Showing papers in "Physica E-low-dimensional Systems & Nanostructures in 2018"

Synthesis, photoluminescence and Magnetic properties of iron oxide (α-Fe2O3) nanoparticles through precipitation or hydrothermal methods

Abstract: In this work the iron oxide (α-Fe 2O3 ) nanoparticles are synthesized using two different methods: precipitation and hydrothermal. Size, structural, optical and magnetic properties were determined and compared using X-ray diffraction (XRD), Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), Fourier Transform Infra-Red (FT-IR), Raman spectroscopy , Differential Thermal Analysis (DTA), Thermogravimetric Analysis (TGA), Ultraviolet–Visible (UV–Vis) analysis, Superconducting QUantum Interference Device (SQUID) magnetometer and Photoluminescence (PL). XRD data further revealed a rhombohedral (hexagonal) structure with the space group (R-3c) and showed an average size of 21 nm for hydrothermal samples and 33 nm for precipitation samples which concorded with TEM and SEM images. FT-IR confirms the phase purity of the nanoparticles synthesized. The Raman spectroscopy was used not only to prove that we have synthesized pure α-Fe 2O3 but also to identify their phonon modes. The TGA showed three mass losses, whereas DTA resulted in three endothermic peaks. The decrease in the particle size of hematite of 33 nm for precipitation samples to 21 nm for hydrothermal samples is responsible for increasing the optical band gap of 1.94–2.10 eV where, the relation between them is inverse relationship. The products exhibited the attractive magnetic properties with good saturation magnetization , which were examined by a SQUID magnetometer. Photoluminescence measurements showed a strong emission band at 450 nm. Pure hematite prepared by hydrothermal method has smallest size, best crystallinity , highest band gap and best value of saturation magnetization compared to the hematite elaborated by the precipitation method.

An experimental study on rheological behavior of a nanofluid containing oxide nanoparticle and proposing a new correlation

Abstract: In this paper, the nanofluid dynamic viscosity composed of CeO2- Ethylene Glycol is examined within 25–50 °C with 5 °C intervals and at six volume fractions (0.05, 0.1, 0.2, 0.4, 0.8 and 1.2%) experimentally. The nanofluid was exposed to ultrasound waves for various durations to study the effect of this parameter on dynamic viscosity of the fluid. We found that at a constant temperature, nanofluid viscosity increases with increases in the volume fraction of the nanoparticles. Also, at a given volume fraction, nanofluid viscosity decreases when temperature is increased. Maximum increase in nanofluid viscosity compared to the base fluid viscosity occurs at 25 °C and volume fraction of 1.2%. It can be inferred that the obtained mathematical relationship is a suitable predicting model for estimating dynamic viscosity of CeO2- Ethylene Glycol (EG) at different volume fractions and temperatures and its results are consistent to laboratory results in the set volume fraction and temperature ranges.

Turbulent flow and heat transfer of Water/Al 2 O 3 nanofluid inside a rectangular ribbed channel

Abstract: In present study, the turbulent flow and heat transfer of Water/Al2O3 nanofluid inside a rectangular channel have been numerically simulated. The main purpose of present study is investigating the effect of attack angle of inclined rectangular rib, Reynolds number and volume fraction of nanoparticles on heat transfer enhancement. For this reason, the turbulent flow of nanofluid has been simulated at Reynolds numbers ranging from 15000 to 30000 and volume fractions of nanoparticles from 0 to 4%. The changes attack angle of ribs have been investigated ranging from 0 to 180°. The results show that, the changes of attack angle of ribs, due to the changes of flow pattern and created vortexes inside the channel, have significant effect on fluid mixing. Also, the maximum rate of heat transfer enhancement accomplishes in attack angle of 60°. In Reynolds numbers of 15000, 20000 and 30000 and attack angle of 60°, comparing to the attack angle of 0°, the amount of Nusselt number enhances to 2.37, 1.96 and 2 times, respectively. Also, it can be concluded that, in high Reynolds numbers, by using ribs and nanofluid, the performance evaluation criterion improves.

