Nano

This paper reviews recent progress in studies on the migration of charged species, including charged lipids, membrane-attached proteins and vesicles, and integrated membrane proteins, in lipid bilayer membranes under an external electric field. The migration of these charged substances is controlled by the interplay of electrophoresis and electroosmosis. This phenomenon can be employed to separate the charged lipids and membrane-attached proteins, and concentrate integrated membrane proteins.

An exact analysis is carried out to study the radiation effects on an unsteady natural convective flow of a nanofluid past an impulsively started infinite vertical plate. The nanofluids containing nanoparticles of aluminium oxide, copper, titanium oxide and silver with nanoparticle volume fraction range less than or equal to 0.04 are considered. The partial differential equations governing the flow are solved by Laplace transform technique. The influence of various parameters on velocity and temperature profiles, as well as Nusselt number and skin-friction coefficient, are examined and presented graphically. An increase in radiation parameter and time leads to fall in temperature of the fluid. The presence of nanoparticles and thermal radiation increases the rate of heat transfer and skin friction. The effect of heat transfer is found to be more pronounced in silver water nanofluid than in the other nanofluids. It is observed that the fluid velocity increases with an increase in Grashof number and time. Excellent validation of the present results is achieved with existing results in the literature.

Electrical tree propagation in a polymer nanocomposite is affected by the presence of nanoparticles. A 2D cellular automata (CA) model is presented for the simulation of electrical tree propagation in polymer nanocomposites. The effect of the nanoparticles size, the nanoparticles loading and the appearance of microvoids on electrical tree propagation in titania (TiO₂)/epoxy nanocomposites under the application of DC voltage is examined with the aid of the CA model. It has been observed that the tree length is affected by nanoparticles size and nanoparticles loading. A resistance in electrical tree propagation has been noticed, as nanoparticles size decreases or as nanoparticles loading increases. The presence of microvoids in the polymer nanocomposite is another factor that has been examined. The propagation of electrical trees that initiate from microvoids in the polymer nanocomposite has also been simulated by the use of the CA model.

Gold nanoparticles are widely used as high efficient photon–thermal energy converters in a broad range of applications. This paper presents a theoretical investigation on using the optothermal properties of gold nanoparticle arrays to generate nanoscale molten and rubbery regions on the surface of an amorphous polymeric film. Nanoparticles are assumed to be embedded in a transparent silica layer and illuminated with a 7.5 ns pulsed laser at 532 nm. Simulation results are presented for systems with single gold nanoparticles, dimers and chains. Both electromagnetic and thermal interaction between nanoparticles are found to be important factors in determining the result of surface processing. This effect allows us to control the shape and spatial characteristics of the phase transmitted regions with various parameters such as particles size, incident light fluence, polarization and direction, interparticle distance and chain length.

Graphene(RGO)/MnO₂/[N-butyl-3,6-carbazolevinylene-alt-(2,5-dioctyloxy)-p-phenylenevinylene] (PPH–CAR) ternary nanocomposite is fabricated by a simple two-step method, which includes electrochemical reduction of graphene oxide (GO) and oxidation of Mn(CH₃COO)₂ simultaneously and an ultrathin PPH–CAR layer coated on the RGO/MnO₂ surface. The structure of the composite is investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and field-emission scanning electron microscopy (FESEM). The results suggest that the composite is correctly synthesized and each component has good dispersion. Cycle voltammetry (CV), charge and discharge measurements and cycle stability test are used to evaluate its electrochemical performance. Because of the synergistic effect of each component, the composite exhibits excellent electrochemical properties with specific capacitance of 175 F/g, which is a 46% increase compared with RGO/MnO₂. Moreover, it reveals outstanding cycling performance with more than 90% capacitance retention over 1000 cycles. Such ternary composite is a candidate for high performance supercapacitors with great promise.

Magnetic Ni micro/nanostructures with controlled morphology have drawn intensive attention due to their interesting physicochemical properties and potential applications in micro/nanodevices. In this study, one-dimensional Ni nanochains with an average diameter of about 140 nm were prepared by a magnetic-field-assisted chemical reduction of Ni²⁺ with hydrazine hydrate free of any template or surfactant. It was found that the morphology and the size of the Ni chains could be adjusted by changing the complexant used in the synthesis. The usage of surfactant in the synthesis would retard the firm connection of Ni nanoparticles and thus resulted in the formation of Ni nanochains consisting of loosely aggregated Ni nanoparticles. The magnetic measurement at room temperature indicated that the coercivity of the Ni sample reached 133.2 Oe, which was much higher than that of bulk Ni metal.

This paper demonstrates the application of negative charge-functionalized carbon-encapsulated superparamagnetic colloidal nanoparticles being as nanoadsorbents for the removal of cationic dyes from aqueous solutions. Adsorption characteristics of the magnetic nanoadsorbents were examined using methylene blue as adsorbates, exhibiting excellent ability to remove cationic dyes from aqueous solutions. In addition, the influences of uptake time, concentration of nanoadsorbents and pH values of aqueous solution on the removal of cationic dyes have been discussed. Results show that the removal efficiency can be up to 90% at a dye concentration of 100 mg L^-1 when the uptake time is 1 min, which indicates rapidly removal ability of the magnetic nanoadsorbents. Furthermore, other cationic dyes including rhodamine B and methyl violet were used to examine the universality of nanoadsorbents.

