Studies on Electrochemical Property of LiFePO4/C as Cathode Material for Lithium Ion Batteries

IntroductionLithium ion batteries are key components of mobiletelephones and portable computers.Among the knownLi-intercalation materials for lithium ion battery cath-odes,LiCoO2,LiNiO2,and LiMn2O4have been stud-ied extensively[1—3].LiCoO2is nowused in c…     

Thermodynamics of the dissociation of 2-aminopyridinium ion in synthetic seawater and a standard for pH in marine systems

Buffer solutions composed of 2-aminopyridinium chloride and 2-aminopyridine in synthetic seawater are useful as a supplement to buffers of Tris (pH 8.2) and Bis (pH 8.8) in standardizing measurements of hydrogen ion concentration (pm _H or pH(SWS)) in oceanography. The dissociation constant of 2-amino-pyridinium ion over the range of salinities (S) from 30 to 40 has now been determined from the emf of cells without liquid junction at eight temperatures (T) from 278.15 to 313.15 K. The results fit the equation pK=2498.31/T–15.3274+2.4050 lnT+S(0.012928–2.9417×10^–5T) with a standard deviation of 0.0023. Thermodynamic constants for the dissociation process and standard reference values of pm _H and pH(SWS) were derived from the data. The pm _H of the buffer consisting of 2-aminopyridinium chloride and 2-aminopyridine (each 0.04 molal) in synthetic seawater of salinity 35 varies from 7.356 at 278.15 K to 6.601 at 313.15 K.     

Synthesis and ion selectivity of macrocyclic metacyclophanes analogous to spherand-type calixarenes

Novel macrocyclic compounds, hexahydroxy[1.0.1.0.1.0]- (2b) and octahydroxy[1.0.1.0.1.0.1.0]metacyclophane (2c) have been prepared in 50–70% yield by base-catalyzed condensation of 5,5-di-tert-butyl-2,2-dihydroxybiphenyl (1) with formaldehyde in refluxing xylene. An attempted alkylation of the flexible macrocycles2b and2c with ethyl bromoacetate in the presence of Cs₂CO₃ under acetonitrile reflux gave only one pure stereoisomer3 and4, respectively, while other possible isomers were not observed. The structural characterization of these products is also discussed. The two-phase solvent extraction data indicated that hexaethyl ester3 and octaethyl ester4 show strong metal affinity, comparable with that of the corresponding calix[n]arenes, and a high K⁺ selectivity was observed for octaethyl ester4.¹H-NMR titration of hexaethyl ester3 and octaethyl ester4 with KSCN clearly demonstrate that a 11 complex is formed which is stable on the NMR time scale.This paper is dedicated to the commemorative issue on the 50th anniversary of calixarenes.     

Cyclic Voltammetric Study of the Oxidation of Catechols in the Presence of Cyanide Ion

Electrochemical oxidation of catechols has been studied in the presence of cyanide ion as nucleophile in aqueous solution, by means of cyclic voltammetry and controlled‐potential coulometry. The results indicate that the participation of catechols in the Michael reaction with cyanide ion to form the corresponding o‐dihydroxybenzonitrile. Based on an EC mechanism, the homogeneous rate constants were estimated by comparing the experimental cyclic voltammetric responses with the digital simulated results.     

低共熔混合锂盐相图的绘制及应用

采用热分析法对不同组成的混合锂盐二元体系进行研究, 绘制了混合锂盐体系的步冷曲线和T-x相图, 结果表明体系均为具有最低共熔点的二元体系. LiOH-LiNO3、LiOH-LiCl、LiOH-Li2CO3及LiNO3-LiCl体系的最低共熔点分别为175.7、294.5、418.2及221.6 ℃. 利用低共熔混合物LiNO3-LiOH为锂盐与不同前驱体反应, 制备出了层状结构良好的锂离子电池正极材料LiNiO2、LiNi0.8Co0.2O2及LiNi1/3Co1/3Mn1/3O2. X射线衍射分析表明, 合成的材料具有规整的层状NaFeO2结构, 且XRD衍射峰强度之比I(003)/I(104)>2.0, 电性能测试表明, 在2.7-4.3 V(vs Li/Li+)的电压范围内进行0.1C倍率充放电, LiNiO2、LiNi0.8Co0.2O2、LiNi1/3Co1/3Mn1/3O2首次充电比容量分别达168.0、225.4、194.0 mAh·g-1, 放电比容量分别为138.4、165.8、157.7 mAh·g-1.     