Biosynthesis of silver nanoparticles: A colorimetric optical sensor for detection of hexavalent chromium and ammonia in aqueous solution

Abstract: The current study is focussed on bio-fabrication of single step Durenta erecta (D. erecta ) fruit extract synthesis of silver nanoparticles (Ag NPs). The prepared materials were examined through UV–Vis spectrophotometry due to localized surface plasmon resonance (SPR) and were found highly stable. X-ray diffraction (XRD) revealed face centered cubic (fcc) crystalline nature of Ag NPs. Morphologies and average size of Ag NPs was evaluated by field emission-scanning electron microscopy (FE-SEM), while elemental analysis was carried out by energy dispersive X-rays spectroscopy (EDS) and X-ray photo electron spectroscopy (XPS). Fourier transform infrared spectroscopy (FTIR) displayed the presence of the functional groups responsible for reducing as well as stabilizing of Ag NPs. The prepared Ag NPs were applied as colorimetric optical sensors for the detection of carcinogenic hexavalent chromium (Cr 6+) and ammonia and the kinetic shift in λmax and change in color for both Cr6+ and ammonia was found to be extremely fast and took a few seconds. Characteristic SPR, low-cost, high sensitivity, simplicity, lower detection limit up to 0.1 ppm and fast response time of Ag NPs are very useful for the colorimetric detection of Cr 6+ and ammonia and can be used as an optical sensor for clinical diagnosis at room temperature.

Highly sensitive nano-scale plasmonic biosensor utilizing Fano resonance metasurface in THz range: Numerical study

Abstract: We report a numerical study of the tunable-enhanced sensitivity of a nano-scale plasmonic biosensor in THz range. In the structure, gold Metasurface is utilized to excite of Fano resonance modes that their dispersion properties can be harnessed with different geometrical parameters. Here, the coupling of the incident beam to the surface modes of the structure is used to improve the performance parameters including figure of merit, sensitivity, and footprint. The Fano resonance, which is strongly rely on any change in refractive index of the material, is excited in the structure by changing geometrical parameters. The structure is numerically simulated by the finite difference time domain method . In the optimum design of the proposed sensor, the maximum value of sensitivity is achieved as high as S = 1700 nm/refractive index unit with a large value of figure of merit (FoM = 283.3 1/refractive index unit) and a narrow linewidth of Δ λ = 6 nm. Moreover, the structure has a nano-scale footprint of 500 nm × 500 nm × 190 nm. It is also shown that Fano resonance can be controlled through manipulating the external parameters such as incident angle and various bio-materials. Therefore, we expect that this theoretical result leads to remarkable applications in plasmonic integrated circuits , e.g. optical biosensors.

Closed-form solutions in stress-driven two-phase integral elasticity for bending of functionally graded nano-beams

Abstract: Strain-driven and stress-driven integral elasticity models are formulated for the analysis of the structural behaviour of fuctionally graded nano-beams. An innovative stress-driven two-phases constitutive mixture defined by a convex combination of local and nonlocal phases is presented. The analysis reveals that the Eringen strain-driven fully nonlocal model cannot be used in Structural Mechanics since it is ill-posed and the local-nonlocal mixtures based on the Eringen integral model partially resolve the ill-posedeness of the model. In fact, a singular behaviour of continuous nano-structures appears if the local fraction tends to vanish so that the ill-posedness of the Eringen integral model is not eliminated. On the contrary, local-nonlocal mixtures based on the stress-driven theory are mathematically and mechanically appropriate for nanosystems. Exact solutions of inflected functionally graded nanobeams of technical interest are established by adopting the new local-nonlocal mixture stress-driven integral relation. Effectiveness of the new nonlocal approach is tested by comparing the contributed results with the ones corresponding to the mixture Eringen theory.

