共查询到20条相似文献,搜索用时 62 毫秒
1.
Zhao Yang Gao-Shao Cao Jian Xie Xin-Bing Zhao 《Journal of Solid State Electrochemistry》2012,16(3):1271-1277
LiMnPO4, with a particle size of 50–150 nm, was prepared by oleic acid-assisted solid-state reaction. The materials were characterized
by X-ray diffraction, field emission scanning electron microscopy, and transmission electron microscopy. The electrochemical
properties of the materials were investigated by galvanostatic cycling. It was found that the introduction of oleic acid in
the precursor led to smaller particle size and more homogeneous size distribution in the final products, resulting in improved
electrochemical performance. The electrochemical performance of the sample could be further enhanced by Co doping. The mechanism
for the improvement of the electrochemical performance was investigated by Li-ion chemical diffusion coefficient
( [(D)\tilde]\textLi ) \left( {{{\tilde{D}}_{\text{Li}}}} \right) and electrochemical impedance spectroscopy measurements. The results revealed that the
[(D)\tilde]\textLi {\tilde{D}_{\text{Li}}} values of LiMnPO4 measured by cyclic voltammetry method increase from 9.2 × 10−18 to 3.0 × 10−17 cm2 s−1 after Co doping, while the charge transfer resistance (R
ct) can be decreased by Co doping. 相似文献
2.
Yu. A. Titov N. S. Slobodyanik V. V. Polubinskii V. V. Chumak 《Theoretical and Experimental Chemistry》2012,47(6):394-398
We have established and analyzed the sequences of phase transitions in synthesis of layered compounds in the AnBn–1O3n family (
\textA3\textII\textLnB3\textV\textO12 {\text{A}}_3^{\text{II}}{\text{LnB}}_3^{\text{V}}{{\text{O}}_{{12}}} (AII = Ba, Sr, Ln = La, Nd, BV = Nb, Ta) and La4Ti3O12 with n = 4) from coprecipitated hydroxocarbonate and hydroxide systems, including steps involving the formation, solid-phase
reaction, or structural rearrangement of intermediates. 相似文献
3.
Wang B Shang JZ Qin YJ Yan BN Guo XH 《Journal of the American Society for Mass Spectrometry》2011,22(8):1453-1462
Electrospray ionization coupled with low energy collision induced dissociation (CID) in an ion trap mass spectrometer was
used to examine the fragmentation patterns of the [M + Na]+ of eight pairs of heptapeptides containing α- or β-Asp residues in second and sixth amino acid positions, respectively. Selective
cleavages at the peptide backbone C-terminal to two Asp residues were observed, which generated a series of C-terminal y5 ions and N-terminal b6 ions. Two typical ions:
[ \texty5 + \textNa-\textH ] + {\left[ {{{\text{y}}_{{5}}} + {\text{Na}}-{\text{H}}} \right]^{ + }} and
[ \textb6 + \textNa + \textOH ] + {\left[ {{{\text{b}}_{{6}}} + {\text{Na}} + {\text{OH}}} \right]^{ + }} , produced by α-Asp containing peptides were noted to be much more abundant than those of the peptides with β-Asp, which could
be used for distinction of the isomers in Asp2 and Asp6, respectively. In addition, a series of internal ions generated by
simultaneous cleavages at Asp residues were detected. Competitive reactions of carboxylic groups occurred between Asp6 side
chain and C-terminus. Formation mechanisms of most product ions are proposed. The results obtained in this work are significant
since low energy CID has been demonstrated to be effective for the distinction of Asp isomers. 相似文献
4.
