[Show abstract][Hide abstract] ABSTRACT: Some of the prospective electrode materials for lithium-ion batteries are known to have electronic transport limitations preventing them from being used in the electrodes directly. In many cases, however, these materials may become practical if they are applied in the form of nanocomposites with a carbon component, e.g. via incorporating nanoparticles of the phase of interest into a conducting network of carbon nanotubes. A simple way to prepare oxide–carbon nanotube composites suitable for the electrodes of lithium-ion batteries is presented in this paper. The method is based on low-energy ball milling. An electrochemically active but insulating phase of LiFeTiO4 is used as a test material. It is demonstrated that the LiFeTiO4 –carbon nanotube composite is not only capable of having significantly higher capacity (~105–120 mA h g-1 vs. the capacity of ~65–70 mA h g-1 for the LiFeTiO4 nanoparticles) at a slow current rate but may also operate at reasonably high current rates.
[Show abstract][Hide abstract] ABSTRACT: A novel nanocomposite architecture of a Fe2O3-SnO2-C anode, based on clusters of Fe2O3 and SnO2 nanoparticles dispersed along the conductive chains of Super P Li™ carbon black (Timcal Ltd.), is presented as a breathable structure in this paper for lithium-ion batteries. The synthesis of the nanocomposite is achieved by combining a molten salt precipitation process and a ball milling method for the first time. The crystalline structure, morphology, and electrochemical characterization of the synthesised product are investigated systematically. Electrochemical results demonstrate that the reversible capacity of the composite anode is 1110 mA h g(-1) at a current rate of 158 mA g(-1) with only 31% of initial irreversible capacity in the first cycle. A high reversible capacity of 502 mA h g(-1) (higher than the theoretical capacity of graphite, ∼372 mA h g(-1)) can be obtained at a high current rate of 3950 mA g(-1). The electrochemical performance is compared favourably with those of Fe2O3-SnO2 and Fe2O3-SnO2-C composite anodes for lithium-ion batteries reported in the literature. This work reports a promising method for the design and preparation of nanocomposite electrodes for lithium-ion batteries.
[Show abstract][Hide abstract] ABSTRACT: The mineral ilmenite is one of the most abundant ores in the Earth's crust and it is the main source for the industrial production of bulk titanium oxide. At the same time, methods to convert ilmenite into nanostructures of TiO(2) (which are required for new advanced applications, such as solar cells, batteries, and photocatalysts) have not been explored to any significant extent. Herein, we describe a simple and effective method for the preparation of rutile TiO(2) nanorods from ball-milled ilmenite. These nanorods have small dimensions (width: 5-20 nm, length: 50-100 nm, thickness: 2-5 nm) and possess large specific surface areas (up to 97 m(2) g(-1) ). Dissolution/hydrolysis/precipitation is proposed as a growth mechanism. The nanorods were found to have attractive photocatalytic properties in the degradation of oxalic acid. Their photocatalytic activity is close to that of the benchmark Degussa P25 material and better than that of a commercial high-surface-area rutile powder.
Chemistry - A European Journal 11/2012; · 5.93 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A new combination method consisting of ball milling, carbothermic reduction and hydrochloric acid leaching was proposed for the preparation of nanosized synthetic rutile from natural ilmenite. The ball milling was employed to grind ilmenite into small particles. The carbothermic reduction was carried out to yield a high titanium slag, which would be easily purified by subsequent leaching procedure. Factors affecting the hydrochloric acid process, namely the leaching time, temperature, and acid concentration, were studied. After leaching and calcining the milled and annealed mixture of FeTiO3/C under the optimal conditions, the TiO2 nanoparticles with size of 10-200 nm and purity>98.0% were obtained.