A comparison of performance of several artificial intelligence methods for predicting the dynamic viscosity of TiO2/SAE 50 nano-lubricant

Abstract: Since the conventional thermal fluids such as water, oil, and ethylene glycol have poor thermal properties, the tiny solid particles are added to these fluids to increase their heat transfer improvement. As viscosity determines the rheological behavior of a fluid, studying the parameters affecting the viscosity is crucial. Since the experimental measurement of viscosity is expensive and time consuming, predicting this parameter is the apt method. In this work, three artificial intelligence methods containing Genetic Algorithm-Radial Basis Function Neural Networks (GA-RBF), Least Square Support Vector Machine (LS-SVM) and Gene Expression Programming (GEP) were applied to predict the viscosity of TiO2/SAE 50 nano-lubricant with Non-Newtonian power-law behavior using experimental data. The correlation factor (R2), Average Absolute Relative Deviation (AARD), Root Mean Square Error (RMSE), and Margin of Deviation were employed to investigate the accuracy of the proposed models. RMSE values of 0.58, 1.28, and 6.59 and R2 values of 0.99998, 0.99991, and 0.99777 reveal the accuracy of the proposed models for respective GA-RBF, CSA-LSSVM, and GEP methods. Among the developed models, the GA-RBF shows the best accuracy.

3D magneto-convective heat transfer in CNT-nanofluid filled cavity under partially active magnetic field

Abstract: A computational study has been performed to investigate the effects of partially active magnetic field on natural convection heat transfer in CNT-nanofluid filled and three-dimensional differentially heated closed space. Two cases are considered to see this effect as magnetic field is applied to upper half (Case I) and lower half (Case II) while remaining walls are insulated. The finite volume method is used to solve governing equations and results are obtained for different governing parameters as Hartmann number (0 ≤ Ha ≤ 100), nanoparticle volume fraction (0 ≤ φ ≤ 0.05) and height of the active zone (0 ≤ L B ≤ 1). It is found that location of magnetic field plays an important role even at the same Hartmann number. Thus, it can be a good parameter to control heat and fluid flow inside the closed space.

Investigation of permeability effect on slip velocity and temperature jump boundary conditions for FMWNT/Water nanofluid flow and heat transfer inside a microchannel filled by a porous media

Abstract: The fluid flow and heat transfer of a nanofluid is numerically examined in a two dimensional microchannel filled by a porous media. Present nanofluid consists of the functionalized multi-walled carbon nanotubes suspended in water which are enough stable through the base fluid. The homogenous mixture is in the thermal equilibrium which means provide a single phase substance. The porous media is considered as a Darcy- Forchheimer model. Moreover the slip velocity and temperature jump boundary conditions are assumed on the microchannel horizontal sides which mean the influences of permeability and porosity values on theses boundary conditions are presented for the first time at present work. To do this, the wide range of thermo physical parameters are examined as like Da = 0.1 to 0.001, Re = 10,100, dimensionless slip coefficient from 0.001 to 0.1 at different mass fraction of nanoparticles. It is observed that less Darcy number leads to more local Nusselt number and also applying the porous medium corresponds to higher slip velocity.

Analysis of natural convection in nanofluid-filled H-shaped cavity by entropy generation and heatline visualization using lattice Boltzmann method

Abstract: The lattice Boltzmann simulation of natural convection in H-shaped cavity filled with nanofluid is performed. The entropy generation analysis and heatline visualization are employed to analyze the considered problem comprehensively. The produced nanofluid is SiO2-TiO2/Water-EG (60:40) hybrid nanofluid , and the thermal conductivity and dynamic viscosity of used nanofluid are measured experimentally. To use the experimental data of thermal conductivity and dynamic viscosity, two sets of correlations based on temperature for six different solid volume fractions of 0.5, 1, 1.5, 2, 2.5 and 3 vol% are derived. The influences of different governing parameters such different aspect ratio, solid volume fractions of nanofluid and Rayleigh numbers on the fluid flow, temperature filed, average/local Nusselt number , total/local entropy generation and heatlines are presented.

Hygrothermal wave propagation in viscoelastic graphene under in-plane magnetic field based on nonlocal strain gradient theory

Abstract: A size-dependent model is developed for the hygrothermal wave propagation analysis of an embedded viscoelastic single layer graphene sheet (SLGS) under the influence of in-plane magnetic field. The bi-Helmholtz nonlocal strain gradient theory involving three small scale parameters is introduced to account for the size-dependent effects. The size-dependent model is deduced based on Hamilton's principle. The closed-form solution of eigenfrequency relation between wave number and phase velocity is achieved. By studying the size-dependent effects on the flexural wave of SLGS, the dispersion relation predicted by the developed size-dependent model can show a good match with experimental data. The influence of in-plane magnetic field, temperature and moisture of environs, structural damping, damped substrate, lower and higher order nonlocal parameters and the material characteristic parameter on the phase velocity of SLGS is explored.