Crystal structure and ionic conductivity of the series A2Bi24Mo8X2O68 (A = Ca, Sr and Ba and X = Cr and W) in the Bi2O3?MoO3 system

A series of A₂Bi₂₄Mo₈X₂O₆₈ compounds, Ca₂Bi₂₄Mo₈Cr₂O₆₈ (CBMC), Sr₂Bi₂₄Mo₈Cr₂O₆₈ (SBMC), Pb₂Bi₂₄Mo₈Cr₂O₆₈ (PBMC) and Ba₂Bi₂₄Mo₈W₂O₆₈ (BBMW) have been synthesized by the solid-state method and characterized by single crystal X-ray diffraction. The compounds index into the monoclinic P2/c system with a=11.687(4) ?, 5.784(2) ?, 24.728(9) ?, 101.911(6)°, Z=1; 11.673(6) ?, 5.775(3) ?, 24.670(2) ?, 101.757(8)°, Z=1; 11.638(3) ?, 5.790(1) ?, 24.655(6) ?, 101.716(4)°, Z=1 and 11.718(6) ?, 5.818(3) ?, 24.716(12) ?, 101.835(9)°, Z=1 for CBMC, SBMC, PBMC and BBMW, respectively. The structures were solved by direct methods and refined to R indices of 0.081, 0.065, 0.080 and 0.079 respectively. These compounds are isostructural with Bi₂₆Mo₁₀O₆₉ and the structure consists of columns of [Bi₁₂O₁₄] along the b-axis, surrounded by Mo/Cr/WO₄ tetrahedra. a.c. impedance studies indicate higher values of ionic conductivity for the tungsten-substituted compounds. Supplementary material The crystal data of CBMC, SBMC, PBMC and BBMW have been deposited at the Fachinformationszentrum Karlsruhe (FIZ) with the numbers CSD 415143, CSD 415145, CSD 415144 and CSD 415142, respectively.     

桑蚕丝素蛋白初始结构对其矿化作用的影响

以碱金属离子诱导桑蚕丝素蛋白溶液发生构象转变, 研究了蛋白质初始结构对其矿化作用的影响. FT-IR, XRD和SEM等测试结果显示, 未经任何处理的桑蚕丝素蛋白溶液矿化后形成片状复合物, 其无机相以二水磷酸氢钙(DCPD)为主; 而经过K^＋和Na^＋金属离子处理后, 桑蚕丝素溶液的结构由无规线团/螺旋构象向β-折叠发生转变, 矿化后成纤维状, 并相互结合呈现纳米级的三维多孔结构, 其无机相以热力学稳定的羟基磷灰石(HA)为主. 可以认为, 丝素蛋白结构转化为较伸展的β-折叠后, 使得更多的亲水基团暴露在外面, 在丝素蛋白分子不断凝聚成纤过程中, HA结晶快速生长并附着在这些微纤上, 最终形成纤维状的丝素蛋白/HA复合物. 该结果为阐明蛋白质的生物矿化过程及其调控机理提供了理论依据, 同时可以从矿化复合物的形成来反映这些微量元素可能对骨组织形成的影响, 为临床骨组织的修复提供一定的参考.     

