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1.
The specific adsorption of sulfate ions on Cr2O3 was studied by a radiotracer technique using 35S-labelled sulfuric acid in low concentrations (c<10–3 mol dm–3) in the presence of a large excess of perchlorate supporting electrolyte. The pH and concentration dependence were determined.
It was found that the extent of adsorption is determined by the protonation of the surface sites, similar to other oxides
studied previously. A comparison of Cr2O3 and Al2O3 in this respect shows that the protonation of the former takes place at significantly lower pH values than that of the latter.
The indirect radiotracer study of the adsorption of chromate on Al2O3 was carried out using labelled sulfate ions as indicator species. The results obtained show that the adsorption strength
of chromate species is very low in comparison to sulfate ions and a regular Langmuir-like adsorption behaviour can be observed.
It is believed that the observations presented may contribute to a better understanding of the behaviour of surface layers
with a mixed oxide content.
Electronic Publication 相似文献
2.
G. Horányi 《Journal of Solid State Electrochemistry》2002,6(7):463-467
The specific adsorption of sulfate and chloride ions on powdered CuO was studied by radiotracer techniques in acidified of
0.5 mol dm–3 NaClO4 supporting electrolyte. It was found that the pH and concentration dependence of the adsorption of labelled sulfates could
be determined over a wide pH range (2.0≤pH≤7.0), despite the gradual dissolution of the copper oxide. No specific adsorption
was found at pH≥7.0. It was postulated that the specific adsorption was preceded by the protonation of the CuO surface. No
reliable relationships were found for labelled chlorides, owing to the relatively high desorption rate of the surface complexes
formed in the sorption process. The apparent adsorbability of sulfate ions was significantly higher than that of the chloride
ions, as shown by the results of competitive adsorption of the two species. This observation was in agreement with the postulated
lower desorption rate of the surface complex formed with sulfates than that of species formed with chlorides.
Electronic Publication 相似文献
3.
Izabela Witoska Stanisaw Karski Joanna Gouchowska 《Reaction Kinetics and Catalysis Letters》2007,90(1):107-115
Hydrogenation of nitrate (NO3
−) in water was studied with 0.8 ×10−3–3.2 ×10−3 mol/dm3 of reactant in the temperature range of 293–313 K over palladium promoted Ag catalysts. Pd-Ag catalysts with a low ratio
of Ag/Pd were characterized by high efficiency in the reduction of nitrates. The degradation of nitrates followed approximately
first order decay and the estimated apparent activation energy was about 4 kJ/mol. 相似文献
4.
Nai-Xing Wang Lei Wang Wei Jiang Yue-Zhen Ren Zhi-Kun Si Xun-Xing Qiu Gao-Ying Du Ping Qi 《Analytical and bioanalytical chemistry》1998,361(8):821-824
Norfloxacin (NFX) is proposed as reagent for the derivative spectrophotometric determination of neodymium, holmium and erbium
in mixed rare earths. The absorption spectra of 4f electron transitions of the systems of neodymium, holmium and erbium complexes
with norfloxacin in presence of cetylpyridinium chloride were studied by normal and derivative spectra. The absorption bands
found normally at 575 nm for neodymium, 450 nm for holmium and 523 nm for erbium were enhanced markedly. Using the second
derivative spectrum, Beer’s Law is obeyed from 5.0 × 10–5∼ 2.5 × 10–4 mol dm–3 for neodymium, holmium and erbium. The relative standard deviations are 1.0, 1.4 and 1.1% for 6.9 × 10–5 mol dm–3 of neodymium, 6.1 × 10–5 mol dm–3 of holmium and 6.0 × 10–5 mol dm–3 of erbium, respectively. A method for the direct determination of neodymium, holmium and erbium in mixtures of rare earth
elements with good accuracy and selectivity, is described.
Received: 18 December 1997 / Revised: 23 February 1998 / Accepted: 26 February 1998 相似文献
5.
