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1.
The kinetics of the diazotization reaction of procaine in the presence of anionic micelles of sodium dodecyl sulfate (SDS) and cationic micelles of cetyltrimethyl ammonium bromide (CTAB), dodecyltrimethyl ammonium bromide (DDTAB) and tetradecyltrimethyl ammonium bromide (TDTAB) were carried out spectrophotometrically at λmax = 289 nm. The values of the pseudo first order rate constant were found to be linearly dependent upon the [NaNO2] in the concentration range of 1.0 × 10−3 mol dm−3 to 12.0 × 10−3 mol dm−3 in the presence of 2.0 × 10−2 mol dm−3 acetic acid. The concentration of procaine was kept constant at 6.50 × 10−5 mol dm−3. The addition of the cationic surfactants increased the reaction rate and gave plateau like curve. The addition of SDS micelles to the reactants initially increased the rate of reaction and gave maximum like curve. The maximum value of the rate constant was found to be 9.44 × 10−3 s−1 at 2.00 × 10−3 mol dm−3 SDS concentration. The azo coupling of diazonium ion with β-naphthol (at λmax = 488) nm was found to linearly dependent upon [ProcN2+] in the presence of both the cationic micelles (CTAB, DDTAB and TDTAB) and anionic micelles (SDS). Both the cationic and anionic micelles inhibited the rate of reactions. The kinetic results in the presence of micelles are explained using the Berezin pseudophase model. This model was also used to determine the kinetic parameters e.g. km, Ks from the observed results of the variation of rate constant at different [surfactants].  相似文献   

2.
Electrochemical lithium intercalation within graphite from 1 mol dm 3 solution of LiClO4 in propylene carbonate (PC) was investigated at 25 and − 15 °C. Lithium ions were intercalated into and de-intercalated from graphite reversibly at − 15 °C despite the use of pure PC as the solvent. However, ceaseless solvent decomposition and intense exfoliation of graphene layers occurred at 25 °C. The results of the Raman spectroscopic analysis indicated that the interaction between PC molecules and lithium ions became weaker at − 15 °C by chemical exchange effects, which suggested that the thermodynamic stability of the solvated lithium ions was an important factor that determined the formation of a solid electrolyte interface (SEI) in PC-based solutions. Charge–discharge analysis revealed that the nature of the SEI formed at − 15 °C in 1 mol dm 3 of LiClO4 in PC was significantly different from that formed at 25 °C in 1 mol dm 3 of LiClO4 in PC containing vinylene carbonate, 3.27 mol kg 1 of LiClO4 in PC, and 1 mol dm 3 of LiClO4 in ethylene carbonate.  相似文献   

3.
The effect of cationic micelles of cetyltrimethylammonium bromide (CTAB) on the interaction of dipeptide glycyl-tyrosine (Gly-Tyr) with ninhydrin under varying conditions has been studied spectrophotometrically at 70 °C and pH 5.0. The reaction followed first- and fractional-order kinetics with respect to [Gly-Tyr] and [ninhydrin], respectively. Increase in total concentration of CTAB from 0 to 70 × 10−3 mol dm−3 resulted in an increase in the pseudo-first-order rate constant (kψ) by a factor of ca. 3. Quantitative kinetic analysis of kψ  [CTAB] data was performed on the basis of pseudo-phase model of the micelles (proposed by Menger and Portnoy and developed by Bunton) and Piszkiewicz model. A possible mechanism has been proposed and the kinetic data have been used to evaluate the micellar binding constants KS (268 mol−1 dm3 for Gly-Tyr) and KN (64 mol−1 dm3 for ninhydrin).  相似文献   

4.
Cyclic voltammetry of the CuCl powder in a cavity microelectrode revealed direct electro-reduction in solid state in 1-butyl-3-methylimidazolium hexafluorophosphate. Potentiostatic electrolysis of the salt powder (attached to a current collector) in the ionic liquid produced Cu nanoparticles as confirmed by X-ray diffraction, energy dispersive X-ray analysis, scanning and transmission electron microscopy. The particle size decreased down to 10 nm when the electrode potential was shifted from −0.9 V to −1.8 V (versus Ag/Ag+). The electro-reduction and the nanoparticle formation mechanisms were investigated in the ionic liquid and also in aqueous 0.1 mol L−1 KClO4 in which larger Cu particles were obtained.  相似文献   