We synthesized the nanoparticles of Bi₄V₂O₁₁ with particle size less than 30 nm by combustion method and they were found to be in monoclinic phase (i.e., α-phase), confirmed by X-ray diffraction, Raman and Fourier transform Infrared spectroscopy. Morphology of the α-Bi₄V₂O₁₁ was analyzed by transmission electron microscopy and scanning electron microscopy techniques. Photocatalytic activity of α-Bi₄V₂O₁₁ in degradation of common organic dyes, such as, Rhodamine B (Rh B) and Methylene Blue (MB) was investigated under UV irradiation. Furthermore, γ-Bi₄V₂O₁₁ was obtained by post annealing treatment of α-Bi₄V₂O₁₁ to investigate the phase transition and size dependent effects on photocatalytic activity. α-Bi₄V₂O₁₁ has shown better photocatalytic activity compared to γ-Bi₄V₂O₁₁ which is attributed to its smaller particle size enhancing its surface to volume ratio and being in a different phase. BET measurement is also performed in order to observe the effect of surface area on photocatalytic activity. Complete removal of aqueous Rh B dye was realized after UV light irradiation for 45 min with α-Bi₄V₂O₁₁ as the photocatalyst.

Tin oxide (SnO₂)-doped Si nanorings of diameter in the range of 100 nm to 170 nm with an average width of 25 nm are synthesized by off-axis laser ablation (PLD) and are characterized by different techniques. The AFM observations show that the surface morphological features of films depend on the tin oxide concentration. The bandgap energies of undoped quantum dots are found to be 2.29 eV, while it decreases to 2.15 eV and 1.5 eV for 3 wt.% and 0.1 wt.% SnO₂-doped samples, respectively. The increase in the value of bandgap energy can be attributed to size reduction of particles. The Raman spectra of SnO₂-doped films are characterized by a broad Raman band with intensity maximum around 478 cm^-1. Raman spectrum shows frequency shift which may be due to changes in the Si–O bond length or Si–O–Si bond angle. The activation energy at higher temperature is found to be 16.99 meV for 3SnSi209, 21 meV for 0.1SnSi209 and 18.1 meV for undoped silicon which shows that defect levels are present in all the samples, the conduction is due to the presence of holes. The synthesized films exhibit PL peak in the visible region. The PL emission peak and PL intensity depend on dopants and it is concluded that luminescence does not originate from localized states in gap but from extended states. The size and shape of nanostructures depend on the SnO₂ concentration and the doping effects can be used as a significant guideline for tuning the electronic and optical properties of Si.

A model for explaining deviations of positions in self-organized nanoparticles on a substrate from their corresponding positions in perfect organization is proposed. The model predictions were compared with SEM/TEM images and reported by some authors. We found a consistence between the model predictions with the data of Ag, Fe₃O₄ and SiO₂ nanoparticles organization on various substrates.

Single-crystalline W nanowires, with approximately 150 nm in diameter and 15 μm in length, have been successfully synthesized on SiO₂ substrates by chemical vapor deposition (CVD) with the assistance of Ni catalysts at 950°C. The catalysts located at the tip of W nanowires were found to be Ni₄W in a solid state, rather than a liquid state. The low-temperature growth of W nanowires using the solid catalysts can be generally accessible, provided that the appropriate combination of solid catalysts and nanowires are thermodynamically available, thus suggesting the implication for the potentially large-area integrated growth on various substrates. The growth direction of the generated [100]-oriented W nanowires was presumed to be determined by the orientation relationship between the solid Ni catalyst particle and the W precipitate. A possible catalytic growth model was proposed according to the analysis of the experimental results. The orientation relationship between the solid catalyst particle and the corresponding nanowire was expected to be also valid for some other nanowires induced by solid catalyst.

In this paper, the dynamics analysis of single walled boron nitride nanotubes (SWBNNT) as a resonant nanomechanical sensor by using the finite element method has been reported. Molecular structural mechanics-based finite element model (FEM) has been developed by using three-dimensional elastic beams and point masses, such that the proximity of the model to the actual atomic structure of nanotube is significantly retained. Different types of armchair layups of SWBNNTs are considered with cantilevered and bridged end constraints. By implementing the finite element simulation approach, the resonant frequency shift-based mass sensitivity analysis is performed for both types of end constraints for considered armchair form of the SWBNNTs with different aspect ratios. For both types of end constraint, continuum mechanics-based analytical formulations, considering effective wall thickness of nanotubes are used to validate the present FEM-based simulation approach. The intermediate landing position of the added mass is analyzed, considering variations in resonant frequency shifts of the different fundamental modes of vibrations for both types of end constraints. The FEM-based simulation results for both types of end constraints found in good agreement with the continuum mechanics-based analytical results for the aspect ratio of range of 9–15. The mass sensitivity limit of 10^-1 zg is achieved for SWBNNT-based resonant nanomechanical sensors. The resonant frequency shift for higher-order fundamental vibrational modes become stable as the attached mass moves away from the fixed ends for particular magnitude of attached mass. The present finite element-based approach is found to be effectual in terms of dealing different atomic structures, boundary conditions and consideration of added mass to analyze the dynamic behavior of the SWBNNT-based resonant nanomechanical sensors.