Buckling analysis of piezo-magnetoelectric nanoplates in hygrothermal environment based on a novel one variable plate theory combining with higher-order nonlocal strain gradient theory

Abstract: In the present investigation, a new first-order shear deformation theory (OVFSDT) on the basis of the in-plane stability of the piezo-magnetoelectric composite nanoplate (PMEN) has been developed, and its precision has been evaluated. The OVFSDT has many advantages compared to the conventional first-order shear deformation theory (FSDT) such as needless of shear correction factors, containing less number of unknowns than the existing FSDT and strong similarities with the classical plate theory (CPT). The composite nanoplate consisted of BaTiO3-CoFe2O4 , a kind of material by which coupling between piezoelectric and piezomagnetic in nanosize was established. The plate is surrounded by a motionless and stationary matrix that is embedded in a hygrothermal surround in order to keep it more stable, and to take into consideration the influences of the moisture and temperature on the plate's mechanical behavior. The governing equilibrium equations for the smart composite plate have been formulated using the higher-order nonlocal strain gradient theory within which both stress nonlocality and second strain gradient size-dependent terms are taken into account by using three independent length scale parameters. The extracted equations are solved by utilizing the analytical approaches by which numerical results are obtained with various boundary conditions. In order to evaluate the proposed theory and methods of solution, the outcomes in terms of critical buckling loads are compared with those from several available well-known references. Finally, after determining the accuracy of the results of the new plate theory, several parameters are investigated to show the influences of material properties of the ceramic composite nanoplate on the critical buckling loads.

Natural convection analysis employing entropy generation and heatline visualization in a hollow L-shaped cavity filled with nanofluid using lattice Boltzmann method- experimental thermo-physical properties

Abstract: The natural convection heat transfer and fluid flow is analyzed using lattice Boltzmann numerical method . The entropy generation analysis and heatline visualization are used to study the convective flow field comprehensively. The hollow L-shaped cavity is considered and filled with SiO2-TiO2/Water-EG (60:40) hybrid nanofluid . The thermal conductivity and dynamic viscosity of nanofluid are measured experimentally. To use the experimental data of thermal conductivity and dynamic viscosity, two sets of correlations based on temperature for six different solid volume fractions of 0.5, 1, 1.5, 2, 2.5 and 3 vol% are derived. The influences of different governing parameters such different aspect ratios, solid volume fractions of nanofluid and Rayleigh numbers on the fluid flow, temperature filed, average/local Nusselt number , total/local entropy generation and heatlines are presented.

Stability of direct band gap under mechanical strains for monolayer MoS2, MoSe2, WS2 and WSe2

Abstract: Single layer transition-metal dichalcogenides materials (MoS2, MoSe2, WS2 and WSe2) are investigated using the first-principles method with the emphasis on their responses to mechanical strains. All these materials display the direct band gap under a certain range of strains from compressive to tensile (stable range). We have found that this stable range is different for these materials. Through studying on their mechanical properties again using the first-principles approach, it is unveiled that this stable strain range is determined by the Young's modulus. More analysis on strains induced electronic band gap properties have also been conducted.

GeAs and SiAs monolayers: Novel 2D semiconductors with suitable band structures

Abstract: Two dimensional (2D) materials provide a versatile platform for nanoelectronics, optoelectronics and clean energy conversion. Based on first-principles calculations, we propose a novel kind of 2D materials – GeAs and SiAs monolayers and investigate their atomic structure, thermodynamic stability, and electronic properties. The calculations show that monolayer GeAs and SiAs sheets are energetically and dynamically stable. Their small interlayer cohesion energies (0.191 eV/atom for GeAs and 0.178 eV/atom for SiAs) suggest easy exfoliation from the bulk solids that exist in nature. As 2D semiconductors, GeAs and SiAs monolayers possess band gap of 2.06 eV and 2.50 eV from HSE06 calculations, respectively, while their band gap can be further engineered by the number of layers. The relatively small and anisotropic carrier effective masses imply fast electric transport in these 2D semiconductors. In particular, monolayer SiAs is a direct gap semiconductor and a potential photocatalyst for water splitting. These theoretical results shine light on utilization of monolayer or few-layer GeAs and SiAs materials for the next-generation 2D electronics and optoelectronics with high performance and satisfactory stability.