5.
H radicals react with chlorobenzoic acids and chlorobenzene (k(H+substrates)=(0.7–1.5)×109 dm3 mol−1 s−1) by addition to the benzene ring forming H adducts with characteristic absorption bands in the range of 310–360 nm. The rate constants for their second-order decay are 2k=(3.5–6)×108 dm3 mol−1 s−1. By reduction with eaq fragmentation and chloride release was established for 2- and 4-chlorobenzoic acid, for 3-chlorobenzoic acid the addition of electrons to the carboxylate group was observed by pulse radiolysis. By gamma radiolysis could be proved that these radical anions undergo intramolecular electron transfer and quantitave dechlorination. The efficiency in degradation was 4-chlorobenzoic acid>3-chlorobenzoic acid>2-chlorobenzoic acid. Benzoic acid was found as final product for all substrates.  相似文献   

6.
The radiation induced degradation of 4-nitrophenol (4-NP) has been studied by gamma irradiation, while the reactivity and spectral features of the short lived transients formed by reaction with primary transient radicals at different pHs has been investigated by pulse radiolysis technique. In steady state radiolysis a dose of 4.4 k Gy is able to degrade 98% of 1×10−4 mol dm−3 4-NP. 4-NP has pKa at 7.1, above which it is present in the anionic form. At pH 5.2, OH and N3 radicals were found to react with 4-NP with rate constants of 4.1×109 dm3 mol−1 s−1 and 2.8×108 dm3 mol−1 s−1, respectively. Differences in the absorption spectra of species formed in the reactions of 4-NP with OH and N3 radicals suggested that OH radicals add to the aromatic ring of 4-NP along with electron transfer reaction, whereas N3 radicals undergo only electron transfer reaction. At pH 9.2, rate constants for the reaction of OH radicals with 4-NP was found to be higher by a factor of 2 compared to that at pH 5.2. This has been assigned to the deprotonation of 4-NP at pH 9.2.  相似文献   

7.
The reaction of OH with naringenin (4′,5,7-trihydroxyflavanone) in the presence of air induced the formation of the hydroxylation product eriodictyol (3′,4′,5,7-tetrahydroxyflavanone). Its yield was dependent on pH. The initial degradation yield of naringenin was Gi(-Nar)=(2.5±0.2)×10−7 mol dm−3 J−1. For the reaction with OH, a rate constant k (OH+naringenin)=(7.2±0.7)×109 M−1 s−1 was determined. In the presence of N2O and NaN3/N2O, no eriodyctiol was formed. Apigenin (4′,5,7-trihydroxyflavon) was detected as decay product of the naringenin phenoxyl radicals. In Ar-saturated solutions, naringenin exhibited a pronounced radiation resistance, G(-naringenin) ∼0.3×10−7 mol dm−3 J−1.  相似文献   

8.
Pulse radiolytic reduction of bovine serum albumin (BSA) and lysozyme by CO2 radical in presence of polyvinyl alcohol (PVA) has been studied. At pH 6.8 in presence of 2% (w/v) PVA, reduction of BSA and lysozyme (both at 1×10−4 mol dm−3) give an additional transient peak at 390 nm along with the usual 420 nm peak. The bimolecular rate constants for the reaction of CO2 radical at pH 6.8±0.2 with BSA are 2.7×108 and 7.13×108 dm3 mol−1 s−1 at 420 nm and 390 nm respectively. The same for lysozyme are 3.2×108 and 5.6×108 dm3 mol−1 s−1 at 420 nm and 390 nm, respectively. Dimethyl disulfide also gives 390 nm and 420 nm peaks in this system upon reduction with CO2 radical. The 390 nm peak is ascribed to the sulfenium radical (RSS(H)R). Studies on the variation of pH suggests the protonation of RSSR radical (420 nm) to form RSS(H)R radical (390 nm) in this viscous media. The decay of RSS(H)R radical occurs via formation of RS radical and RS(H)S(H)R, the final product being RSH in both cases.  相似文献   

