Current Nanoscience (v.13, #4)

Meet Our Editorial Board Member by Chunwen Sun (331-331).

Editorial: Nanomaterials for Energy-Related Applications by Zhiping Luo, Dong Fang (332-332).

Background: Increasing demand on the large scale H2 generation with the uttermost purity as required by the fuel cells is now totally depending on water splitting. The major energy consuming reaction in water splitting is the thermodynamically un-favoured oxygen evolution reaction (OER) for which the noble metal oxides such as IrO2 and RuO2 have so far been extensively used as efficient electrocatalysts. However, the increased metal dissolution at high anodic overpotential and expenses associated with these materials render its implementation in large scale H2 production. This report provides an alternative way of reducing the total RuO2 content with concomitantly increased corrosion resistance by alloying with NaPO3 at nano-scale.

Methods: A detailed research and review on the existing literature has been carried out. The synthesis was carried out utilizing conventional wet-chemical and thermal annealing routes. The same was then characterized in and screened as an electrocatalyst for OER in acidic electrolyte of pH 1.

Results: The successful synthesis of RuO2-NaPO3 nanocomposite was confirmed by various advanced characterizations such as XRD, HRTEM, XPS and EDS. Then the same was screened for acidic OER in comparison with the commercial catalyst RuO2 procured from Sigma. The results have shown that RuO2-NaPO3 nanocomposite required a very low overpotential of 250 mV at a current density of 10 mAcm-2 for which the commercial catalyst required 85 mV higher potential than RuO2- NaPO3 nanocomposite. Comparatively lower Tafel slope (110 mVdec-1) and minimum increase in overpotential at 10 mAcm-2 after cycling test for RuO2-NaPO3 nanocomposite had once again proven the advantages of alloying RuO2 with NaPO3 for harvesting synergistically enhanced OER activity with improved corrosion stability.

Conclusion: A comparatively easier synthesis of RuO2-NaPO3 nanocomposite enabled the use of RuO2 with comparatively reduced loading to harvest maximum catalytic efficiency. The intentionally incorporated NaPO3 had increased the catalytic performance of RuO2 and also increased the corrosion stability as revealed by the electrochemical characterizations. The proposed approach is undoubtedly adaptable for the fabrication of highly active other electrocatalysts for OER with improved corrosion stability.

Enhanced Electrochemical Properties of Bi Nanowires as Anode Materials in Lithium and Sodium Batteries by Zhi Zhou, Shengxiong Huang, Wei Luo, Chang Wang, Xin Fan, Nan Zhou, Renzhuo Wan, Dong Fang (342-348).
Background: Bismuth (Bi) has been studied due to its high theoretical gravimetric capacity of 385 mAh g-1, which is as important as gravimetric capacity for the practical application of battery systems in electronic mobile devices. However, there have been limited fundamental explorations on the electrochemical performances of Bi. Furthermore, the mechanism differences for the Bi anodes in lithium-ion batteries (LIBs) and sodium-ion batteries (NIBs) should be further investigated.

Methods: The Bi nanowires were fabricated by vacuum melting and pressure injection method. Briefly, a Bi bulk was placed into an injection apparatus and heated up above 275 A°C (melt point of Bi: 271.3 A°C), and then the melt was injected into the AAO pores by a hydraulic force. After the injection process, the chamber was kept in vacuum to cool down slowly. Subsequently, the AAO template was dissolved away slowly in the etching solution (0.4 M H3PO4+ 0.2 M CrO3) at 60 A°C for 72 h to expose Bi nanowires. Finally, after sonication dispersion, centrifugal sedimentation and rinsing with deionized water several times to remove the excess H3PO4-CrO3 mixture, the free-standing Bi nanowires were collected.

Results: The morphologies of AAO, AAO/Bi and Bi nanowires were tested and presented in detail. It found that the Bi nanowires can be obtained by pressure injection method followed with dissolve the AAO template. After boll milling with C to form Bi/C nanocomposites, the nanocomposites were assembled as an electrode of LIBs or NIBs. It exhibited high capacities in LIBs, while for NIBs, the capacity retention was relatively low.