Transactions of Nonferrous Metals Society of China 05/2012; 22(5):1232–1238. · 0.92 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This study investigated the mechanisms underlying the propagation of cytoplasmic calcium waves and the genesis of systolic Ca(2+) alternans in cardiac myocytes lacking transverse tubules (t-tubules). These correspond to atrial cells of either small mammals or large mammals that have lost their t-tubules due to disease-induced structural remodeling (e.g., atrial fibrillation). A mathematical model was developed for a cluster of ryanodine receptors distributed on the cross section of a cell that was divided into 13 elements with a spatial resolution of 2 μm. Due to the absence of t-tubules, L-type Ca(2+) channels were only located in the peripheral elements close to the cell-membrane surface and produced Ca(2+) signals that propagated toward central elements by triggering successive Ca(2+)-induced Ca(2+) release (CICR) via Ca(2+) diffusion between adjacent elements. Under control conditions, the Ca(2+) signals did not fully propagate to the central region of the cell. However, with modulation of several factors responsible for Ca(2+) handling, such as the L-type Ca(2+) channels (Ca(2+) influx), SERCA pumps (sarcoplasmic reticulum (SR) Ca(2+) uptake), and ryanodine receptors (SR Ca(2+) release), Ca(2+) wave propagation to the center of the cell could occur. These simulation results are consistent with previous experimental data from atrial cells of small mammals. The model further reveals that spatially functional heterogeneity in Ca(2+) diffusion within the cell produced a steep relationship between the SR Ca(2+) content and the cytoplasmic Ca(2+) concentration. This played an important role in the genesis of Ca(2+) alternans that were more obvious in central than in peripheral elements. Possible association between the occurrence of Ca(2+) alternans and the model parameters of Ca(2+) handling was comprehensively explored in a wide range of one- and two-parameter spaces. In addition, the model revealed a spontaneous second Ca(2+) release in response to a single voltage stimulus pulse with SR Ca(2+) overloading and augmented Ca(2+) influx. This study provides what to our knowledge are new insights into the genesis of Ca(2+) alternans and spontaneous second Ca(2+) release in cardiac myocytes that lack t-tubules.
[Show abstract][Hide abstract] ABSTRACT: A highly uniform nanocomposite of MoO3 and carbon with a weight ratio of 1:1 is prepared by employing a simple procedure of ball milling. Such composite as electrochemical pseudocapacitor materials for potential energy storage applications exhibits a high specific capacitance of ~ 179 F/g at a charge and discharge current density of 50 mA/g with excellent cycling ability over 1000 cycles. Compared with the capacitance of pure milled graphite (~ 22 F/g) and MoO3 (< 10 F/g), an enhanced electrochemical performance of the composite with a weight ratio of 1:1 is attributed to its unique structure, in which MoO3 nanoparticles (with a size range of 1–180 nm) are uniformly dispersed in an electrically conductive carbon host.
[Show abstract][Hide abstract] ABSTRACT: Pronounced and stable pseudocapacitance has been found in flowerlike FeTiO3 nanostructures that were synthesized from ball-milled ilmenite (natural mineral) under mild hydrothermal conditions. Each nanoflower is composed of many thin petals with a thickness of 5–20 nm and a width of 100–200 nm. The formation of these flowerlike nanostructures is attributed to a dissolution–precipitation mechanism involving an intermediate sodium-containing phase. Electrochemical properties of the obtained FeTiO3 nanostructures are evaluated in aqueous electrolytes. The capacitance of 122 ± 14.5 F/g is measured in 1 M KOH aqueous electrolyte at the current rate of 500 mA/g, and 50 ± 6 F/g is retained at 5 A/g. The material has good long-term cycling stability. According to our data, FeTiO3 nanostructures show functionality as an electrode material for supercapacitors.
The Journal of Physical Chemistry C. 08/2011; 115(35).