9.
The molar enthalpies of reaction of metallic barium with 0.047 mol·dm−3 HClO4 as well as the molar enthalpies of dissolution of BaCl2 in 1.01 mol·dm−3 HCl and in water have been measured at T=298.15 K in a sealed swinging calorimeter with an isothermal jacket. From these results the standard molar enthalpy of formation of the barium ion in an aqueous solution at infinite dilution, as well as the enthalpies of formation of barium chloride and barium perchlorate, are calculated to be: ΔfH0m(Ba2+,aq)=−(535.83±1.25) kJ · mol−1; ΔfH0m(BaCl2,cr)=−(855.66±1.28) kJ · mol−1; and ΔfH0m(BaClO4,cr)=−(796.26±1.35) kJ · mol−1. The results obtained are discussed and compared with previous experimental values.  相似文献   

10.
A direct borohydride fuel cell with a Pd/Ir catalysed microfibrous carbon cathode and a gold-catalysed microporous carbon cloth anode is reported. The fuel and oxidant were NaBH4 and H2O2, at concentrations within the range of 0.1–2.0 mol dm−3 and 0.05–0.45 mol dm−3, respectively. Different combinations of these reactants were examined at 10, 25 and 42 °C. At constant current density between 0 and 113 mA cm−2, the Pd/Ir coated microfibrous carbon electrode proved more active for the reduction of peroxide ion than a platinised-carbon one. The maximum power density achieved was 78 mW cm−2 at a current density of 71 mA cm−2 and a cell voltage of 1.09 V.  相似文献   

11.
The molar enthalpies of solution of 2MgO · 2B2O3 · MgCl2 · 14H2O in approximately 1 mol · dm−3 aqueous hydrochloric acid (HCl) and of MgCl2 · 6H2O(s) in aqueous (approximately 1 mol · dm−3 HCl + MgCl2 + H3BO3) at T=298.15 K were determined. From a combination of these results with measured enthalpies of solution of boric acid (H3BO3) in HCl(aq) and of magnesium oxide (MgO) in aqueous (HCl + H3BO3) solution, together with the standard molar enthalpies of formation of MgO(s), H3BO3(s), MgCl2 · 6H2O(s) and H2O(l), the standard molar enthalpy of formation of −(8812 ± 3) kJ · mol−1 of 2MgO · 2B2O3 · MgCl2 · 14H2O was obtained. Thermodynamic properties of this compound were also calculated by group contribution method.  相似文献   

12.
Photodegradation of 4-nitrophenol (4-Np) in the presence of zinc tetrasulfophthalocyanine (ZnPcS4), zinc octacarboxyphthalocyanine (ZnPc(COOH)8) and a sulfonated ZnPc containing a mixture of differently sulfonated derivatives (ZnPcSmix), as photocatalysts is reported. ZnPcSmix is the most effective catalyst in terms of a high quantum yield for 4-Np degradation and the stability of the catalyst. However ZnPc(COOH)8 degrades readily during the catalysis, but it has a higher quantum yield (Φ4-Np) for 4-Np degradation than the rest of the complexes. The Φ4-Np values were closely related to the singlet oxygen quantum yields ΦΔ and hence aggregation. The rate constants for the reaction with 4-Np were kr = 0.67 × 106 mol−1 dm3 s−1 for ZnPcSmix and 2.8 × 108 mol−1 dm3 s−1 for ZnPc(COOH)8.  相似文献   

13.
Excess molar volumes VmE of binary mixtures of 2,2,2-trifluoroethanol with water, or acetone, or methanol, or ethanol, or 1-alcholos, or 1,4-difluorobenzene, or 4-fluorotoluene or α,α,α-trifluorotoluene were measured in a vibrating tube densimeter at temperature 298.15 K and pressure of 101 kPa. The VmE extrema are: 1.540 cm3 · mol−1 for (2,2,2-trifluoroethanol + 1-heptanol); 1.452 cm3 · mol−1 for (2,2,2-trifluoroethanol + 1-hexanol); 1.238 cm3 · mol−1 for (2,2,2-trifluoroethanol + 1-butanol); 0.821 cm3 · mol−1 for (2,2,2-trifluoroethanol + 4-fluorotoluene); 0.817 cm3 · mol−1 for (2,2,2-trifluoroethanol + ethanol); 0.647 cm3 · mol−1 for (2,2,2-trifluoroethanol + methanol); 0.618 cm3 · mol−1 for (2,2,2-trifluoroethanol + acetone); 0.605 cm3 · mol−1 for (2,2,2-trifluoroethanol + α,α,α-trifluorotoluene); 0.485 cm3 · mol−1 for (2,2,2-trifluoroethanol + 1,4-difluorobenzene); and −0.656 cm3 · mol−1 for (2,2,2-trifluoroethanol + water). The limiting excess partial molar volumes are estimated.  相似文献   