Nai-Xing Wang Lei Wang Wei Jiang Yue-Zhen Ren Zhi-Kun Si Xun-Xing Qiu Gao-Ying Du Ping Qi 《Fresenius' Journal of Analytical Chemistry》1998,361(8):821-824
Norfloxacin (NFX) is proposed as reagent for the derivative spectrophotometric determination of neodymium, holmium and erbium
in mixed rare earths. The absorption spectra of 4f electron transitions of the systems of neodymium, holmium and erbium complexes
with norfloxacin in presence of cetylpyridinium chloride were studied by normal and derivative spectra. The absorption bands
found normally at 575 nm for neodymium, 450 nm for holmium and 523 nm for erbium were enhanced markedly. Using the second
derivative spectrum, Beer’s Law is obeyed from 5.0 × 10–5∼ 2.5 × 10–4 mol dm–3 for neodymium, holmium and erbium. The relative standard deviations are 1.0, 1.4 and 1.1% for 6.9 × 10–5 mol dm–3 of neodymium, 6.1 × 10–5 mol dm–3 of holmium and 6.0 × 10–5 mol dm–3 of erbium, respectively. A method for the direct determination of neodymium, holmium and erbium in mixtures of rare earth
elements with good accuracy and selectivity, is described.
Received: 18 December 1997 / Revised: 23 February 1998 / Accepted: 26 February 1998 相似文献
6.
G. Horányi 《Reaction Kinetics and Catalysis Letters》1996,59(2):211-217
The adsorption of Cl– ions on rhodium black layer (rhodized electrodes) was studied by radiotracer technique at low Cl– ion concentrations (c10–5 mol dm–3) in 1 mol dm–3 H2SO4 supporting electrolyte. The specific adsorption of Cl– ions was treated in terms of partition between solution phase and electrodeposited Rh black layer. The potential dependence of the partition coefficient is determined. 相似文献
7.
The specific adsorption of sulfate ions on powdered Cr was studied by a radiotracer technique using 35S-labeled sulfuric acid in low concentration (c<10–3 mol dm–3) in the presence of a large excess of perchlorate supporting electrolyte. The pH and concentration dependence were determined. On the basis of a comparison of the results obtained for Cr2O3 and Cr, it can be assumed that, similar to other metals, the overall sorption behavior of Cr is determined by the protective oxide film present on the surface. 相似文献
8.
The kinetics of oxidation of l-Cysteine by pyridinium chlorochromate (PCC) was studied at 0.1–0.3 mol dm−3 HClO4 in the range 25–40 °C. The reaction exhibits first order dependence with respect to PCC and fractional order in cysteine.
The increase in the oxidation rate with acidity suggests the involvement of a protonated chromium(VI) species in the rate-determining
step. Cysteic acid is identified as the product of oxidation. A suitable mechanism involving the formation of a complex is
proposed. The activation parameters of the rate-determining step are computed using the linear least squares method and the
values of E
a and ΔS
# are found to be 46.0 ± 2.0 KJ mol−1 and −38.0 ± 3.2 JK−1 mol−1 respectively. 相似文献
9.
Guru C. Pradhan 《Transition Metal Chemistry》1992,17(5):443-445
The kinetics of the base hydrolysis ofcis-[Co(en)2(RNH2)-(SalH)]2+ (R=Me or Et; SalH=HOC6H4CO
2
−
) were investigated in aqueous ClO
4
−
in the 0.004–0.450 mol dm−3 [OH−] range, I=0.50 mol dm−3 at 30–40°C. The phenoxide species is hydrolysed via [OH−]-independent and [OH−]-dependent paths, the latter being first order in [OH−]. The high rate of alkali-independent hydrolysis of the phenoxide species is associated with high ΔH≠ and ΔS≠ values, in keeping with the SNICB mechanism involving an amido conjugate base generated by the phenoxide-assisted NH-deprotonation
of the coordinated amine. The [OH−]-dependent path also involves the conventional SN1 CB mechanism. The rate constant, k1, for the SNICB path exhibits a steric acceleration with the increasing size of the non-labile alkylamine, whereas the rate
constant, k2, for the SN1CB path shows a reverse trend.
TMC 2578 相似文献
10.