Anne Vuorema Philip John A. Toby A. Jenkins Frank Marken 《Journal of Solid State Electrochemistry》2006,10(10):865-871
Colloidal indigo is reduced to an aqueous solution of leuco-indigo in a mediated two-electron process converting the water-insoluble dye into the water-soluble leuco form. The colloidal dye does not interact directly with the electrode surface, and to employ an electrochemical process for this reduction, the redox mediator 1,8-dihydroxyanthraquinone (1,8-DHAQ) is used to transfer electrons from the electrode to the dye. The mediated reduction process is investigated at a (500-kHz ultrasound-assisted) rotating disc electrode, and the quantitative analysis of voltammetric data is attempted employing the Digisim numerical simulation software package. At the most effective temperature, 353 K, the diffusion coefficient for 1,8-DHAQ is (0.84±0.08)×10−9 m2 s−1, and it is shown that an apparently kinetically controlled reaction between the reduced form of the mediator and the colloidal indigo occurs within the diffusion layer at the electrode surface. The apparent bimolecular rate constant k
app=3 mol m−3 s−1 for the rate law
\fracd[ \textleuco - \textindigo ] dt = k\textapp ×[ \textmediator ] ×[ \textindigo ]\frac{{d{\left[ {{\text{leuco}} - {\text{indigo}}} \right]}}} {{dt}} = k_{{{\text{app}}}} \times {\left[ {{\text{mediator}}} \right]} \times {\left[ {{\text{indigo}}} \right]} is determined and attributed to a mediator diffusion controlled dissolution of the colloid particles. The average particle size and the number of molecules per particles are estimated from the apparent bimolecular rate constant and confirmed by scanning electron microscopy. 相似文献
5.
Ricardo Picciochi Hermínio P. Diogo Manuel E. Minas da Piedade 《Journal of Thermal Analysis and Calorimetry》2010,100(2):391-401
Combustion calorimetry, Calvet-drop sublimation calorimetry, and the Knudsen effusion method were used to determine the standard
(p
o = 0.1 MPa) molar enthalpies of formation of monoclinic (form I) and gaseous paracetamol, at T = 298.15 K:
\Updelta\textf H\textm\texto ( \textC 8 \textH 9 \textO 2 \textN,\text cr I ) = - ( 4 10.4 ±1. 3)\text kJ \textmol - 1 \Updelta_{\text{f}} H_{\text{m}}^{\text{o}} \left( {{\text{C}}_{ 8} {\text{H}}_{ 9} {\text{O}}_{ 2} {\text{N}},{\text{ cr I}}} \right) = - ( 4 10.4 \pm 1. 3){\text{ kJ}}\;{\text{mol}}^{ - 1} and
\Updelta\textf H\textm\texto ( \textC 8 \textH 9 \textO 2 \textN,\text g ) = - ( 2 80.5 ±1. 9)\text kJ \textmol - 1 . \Updelta_{\text{f}} H_{\text{m}}^{\text{o}} \left( {{\text{C}}_{ 8} {\text{H}}_{ 9} {\text{O}}_{ 2} {\text{N}},{\text{ g}}} \right) = - ( 2 80.5 \pm 1. 9){\text{ kJ}}\;{\text{mol}}^{ - 1} . From the obtained
\Updelta\textf H\textm\texto ( \textC 8 \textH 9 \textO 2 \textN,\text cr I ) \Updelta_{\text{f}} H_{\text{m}}^{\text{o}} \left( {{\text{C}}_{ 8} {\text{H}}_{ 9} {\text{O}}_{ 2} {\text{N}},{\text{ cr I}}} \right) value and published data, it was also possible to derive the standard molar enthalpies of formation of the two other known