[Show abstract][Hide abstract] ABSTRACT: A MoO3-carbon nanocomposite was synthesized from a mixture of MoO3 and graphite by a controlled ball milling procedure. The as-prepared product consists of nanosized MoO3 particles (2-180 nm) homogeneously distributed in carbon matrix. The nanocomposite acts as a high capacity anode material for lithium-ion batteries and exhibits good cyclic behavior. Its initial capacity exceeds the theoretical capacity of 745 mA h g-1 in a mixture of MoO3 and graphite (1 : 1 by weight), and the stable capacity of 700 mA h g-1 (94% of the theoretical capacity) is still retained after 120 cycles. The electrode performance is linked with the unique nanoarchitecture of the composite and is compared with the performance of MoO3-based anode materials reported in the literature previously (nanoparticles, ball milled powders, and carbon-coated nanobelts). The high value of capacity and good cyclic stability of MoO3-carbon nanocomposite are attractive in respect to those of the reported MoO3 electrodes.
Journal of Materials Chemistry 01/2011; 21(25):9350-9355. · 6.63 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Tree-like SnO2 nanowires have been grown by a vapor–solid process using a milled SnO2 powder as the evaporation source. Phase, structural evolution and chemical composition were investigated using X-ray diffraction (XRD), X-ray spectrometry (EDS), and scanning electron microscopy (SEM). The process yields a large proportion of ultra-long rutile nanowires of 50–150nm diameter and lengths up to several tens of micrometers. High-resolution transmission electron microscopy (HRTEM) shows that the SnO2 nanowires are single crystals in the (101) growth direction with scattered smaller crystals or nanowires as the tree branches. The SnO2 nanostructures were also examined using Fourier transform infra-red (FT-IR) and photoluminescence (PL) spectroscopy. A strong emission band centered at 548nm dominated the PL spectrum of the tree-like nanowires.
Materials Chemistry and Physics - MATER CHEM PHYS. 01/2011; 126(1):128-132.
[Show abstract][Hide abstract] ABSTRACT: SnO2 nanoribbons have been synthesized by annealing of a milled SnO2 powder, which is able to evaporate efficiently at the temperature as low as 1100 degrees C due to the metastable structure created by ball milling treatment. When the milled powder was annealed in an assembly of two combustion boats, SnO2 nanoribbons formed on the surface of the milled powder. The nanoribbons tend to grow along the  crystallographic direction and their side surfaces are represented by +/- (010) and +/- (101) facets. The oxygen plays an important role in enhancing their formation.
Journal of Nanoscience and Nanotechnology 08/2010; 10(8):5015-9. · 1.15 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The evaporation behaviour of a ball milled SnO2 powder has been investigated. It is observed that the milled powder starts to evaporate at the temperatures above 950 °C while the unmilled SnO2 powder does not generate any vapor at this temperature. The effect is likely to be related to structural changes in the milled material and, particularly, a certain degree of reduction of the SnO2 powder in the course of milling. The milled powder can be used as a vapor source for producing various types of nanostructures of SnO2.
Journal of Alloys and Compounds 01/2010; 504. · 2.73 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Ilmenite (FeTiO3) is an inexpensive abundant natural mineral and it would be a perfect precursor for the production of porous TiO2 if a suitable synthesis method was developed. A new method combining a series of processing steps of ball milling, high-temperature annealing, selective chemical leaching and final calcining in air is proposed in this paper. The resulting TiO2 is a porous material with a bimodal pore structure. The pore size distribution has two clear maxima corresponding to small mesopores (2–30 nm) and large meso- and macropores (centered at around 50–80 nm). It was found that the duration of the annealing step could alter the contribution of each type of pores. A short annealing time (0.5 h) lead to the preferential formation of pores within 2–30 nm while pores centered at 50–80 nm dominated the pore size distribution after a relatively long annealing (1.5 h). The obtained porous rutileTiO2 shows a better photocatalytic activity than that of a commercial rutileTiO2 powder.
