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1.
The protolysis equilibria of 2-hydroxybenzohydroxamic acid, H2SAX, have been studied at 25 degrees C in different ionic media by potentiometric titration with a glass electrode. The media were 0.513, 1.05, 2.21 and 3.5 mol/kg NaClO4. The constants beta(-p)(H2SAX<==>H(2-p)SAX(-p)+pH+), combined with salting effects of NaClO4 on H2SAX deduced from solubility determinations, were processed by the specific interaction theory, SIT, to give equilibrium constants at infinite dilution, log beta(-1)(o) = -7.655 +/- 0.013 and log beta(-2)(o) = -17.94 +/- 0.04, as well as specific interaction coefficients b(HSAX-,Na+) = 0.12 +/- 0.01 and b(SAX2-,Na+) = 0.17 +/- 0.02, molal(-1). 相似文献
2.
The complex formation equilibria between iron(II) and sulfate ions have been studied at 25 degrees C in 3 M NaClO4 ionic medium by measuring with a glass electrode the competition of Fe2+ and H+ ions for the sulfate ion. The concentrations of the metal and of the ligand were varied in the ranges 0.01 to 0.125 and 0.01 to 0.250 M, respectively. The analytical concentration of strong acid was chosen to be 0.01 or 0.03 M. The potentials of the glass electrode, corrected for the effect of replacement of medium ions with reagent species, have been interpreted with the equilibria [formula: see text] Stability constants valid in the infinite dilution reference state, logK zero = 1.98 +/- 0.16, log beta 1 zero = 2.1(5) +/- 0.2 and log beta 2 = 2.5 +/- 0.2, have been estimated by assuming the validity of the specific interaction theory. 相似文献
3.
The reaction of esterification of benzoic acid with benzyl chloride was chosen as a model reaction to study the esterification by SN2 promoted by tertiary amine as deprotonating agent. The use of ionic liquid (IL) 1,3-dimethylimidazolium methanesulfonate [MMIm][OMs] as reaction medium has proven to give quantitative yield of the ester, but interestingly the reaction does occur even in solvent-free conditions, where the acid + the amine form a liquid system (a protic IL) in situ. This last methodology was extended to several carboxylic acids in conditions of atom economy (i.e., without excess of any reagent), giving moderately good yields of esters (54–78%) recovered by weight in pure form. 相似文献
4.
The complex formation equilibria between titanium(IV) and fluoride ions have been studied at 25°C in 3 M(Na)Cl ionic medium by measuring, with an ion selective electrode for F?, the free HF concentration in acid Ti(IV) solutions. The [H+] was kept within 0.25 and I M where the predominant form of uncomplexed metal is the dihydroxotitanium(IV) ion, Ti(OH)2+2. The potentiometric data have been explained by assuming Ti(OH)2F+, TiF4 and HTiF?6, with equilibrium constants given in Table 3. Within the accuracy of the present e.m.f. study, ±0.2 mV, no evidence for intermediate complexes bearing 2, 3 and 5 F? was found.From a special series of measurements, carried out by replacing a large part of the Cl? with ClO?4, it is concluded that no appreciable amount of Ti(IV)Cl complexes is formed at the 3 M level employed as ionic medium. 相似文献
5.
Manna L Wang LW Cingolani R Alivisatos AP 《The journal of physical chemistry. B》2005,109(13):6183-6192
Equilibrium geometries, surface energies, and surfactant binding energies are calculated for selected bulk facets of wurtzite CdSe with a first-principles approach. Passivation of the surface Cd atoms with alkyl phosphonic acids or amines lowers the surface energy of all facets, except for the polar 000 facet. On the nonpolar facets, the most stable configuration corresponds to full coverage of surface Cd atoms with surfactants, while on the polar 0001 facet it corresponds only to a partial coverage. In addition, the passivated surface energies of the nonpolar facets are in general lower than the passivated polar 0001 facet. Therefore, the polar facets are less stable and less efficiently passivated than the nonpolar facets, and this can rationalize the observed anisotropic growth mechanism of wurtzite nanocrystals in the presence of suitable surfactants. 相似文献
6.
Shape Control of Colloidal Semiconductor Nanocrystals 总被引:2,自引:0,他引:2
Shape control of inorganic nanocrystals is important for understanding basic size- and shape-dependent scaling laws, and may be useful in a wide range of applications. Methods for controlling the shapes of inorganic nanocrystals are evolving rapidly. This paper will focus on how we currently control the shape of semiconductor nanocrystals using CdSe as example. 相似文献
7.
Dorfs D Härtling T Miszta K Bigall NC Kim MR Genovese A Falqui A Povia M Manna L 《Journal of the American Chemical Society》2011,133(29):11175-11180
We demonstrate that colloidal Cu(2-x)Se nanocrystals exhibit a well-defined infrared absorption band due to the excitation of positive charge carrier oscillations (i.e., a valence band plasmon mode), which can be tuned reversibly in width and position by varying the copper stoichiometry. The value of x could be incrementally varied from 0 (no plasmon absorption, then a broad peak at 1700 nm) to 0.4 (narrow plasmon band at 1100 nm) by oxidizing Cu(2)Se nanocrystals (upon exposure either to oxygen or to a Ce(IV) complex), and it could be incrementally restored back to zero by the addition of a Cu(I) complex. The experimentally observed plasmonic behavior is in good agreement with calculations based on the electrostatic approximation. 相似文献
8.
Antognazza MR Scotognella F Miszta K Dorfs D Zanella M Zavelani-Rossi M Manna L Lanzani G Tassone F 《Physical chemistry chemical physics : PCCP》2011,13(33):15326-15330
Colloidal branched nanocrystals have been attracting increasing attention due to evidence of an interesting relationship between their complex shape and charge carrier dynamics. Herein, continuous wave photoinduced absorption (CW PIA) measurements of CdSe/CdS octapod-shaped nanocrystals are reported. CW PIA spectra show strong bleaching due to the one-dimensional (1D) CdS pod states (480 nm) and the zero-dimensional (0D) CdSe core states (690 nm). The agreement with previously reported ultrafast pump-probe experiments indicates that this strong bleaching signal may be assigned to state filling. Additional bleaching features at 520 and 560 nm are characterized by a longer lifetime and are thus ascribed to defect states, localized at the pod-core interface of the octapod, showing that some of the initially photogenerated carriers get quickly trapped into these long-lived defect states. However, we remark that a relevant part of electrons remain untrapped: this opens up the opportunity to exploit octapod shaped nanocrystals in photovoltaics applications, as electron acceptor materials, considering that several efficient hole extracting materials are already available for the realization of a composite bulk heterojunction. 相似文献
9.
正Perovskite nanocrystals and quantum dots(QDs) have attracted great attention due to their potential in optical and optoelectronic applications, especially in ultra-high definition displays because of their high purity of photo/electroluminescence(PL/EL) [1,2]. Although the external quantum efficiency(EQE) of light-emitting diodes(LEDs) based on perovskite quantum dots(PeQDs) has been over 20% [3,4],another key problem, the PL/EL stability, still remains open.The thermal PL/EL quenching phenomenon, which is ubiquitously observed, has not aroused enough attention in this 相似文献
10.
A method for the determination of copper in complex matrices by electrothermal atomic-absorption spectrometry has been developed. It uses neocuproine as complexing agent. The detection limit is 0.2 ng/ml, and interferences are minimized. 相似文献