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111.
CHEN Kai ZHU Zhong-liang ZHANG De-jun 《高等学校化学研究》2006,22(4):435-438
IntroductionStudies on reversible kinetic systems are consi-dered as a hotspot of chemical and biochemical kineticresearches[1,2]. Of late, some researches have been fo-cused on the simultaneous optimization of the obverseand reverse rate constants[3,4].H… 相似文献
112.
Yanchen Liu Chenchen Wang Shuo Zhao Lin Zhang Kai Zhang Fujun Li Jun Chen 《Chemical science》2021,12(3):1062
Layered manganese-based oxides are promising candidates as cathode materials for sodium-ion batteries (SIBs) due to their low cost and high specific capacity. However, the Jahn–Teller distortion from high-spin Mn3+ induces detrimental lattice strain and severe structural degradation during sodiation and desodiation. Herein, lithium is introduced to partially substitute manganese ions to form distorted P′2-Na0.67Li0.05Mn0.95O2, which leads to restrained anisotropic change of Mn–O bond lengths and reinforced bond strength in the [MnO6] octahedra by mitigation of Jahn–Teller distortion and contraction of MnO2 layers. This ensures the structural stability during charge and discharge of P′2-Na0.67Li0.05Mn0.95O2 and Na+/vacancy disordering for facile Na+ diffusion in the Na layers with a low activation energy barrier of ∼0.53 eV. It exhibits a high specific capacity of 192.2 mA h g−1, good cycling stability (90.3% capacity retention after 100 cycles) and superior rate capability (118.5 mA h g−1 at 1.0 A g−1), as well as smooth charge/discharge profiles. This strategy is effective to tune the crystal structure of layered oxide cathodes for SIBs with high performance.Li-Substitution in P′2-Na0.67MnO2 mitigates the anisotropic change of Mn–O bonds and Na/vacancy ordering, and hence significantly promotes its cycling stability and rate capability as a cathode material for sodium-ion batteries. 相似文献
113.
The isolation and identification of twenty‐one components (including four new triterpenoid saponins and one new triterpenoid acid) from the root of Rhaponticum uniflorum (L.) DC. (Compositae) are described. Their structures were determined on the basis of spectral analysis and chemical trans formation. The new compounds were identified as 3‐O‐α‐L‐arabinopyranosyl‐urs‐12,18(19)‐dien‐28‐oic acid β‐D‐glucopyranosyl ester, 3β‐ hydroxyurs‐12,18(19)‐dien‐28‐oic acid β‐D‐glucopyranosyl ester, 3β‐hydroxyurs‐12,19(29)‐dien‐28‐oic acid β‐D‐glucopyranosylester, 3‐O‐α‐L‐arabinopyranosyl‐urs‐9(11),12‐dien‐28‐oic acid β‐D‐glucopyranosyl ester and 2 α,3 α, 19α,25‐tetrahydroxyurs‐12‐en‐23,28‐dioic acid. 相似文献
114.
Capillary electrochromatography (CEC) has been performed with a series of C14, methlyacrylamide based monolithic columns. These monoliths with different porosities were prepared by in-situ copolymerization in fused-silica capillaries. The porous properties of monoliths were further observed using scanning electron micrographs (SEM) and measured using a mercury porosimeter. The effect of various alcohols as porogens on porous structural properties and chromatographic behaviors were also investigated. The effects of organic additive, pH value and ionic strength in mobile phase on electroosmosis flow (EOF) and separation were further discussed. Meanwhile, the baseline separation of 6 neutral compounds can be well obtained. In addition, the monolithic column demonstrates the high column efficiency and satisfactory reproducibility.Acknowledgements We gratefully acknowledge the support of the National Natural Science Foundation of China. 相似文献
115.
建立了同时测定化妆品中苯扎溴铵、2-溴-2-硝基-1,3-丙二醇、5-溴-5-硝基-1,3-二■烷、甲基二溴戊二腈、溴氯芬5种含溴防腐剂的高效液相色谱-电感耦合等离子体质谱法(HPLC-ICP-MS)。样品经含0.1%甲酸的甲醇溶液超声提取后,采用Agilent Eclipse-C_(18)(150 mm×4.6 mm,5μm)色谱柱分离,以0.1%甲酸-甲醇为流动相进行梯度洗脱,ICP-MS测定组分中的~(79)Br,以保留时间定性,外标法定量。5种含溴防腐剂均在0.5~100 mg/L范围内线性关系良好(r0.999),检出限为1.5~3.0μg/g,不同基质化妆品中的回收率为91.2%~108%,相对标准偏差(n=6)为1.3%~4.2%。该方法快速、准确、灵敏、专属性强,适用于化妆品中5种含溴防腐剂的定性定量分析。 相似文献
116.
Robert Franzén 《高等学校化学研究》2006,22(5):602-605
IntroductionAqueous hydrogen peroxide is considered to be a“green”oxidant with a high oxidation efficiency due toits low molecular weight,cleanness in the oxidationprocess in which only harmless water is produced,lowcost of production and safe transport… 相似文献
117.
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119.
纳米尺寸团簇NinZrn(n=3~5)的几何结构与成键规律研究 总被引:3,自引:0,他引:3
根据化学键理论与拓扑原理,设计了团簇NinZrn(n=3-5)的可能几何构型,并用从头算方法进行构型优化,结果表明,由NiZr组成的团簇原子间的Zr-Zr和Zr-Ni键明显较强,而Ni-Ni的成键较弱,并发与NinZrn(n=3-5)团簇电子性质与有机烯烃分子等瓣相似,原子之间的成键按照强弱相间的规则分布。 相似文献
120.
在密度泛函理论的框架下, 采用嵌入点电荷簇模型研究了O2在MgO(001)完整和缺陷表面上的吸附.用电荷自洽的方法确定了点电荷的值.计算结果表明, O2倾向吸附在低配位的角Mg2+端.并且发现, 当O2为平躺吸附时,键长有较大的拉伸,将有利于O2的解离.同时,分别计算了使用裸簇和嵌入表观±2.0 e点电荷簇模型时的吸附能,并与采用电荷自洽方法的计算值进行了比较.结果表明,电荷自洽方法更能有效反映簇周围的环境,得到的计算结果能够较好地与实验值吻合.最后,分别计算了不同吸附情况下O2的振动频率. 相似文献