Large Ratio Of Surface Research Articles

CFD study of Convective Heat Transfer of Water Flow Through Micro-Pipe with Mixed Constant Wall Temperature and Heat Flux Wall Boundary Conditions

The dissipation of heat in tiny engineering systems can be achieved with fluid flow through micro pipes. They have the advantage of less volume to large surface ratio convective heat transfer. There are deep-rooted analytical relations for convective heat transfer available for fluid flow through macro size pipes. But differences exist between the convective heat transfer for fluid flow through macro and micro pipes. Therefore, there is a good scope of work in micro convection heat transfer to study the mechanism of fundamental flow physics. There have been studies with either constant heat flux wall boundary conditions or constant wall temperature boundary conditions with constant and variable property flows. In this article, first, the numerical simulations are validated with the experimental data for 2D axisymmetric conventional pipe with pipe diameter of 8 mm is taken with laminar, steady, and single-phase water flows with constant wall heat flux boundary condition of 1 W/cm2. The computed Nusselt number is compared to the experimental results at different Reynolds numbers of 1350, 1600 and 1700. In the next study, three-dimensional micropipe laminar flow is studied numerically using water with an inlet velocity of 3 m/s and pipe diameter of 100 µm. The mixed wall boundary conditions with upper half pipe surface subjecting to constant wall temperature of 313 K and lower half surface subjecting to 100 W/cm2 are used in the simulations. The focus of research would be to consider the effect of temperature-dependent properties like thermal conductivity, viscosity, specific heat, and density (a combined effect we call it as variable properties) on micro-pipe flow characteristics like Nusselt number at mixed wall boundary conditions and compare it with the constant property flows. The conventional pipe showed no significant difference with variable and constant property flows with different Reynolds numbers. On contrary the flow through 3D micropipe shows that the Nusselt number with variable property flows is less as compared to the constant property flows.

Electrospun acrylonitrile butadiene styrene nanofiber film as an efficient nanosorbent for head space thin film microextraction of polycyclic aromatic hydrocarbons from water and urine samples

In the present study, acrylonitrile butadiene styrene (ABS) nanofiber film was fabricated on the aluminum foil via a one-step and facile electrospinning strategy. Thereafter, the fabricated film was utilized as a novel and efficient nanosorbent for headspace thin film microextraction (HS-TFME) of polycyclic aromatic hydrocarbons (PAHs). Some properties of the prepared nanofiber film like morphology, chemical structure, stability, wettability, and extraction efficiency were investigated systematically. The fabricated nanofiber films showed a large ratio of surface to volume, high stability, good hydrophobicity and porous fibrous structure; hence an excellent extraction performance has been achieved. The π-π and hydrophobic interactions play crucial roles in the tendency of PAHs towards fabricated nanosorbent. The effective parameters on the adsorption performance of the developed headspace thin film microextraction-gas chromatography-mass spectroscopy (HS-TFME-GC-MS) method were optimized. At the optimized conditions of the proposed method, a broad linearity range with high coefficient of determination (R2≥0.998) was obtained and the limit of detections (LODs) were in the range of 0.08–0.2 ng mL−1 for six PAHs. The developed HS-TFME-GC-MS method has been applied for the measurement of PAHs in drinking and industrial water samples and urine samples of a smoker and also a non-smoker with satisfactory recoveries in the range of 83–98%, with relative standard deviations (RSDs) lower than 8.8%. The proposed HS-TFME-GC-MS method demonstrated to be a sensitive, efficient, uncomplicated, cost-effective and rapid approach, which can be introduced to analyze trace amounts of PAHs in various samples.