Conclusion: Bi nanowires have been prepared by mechanical pressure injection method and thoroughly dissolution of the AAO template. After successive milling of Bi nanowires with carbon black, Bi/C nanocomposites are obtained. The Bi/C nanocomposites used as electrode in LIBs exhibit high capacities and the initial discharge/charge capacities of Bi/C anode are around 1223.4/571.9, 905.9/412.3, 829.2/ 362.6 mAh g-1 at current densities of 20, 200 and 500 mA g-1, respectively. The enhanced electrical performances are attributed to the smaller size of Bi nanowires and the introduced carbon black to buffer the volume changes during discharge/charge process. In NIBs, the capacity retention after 50 cycles reaches 284.7, 196.2 and 168.3 mAh g-1 at current densities of 20, 200 and 500 mA g-1, respectively. Furthermore, in LIBs, Bi and Li+ ions combine together through an alloying process, while in NIBs, only an intercalation process occurs for Bi and Na+ without indication of alloying.

Effects of Anchoring Boundary Conditions on Active Nematics by Zhenlu Cui, Jianbing Su, Xiaoming Zeng (349-353).
Background: Extensive theoretical efforts in active nematics have been carried out in the past decade, but the effects of initial and boundary conditions are scarcely studied. Most studies only consider either tangential or normal anchoring boundary conditions. However, it is well known that boundary effects and confinement can play a very important role in the formation of self-organized patterns. We consider an oblique anchoring boundary conditions extending the previous studies from tangential and normal boundary conditions to neither of them in both shear and Poiseuille flows. Methods: Mathematical modeling, analysis and numerical simulations.

Results: We have established the asymptotic formulas of the steady boundary-value problem subject to a steady weak shear and plane Poiseuille flows. We have also found remarkable dualities of active nematics in the systems.

Conclusion: The director anchoring boundary condition plays a very important role in the hydrodynamics and stability of active nematic systems. The Leslie's angle is the boundary for the stability region.

Numerical Study of Mixed Convection Insidea-Shaped Cavity with Mg(OH2)-EG Nanofluids by Mohammad Hemmat Esfe, Ali Akbar Abbasian Arani, Wei Mon Yan, Alireza Aghaei (354-363).
Background: Due to the wide range of the mixed convection dilemma, it becomes one of the main topics of research in the last two decades. These types of fluid flow and heat transfer occur in technological and industrial applications, such as electronic cooling, crystal growth, and solar collectors, energy-saving household, double-wall thermal insulation and oil extraction. In addition, the view of nanofluid and convection inside an enclosure and considering its complex shape, make it much more significant in these applications which motivate us to consider the present type of problem.

Method: The finite volume method and the SIMPLER algorithm are employed to solve the governing mass, momentum, and energy equations. The first step of discretizing the governing equations is to generate a finite difference mesh in the computational domain. A control volume is used around each node of the mesh afterwards. The governing equations are then integrated over each control volume. The diffusion terms are replaced using a second-order central difference scheme; while, a hybrid scheme is employed for the convective terms to obtain stable solutions for convectiondominated cases. An under relaxation scheme is adopted to obtain the converged solutions.

Results: Results show that for all inclination angles at various aspect ratios ranging from 0.15 to 0.5, with increasing solid nanoparticles volume fraction up to 0.015, the average Nusselt number enhances and then decreases. In these aspect ratios, for all solid nanoparticles volume fractions, the average Nusselt number at inclination angle equal to 90A° is greater than it at the other. Furthermore, with increasing inclination angle from 0 to 90A°, the maximum enhancement of average Nusselt number is 39.8% which occurs at nanoparticles volume fraction of 0.008 and aspect ratio of 0.75.

Conclusion: At low solid volume fraction (φ=0.002), there is not a distinct differences in the temperature and streamline counters of nanofluid compared to those of the base fluid. 3. In addition, with increasing inclination angle from 0 to 90A°, the maximum enhancement of average Nusselt number is 39.8% which occurs at volume fraction of 0.008 and aspect ratio of 0.75.

A Review on X-ray Detection Using Nanomaterials by Zhiping Luo, John G Moch, Shardai S Johnson, Chien Chon Chen (364-372).
Background: Since the discovery of X-rays by Röntgen in 1895, X-rays have been widely applied in multiple disciplines and industries. Since the X-rays are well beyond human visibility, materials are used for the high-energy X-ray detections. This review focuses on the X-ray detection using nanomaterials.

Methods: X-rays can be detected by (1) X-ray films, which is a traditional method for imaging; (2) phosphor- or scintillator-based detectors, which are used as an indirect detection method to convert the X-rays into visible lights; (3) semiconductor-based detectors, which are used as a direct detection method for X-ray imaging and X-ray exposure measurements; and (4) gas detectors, which are used for X-ray exposure measurements.