14.
The release of uranium from geologic nuclear waste repositories under oxidizing conditions can only be modeled if the thermodynamic properties of the secondary uranyl minerals that form in the repository setting are known. Toward this end, we synthesized soddyite ((UO2)2(SiO4)(H2O)2), and performed solubility measurements from both undersaturation and supersaturation. The solubility measurements rigorously constrain the value of the solubility product of synthetic soddyite, and consequently its standard-state Gibbs free energy of formation. The log solubility product (lg Ksp) with its error (1σ) is (6.43 + 0.20/−0.37), and the standard-state Gibbs free energy of formation is (−3652.2 ± 4.2 (2σ)) kJ mol−1. High-temperature drop solution calorimetry was conducted, yielding a calculated standard-state enthalpy of formation of soddyite of (−4045.4 ± 4.9 (2σ)) kJ · mol−1. The standard-state Gibbs free energy and enthalpy of formation yield a calculated standard-state entropy of formation of soddyite of (−1318.7 ± 21.7 (2σ)) J · mol−1 · K−1. The measurements and associated thermodynamic calculations not only describe the T = 298 K stability and solubility of soddyite, but they also can be used in predictions of repository performance through extrapolation of these properties to repository temperatures.  相似文献   

15.
Two pure zinc borates with microporous structure 3ZnO·3B2O3·3.5H2O and 6ZnO·5B2O3·3H2O have been synthesized and characterized by XRD, FT-IR, TG techniques and chemical analysis. The molar enthalpies of solution of 3ZnO·3B2O3·3.5H2O(s) and 6ZnO·5B2O3·3H2O(s) in 1 mol · dm−3 HCl(aq) were measured by microcalorimeter at T = 298.15 K, respectively. The molar enthalpies of solution of ZnO(s) in the mixture solvent of 2.00 cm3 of 1 mol · dm−3 HCl(aq) in which 5.30 mg of H3BO3 were added were also measured. With the incorporation of the previously determined enthalpy of solution of H3BO3(s) in 1 mol · dm−3 HCl(aq), together with the use of the standard molar enthalpies of formation for ZnO(s), H3BO3(s), and H2O(l), the standard molar enthalpies of formation of −(6115.3 ± 5.0) kJ · mol−1 for 3ZnO·3B2O3·3.5H2O and −(9606.6 ± 8.5) kJ · mol−1 for 6ZnO·5B2O3·3H2O at T = 298.15 K were obtained on the basis of the appropriate thermochemical cycles.  相似文献   

16.
This work reports on a novel chitosan–hematite nanotubes composite film on a gold foil by a simple one-step electrodeposition method. The hybrid chitosan–hematite nanotubes (Chi–HeNTs) film exhibits strong electrocatalytic reduction activity for H2O2. Interestingly, two electrocatalytic reduction peaks are observed at −0.24 and −0.56 V (vs SCE), respectively, one controlled by surface wave and the other controlled by diffusion process. The Chi–HeNTs/Au electrode shows a linear response to H2O2 concentration ranging from 1 × 10−6 to 1.6 × 10−5 mol L−1 with a detection limit of 5 × 10−8 mol L−1 and a sensitivity as high as 1859 μA μM−1 cm−2.  相似文献   