On-chip suspended gold nanowire electrode with a rough surface: Fabrication and electrochemical properties

Nanoporous materials have attracted great attention due to the large ratio of surface over volume. Similarly, nanomaterials with big surface roughness have also high surface/volume ratio. The present work investigates the electrochemical behavior of a nanowire electrode with a big surface roughness. An on-chip individually addressable suspended gold nanowire (width: 340 nm, thickness: 90 nm, and length: 5.5 μm) electrode with an arithmetic mean surface roughness of 15.02 ± 2.95 nm was fabricated by using the electron beam lithography and reactive ion etching technique. The Cyclic Voltammograms (CV) of the suspended Au nanowire electrode in both the potassium ferricyanide and the sulfuric acid electrolytes show noticeably different characteristics from that of the control Au thin film electrode. The suspended nanowire shows an excellent room-temperature cyclic reliability, with only ±3% variation in the integrated capacitance after 600 cycles at the scanning rate of 0.1 Vs-1. The facile on-chip fabrication, large effective surface area, and excellent cyclic stability make the suspended gold nanowire electrode an ideal candidate for many emerging applications such as electrochemical catalysts, biosensors, and detectors.

A new drug carrier with oxygen generation function for modulating tumor hypoxia microenvironment in cancer chemotherapy.

Hypoxia is the main characteristic of tumor microenvironment, and the one of the key factors that cause the drug resistance of cancer cells for chemotherapy. Anticancer drug such as DOX cannot react with sufficient oxygen to produce reactive oxygen species (ROS) in hypoxic environment, which affects the therapeutic efficiency of the drug. In this work, we constructed a multi-functional nano-carrier (named as FeSiAuO) containing Fe3O4, mesoporous SiO2 and Au2O3 with magnetic, large surface ratio and light induced oxygen production properties. The Au2O3 may decompose into oxygen (O2) and Au under the light irradiation to improve the oxygen concentration of the microenvironment of cancer cells, which increases the sensitivity of cancer cells to drug (DOX), reduces the drug resistance, and effectively exerts the anticancer effect of DOX. Meanwhile, the release of the as-loaded DOX molecule from the porous of SiO2 will be also promoted under light irradiation in diverse pH conditions. With the helping of the magnet effect of the Fe3O4, the DOX can be also targeted delivered to the tumor site under the magnetic field. All of above results were thoroughly examined by the cell and small animal assays, which demonstrate that the FeSiAuO can be served as the multifunctional drug nano-carrier to achieve the targeted high-efficient cancer therapy.

Progress in Preparation of Monodisperse Polymer Microspheres

The monodisperse crosslinked polymer microspheres have attracted much attention because of their superior thermal and solvent resistance, mechanical strength, surface activity and adsorption properties. They are of wide prospects for using in many fields such as biomedicine, electronic science, information technology, analytical chemistry, standard measurement and environment protection etc. Functional polymer microspheres prepared by different methods have the outstanding surface property, quantum size effect and good potential future in applications with its designable structure, controlled size and large ratio of surface to volume. Scholars of all over the world have focused on this hot topic. The preparation method and research progress in functional polymer microspheres are addressed in the paper.

Fabrication and photovoltaic effect of ZnO/silicon nanopillars heterojunction solar cell

A 300 nm thickness layer of zinc oxide (ZnO) film covers on the p-type silicon nanopillars surface to heterojunction solar cell. The original nanopillars are about 200 nm average diameter and 1 µm height with narrow-top and wide-root morphology, which is easy to film pack. The ZnO film covers on the silicon surface by RF magnetron sputtering. Next, a layer of ITO film is sputtered on the front side of ZnO surface. Finally, the Ti/Ag are deposited onto the surface of ITO film as electrodes. The X-ray diffraction pattern shows that the crystalline ZnO grows on the nanopillars surface at different crystal orientation. On the one hand, the nanopillars wafer has lower reflectance than the planar one both before and after the ZnO film covering, which is helpful for photovoltaic performance improvement. On the other hand, the nanopillars have the large surface ratio, which can increase the light absorption and the heterojunction surface. The photovoltaic conversion efficiency of the nanopillar solar cell is 1.20%, which is higher than 1.09% that of the planar one.