Results: Materials for X-ray detection were summarized, including phosphors, scintillators, and semiconductors. Their characteristic properties were compared. Nano size effects on the X-ray detection were discussed. X-rays can be detected using random nanomaterials (nanoparticles, nanofibers and nanowires, nanocomposites). The scintillator and phosphor nanoparticles were found to exhibit enhanced luminescence and shortened decay time, while luminescence suppression was also observed. Assembly of a core/shell structure was suggested as a strategy to increase such luminescence intensity. Nanofibers and nanowires have been prepared for improved spatial resolution. Since it is expensive and also technically challenging to grow high-quality single crystal scintillators, alternative ways have been developed to fabricate nanocomposites with scintillator or phosphor nanoparticles that demonstrated high performance. For X-ray imaging, it is preferable to vertically align scintillator material to reduce light cross scattering and to achieve higher spatial resolution; ideally by confining the scintillator inside of walls with light guides. Finally, scintillators have been made in nanochannels for improved spatial resolution and light output.

Conclusion: The application of nanomaterials for X-ray detection is limited when compared to other applications using nanomaterials. The research on X-ray detection using nanomaterials is an open field for conducting studies of excitation mechanisms, exploration of new scintillator materials, and applications of active compounds.

Background: We present a review on recent progress in the research and development of titanium dioxide (TiO2) nanomaterials. Based on the studies reported in the literature, titanium oxide nanoparticles and nanotubes (NPs and NTs) can be fabricated by inexpensive methods, such as solgel deposition and anodization process. Typically, TiO2 NPs are synthesized in a particle size less than 10 nm, and the featured dimensions of TiO2 NTs are about 100 nm in pore diameter, 1010 pores/cm2 in pore density, 25 nm for wall thickness, and several microns in length perpendicular to surface.

Methods: Anodic oxide films are normally amorphous because of the formation of defect clusters and the presence of considerable internal mechanical stresses. However, a careful pre-polishing procedure and a slow increasing rate in anodizing voltage (0.1 mV/s) is beneficial to fabricate crystalline epitaxial thin films. Furthermore, with an ultra-slow anodizing condition up to 1 V (saturated calomel electrode; SCE), crystalline TiO2 with a thickness of 1.65 nm can be formed.

Results: In order to increase the effective surface area of TiO2, the TiO2 NPs are deposited on TiO2 NT surfaces. The effect of the TiCl4 treatment on TiO2 NT films has been reported to increase the surface area, and thus to enhance the photocatalytic applications. During the deposition process, the Ti(OH)4 is formed from TiF4 or TiCl4 solution by controlling pH value and temperature. Then, the Ti(OH)4 can be transformed to TiO2 after heat treatment. TiO2 NTs/NPs have a larger surface area than a compact TiO2 film, more materials can be absorbed on the TiO2 NT surface. With the anodic electrolyte of a higher pH value, the TiO2 NT film with a longer length and a higher surface area will be produced. Large-scale manufacturing of high-quality and inexpensive TiO2 NTs/NPs film can be potentially utilized for academic research and industrial applications.

Conclusion: The dense TiO2 film can be formed on matrix Ti through heat-treatment or interference anodization methods. However, anodizing titanium foil in a F- ions and minimizing water content in non-aqueous organic polar electrolyte are beneficial for the formation of closely packed and vertically aligned nanotubes.

A Review on the Electrospun Oxide Nanofibers for Anode Electrodes in Lithium-Ion Batteries by Chang Wang, Xiujuan Li, Ziqing Cai, Jing Huang, Xin Fan, Hui Liu, Weilin Xu, Dong Fang (394-409).
Background: Many studies on the electrochemical properties of electrospun nanofiber in lithium-ion batteries (LIBs) have been performed. To the best of our knowledge, no work has yet summarized the use of electrospun one-dimensional materials as anode materials and also assessed the influence of this unique morphology on the properties of LIBs properties. This review describes recent advances in the synthesis and characterization of a variety of 1D multifunctional oxides, oxide composites and oxide-carbon composites electrospun nanofibers used as anodes in LIBs, which provide both excellent capacity and high mechanical integrity.

Method: Oxide, oxide composite and oxide-carbon composite electrospun nanofibers are reviewed as anodes in LIBs. For each material type, we report on the structural and electrochemical properties, and also discuss how to control the structures of the resulting materials and improve the electrochemical performance characteristics (e.g., capacity, cycle life, and rate capability). We apply correlation method and step-to-step focusing method to present the references.

