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Search Results: 1 - 10 of 207265 matches for " Richard G. Compton "
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荧光胺电化学检测水溶液中的氨:荧光检测与伏安分析比较
Janjira Panchompoo,Richard G. Compton
电化学 , 2012,
Abstract: 荧光胺是一种非荧光剂,其易与伯胺反应形成荧光产物,被普遍用于伯胺的荧光光谱定量分析.本文利用荧光胺与伯胺反应发展了一种新型灵敏的伏安法用于检测水溶液中的伯胺.首先,在有、无伯胺的0.1molL-1PBS(pH9.0)缓冲液中,研究了玻碳电极表面荧光胺的循环伏安电化学行为.荧光胺的不可逆氧化峰出现在0.70V(vs.SCE),当加入伯胺时,在0.46V(vs.SCE)出现另一不可逆的氧化峰,为荧光胺与伯胺反应的产物.继续加入氨水,荧光胺的氧化峰变弱,反应产物的氧化峰则由于荧光胺按反应化学计量比随氨消耗增多而随之增大.上述两个阳极峰分别对应于荧光胺及其反应产物,采用方波伏安和荧光光谱技术可实现水溶液中伯胺的定量检测.在0~60μmolL-1氨浓度范围内,该反应产物方波伏安检测成线性响应.S/N=3或3σ时检测下限分别为0.71μmolL-1和3.17μmolL-1,与荧光法检测的结果相近.
Investigating the Mechanism for the Covalent Chemical Modification of Multiwalled Carbon Nanotubes Using Aryl Diazonium Salts
Poobalasingam Abiman, Gregory G. Wildgoose and Richard G. Compton
International Journal of Electrochemical Science , 2008,
Abstract: The mechanism involved in the modification of carbon nanotubes (CNTs) funtionalised using diazonium salts has been investigated. Bamboo-like and hollow-tube multiwalled carbon nanotubes (MWCNTs) were covalently modified using 4-nitrobenzenediazonium tetrafluoroborate. The MWCNTs were derivatised in the presence and absence of hypophosphorous acid as a mild reducing agent and the resulting materials were characterised using cyclic voltammetry. The observed peak potentials for the modified materials were found to differ depending on the derivatisation conditions (presence / absence of hypophosphorous acid, diazonium salt concentration and temperature) and these defferences were interpreted mechanically. The experimental results suggest that, in the absence of hypophosphorous acid, the derivatisation mechanism likely proceeds through a cationic intermediate, whilst in the presence of the hypophosphorous acid the mechanism probably involves either a purely radical intermediate or a mixture of radical and cationic species depending on the concentration of the hypophosphorous acid reducing agent and the reaction temperature. Polymerisation of the nitrophenyl groups on the surface of nanotubes was studied using different concentrations of 4-nitrobenzenediazonium tetrafluoroborate and was found to increase with increasing concentration of cationic intermediates. The effect of the reaction temperature on the derivatisation was explored over a range of temperatures from 5 to 50 0C and the optimum derivatisation temperature was determined in the presence and absence of hypophosphorous acid. It was found to be 20 0C and 35 0C in the presence and absence of hypophosphorous acid respectively.
Voltammetry at porous electrodes: A theoretical study
Edward O. Barnes,Xiaojun Chena,Peilin Li,Richard G. Compton
Physics , 2014, DOI: 10.1016/j.jelechem.2014.03.028
Abstract: Theory is presented to simulate both chronoamperometry and cyclic voltammetry at porous electrodes fabricated by means of electro-deposition around spherical templates. A theoretical method to extract heterogeneous rate constants for quasireversible and irreversible systems is proposed by the approximation of decoupling of the diffusion within the porous electrode and of bulk diffusion to the electrode surface.