Fabrication and Photosensitivity of CdS/Silicon Nanoscrew Photoresistor

AbstractSilicon nanoscrews with aspect ratio of 3, 6 and 9 corresponding to 4, 8 and 12 etching cycles are fabricated by CsCl self‐assembly lithography and inductively coupled plasma (ICP) dry etching with “Bosch Process”, which can reduce the reflection to below to 10% for wavelength from 400 to 1000 nm. A layer of Cadmium sulfide (CdS) film covers onto the silicon nanoscrews surface to photoresistor. The XRD pattern shows the CdS packed both on the nanoscrew and planar surface are well‐crystallized. The nanoscrew substrate with the large surface ratio can increase the light absorption and quantity of sensitive material, which can improve the photosensitivity of the CdS photoresistor compared to the planar one obviously. However, the aspect ratio of nanoscrew is not the larger the better for that the high aspect ratio also increases the difficulty of CdS package. The photosensitivity response test results show that the nanoscrew photoresistor with 6 aspect ratio has the best performance under different illumination. With 10000 μW/cm2, the best photosensitivity response achieves to 141 for nanoscrew sample.

MoS2-LA-PEI nanocomposite carrier for real-time imaging of ATP metabolism in glioma stem cells co-cultured with endothelial cells on a microfluidic system

Stimuli-responsive carriers have extensively attracted attention in recent years. However, long-term and real-time tracking ability with stimuli-responsive carrier is still in its infant stage due to the limitations such as, low efficacy, instability and cytotoxicity in a bio-environment. In this work, we developed a reduction-sensitive carrier composed of lipoic acid-modified low molecular weight polyethyleneimine (LA-PEI) and large surface ratio MoS2 nanosheet integrated via disulfide bond to mimic a high molecular weight PEI. The positively charged carriers loading negatively charged aptamer enter the cells for a real time long-term tracking of adenosine triphosphate (ATP) metabolism in glioma stem cells (GSCs) when stimulated by TGFβ factor secreted from HUVECs. We envision that MoS2-LA-PEI carrier has a promising potential for delivery and monitoring the changes in live cells with low cytotoxicity and high efficiency.

Atomically dispersed Co atoms on MoS2 monolayer: A promising high-activity catalyst for CO oxidation

We systematic investigated the CO oxidation reaction over a single Co atom supported by MoS2 monolayer (Co/MoS2) on the basis of density functional theory calculations and ab initio molecular dynamics simulations. The binding energy of a single Co atom onto MoS2 monolayer is up to 2.80eV, making the diffusion and aggregation of supported Co atom difficult. For CO oxidation reaction, both Eley–Rideal and Langmuir–Hinshelwood mechanisms are considered. The energy barriers of CO oxidation through the Langmuir–Hinshelwood mechanism for the rate-limiting step of formation the peroxide-like O-C-O-O intermediate is only 0.57eV. The relatively high CO oxidation activity of Co/MoS2 may be attributed to the strong electronic resonance among the 3d orbital of the Co atoms and the antibonding 2π* orbitals of adsorbed CO and O2. We proposal that the MoS2 monolayer can serve as a defect-free two dimensional single atom catalysts substrate for CO oxidation reaction. It provides not only a large surface ratio, but also a uniform distribution anchoring points for fixing metal atoms as activation sites. We hope that this work contributes to design more effective nonprecious-metal single-atom catalysts for CO oxidation and widen the applications of monolayer MoS2 materials.

Gas sensor based on ZnO film/silica pillars

Silica submicron pillars are used as substrate for Zinc oxide (ZnO) gas sensor for the first time. The submicron pillars with the large surface ratio can improve the gas sensing performance obviously. Silicon pillars are fabricated by cesium chloride (CsCl) self-assembly lithography and inductively coupled plasma dry etching as substrate, the ZnO film is deposited on the pillars surface by RF magnetron sputtering. With this method, the pillar based gas sensor has the higher gas response, the shorter response and recovery time than the planar one with different working temperatures, different gas concentrations. 300 °C is the best working temperature, for planar gas sensor, the gas response is 22.81 for 1520 ppm ethanol, the response time is 55 s and the recovery time is 169 s. While for the pillar based one, the gas response is 28.20, the response time is 51 s and the recovery time is 92 s.