Synthesis, structural, morphological, optical and magnetic characterization of iron oxide (α-Fe 2 O 3 ) nanoparticles by precipitation method: Effect of varying the nature of precursor

Abstract: α-Fe 2 O 3 nanoparticles were prepared via a precipitation method using each of three different precursors ((FeCl 3 , 6H 2 O), (Fe (C 5 H 7 O 2 ) 3 ) and (Fe (NO 3 ) 3 , 9H 2 O)). The impact of varying the nature of the precursor on crystalline phase, size and magnetic parameters of α-Fe 2 O 3 was examined. Powder X-ray diffraction pattern disclosed rhombohedral structure. The TEM and SEM results showed that the size of α-Fe 2 O 3 nanocrystals was between 21 and 38 nm. FT-IR confirms the phase purity of prepared compounds. Raman studies showed the phonon modes. The TGA showed three mass losses, whereas DTA resulted in three endothermic peaks. The optical investigation exhibited that samples have an optical gap of 2.1 eV. The products exhibited the attractive magnetic properties with high saturation magnetization, which were examined by a vibrating sample magnetometer (VSM).

Effect of surface dangling bonds on transport properties of phosphorous doped SiC nanowires

Abstract: Based on the semiconductor transport theory, a computational model for the axial conductivity of one-dimensional nanowires is established. Utilizing the band structure data from the first principles, the conductivity, carrier concentration and mobility of phosphorus doped SiCNWs (P-SiCNWs) before and after passivation were numerically simulated. The results show that hydrogen passivation can greatly improve the conductivity of P-SiCNWs, above room temperature, the conductivity is improved nearly two orders of magnitude, and enhance the thermal stability. The reason is that hydrogen passivation saturates the surface dangling bonds, leading to the disappearance of discrete impurity band of P-SiCNWs. In addition, the surface dangling bonds lead to greater thermal instability of conductivity under room temperature, but this thermal instability decrease rapidly with the increase of temperature. The study will help us to understand the transport properties of low dimensional semiconductors, and provide theoretical support for the research of nano electronic and optoelectronic devices.

A new experimental correlation for non-Newtonian behavior of COOH-DWCNTs/antifreeze nanofluid

Abstract: In this paper, the rheological behavior of nano-antifreeze consisting of 50%vol. water, 50%vol. ethylene glycol and different quantities of functionalized double walled carbon nanotubes has been investigated experimentally. Initially, nano-antifreeze samples were prepared with solid volume fractions of 0.05, 0.1, 0.2, 0.4, 0.6, 0.8 and 1% using two-step method. Then, the dynamic viscosity of the nano-antifreeze samples was measured at different shear rates and temperatures. At this stage, the results showed that base fluid had the Newtonian behavior, while the behavior of all nano-antifreeze samples was non-Newtonian. Since the behavior of the samples was similar to power law model, it was attempted to find the constants of this model including consistency index and power law index. Therefore, using the measured viscosity and shear rates, consistency index and power law index were obtained by curve-fitting method. The obtained values showed that consistency index amplified with increasing volume fraction, while reduced with enhancing temperature. Besides, the obtained values for power law index were less than 1 for all samples which means shear thinning behavior. Lastly, new correlations were suggested to estimate the consistency index and power law index using curve-fitting.

Vibration analysis of rotating nanobeam systems using Eringen's two-phase local/nonlocal model

Abstract: Due to the inability of differential form of nonlocal elastic theory in modelling cantilever beams and inaccurate results for some type of boundaries, in this study, a reliable investigation on transverse vibrational behavior of rotating cantilever size-dependent beams is presented. Governing higher order equations are written in the framework of Eringen's two-phase local/nonlocal model and solved using a modified generalized differential quadrature method. In order to indicate the influence of different material and scale parameters, a comprehensive parametric study is presented. It is shown that increasing the nonlocality term leads to lower natural frequency terms for cantilever nanobeams especially for the fundamental frequency parameter which differential nonlocal model is unable to track appropriately. Moreover, it is shown that rotating speed and hub radius have a remarkable effect in varying the mechanical behavior of rotating cantilever nanobeams. This study is a step forward in analyzing nanorotors, nanoturbines, nanoblades, etc.