Voltammetry at micro-mesh electrodes
Wadhawan, Jay D.;Welford, Peter J.;Yunus, Kamran;Fisher, Adrian C.;Compton, Richard G.;
Journal of the Brazilian Chemical Society , 2003, DOI: 10.1590/S0103-50532003000400004
Abstract: the voltammetry at three micro-mesh electrodes is explored. it is found that at sufficiently short experimental durations, the micro-mesh working electrode first behaves as an ensemble of microband electrodes, then follows the behaviour anticipated for an array of diffusion-independent micro-ring electrodes of the same perimeter as individual grid-squares within the mesh. during prolonged electrolysis, the micro-mesh electrode follows that behaviour anticipated theoretically for a cubically-packed partially-blocked electrode. application of the micro-mesh electrode for the electrochemical determination of carbon dioxide in dmso electrolyte solutions is further illustrated.
Double potential step chronoamperometry at a microband electrode: Theory and experiment
Edward O. Barnes,Linhongjia Xiong,Kristopher R. Ward,Richard G. Compton
Physics , 2013, DOI: 10.1016/j.jelechem.2013.05.002
Abstract: Numerical simulation is used to characterise double potential step chronoamperometry at a microband electrode for a simple redox process A + e- goes to B, under conditions of full support such that diffusion is the only active form of mass transport. The method is shown to be highly sensitive for the measurement of the diffusion coefficient of both A and B, and is applied to the one electron reduction of decamethylferrocene (DMFc), DMFc - e- goes to DMFc+, in the room temperature ionic liquid 1-propyl-3-methylimidazolium bistrifluoromethylsulfonylimide. Theory and experiment are seen to be in excellent agreement and the following values of the diffusion coefficients were measured at 298 K: D_(DMFc) = 2.50 x 10^(-7) cm^(2) s^(-1) and D_(DMFc+) = 9.50 x 10^(-8) cm^(2) s^(-1).
One electron oxygen reduction in room temperature ionic liquids: A comparative study of Butler-Volmer and Symmetric Marcus-Hush theories using microdisc electrodes
Eden E. L. Tanner,Linhongjia Xiong,Edward O. Barnes,Richard G. Compton
Physics , 2015, DOI: 10.1016/j.jelechem.2014.05.022
Abstract: The voltammetry for the reduction of oxygen at a microdisc electrode is reported in two room temperature ionic liquids: 1-butyl-1-methylpyyrolidinium bis(trifluoromethylsulfonyl) imide ([Bmpyrr][NTf2]) and trihexyltetradecylphosphonium bis9trifluoromethylsulfonyl) imide ([P14,6,6,6][NTf2]) at 298 K. Simulated voltammograms using Butler-Volmer theory and Symmetric Marcus-Hush (SMH) theory were compared with experimental data. Butler-Volmer theory consistently provided experimental parameters with a higher level of certainty than SMH theory. A value of solvent reorganisation energy for oxygen reduction in ionic liquids was inferred for the first time as 0.4-0.5 eV, which is attributable to inner-sphere reorganisation with a negligible contribution from solvent reorganisation. The developed Butler-Volmer and Symmetric Marcus-Hush programs are also used to theoretically study the possibility of kinetically limited steady state currents, and to establish an approximate equivalence relationship between microdisc electrodes and spherical electrodes resting on a surface for steady state voltammetry for both Butler-Volmer and Symmetric Marcus-Hush theory.
Equality of diffusion-limited chronoamperometric currents to equal area spherical and cubic nanoparticles on a supporting electrode surface
Enno K?telh?n,Edward O. Barnes,Kay J. Krause,Bernhard Wolfrum,Richard G. Compton
Physics , 2014, DOI: 10.1016/j.cplett.2014.01.036
Abstract: We computationally investigate the chronoamperometric current response of spherical and cubic particles on a supporting insulating surface. By using the method of finite di?erences and random walk simulations, we can show that both systems exhibit identical responses on all time scales if their exposed surface areas are equal. This result enables a simple and computationally effcient method to treat certain spherical geometries in random walk based noise investigations.