Fabrication and Photovoltaic Effect of CdS/Silicon Nanopillars Heterojunction Solar Cell

AbstractA 200 nm thickness layer of Cadmium sulfide (CdS) film covers on the silicon nanopillars surface to heterojunction solar cell. The nanopillars with the large surface ratio can increase the heterojunction surface and the light absorption, which can improve the photovoltaic performance of solar cell. Silicon nanopillars are fabricated by Cesium Chloride self‐assembly lithography and inductively coupled plasma dry etching as substrate. CdS film covers the silicon nanopillars surface by the RF magnetron sputtering using CdS ceramic target. The X‐ray diffraction patterns of the nanopillar and planar substrates after CdS film covering indicate that all the deposited films are crystal. The nanopillars wafer has lower reflectance than the planar one both before and after the CdS film covering for the wavelength ranging from 350 to 1050 nm. With this method, the nanopillar based CdS/Silicon heterojunction solar cell has the better photovoltaic performance than the planar one. The Jsc increases from 7.12 to 13.92 mA/cm2 and the energy conversion efficiency increases from 1.32 % to 1.83 %. The large surface ratio nanopillars might be a potential substrate for high efficiency heterojunction solar cell.

Fabrication and photosensitivity of CdS photoresistor on silica nanopillars substrate

Silica nanopillars are used as substrate for Cadmium sulfide (CdS) photoresistor for the first time. The nanopillars substrate with the large surface ratio can increase the quantity of sensitive material and the surface of light response, which can improve the photosensitivity of the CdS photoresistor obviously. Silicon nanopillars are fabricated by Cesium Chloride (CsCl) self-assembly lithography and inductively coupled plasma (ICP) dry etching, after oxidation, the silicon nanopillars changes to silica nanopillars totally, then the 200nm thickness CdS film is deposited on the nanopillars surface by RF magnetron sputtering using CdS ceramic target. XRD patterns of the nanopillar and planar substrates after CdS film covering indicate that all the deposited films are crystal. Photosensitivity properties of the photoresistor are tested by a home-made instrument in our group. The test results show that the nanopillar based photoresistor has the higher photosensitivity response than the planar one with different irradiance from 400 to 11,000μW/cm2. With 10,000μW/cm2 irradiance at the room temperature, the photosensitivity response for the planar sample is only 62, while the response for the nanopillar sample achieves to 137, which is more than double of the planar one. The result reveals that the nanopillars morphology can be used as substrate to increase the property of the photoresistor.

Antibacterial effect assessment of ZnS: Ag nanoparticles

Objective(s): A large ratio of surface to volume of nanoparticles in comparison with bulk ones, will increase the cell penetration and therefore their toxicity. Materials and Methods: Chemical precipitation method was used in order to synthesis of ZnS:Ag quantum dots. Their Physical properties and characteristics were assessed by X-ray diffraction, Ultra Violet-Visible Spectrophotometer, Transmission Electron Microscope and it was shown that the obtained ZnS:Ag quantum dots are cubic with high-quality. Antibacterial effects of ZnS:Ag nanoparticles against Pseudomonas aeroginosa, Staphylococcus aureus and Salmonella typhi were investigated. Disc bacteriological tests were used in order to assessment of the antibacterial effects of ZnS:Ag nanoparticles. Results: The size of inhibition zone was different according to the type of bacteria and the concentrations of ZnS:Ag QDs. The maximum diameter was happened for S. aureus. The results of MICs obtained fromBroth Dilution for Pseudomonas aeruginosa , Staphylococcus aureus and Salmonella typhi, are 3.05 , 3.05 and 6.1 mg/ml whereas the amounts of obtained MBCs are 12.2 , 6.1 and 12.2 mg/ml respectively. Conclusion: In conclusion, by increasing the nanoparticle concentration in wells and discs, the growth inhibition and diameter of inhibition zone has also been increased.