polymorphs of paracetamol (forms II and III), at 298.15 K:
\Updelta\textf H\textm\texto ( \textC 8 \textH 9 \textO 2 \textN,\text crII ) = - ( 40 8.4 ±1. 3)\text kJ \textmol - 1 \Updelta_{\text{f}} H_{\text{m}}^{\text{o}} \left( {{\text{C}}_{ 8} {\text{H}}_{ 9} {\text{O}}_{ 2} {\text{N}},{\text{ crII}}} \right) = - ( 40 8.4 \pm 1. 3){\text{ kJ}}\;{\text{mol}}^{ - 1} and
\Updelta\textf H\textm\texto ( \textC 8 \textH 9 \textO 2 \textN,\text crIII ) = - ( 40 7.4 ±1. 3)\text kJ \textmol - 1 . \Updelta_{\text{f}} H_{\text{m}}^{\text{o}} \left( {{\text{C}}_{ 8} {\text{H}}_{ 9} {\text{O}}_{ 2} {\text{N}},{\text{ crIII}}} \right) = - ( 40 7.4 \pm 1. 3){\text{ kJ}}\;{\text{mol}}^{ - 1} . The proposed
\Updelta\textf H\textm\texto ( \textC 8 \textH 9 \textO 2 \textN,\text g ) \Updelta_{\text{f}} H_{\text{m}}^{\text{o}} \left( {{\text{C}}_{ 8} {\text{H}}_{ 9} {\text{O}}_{ 2} {\text{N}},{\text{ g}}} \right) value, together with the experimental enthalpies of formation of acetophenone and 4′-hydroxyacetophenone, taken from the
literature, and a re-evaluated enthalpy of formation of acetanilide,
\Updelta\textf H\textm\texto ( \textC 8 \textH 9 \textON,\text g ) = - ( 10 9. 2 ± 2. 2)\text kJ \textmol - 1 , \Updelta_{\text{f}} H_{\text{m}}^{\text{o}} \left( {{\text{C}}_{ 8} {\text{H}}_{ 9} {\text{ON}},{\text{ g}}} \right) = - ( 10 9. 2\,\pm\,2. 2){\text{ kJ}}\;{\text{mol}}^{ - 1} , were used to assess the predictions of the B3LYP/cc-pVTZ and CBS-QB3 methods for the enthalpy of a isodesmic and isogyric
reaction involving those species. This test supported the reliability of the theoretical methods, and indicated a good thermodynamic
consistency between the
\Updelta\textf H\textm\texto \Updelta_{\text{f}} H_{\text{m}}^{\text{o}} (C8H9O2N, g) value obtained in this study and the remaining experimental data used in the
\Updelta\textr H\textm\texto \Updelta_{\text{r}} H_{\text{m}}^{\text{o}} calculation. It also led to the conclusion that the presently recommended enthalpy of formation of gaseous acetanilide in
Cox and Pilcher and Pedley’s compilations should be corrected by ~20 kJ mol−1. 相似文献
6.
João P. Leal 《Journal of Thermal Analysis and Calorimetry》2010,100(2):441-446
The standard enthalpies of formation of alkaline metals thiolates in the crystalline state were determined by reaction-solution
calorimetry. The obtained results at 298.15 K were as follows:
\Updelta\textf H\textm\texto (\textMSR, \textcr) \Updelta_{\text{f}} H_{\text{m}}^{\text{o}} ({\text{MSR,}}\;{\text{cr}}) /kJ mol−1 = −259.0 ± 1.6 (LiSC2H5), −199.9 ± 1.8 (NaSC2H5), −254.9 ± 2.4 (NaSC4H9), −240.6 ± 1.9 (KSC2H5), −235.8 ± 2.0 (CsSC2H5). These results where compared with the literature values for the corresponding alkoxides and together with values for
\Updelta\textf H\textm\texto ( \textMSH, \textcr) \Updelta_{\text{f}} H_{\text{m}}^{\text{o}} \left( {{\text{MSH}},\;{\text{cr}}}\right) were used to derive a consistent set of lattice energies for MSR compounds based on the Kapustinskii equation. This allows
the estimation of the enthalpy of formation for some non-measured thiolates. 相似文献
7.