First-principles study of intrinsic phononic thermal transport in monolayer C 3 N

Abstract: Very recently, a new graphene-like crystalline, hole-free, 2D-single-layer carbon nitride C3N, has been fabricated by polymerization of 2,3-diaminophenazine and used to fabricate a field-effect transistor device with an on-off current ratio reaching 5 . 5 × 10 10 (Adv. Mater. 2017, 1605625). Heat dissipation plays a vital role in its practical applications, and therefore the thermal transport properties need to be explored urgently. In this paper, we perform first-principles calculations combined with phonon Boltzmann transport equation to investigate the phononic thermal transport properties of monolayer C3N, and meanwhile, a comparison with graphene is given. Our calculated intrinsic lattice thermal conductivity of C3N is 380 W/mK at room temperature, which is one order of magnitude lower than that of graphene (3550 W/mK at 300 K), but is greatly higher than many other typical 2D materials. The underlying mechanisms governing the thermal transport were thoroughly discussed and compared to graphene, including group velocities, phonon relax time, the contribution from phonon branches, phonon anharmonicity and size effect. The fundamental physics understood from this study may shed light on further studies of the newly fabricated 2D crystalline C3N sheets.

RETRACTED: Optical properties of two-dimensional GaS and GaSe monolayers

Abstract: Optical properties of GaS and GaSe monolayers are investigated using first-principles calculations. The optical properties are studied up to 35 eV. Precisely, our results demonstrated that the optical properties appearance of GaS monolayer is comparative with GaSe monolayer with few informations contrasts. Moreover, the absorption begins in the visible region, although the peaks in the ultraviolet (UV) region. The refractive index values are 1.644 (GaS monolayer) and 2.01 (GaSe monolayer) at zero photon energy limit and increase to 2.092 and 2.698 respectively and both located in the visible region. Furthermore, we notice that the optical properties of both monolayers are obtained in the ultraviolet range and the results are significant. Accordingly, it can be used as a highly promising material in the solar cell, ultraviolet optical nanodevices, nanoelectronics, optoelectronic, and photocatalytic applications.

Evaluation of H 2 S sensing characteristics of metals–doped graphene and metals-decorated graphene: Insights from DFT study

Abstract: The high tendency of graphene to adsorb H2S gas has made it a good choice for the purpose of separating H2S gas from industrial waste streams, and it can also be used as a good H2S sensor. In this research, the adsorption of H2 S molecule on pristine, transition metal (Ni, Cu and Zn)-doped graphene and metal-decorated graphene nanosheets have been investigated via first–principles approach based on Density Functional Theory (DFT). The most stable adsorption geometry, rate of adsorption energy and charge transfer of H 2S molecule on pristine, metal–doped, and metal–decorated graphene nanosheets have been discussed. The adsorption of H2S gas on several kinds of graphene nanosheets was studied by three different models. As H2 S molecule adsorbed on metal–doped graphene nanosheets, we found that the configuration with two hydrogen atoms towards the metal–doped graphene nanosheet as most desirable situation. Moreover, the calculations show that the adsorption energy of H 2S on Cu–doped graphene nanosheet is the highest among all the other metal–doped graphene nanosheet systems. We also investigated the H2 S capability to bind to Ni, Cu and Zn–decorated graphene nanosheets. It was found that after adsorption, the configuration of the sulfur atom, which was located close to the metal–decorated graphene nanosheets was stable thermodynamically. The Ni–decorated graphene nanosheet with large adsorption energy and short binding distance is suitable for chemisorptions . The unfilled d–shells Ni–decorated graphene nanosheets are primarily responsible for increase in the reactivity.

Convective heat transfer and pressure drop of aqua based TiO 2 nanofluids at different diameters of nanoparticles: Data analysis and modeling with artificial neural network

Abstract: In this study, experimental data related to the Nusselt number and pressure drop of aqueous nanofluids of Titania is modeled and estimated by using ANN with 2 hidden layers and 8 neurons in each layer. Also in this study the effect of various effective variables in the Nusselt number and pressure drop is surveyed. This study indicated that the neural network modeling has been able to model experimental data with great accuracy. The modeling regression coefficient for the data of Nusselt number and relative pressure drop is 99.94% and 99.97% respectively. Besides, it represented that the increment of the Reynolds number and concentration made the increment of Nusselt number and pressure drop of aqueous nanofluid .