[Show abstract][Hide abstract] ABSTRACT: Volatile anaesthetics such as halothane, isoflurane and sevoflurane inhibit membrane currents contributing to the ventricular action potential. Transmural variation in the extent of current blockade induces differential effects on action potential duration (APD) in the endocardium and epicardium which may be pro-arrhythmic. Biophysical modelling techniques were used to simulate the functional impact of anaesthetic-induced blockade of membrane currents on APD and effective refractory period (ERP) in rat endocardial and epicardial cell models. Additionally, the transmural conduction of excitation waves in 1-dimensional cell arrays, the tissue's vulnerability to arrhythmogenesis and dynamic behaviour of re-entrant excitation in 2-dimensional cell arrays were studied. Simulated anaesthetic exposure reduced APD and ERP in both epicardial and endocardial cell models. The reduction in APD was greater in endocardial than epicardial cells, reducing transmural APD dispersion consistent with experimental data. However, the transmural ERP dispersion was augmented. All three anaesthetics increased the width of the tissue's vulnerable window during which a premature stimulus could induce unidirectional conduction block but only halothane reduced the critical size of ventricular substrates necessary to initiate and sustain re-entrant excitation. All three anaesthetics accelerated the rate of re-entrant excitation waves, but only halothane prolonged the lifespan of re-entry. These data illustrate in silico, that modest changes in ion channel conductance abbreviate rat ventricular APD and ERP, reduce transmural APD dispersion, but augment transmural ERP dispersion. These changes collectively enhance the propensity for arrhythmia generation and provide a substrate for re-entry circuits with a longer half life than in control conditions.
Journal of Theoretical Biology 03/2009; 257(2):279-91. · 2.35 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Mechanical contraction alternans of the heart is associated with fatal cardiac death. It is manifested by T-wave alternans in the ECG, and is thought to be possibly related to intracellular Ca<sup>2+</sup> transient alternans released from the sarcoplasmic reticulum (SR). However, it is unclear yet how beat-to-beat alternans of intracellular Ca<sup>2+</sup> transient is produced. In this study investigated the mechanism(s) underlying the genesis of intracellular Ca<sup>2+</sup> alternans produced at slow pacing rates by using a mathematical model of a spatially extended cardiac cell with a cluster of coupled ryanodine receptor (RyR) elements. It was shown that the intracellular Ca<sup>2+</sup> alternans was generated by propagating waves of Ca<sup>2+</sup> release and sustained through alternation of SR Ca<sup>2+</sup> content that has a stiff relationship with the Ca<sup>2+</sup> transient. This study provides novel and fundamental insights to understand mechanisms that may underlie intracellular Ca<sup>2+</sup> alternans without the need for refractoriness of L-type Ca or RyR channels under rapid pacing.
[Show abstract][Hide abstract] ABSTRACT: Mechanical alternans in cardiac muscle is associated with intracellular Ca(2+) alternans. Mechanisms underlying intracellular Ca(2+) alternans are unclear. In previous experimental studies, we produced alternans of systolic Ca(2+) under voltage clamp, either by partially inhibiting the Ca(2+) release mechanism, or by applying small depolarizing pulses. In each case, alternans relied on propagating waves of Ca(2+) release. The aim of this study is to investigate by computer modeling how alternans of systolic Ca(2+) is produced. A mathematical model of a cardiac cell with 75 coupled elements is developed, with each element contains L-type Ca(2+) current, a subspace into which Ca release takes place, a cytoplasmic space, sarcoplasmic reticulum (SR) release channels [ryanodine receptor (RyR)], and uptake sites (SERCA). Interelement coupling is via Ca(2+) diffusion between neighboring subspaces via cytoplasmic spaces and network SR spaces. Small depolarizing pulses were simulated by step changes of cell membrane potential (20 mV) with random block of L-type channels. Partial inhibition of the release mechanism is mimicked by applying a reduction of RyR open probability in response to full stimulation by L-type channels. In both cases, systolic alternans follow, consistent with our experimental observations, being generated by propagating waves of Ca(2+) release and sustained through alternation of SR Ca(2+) content. This study provides novel and fundamental insights to understand mechanisms that may underlie intracellular Ca(2+) alternans without the need for refractoriness of L-type Ca or RyR channels under rapid pacing.