Chemically induced dynamic electron polarization (CIDEP) spectrum and transient absorptive spectrum are recorded in photolysis
of duroquinone (DQ) in 1,2-propanodiol (PG). Durosemiquinone neutral radical DQH• and PG ketyl radical
\textCH3[(\textC)\dot]\textOHCH2\textOH{\text{CH}}_{3}{{{\dot{\text{C}}}\text{OHCH}}}_{2}{\text{OH}} are produced through hydrogen transfer reaction from PG to 3DQ*. When stable radical TEMPO is added to DQ/PG solution, photolysis results in CIDEP on TEMPO, which can be interpreted
as a quartet precursor radical-triplet pair mechanism (QP-RTPM). There is competition between PG and TEMPO to quench 3DQ*. The CIDEP intensity of DQH• decreases with the increase of TEMPO concentration. The quenching dynamics in photolysis of DQ/TEMPO/PG system is analyzed
in detail. Based on the dynamics analysis and the measurement of the lifetime of 3DQ* by its transient absorbance decay, the quenching rate constant of 3DQ* by TEMPO in PG is obtained as 1.34 × 107 L mol−1 s−1. This quenching rate constant is closely diffusion-controlled. 相似文献
8.
Mohammad Ali Kamyabi Z. Asgari H. Hosseini Monfared 《Journal of Solid State Electrochemistry》2010,14(9):1547-1553
A carbon past electrode modified with [Mn(H2O)(N3)(NO3)(pyterpy)],
( \textpyterpy = 4¢- ( 4 - \textpyridyl ) - 2,2¢:\text6¢,\text2¢¢- \textterpyridine ) \left( {{\text{pyterpy}} = 4\prime - \left( {4 - {\text{pyridyl}}} \right) - 2,2\prime:{\text{6}}\prime,{\text{2}}\prime\prime - {\text{terpyridine}}} \right) complex have been applied to the electrocatalytic oxidation of nitrite which reduced the overpotential by about 120 mV with
obviously increasing the current response. Relative standard deviations for nitrite determination was less than 2.0%, and
nitrite can be determined in the ranges of 5.00 × 10−6 to 1.55 × 10−2 mol L−1, with a detection limit of 8 × 10−7 mol L−1. The treatment of the voltammetric data showed that it is a pure diffusion-controlled reaction, which involves one electron
in the rate-determining step. The rate constant k′, transfer coefficient α for the catalytic reaction, and diffusion coefficient of nitrite in the solution, D, were found to be 1.4 × 10−2, 0.56× 10−6, and 7.99 × 10−6 cm2 s−1, respectively. The mechanism for the interaction of nitrite with the Mn(II) complex modified carbon past electrode is proposed.
This work provides a simple and easy approach to detection of nitrite ion. The modified electrode indicated reproducible behavior,
anti-fouling properties, and stability during electrochemical experiments, making it particularly suitable for the analytical
purposes. 相似文献
9.
Ponnusamy Sami Kandasamy Venkateshwari Natarajan Mariselvi Arunachalam Sarathi Kasi Rajasekaran 《Transition Metal Chemistry》2010,35(2):137-142
l-cysteine undergoes facile electron transfer with heteropoly 10-tungstodivanadophosphate,
[ \textPV\textV \textV\textV \textW 1 0 \textO 4 0 ]5 - , \left[ {{\text{PV}}^{\text{V}} {\text{V}}^{\text{V}} {\text{W}}_{ 1 0} {\text{O}}_{ 4 0} } \right]^{5 - } , at ambient temperature in aqueous acid medium. The stoichiometric ratio of [cysteine]/[oxidant] is 2.0. The products of the
reaction are cystine and two electron-reduced heteropoly blue, [PVIVVIVW10O40]7−. The rates of the electron transfer reaction were measured spectrophotometrically in acetate–acetic acid buffers at 25 °C.
The orders of the reaction with respect to both [cysteine] and [oxidant] are unity, and the reaction exhibits simple second-order
kinetics at constant pH. The pH-rate profile indicates the participation of deprotonated cysteine in the reaction. The reaction
proceeds through an outer-sphere mechanism. For the dianion −SCH2CH(NH3
+)COO−, the rate constant for the cross electron transfer reaction is 96 M−1s−1 at 25 °C. The self-exchange rate constant for the
- \textSCH2 \textCH( \textNH3 + )\textCOO - \mathord