Experimental and theoretical investigation of thermal conductivity of ethylene glycol containing functionalized single walled carbon nanotubes

Abstract: In this paper, functionalized single walled carbon nanotubes (FSWCNTs) were suspended in Ethylene Glycol (EG) at different volume fractions. A KD2 pro thermal conductivity meter was used to measure the thermal conductivity in the temperature range from 30 to 50 °C. Nanofluids were prepared in solid volume fraction of 0.02, 0.05, 0.075, 0.1, 0.25, 0.5 and, 0.75%. Experimental results revealed that the thermal conductivity of the nanofluid is a non-linear function of temperature and SWCNTs volume fraction in the range of this investigation. Thermal conductivity increases with temperature and nanoparticles volume fraction as usual for this type of nanofluid. Maximum increment in thermal conductivity of the nanofluids was found to be about 45% at 0.75 vol fractions loading at 50 °C. Finally, a new correlation based on artificial neural network (ANN) approach has been proposed for SWCNT-EG thermal conductivity in terms of nanoparticles volume fraction and temperature using the experimental data. Used ANN approach has estimated the experimental values of thermal conductivity with the absolute average relative deviation lower than 0.9%, mean square error of 3.67 × 10−5 and regression coefficient of 0.9989. Comparison between the suggested techniques with various used correlation in the literatures established that the ANN approach is better to other presented methods and therefore can be proposed as a useful means for predicting of the nanofluids thermal conductivity.

Plasmonic absorption characteristics based on dumbbell-shaped graphene metamaterial arrays

Abstract: In this paper, we proposed a theoretical model in the far-infrared and terahertz (THz) bands, which are dumbbell-shaped graphene metamaterial arrays with a combination of graphene nanobelt and two semisphere-suspended heads. We report a detailed theoretical investigation on how to enhance localized electric field and the absorption in the dumbbell-shaped graphene metamaterial arrays. The simulation results show that absorption characteristics can be changed by changing the geometrical parameters of the structure and the Fermi level of graphene . Furthermore, we have discovered that the resonant wavelength is insensitive to TM polarization. In addition, we also find that the double-layer graphene arrays have better absorption characteristics than single-layer graphene arrays. This work allows us to achieve tunable terahertz absorber and may also provide potential applications in optical filter and biochemical sensing.

First-principles investigation on structural and electronic properties of antimonene nanoribbons and nanotubes

Abstract: The electronic properties of antimonene nanotubes and nanoribbons hydrogenated along the zigzag and armchair borders are investigated with the help of density functional theory (DFT) method. The structural stability of antimonene nanostructures is confirmed with the formation energy. The electronic properties of hydrogenated zigzag and armchair antimonene nanostructures are studied in terms of highest occupied molecular orbital (HOMO) & lowest unoccupied molecular orbital (LUMO) gap and density of states (DOS) spectrum. Moreover, due to the influence of buckled orientation, hydrogen passivation and width of antimonene nanostructures, the HOMO-LUMO gap widens in the range of 0.15–0.41 eV. The findings of the present study confirm that the electronic properties of antimonene nanostructures can be tailored with the influence of width, orientation of the edges, passivation with hydrogen and morphology of antimonene nanostructures (nanoribbons, nanotubes), which can be used as chemical sensor and for spintronic devices.