Dual Band Electrodes in Generator-Collector Mode: Simultaneous Measurement of Two Species
Edward O. Barnes,Grace E. M. Lewis,Sara E. C. Dale,Frank Marken,Richard G. Compton
Physics , 2013, DOI: 10.1016/j.jelechem.2013.05.022
Abstract: A computational model for the simulation of a double band collector-generator experiment is applied to the situation where two electrochemical reactions occur concurrently. It is shown that chronoamperometric measurements can be used to take advantage of differences in diffusion coefficients to measure the concentrations of both electroactive species simultaneously, by measuring the time at which the collection efficiency reaches a specific value. The separation of the electrodes is shown to not affect the sensitivity of the method (in terms of percentage changes in the measured time to reach the specified collection efficiency), but wider gaps can provide a greater range of (larger) absolute values of this characteristic time. It is also shown that measuring the time taken to reach smaller collection efficiencies can allow for the detection of smaller amounts of whichever species diffuses faster. The case of a system containing both ascorbic acid and opamine in water is used to exemplify the method, and it is shown that mole fractions of ascorbic acid between 0.055 and 0.96 can, in principle, be accurately measured.
The electrochemistry of simple inorganic molecules in room temperature ionic liquids
Silvester, Debbie S.;Rogers, Emma I.;Barrosse-Antle, Laura E.;Broder, Tessa L.;Compton, Richard G.;
Journal of the Brazilian Chemical Society , 2008, DOI: 10.1590/S0103-50532008000400002
Abstract: the electrochemistry of simple inorganic compounds in room temperature ionic liquids (rtils) is reviewed and some new work in this area is presented. this paper focuses on the comparison between electrochemical behaviour in rtils and in conventional aprotic solvents. some compounds (iodides, o2, no2, so2, nh3) display similar reactions and mechanisms in rtils as in aprotic solvents (as is observed for organic compounds). however other species (nitrates, pcl3, pocl3) show remarkably different behaviour to traditional solvents. this makes rtils very promising media for the study of inorganic compounds, and highlights the need for more investigations in this exciting area.
Moving Your Sons to Safety: Galls Containing Male Fig Wasps Expand into the Centre of Figs, Away From Enemies
Hui Yu, Stephen G. Compton
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0030833
Abstract: Figs are the inflorescences of fig trees (Ficus spp., Moraceae). They are shaped like a hollow ball, lined on their inner surface by numerous tiny female flowers. Pollination is carried out by host-specific fig wasps (Agaonidae). Female pollinators enter the figs through a narrow entrance gate and once inside can walk around on a platform generated by the stigmas of the flowers. They lay their eggs into the ovules, via the stigmas and styles, and also gall the flowers, causing the ovules to expand and their pedicels to elongate. A single pollinator larva develops in each galled ovule. Numerous species of non-pollinating fig wasps (NPFW, belonging to other families of Chalcidoidea) also make use of galled ovules in the figs. Some initiate galls, others make use of pollinator-generated galls, killing pollinator larvae. Most NPFW oviposit from the outside of figs, making peripherally-located pollinator larvae more prone to attack. Style length variation is high among monoecious Ficus spp. and pollinators mainly oviposit into more centrally-located ovules, with shorter styles. Style length variation is lower in male (wasp-producing) figs of dioecious Ficus spp., making ovules equally vulnerable to attack by NPFW at the time that pollinators oviposit. We recorded the spatial distributions of galled ovules in mature male figs of the dioecious Ficus hirta in Southern China. The galls contained pollinators and three NPFW that kill them. Pollinators were concentrated in galls located towards the centre of the figs, NPFW towards the periphery. Due to greater pedicel elongation by male galls, male pollinators became located in more central galls than their females, and so were less likely to be attacked. This helps ensure that sufficient males survive, despite strongly female-biased sex ratios, and may be a consequence of the pollinator females laying mostly male eggs at the start of oviposition sequences.
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