Results: 176 papers were included in the review; 6 tables and 7 figures are shown in this paper. The manuscript is divided into 5 parts. For the electrospinning parameters of nanofibers, different conditions were compared, such as polymer, solvent, polymer concentration, voltage level, and tip-tocollector distance. The processing conditions of electrospun oxides nanofibers are also discussed, including the oxide precursor, solvent, voltage level, calcination temperature/heating rate. The performance of electrospun oxide nanofibers as electrodes in LIBs are summarized including metal oxide- metal, metal oxide- metal oxide, and metal oxide-carbon composites.

Conclusion: The findings of this review confirm that prepared electrospun electrode materials tend to form 3D interconnected networks, which can enhance electrochemical activities of electrode materials via facilitating electronic/ionic transfers. The electrochemical performance of electrospun MexOy nanofibers depends on process parameters and also the component structure such as metalembedded, carbon coated/doped, and metal oxide hybrid material. However, the electrospun MexOy nanofibers require additional development before commercial application. To utilize the described materials as effective anodes in commercial LIBs, especially for electric vehicle applications, additional research work is required.

A Review on Nanocarbon-Reinforced Cu-Matrix Nanocomposites with High Mechanical Strengths by Wanxia Liu, Xiaosong Jiang, Zhenyi Shao, Degui Zhu, Minhao Zhu, Shardai S. Johnson, Zhiping Luo (410-420).
Background: Despite of the fact that nanocarbon can effectively improve mechanical properties and reduce mass density of Cu-matrix composites, there are lacking comprehensive reviews on preparation and properties of nanocarbon-reinforced Cu-matrix composites synthesized with carbon nanotubes (CNTs) or graphene nanoplates (GNPs). This review presents research on interfaces between nanocarbon/Cu and strengthening mechanisms of nanocarbon-reinforced Cumatrix composites, and existing problems in the research on these nanocomposites.

Methods: Research articles in open literature related to nanocarbon-reinforced Cu-matrix composites were critically reviewed. Original research on this topic was also presented in this article.

Results: Research results have shown that Cu-matrix composite materials have advantages of high strengths while retaining sufficient thermal and electrical conductivities. Nanocarbon can effectively improve mechanical properties, and reduce mass density of the Cu-matrix composites. Effective mechanical lock is formed between nanocarbon and Cu matrix, which enhances the properties of the composites. Since CNTs and GNPs have different characteristics, and consequently, Cu matrix can be enhanced to maintain its high conductivity, high mechanical properties and high wear resistance.

Conclusion: Nanocarbon-reinforced Cu-matrix composites have been studied for the new energy applications, and these composites possess the potentials to reach the requirements for being light weighted and with enhanced mechanical and physical properties. Designed nanocarbon-reinforced Cu-matrix composites should satisfy application and environmental requirements in the new energy field with enhanced mechanical, physical and chemical properties.

Background: One of the important molecules in the human body is protein. The proteins are incredibly complex chains of smaller molecules namely amino acids. After the invention of biosensor, optical sensing mechanisms received considerable attention in the applications of the chemical and biochemical sensors in various applications such as industrial process control. Photonic crystals (PhCs) are as an attractive sensing platforms due to the control light in very small dimensions. The photonic crystals can control and guide the photons in the periodic lattice. In this paper, an optical biochemical sensor is presented based on photonic crystal nano-ring resonators for detection of protein concentration.

Methods: In biochemical sensors, the effective refractive index of sensing hole can be changed by binding the biomolecule to the sensing hole. The resonant wavelength of the transmission spectrum or intensity of the transmission spectrum can be shifted resulting from refractive index variations. The proposed biochemical sensor constructed by photonic crystal nano-ring resonator using twodimensional PhC is designed and simulated. In our design, the hexagonal lattice of air holes in the dielectric slab is used.

Results: Two-dimensional finite-difference time-domain (2-D FDTD) method is used for simulating the propagation of electromagnetism wave and plane-wave expansion (PWE) approach is applied to analyze the proposed sensor. Biochemical sensor is presented for identifying small changes in the refractive index. The detection of protein concentration from 0% to 35% as one of its applications has been presented. The biochemical sensor structure includes a ring resonator shaped by consecutive curves and two waveguides. By binding protein concentration into the sensing hole, the refractive index of sensing hole is changed and the intensity of the transmission spectrum is shifted to the lower values. The results reveal that the quality factor and the sensitivity of proposed biochemical sensor are respectively obtained about 2960 and 925.02 a.u./RIU.

