: The structural stability and physicochemical properties of the N-rich BN fullerene, B24N36, have been analyzed by means of the density functional theory at the level of the generalized gradient approximation For this purpose, the Heyd–Scuseria–Ernzerhof (HSE) screened hybrid density functional and the 6-31G(d) basis set were used The results indicate that the B24N36 fullerene is stable and behaves as a semiconductor compound It has been found that while the polarity of the B24N36 fullerene is comparable with that of C60 fullerene, its chemical reactivity is notoriously higher The spatial charge distribution of the BN fullerene allows nitric oxide adsorption, without compromising structural stability Although the interaction between the NO molecule and BN fullerene is through van der Waals forces (dipole–dipole attraction), it has strong influence on the dipole moment, vibrational modes, HOMO–LUMO gap and work function energy; suggesting that this nanostructure could be used as a molecular sensor or drug carrier with enhanced bioavailability

Nonlinear vibration of double layered viscoelastic nanoplates based on nonlocal theory

Abstract: This figure presents the influence of small scale coefficient on the nonlinear frequency ratio of the first nonlinear normal mode (NNM) for the double layered nanoplates with simply supported boundary condition. The figure shows that the frequency ratio increases with the augment of the nonlocal parameter for a given mode amplitude (a1/h). This fact reveals that with the increase of the nonlocal coefficient the nonlinearity for the first NNM is enhanced. abstract The nonlinear flexural vibration properties of double layered viscoelastic nanoplates are investigated based on nonlocal continuum theory. The von Kaman strain-displacement relation is employed to model the geometrical nonlinearity. Based on the classical plate theory, the formulations are derived by the Hamilton's principle in conjunction with Eringen's nonlocal elasticity theory, and are further discretized by the Galerkin's method. The coordinate transformation is adopted to obtain the nonlinear governing equations of motion in the modal coordinate system. On the basis of these equations, the frequency responses of double layered nanoplates with simply supported and clamped boundary conditions are derived by the method of multiple scales. The influences of small scale and other structural parameters (e.g. the aspect ratio of the plate, van der Walls (vdW) interaction and the viscidity of the plate) on the nonlinear vibration characteristics are discussed. From the result, the vdW interaction has obvious effects on the nonlinear frequency corresponding to the second nonlinear normal mode (NNM). The non- existence of the internal resonance is also induced from the vdW forces between the plates. The influ- ence of the elastic matrix is also discussed. The hardening nonlinearity is observed for the primary resonance. Additionally, some interesting phenomena different from the linear vibration are observed.

Effect of calcination temperature on phase transformation, structural and optical properties of sol–gel derived ZrO2 nanostructures

Abstract: Zirconia (ZrO 2 ) nanostructures of various sizes have been synthesized using sol–gel method followed by calcination of the samples from 500 to 700 °C The calcined ZrO 2 powder samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier-transform infra-red spectroscopy (FT-IR), UV–visible spectroscopy (UV–vis), Raman spectroscopy (RS) and thermogravimetric analysis (TGA) The phase transformation from tetragonal (t) to monoclinic (m) was observed The average diameter of the ZrO 2 nanostructures calcined at 500, 600 and 700 °C was calculated to be 8, 17 and 10 nm, respectively The ZrO 2 sample calcined at 500 °C with tetragonal phase shows a direct optical band gap of 51 eV The value of optical band gap is decreased to 43 eV for the ZrO 2 calcined at 600 °C, which contains both tetragonal (73%) and monoclinic (27%) phases On further calcination at 700 °C, where the ZrO 2 nanostructures have 36% tetragonal and 64% monoclinic phases, the optical band gap is calculated to be 48 eV The enhancement in optical band gap for ZrO 2 calcined at 700 °C may be due to the rod like shape of ZrO 2 nanostructures The tetragonal to monoclinic phase transformation was also confirmed by analyzing Raman spectroscopic data The TG analysis revealed that the ZrO 2 nanostructure with dominance of monoclinic phase is found to be more stable over the tetragonal phase In order to confirm the phase stability of the two phases of ZrO 2 , single point energy is calculated corresponding to its monoclinic and tetragonal structures using density functional theory (DFT) calculations The results obtained by theoretical calculations are in good agreement with the experimental findings

Effect of thermal stratification on free convection in a square porous cavity filled with a nanofluid using Tiwari and Das' nanofluid model