Structure, temperature and frequency dependent electrical conductivity of oxidized and reduced electrochemically exfoliated graphite

Abstract: The article presents the influence of reduction by hydrogen in statu nascendi and modification by hydrogen peroxide on the structure and electrical conductivity of electrochemically exfoliated graphite. It was confirmed that the electrochemical exfoliation can be used to produce oxidized nanographite with an average number of 25 graphene layers. The modified electrochemical exfoliated graphite and reduced electrochemical exfoliated graphite were characterized by high thermal stability, what was associated with removing of labile oxygen-containing groups. The presence of oxygen-containing groups was confirmed using Fourier-transform infrared spectroscopy . Influence of chemical modification by hydrogen and hydrogen peroxide on the electrical conductivity was determined in wide frequency (0.1 Hz–10 kHz) and temperature range (−50 °C–100 °C). Material modified by hydrogen peroxide (0.29 mS/cm at 0 °C) had the lowest electrical conductivity. This can be associated with oxidation of unstable functional groups and was also confirmed by analysis of Raman spectra . The removal of oxygen-containing functional groups by hydrogen in statu nascendi resulted in a 1000-fold increase in the electrical conductivity compared to the electrochemical exfoliated graphite.

Complex modal analysis of transverse free vibrations for axially moving nanobeams based on the nonlocal strain gradient theory

Abstract: We investigate the transverse free vibration behaviour of axially moving nanobeams based on the nonlocal strain gradient theory. Considering the geometrical nonlinearity, which takes the form of von Karman strains, the coupled plane motion equations and related boundary conditions of a new size-dependent beam model of Euler-Bernoulli type are developed using the generalized Hamilton principle. Using the simply supported axially moving nanobeams as an example, the complex modal analysis method is adopted to solve the governing equation; then, the effect of the order of modal truncation on the natural frequencies is discussed. Subsequently, the roles of the nonlocal parameter, material characteristic parameter, axial speed, stiffness and axial support rigidity parameter on the free vibration are comprehensively addressed. The material characteristic parameter induces the stiffness hardening of nanobeams, while the nonlocal parameter induces stiffness softening. In addition, the roles of small-scale parameters on the flutter critical velocity and stability are explained.

Removal of textile dyes by carbon nanotubes: A comparison between adsorption and UV assisted photocatalysis

Abstract: Amorphous carbon nanotubes were synthesized using low temperature solid state reaction. The as synthesized a-CNTs were used to remove two different textile dyes, Methyl Orange and Rhodamine B from water. Two ways of removal were followed; i.e. Adsorption and UV assisted catalysis. Adsorption experiment was carried out under various conditions. Analysis of the adsorption data was performed using Langmuir, Freundlich and Temkin models. It has been shown that the as prepared samples can effectively be used as adsorbent of textile dyes. Exposure of visible or UV light can make no significant additional effect to the removal efficiency. The mechanism of the adsorption has been found to be following a pseudo 1st order mechanism with corresponding correlation factor >0.95. Also it has been shown that presence of impurities can drastically kill the performance of the sample. This detail comparative study has been reported for the first time.

Nitrogen doped graphene nanosheet-epoxy nanocomposite for excellent microwave absorption

Abstract: In the present study, nitrogen doped graphene sheets (NGNs) have been synthesized by solvothermal reaction using cow urine as a natural dopant of N atoms, which is an alternative of highly toxic chemicals with excellent reducing capability. As synthesized NGNs have been characterized by Raman spectroscopy , Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), UV–visible spectroscopy (UV–vis), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), surface area (Brunauer-Emmett–Teller (BET)) and X-ray photon spectroscopy (XPS). Raman analysis reveals that the reduction of oxygen occurs from graphene oxide (GO) by cow urine, and reaches Raman D to G band intensity ratio of ∼1.23. XPS analysis validates the Raman signature of removal of oxygen functional groups, simultaneously N-atoms are successfully doped into honeycomb lattice, and produces GNs with high C/O ratio of ∼5.25 having N content ∼3.4 at.%. The presence of N atoms produces defect morphology in graphene structure that eventually enhances the overall electrical properties of NGNs. The NGN-epoxy nanocomposites have been fabricated for the investigation of the electromagnetic responses generated exclusively in the X band (8.2–12.4 GHz). A maximum absorption value of −40.8 dB (99.992% absorption) as well as 1.5 GHz of −10 dB effective bandwidth is observed with 2 wt.% of NGNs loadings. The strong microwave absorption is due to the electric, dielectric , interfacial polarization, and nitrogen generated defect polarization canters. Moreover, NGNs with unique disordered structure can regulate the electromagnetic properties to attain the best impedance matching criteria. This investigation opens a novel useful eco-friendly approach for the development of NGNs structure for highly efficient, light weight and low cost microwave absorber.