Size-dependent buckling and vibration behaviors of piezoelectric nanostructures due to flexoelectricity

The symmetry breaking of inversion in solid crystals will induce electric polarization in all solid crystals, which is well known as flexoelectricity. At the nanometer scale, due to the large ratio of surface to volume, piezoelectric structures always exhibit distinct mechanical and electrical behaviors compared with their bulk counterparts. In the current work, the effects of surface and flexoelectricity on the buckling and vibration of piezoelectric nanowires is investigated based on a continuum framework and the Euler–Bernoulli beam hypothesis. Analytical solutions of the electric field in the piezoelectric nanobeam subjected to electrical and mechanical loads are obtained with the surface, flexoelectric and nonlocal electric effects. Numeric simulations demonstrate that the Young’s modulus and bending rigidity of PZT and BaTiO3 (BT) nanowires are enhanced by flexoelectricity. In addition, the critical buckling voltage is calculated with consideration of the effects of surface and flexoelectricity, and it is found that the effects of surface piezoelectricity, flexoelectricity and residual surface stress play significant roles in determining the critical buckling voltage. Results obtained for the first resonance frequency also indicate that the effects of surface and flexoelectricity are more significant at a narrow range of beam thickness. The first resonance frequency of PZT and BT nanowires is also influenced by the residual surface stress and external applied voltage. The current work is expected to provide a fundamental study on the buckling and vibration behaviors of piezoelectric nanobeams, and it might also be helpful in devising piezoelectric nanowire-based nanoelectronics.

Surface effects on the post-buckling of piezoelectric nanowires

Due to the large ratio of surface to volume, surface effects play an essential role in determining the physical properties of nanoscaled structures. A theoretical model is developed in this work to investigate the effect of surface on the postbuckling behavior of piezoelectric nanowires, in which the residual surface stresses, surface piezoelectricity and surface elasticity are taken into consideration. The critical buckling strain and the amplitude of the buckled nanowire are analytically obtained. It is found that the critical buckling strain ratio increase with the decrease of the thickness of piezoelectric nanowire, which demonstrates that the surface becomes prominent when the thickness of piezoelectric nanowire is at nano-scale. The theoretical estimation agrees well with the experimental data on a single crystal ZnO nanowire. This study provided the fundamental understanding of the physical behavior of piezoelectric nanowires and is promising for designing piezoelectric nanowire based stretchable nanoelectronics.

Hydrogen storage in heat welded random CNT network structures

The objective of this study is to investigate hydrogen storage capability of heat welded random carbon nanotube (CNT) network structures. To achieve this objective, different three-dimensional random CNT network structures are generated by using a stochastic algorithm and molecular dynamic simulations. The interaction of CNT networks with hydrogen molecules is then examined via grand canonical Monte Carlo calculations. Hydrogen adsorption capacity of CNT networks having an arbitrarily natured morphology, adjustable porous structure and large surface ratio is investigated. The results show that if cross link density of random CNT networks decreases, hydrogen storage capability of CNT networks increases in terms of the gravimetric capacity. It is observed that random CNT networks could uptake 8.85 wt.% hydrogen at 77 K and this result is very comparable with the results reported in literature where generally ideal ordered nanostructures having no topological irregularities are considered.

Bismuth-rich strategy induced photocatalytic molecular oxygen activation properties of bismuth oxyhalogen: The case of Bi24O31Cl10

Molecular oxygen activation is very important for photocatalytic degradation of organic pollutants. In this paper, Bi24O31Cl10 nanosheets with {100} facets exposure were successfully synthesized by hydromel method and characterized. The size of a single nanosheet is about 5μm in width and 10–30nm in thickness, which results in a large ratio of surface to thickness and higher exposure ratio of {100} facets. The Mott–Schottky test revealed that the conduction band minimum (CBM) of Bi24O31Cl10 is more negative than BiOCl due to the bismuth-rich strategy. And the photocatalytic results showed that as-synthesized Bi24O31Cl10 showed higher photocatalytic properties than BiOCl for activate molecular oxygen to generate superoxide radical (O2•−) under visible light (λ>420nm) irradiation, and generate hydroxyl radical (•OH) under UV–vis light irradiation. This strategy in this work may potentially be extended to other bismuth-based photocatalysts for molecular oxygen activation.