Abstract: Natural convection in a square porous cavity filled with a nanofluid in conditions of thermal stratification has been numerically studied. The mathematical model has been formulated in terms of the dimensionless stream function and temperature using the Darcy–Boussinesq approximation and Tiwari and Das' nanofluid model with new more realistic empirical correlations for the physical properties of the nanofluids. Formulated partial differential equations along with the corresponding boundary conditions have been solved by the finite difference method. Particular efforts have been focused on the effects of the Rayleigh number, thermal stratification parameter, porosity of the porous medium, solid volume fraction parameter of nanoparticles, and the solid matrix of the porous medium (glass balls and aluminum foam) on the local and average Nusselt numbers, streamlines and isotherms. It has been observed an essential effect of thermal stratification parameter on heat and fluid flow fields.

Effect of air annealing on structural, optical, morphological and electrical properties of thermally evaporated CdSe thin films

Abstract: In this paper, a study on effect of air annealing on structural, optical, morphological and electrical properties of CdSe thin films is undertaken. The thin films of thickness 810 nm were deposited on glass and ITO coated glass substrates employing thermal evaporation technique. The glass substrates were used to find structural, optical and morphological properties while ITO coated glass substrates for electrical properties. The as-deposited films were subjected to thermal annealing in air atmosphere at different temperatures 100 °C, 200 °C and 300 °C. The X-ray diffraction pattern shows that the films have cubic phase with preferred orientation (111). The structural parameters like inter-planner spacing, lattice constant, grain size, dislocation density, strain and number of crystallites per unit area are calculated. The grain size is found in the range 27.11–34.03 nm and observed to be varied with air annealing. The dislocation density and strain vary with annealing in the range (0.86–1.36)×1011 cm−2 and 0.276–0.347 respectively. The extinction coefficient is found to be increased at lower annealing temperature and decreased at higher. The refractive index is also calculated and found in the range 2.75–2.80. The AFM studies show that roughness of thin films are increased with annealing. The electrical resistivity is found to be decreased with annealing temperature. The results are in good agreement with the standard data and available literature.

Analysis of graphene based optically transparent patch antenna for terahertz communications

Abstract: With and without multi walled carbon nanotube (MWCNT) loaded graphene based optically transparent patch antennas are designed to resonate at 6 THz. Their radiation characteristics are analyzed in 5.66–6.43 THz band. The optically transparent graphene is deployed as the patch and ground plane of the antennas, which are separated by a 2.5 μm thick flexible polyimide substrate. By shorting the microstrip line and ground plane of the antenna with a MWCNT via, the return loss of the antenna is improved. The peak gain of 3.3dB at 6.2 THz and a gain greater than 3dB in 5.66–6.43 THz band is obtained for antenna loaded without MWCNT. Both the antennas achieved a −10dB impedance bandwidth of 12.83%. Gain, directivity and radiation efficiency of the proposed antennas are compared with conventional transparent patch antennas and graphene based non-transparent antennas. The antenna structures are simulated by using finite element method based electromagnetic simulator-Ansys HFSS.

Free vibration of fractional viscoelastic Timoshenko nanobeams using the nonlocal elasticity theory

Abstract: In this article, the free vibration of a fractional viscoelastic Timoshenko nanobeam is studied through inserting fractional calculus as a viscoelastic material compatibility equations in nonlocal beam theory. The material properties of a single-walled carbon nanotube (SWCNT) are used and two solution procedures are proposed to solve the obtained equations in the time domain. The former is a semi-analytical approach in which the Galerkin scheme is employed to discretize the governing equations in the spatial domain and the obtained set of ordinary differential equations is solved using a direct numerical integration scheme. On the contrary, the latter is entirely numerical in which the governing equations of system on the spatial and time domains are first discretized using general differential quadrature (GDQ) technique and finite difference (FD) scheme, respectively and then the set of algebraic equations is solved to arrive at the time response of system under different boundary conditions. Considering the second solution procedure as the main approach, its validity and accuracy are verified by the semi-analytical approach which is more difficult to enter various boundary conditions. Numerical results are also presented to get an insight into the effects of fractional derivative order, nonlocal parameter, viscoelasticity coefficient and nanobeam length on the time response of fractional viscoelastic Timoshenko nanobeams under different boundary conditions.