Conclusion: The biochemical sensor structure includes a ring resonator and two waveguides. The ring resonator is shaped by consecutive curves. By binding protein concentration into the sensing hole, the refractive index of sensing hole is changed and the intensity of the transmission spectrum is shifted to lower values. By increasing the protein concentration of the sensing hole, the intensity of the transmission spectrum is shifted to lower values. The normalized curve of the intensity of the transmission spectrum shows approximately linear relationship between the protein concentration and intensity shift.

Numerical Study on Convective Heat Transfer Characteristics of Silver/Water Nanofluid in Minichannel by Jefferson Raja Bose, Lazarus Godson Asirvatham, T. Michael N. Kumar, Somchai Wongwises (426-434).
Background: Liquid coolants are generally used for increasing the heat transfer rate of electronic devices. However, the fluids such as normal chemicals like water or ethylene glycol have very low thermal properties. A nanofluid is the mixture of suspended nanoparticles in the base fluid. It is recognized as an advanced heat transfer fluid that exhibits superior heat transfer properties. The aim of this paper is to investigating the hydrodynamic and thermal behavior of silver/water nanofluid flowing in a minichannel heat exchanger. The volume concentration of silver nanoparticle is changed between 0.25% to 0.5% and the Reynolds number value varying from 1000- 100000. A heat flux boundary condition with constant value of q=10000 W/m2 is applied in the test region.

Methods: Based on the literature review, a 2-D finite volume numerical method is used for finding the heat transfer coefficient of silver/water nanofluid in a mini-channel. The continuity, momentum, energy equations are discretized and non-dimensionalzed. Based on the boundary conditions, the problem is solved iteratively under steady state condition using SIMPLE algorithm.

Results: The thermal conductivity, dynamic viscosity and convective heat transfer coefficient (CHTC) of silver–water nanofluid is found for 0.5%, 0.35%, and 0.25% volume concentration of silver nanoparticles. The viscosity, thermal conductivity increases with increase in concentration of silver nanoparticle. The CHTC has the maximum increase in the laminar region at 0.5% concentration of silver nanipartical.

Conclusion: The results prove that there is an acceptable increase in heat transfer coefficient by 45.6% with just 0.5% volume concentration of the silver nanoparticles with respect to that of the base liquid.. Moreover, the increase in heat transfer coefficient is found to be approximately 12% in the laminar regime, and 20–25% in the transition regime when compared with that of the base fluid. For higher Reynolds number, Re>10000, percentage rise in heat transfer coefficient is found to be 30 to 35% in the turbulent regime.

Acousto-Optic Logic Gate Controlled by Third-Order Nonlinear Optical Effects in Bimetallic Au-Pt Nanoparticles by L.F Salcedo Hernández, S. Morales Bonilla, I. Villalpando, C.R Torres San Miguel, M. Trejo Valdez, C Torres Torres (435-440).
Background: Studies about fascinating nonlinear optical effects are a promise to the development of high-sensitive instruments and ultrafast all-optical systems. Particularly, the optical Kerr effect exhibited by bimetallic nanoparticles can be employed to determine vibrations and the vectorial nature of mechanical actions in low-dimensional materials. With this motivation, this work has been devoted to analyze third-order nonlinear optical effects influenced by acousto-optical processes interacting with bimetallic nanoparticles.

Methods: A nanosecond two-wave mixing experiment was employed to explore the nonlinear optical response exhibited by Gold-Platinum nanoparticles embedded in a Titanium dioxide thin solid film under acoustical perturbations.

Results: Significant contributions from acoustical signals to third-order nonlinear optical effects in bimetallic Au-Pt nanoparticles were demonstrated. Vectorial two-wave mixing laser experiments were described by the participation of an optically induced birefringence and an acoustically induced effect responsible for a nonlinear refractive index. It was pointed out the possibility to identify acoustical signals and transduction of quantum mechanical information by interferometry and multi-wave mixing experiments. It was highlighted the attractive results with potential applications for designing nonlinear mechano-optical devices.

Conclusion: The incorporation of Au-Pt nanoparticles in transparent dielectric platforms seems to remarkably enhance the sensibility for measuring acousto-optical signals. It was contemplated that acousto-optical modulation assisted by third-order nonlinear optical effects may be useful for quantum information transduction processes. A low-dimensional OR logic gate system dependent on acoustical interactions and optical Kerr effect signals can be proposed. The large nonlinear optical response together to the double resonances associated to bimetallic nanoparticles makes them useful for potential applications related to ultrafast all-optical systems and digital logic gates.