17.
We have investigated the diffusion properties for an ionic porphyrin in water. Specifically, for the {tetrasodium tetraphenylporphyrintetrasulfonate (Na4TPPS) + water} binary system, the self-diffusion coefficients of TPPS4− and Na+, and the mutual diffusion coefficients were experimentally determined as a function of Na4TPPS concentration from (0 to 4) · 10−3 mol · dm−3 at T = 298.15 K. Absorption spectra for this system were obtained over the same concentration range. Molecular mechanics were used to compute size and shape of the TPPS4− porphyrin. We have found that, at low solute concentrations (<0.5 · 10−3 mol · dm−3), the mutual diffusion coefficient sharply decreases as the concentration increases. This can be related to both the ionic nature of the porphyrin and complex associative processes in solution. Our experimental results are discussed on the basis of the Nernst equation, Onsager–Fuoss theory and porphyrin metal ion association. In addition, self-diffusion of TPPS4− was used, together with the Stokes–Einstein equation, to determine the equivalent hydrodynamic radius of TPPS4−. By approximating this porphyrin to a disk, we have estimated structural parameters of TPPS4−. These were found to be in good agreement with those obtained using molecular mechanics. Our work shows how the self-diffusion coefficient of an ionic porphyrin in water is substantially different from the corresponding mutual-diffusion coefficient in both magnitude and concentration dependence. This aspect should be taken into account when diffusion-based transport is modelled for in vitro and in vivo applications of pharmaceutical relevance.  相似文献   

18.
The speed of sound in {(1  x)CH4 + xN2} has been measured with a spherical acoustic resonator. Two mixtures with x = (0.10001 and 0.19999) were studied along isotherms at temperatures between 220 K and 400 K with pressures up to 20 MPa; a few additional measurements at p = (25 and 30) MPa are also reported. A third mixture with x = 0.5422 was studied along pseudo-isochores at amount-of-substance densities between 0.2 mol · dm−3 and 5 mol · dm−3. Corrections for molecular vibrational relaxation are discussed in detail and relaxation times are reported. The overall uncertainty of the measured speeds of sound is estimated to be not worse than ±0.02%, except for those measurements in the mixture with x = 0.5422 that lie along the pseduo-isochore at the highest amount-of-substance density. The results have been compared with the predictions of several equations of state used for natural gas systems.  相似文献   

19.
Diffusion coefficients of the Fe2(SO4)3)/water system at T = 298.15 K and at concentrations between 0.050 mol · dm−3 and 0.200 mol · dm−3 have been measured, using a conductimetric cell and an automatic apparatus to follow diffusion. The cell uses an open-ended capillary method. A conductimetric technique is used to follow the diffusion process by measuring the resistance of a solution inside the capillaries at recorded times. These data are discussed on the basis of the Onsager–Fuoss model. The diffusion of Fe2(SO4)3 is clearly affected by the Fe (III) hydrolysis. These data permit us to have a better understanding of the structure of such systems and the thermodynamic behaviour of ferric sulphate in different media.  相似文献   

20.
Catalytic reduction of CO2 (saturated in organic polar solvents, e.g. N,N-dimethylfomamide, containing Me4NX or NaBF4) was achieved at smooth gold electrodes and at glassy carbon electrodes galvanostatically capped with a thin layer of gold. Under these quite explicit conditions, very sharp reduction steps were observed near − 1.5 V vs. Ag/AgCl. With small cations listed above, an unexpected behavior was observed, a progressive electrode inhibition occurring upon several scans or after a fixed-potential electrolysis at E <  1.7 V. This phenomenon could be attributed to the insertion of CO2 into gold, leading to the formation of a thick iono-metallic multi-strata layer (less conducting than pure metal) that grows with the electrode charge. The formation of this new interface is due to the concur of three elements: transient CO2 anion radical, the metal, and rather small-sized cations (M+ = Na+ or TMA+), the three possibly associated in a form {Au-CO2,M+} apparently very reactive with oxygen, moisture, and with some organic π-acceptors. Upon multi-scans up to − 2.2 V, the thickness of formed layer progressively increases reaching more than 10 7 to 10 6 mol cm 2. Such multi-layers undergo decomposition in the anodic domain at about + 1.7 V liberating CO2 beforehand trapped in Au. Coulometric analyses demonstrated that insertion (cathodic) and release (anodic) steps are quite equivalent, which permits to consider this process as chemically reversible sequestration of carbon dioxide.  相似文献   

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