Nanoscale mass detection based on vibrating piezoelectric ultrathin films under thermo-electro-mechanical loads

Abstract: The potential applications of piezoelectric nanofilms (PNFs) and double-piezoelectric-nanofilm (DPNF) systems as nanoelectromechanical mass sensors are examined. The PNFs carrying multiple nanoparticles at arbitrary locations are modeled as rectangular nonlocal plates with attached concentrated masses. Using the nonlocal elasticity theory and Hamilton’s principle, the differential equations of motion are derived for both PNF-based and DPNF-based nanosensors. The influences of small scale, initial stress and temperature change on the frequency shifts of the nanoelectromechanical sensors are taken into consideration. Explicit expressions are derived for the resonance frequencies of the nanosensors by employing the Galerkin method. The present results show that when the value of nonlocal parameter decreases, the frequency shifts of piezoelectric nanosensors increase. Further, the frequency shifts of DPNF-based mass sensors are always greater than those of PNF-based mass sensors. The present work would be helpful in the design of nanoelectromechanical mass sensors using PNFs.

Preparation, structural, photoluminescence and magnetic studies of Cu doped ZnO nanoparticles co-doped with Ni by sol-gel method

Abstract: Zn0.96−xNi0.04CuxO nanoparticles have been synthesized by varying different Cu concentrations between 0% and 4% using simple sol–gel method. X-ray diffraction studies confirmed the hexagonal structure of the prepared samples. The formation of secondary phases, CuO (111) and Zn (101) at higher Cu content is due un-reacted Cu2+ and Zn2+ ions present in the solution which reduces the interaction between precursor ions and surfaces of ZnO. Well agglomerated and rod-like structure noticed at Cu=4% greatly de-generate and enhanced the particle size. The nominal elemental composition of Zn, Cu, Ni and O was confirmed by energy dispersive X-ray analysis. Even though energy gap was increased (blue-shift) from Cu=0–2% by quantum size effect, the s–d and p–d exchange interactions between the band electrons of ZnO and localized d electrons of Cu and Ni led to decrease (red-shift) the energy gap at Cu=4%. Presence of Zn–Ni–Cu–O bond was confirmed by Fourier transform infrared analysis. Ultraviolet emission by band to band electronic transition and defect related blue emission were discussed by photoluminescence spectra. The observed optical properties concluded that the doping of Cu in the present system is useful to tune the emission wavelength and hence acting as the important candidates for the optoelectronic device applications. Ferromagnetic ordering of Cu=2% sample was enhanced by charge carrier concentration where as the antiferromagnetic interaction between neighboring Cu–Cu ions suppressed the ferromagnetism at higher doping concentrations of Cu.

Adsorptive removal and kinetics of methylene blue from aqueous solution using NiO/MCM-41 composite

Abstract: Highly ordered mesoporous material MCM-41 was synthesized from tetraethylorthosilicate (TEOS) as Si source and cetyltrimethylammonium bromide (CTAB) as template. Well-dispersed NiO nanoparticles were introduced into the highly ordered mesoporous MCM-41 by chemical precipitation method to prepare the highly ordered mesoporous NiO/MCM-41 composite. X-ray diffraction (XRD) analysis, transmission electron microscopy (TEM) and high-resolution TEM (HRTEM), and nitrogen adsorption–desorption measurement were used to examine the morphology and the microstructure of the obtained composite. The morphological study clearly revealed that the synthesized NiO/MCM-41 composite has a highly ordered mesoporous structure with a specific surface area of 435.9 m2 g−1. A possible formation mechanism is preliminary proposed for the formation of the nanostructure. The adsorption performance of NiO/MCM-41 composite as an adsorbent was further demonstrated in the removal azo dyes of methyl orange (MO), Congo red (CR), methylene blue (MB) and rhodaming B (RB) under visible light irradiation and dark, respectively. The kinetics and mechanism of removal methylene blue were studied. The results show that NiO/MCM-41 composite has a good removal capacity for organic pollutant MB from the wastewater under the room temperature. Compared with MCM-41 and NiO nanoparticles, 54.2% and 100% higher removal rate were obtained by the NiO/MCM-41 composite.

Sn-embedded graphene: An active catalyst for CO oxidation to CO2?