Antibacterial Effect Assessment of CdSe Nanoparticles

Objective(s): A large ratio of surface to volume of nanoparticles in comparison with bulk ones, will increase the cell penetration and therefore their toxicity. Materials and Methods: Chemical precipitation method was used in order to synthesis of ZnS:Ag quantum dots. Their Physical properties and characteristics were assessed by X-ray diffraction, Ultra Violet-Visible Spectrophotometer, Transmission Electron Microscope and it was shown that the obtained ZnS:Ag quantum dots are cubic with high-quality. Antibacterial effects of ZnS:Ag nanoparticles against Pseudomonas aeroginosa, Staphylococcus aureus and Salmonella typhi were investigated. Disc bacteriological tests were used in order to assessment of the antibacterial effects of ZnS:Ag nanoparticles. Results: The size of inhibition zone was different according to the type of bacteria and the concentrations of ZnS:Ag QDs. The maximum diameter was happened for S. aureus. The results of MICs obtained fromBroth Dilution for Pseudomonas aeruginosa , Staphylococcus aureus and Salmonella typhi, are 3.05 , 3.05 and 6.1 mg/ml whereas the amounts of obtained MBCs are 12.2 , 6.1 and 12.2 mg/ml respectively. Conclusion: In conclusion, by increasing the nanoparticle concentration in wells and discs, the growth inhibition and diameter of inhibition zone has also been increased.

Bright and Stable Quantum Dot Structures and Their Application to Display

The synthetic methods to prepare high quality quantum dots (QDs) in the colloidal phase have been developed, and it has been proposed that the advantages of the QDs can be practically realized in various optoelectronic devices in the near future. In particular, red light emitting CdSe-based QDs have been significantly optimized in terms of the emission wavelengths, quantum efficiency, and the tolerance against fabrication conditions such as high temperature curing or chemical treatments. However, QE and stability diminish rapidly as the size of QDs are reduced, because the density of the surface defects are more easily generated by the large ratio of surface to volume and the steric hindrance of capping ligands. Here, we present the novel structure of QD consisting of the alloy core and multi shells (AC/MS) of which the emission could be tuned especially in green region (502 nm ~ 563 nm). For the alloy core, the previously reported CdSe//ZnS interfused gradient alloy structure was used as a blue core (PL=458 nm). And, additional crystalline layer was grown on the surface of the blue light emitting alloy core to build CdSZnS multi shells. Since the CdS has smaller energy band gap than the alloy core and excitons can be delocalized all over the CdSe//ZnS/CdS crystalline structure, the emission of the CdSe//ZnS/CdSZnS QDs shifts to lower energy depending on the thickness of the CdS layer. The CdSe//ZnS/CdSZnS AC/MS QDs showed 100% of quantum efficiency and narrow spectrum width. The AC/MS QDs also have strong stability against intense radiation and thermal process so that they showed 70 % of external quantum efficiency as a green color converter on a blue light emitting diode. A white LED made with optimized red and green QDs showed high efficacy of 45lm/W and about 96 % of color reproducibility compared to the NTSC color space.

Biosynthesis of Silver nanoparticles from Actinomycetes for therapeutic applications

Silver is composed of a large percentage of silver oxide due to their large ratio of surface to bulk silver atoms. Silver nanoparticles have been a potent antibacterial, antifungal, anti-viral and anti-inflammatory agent. A simple, eco-friendly, inexpensive biosynthetic method was employed to synthesize silver nanoparticles. The present study aimed at the comparative study of silver nanoparticles synthesized through microbial and chemical methods. A microbial route to synthesize silver nanoparticles by Actinomycetes sp. was done. Actinomycetes are aerobic, Gram-positive bacteria, generally exhibiting branched filamentous growth and contain high guanine plus cytosine content in their DNA. Chemical methods were employed to synthesize silver nanoparticles. Chemical reduction of silver ions (Ag + ) using sodium borohydride in aqueous solution generally yields silver nanoparticles with particle diameters of several nanometers. It is observed that reduction is slow in chemical methods as compared to rapid microbial synthesis of silver nanoparticles. The obtained silver nanoparticles were characterized using UV-vis spectroscopy and TEM. TEM images of microbially synthesized silver nanoparticles were of smaller size (10-20 nm) compared to chemical methods (60-80 nm). The microbially synthesized silver nanoparticles using Actinomycetes were found to be highly toxic to bacteria and it was found that smaller silver nanoparticles synthesized by microbial route had a greater antibacterial activity when compared to their chemical moieties.