Characterization of Mercury – Humic Acids Interaction by Potentiometric Titration with a Modified Carbon Paste Mercury Sensor

Stability constant for mercury binding by commercial and natural humic acids (HA) were determined using a new potentiometric mercury(II) sensor based on dithiosalicylic acid modified carbon paste electrode. The sensor present a high selective and sensitive response to mercury(II) ions, and a low detection limit of 1.8×10^?8 M. The potentiometric titrations curves of humic acids against mercury(II) ions were modeled. For 1.00×10^?7 to 3.00×10^?4 M mercury(II) ion concentration levels the results are consistent with the presence of two different binding sites in the humic acid macromolecule. The strongest binding sites (log K₁ ranging from 10.1 to 6.8) are probably due to interaction with carboxylic acid and amine groups in the molecule, whereas weakest binding sites (log K₂ ranging from 8.8 to 4.5) can be associated to phenolic groups.     

Kinetics and Mechanism of the Cerium(IV) Oxidation of Arnold's Base and the Protonation and Hydroxylation of Michler's Hydrol Blue

In aqueous H₂SO₄, Ce(IV) ion oxidizes rapidly Arnold's base((p-Me₂NC₆H₄)₂CH₂, Ar₂CH₂) to the protonated species of Michler's hydrol((p-Me₂NC₆H₄)₂CHOH, Ar₂CHOH) and Michler's hydrol blue((p-Me₂NC₆H₄)₂CH⁺, Ar₂CH⁺). With Ar₂CH₂ in excess, the rate law of the Ce(IV)-Ar₂CH₂ reaction in 0.100 M H₂SO₄ is expressed -d[Ce(IV)]/dt = k_app[Ar₂CH₂]₀[Ce(IV)] with k_app = 199 ± 8M^?1s^?1 at25°C. When the consumption of Ce(IV) ion is nearly complete, the characteristic blue color of Ar₂CH⁺ ion starts to appear; later it fades relatively slowly. The electron transfer of this reaction takes place on the nitrogen atom rather than on the methylene carbon atom. The dissociation of the binuclear complex [Ce(III)ArCHAr-Ce(III)] is responsible for the appearance of the Ar₂CH⁺ dye whereas the protonation reaction causes the dye to fade. In highly acidic solution, the rate law of the protonation reaction of Michler's hydrol blue is -d[Ar₂CH⁺]/dt = k_obs[Ar₂CH⁺] where K_obs = ((ac + 1)[H*] + bc[H⁺]²)/(a + b[H⁺]) (in HClO₄) and k_obs= ((ac + 1 + e[HSO₄^?])[H⁺] + bc[H⁺]² + d[HSO₄^?] + q[HSO₄^?]²/[H⁺])/(a + b[H⁺] + f[HSO₄^?] + g[HSO₄^?]/[H⁺]) (in H₂SO₄), and at 25°C and μ = 0.1 M, a = 0.0870 M s, b = 0.655 s, c = 0.202 M^?1s^?1, d = 0.110, e = 0.0070 M^?1, f = 0.156 s, g = 0.156 s, and q = 0.124. In highly basic solution, the rate law of the hydroxylation reaction of Michler's hydrol blue is -d[Ar₂CH⁺]/dt = k_OH[OH^?]₀[Ar₂CH⁺] with k_OH = 174 ± 1 M^?1s^?1 at 25°C and μ = 0.1 M. The protonation reaction of Michler's hydrol blue takes place predominantly via hydrolysis whereas its hydroxylation occurs predominantly via the path of direct OH attack.     

On the effect of low-energy ion bombardment on polystyrene and polymethylmethacrylate etch rates in rf plasmas

The effect of low-energy ion bombardment on CD₄/O₂ and CF₃X (X=F, Cl, Br) plasma etching has been assessed by applying controlled rf bias voltages on polystyrene (PS) and polymethylmethacrylate (PMMA) samples. In both cases ion bombardment has been found to have a chemical effect. In the case of CF₄/O₂ discharges, ion bombardment has been found to change the relative etching efficiency of different mixtures. In the case of CF₃X plasmas, ion bombardment has been found to alter PMMA and PS etch rates in a different way. In particular, the ratios between CF₄ and CF₃X (X=Cl, Br) etch rates of PS have been found to decrease with increasing bias voltage. This effect has been tentatively attributed to an ion bombardment-induced enhancement of the reaction between the aromatic ring and halogen molecules formed in CF₃Cl and CF₃Br discharges.