Abstract: As is well known, looking for an appropriate catalyst which can oxidize the toxic CO molecule is of great importance. In this work, the favorable oxidation reaction of CO by molecular O 2 on Sn-embedded graphene (Sn-graphene) is investigated by using density functional theory calculations. Comparatively, both Eley–Rideal (ER) and Langmuir–Hinshelwood (LH) mechanisms of CO oxidation on Sn-graphene are studied. The CO oxidation reaction over Sn-graphene proceeds through the following steps: CO+O 2 →OOCO→O ads +CO 2 following by O ads +CO→OCO→CO 2 , which passing via LH and ER mechanism, respectively. The barrier energies of these two steps are 0.41 and 0.11 eV, respectively, which are lower than those on the traditional noble metals. Our results reveal that the low-cost Sn-graphene can be used as an efficient catalyst for CO oxidation at room temperature.

Many body effects study of electronic & optical properties of silicene–graphene hybrid

Abstract: Using first principles many-body calculations method, we study electronic and optical properties of 2D silicene–graphene hybrid. Based on phonon-spectrum calculations, we show the absence of soft modes indicating the stability of the system. We also calculate the band gap in both the absence and the presence of quasiparticle corrections. The analysis of optical absorption spectra and the correlation in real space between the excited electron–hole states reveals that the excitonic effects in silicene–graphene hybrid are significant and leads to strong bound excitons. The first active exciton is characterized by a binding energy of 0.81 eV, an effective mass 0.41 m 0 and a Bohr radius of 2.78 A. The results of this work make silicene–graphene hybrid a promising candidate for optoelectronic applications.

Excitonic effects in GeC hybrid: Many-body Green's function calculations

Abstract: Many-body effects on the electronic and optical absorption properties of a GeC sheet are studied by means of first principle many-body Green's function and Bethe–Salpeter equation formalism. The absence of soft modes in the phonon-spectrum indicates the stability of the system. The inclusion of quasiparticle corrections increases significantly the band gap. The local field effects induce significant change in the absorption spectra for the out-plane polarization rendering the GeC monolayer transparent below 7 eV. The excitonic effects are significant on the optical absorption properties. A detailed analysis of the spectrum shows a strong binding energy of 1.82 eV assigned to the lowest-energy bound excitons that is characterized by an effective mass of 1.68 m 0 and a Bohr radius of 2 A. The results of this study hold the promise for potential applications of the GeC hybrid in optoelectronics.

Effects of nanoparticle migration on hydromagnetic mixed convection of alumina/water nanofluid in vertical channels with asymmetric heating

Abstract: The effects of nanoparticle migration on mixed convection of alumina/water nanofluid inside a vertical channel in the presence of a uniform magnetic field have been investigated theoretically. Walls are subjected to different heat fluxes; q l w ' ' for the left wall and q r w ' ' for the right wall, and nanoparticles are assumed to have a slip velocity relative to the base fluid induced by the Brownian motion and thermophoresis. Considering hydrodynamically and thermally fully developed flow, the governing equations including continuity, momentum, and energy equations have been reduced to two-point ordinary boundary value differential equations and they have been solved numerically. It is shown that nanoparticles eject themselves from the heated walls, construct a depleted region, and accumulate in the core region, but they are more likely to accumulate toward the wall with the lower heat flux. In addition, inclusion of nanoparticles in the presence of a magnetic field has a negative effect on the performance.

A new facile route for synthesizing of graphene oxide using mixture of sulfuric–nitric–phosphoric acids as intercalating agent

Abstract: In this work, graphene oxide (GO) has been prepared through three different processes namely, eco-friendly Hummers method, modification in improved Hummers method and a new approach. This new approach has been designed by changing some processing parameters and intercalating agent for significant reduction in processing time and to improve the quantity of GO in comparison to the other two methods. This has been achieved through better oxidization of graphite using nitric–sulfuric acid (HNO3–H2SO4) as intercalating agent. X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), Energy-dispersive X-ray spectroscopy (EDX), Raman spectroscopy, Atomic Force Microscopy (AFM), X-ray photoelectron spectroscopy (XPS), UV–visible spectroscopy, and Thermogravimetric analysis (TGA) are used to characterize the GO prepared through different processes. These characterizations have confirmed an improved exfoliation of graphite, using addition of HNO3 in intercalating agent, in a short processing time and bring on higher yield of GO via this new process.