The kinetics of the acid hydrolysis of chromatopenta-amminecobalt(III) ion has been studied using a stopped-flow method over
the acidity range 0.01≤[H+]<-1.0 mol dm−3 and 20.0°C<-ϕ<-30.0°C at ionic strengths 0.5 and 1.0 mol dm−3 (LiNO3). These studies reveal that the complex is first protonated and subsequently hydrolysed to the aquapentaammine cobalt(III)
ion. The rate constants for the hydrolysis of the mono and diprotonated species at 25°C are 0.83±0.01 s−1 and (1.60±0.02)×104 mol−1 dm−3 s−1, respectively.
TMC 2664 相似文献
11.
The chemical properties of the gravitation dust sediment particles depend on their source. Two samples of the gravitation
dust sediment have been investigated. The first sample, collected in locality Košice – Vel’ká Ida, near by U.S. Steel Ltd.
(a metallurgy plant), represents the metallurgy industry pollutants. The second sample, collected in Košice city, represents
the urban dust. Dust sediments particles create a non-homogeneous system. For this reason, the particles size distribution
has been studied. On the base of the obtained experimental results one sample was divided into two approximately same mass
fractions. The mineralogical composition of the dust particles matrix was determined by DTA, XRD, and SEM-EDS analyses. The
total content of the chosen trace risk elements was defined by various AAS methods. The physical–chemical forms of elements
in the dust sediment are characterised by different mobility and biotoxicity. The single-step extraction was used for the
isolation of various element forms. 1 mol · dm−3 NH4NO3, 0.05 mol · dm−3 EDTA, and 2 mol · dm−3 HNO3 were used as extraction reagents. The content of the elements in extracts was determined by the FAAS method. 相似文献
12.
The differential pulse (dp) polarograms of thiamine in neutral aqueous solutions exhibited six peaks at low depolarizer concentration
(⋦10−4 mol dm−3) and only three peaks at concentrations ≥10−3 mol dm−3. Only one of these was found to correspond to the diffusion-controlled reduction of this compound at the dme and this was
shown to be an irreversible two-electron process. The kinetic parameters derived from the dp polarograms were found to be
in good agreement with those calculated from classical polarograms and were:E
1/2=−1·261 Vvs SCE,an
a=0·54 andD≈3·5×10−6 cm2 sec−1 for 10−3 mol dm−3 thiamine in 0·1 mol dm−3 acetate buffer (pH 6·5). The reduction product has been identified as dihydrothiamine. The effect of pH on the dpp of thiamine
was studied in the pH range 0–7. In the pH region 5·5 to 7·0 only one peak attributable to the B1
+ form of thiamine is present. In the pH region 3·5–5·5 another dpp peak attributable to the protonated form (B1H2+) of thiamine was also observed. At pHs less than 3 only one peak was observed which could be attributed to the doubly protonated
form (B1 H2
3+) of thiamine. Surfactants like triton-X-100 and CTABr were found to inhibit the electroreduction of thiamine due to the strong
adsorption of these compounds on the dme. Thiamine itself was found to have an inhibitory effect on its own electroreduction,
although to a smaller extent. 相似文献
13.
Yuzhong Zhang Guiying Jin Wangxing Cheng 《Journal of Solid State Electrochemistry》2006,10(4):260-263
The stable electroactive thin film of rhein has been investigated by cyclic voltammetry and electrochemical impedance spectroscopy.
Electrochemical impedance spectroscopy of the electrodeposited film derived from rhein indicated the electrode reaction was
kinetically controlled in the region of higher frequency, the charge transfer resistance was 2.6×103 Ω cm2 and capacitance value was 13.2 μF cm2 . The electrodeposited film derived from rhein exhibited a good electrocatalytic activity for myoglobin (Mb) reduction. In
0.30 mol dm−3 H2SO4solution, the catalysis currents were proportional to the concentrations of Mb over the range of 1.5×10−7–1.3×10−5 mol dm−3. The detection limit is 1.0×10−7 mol dm−3 (S/N=3). The relative standard deviation is 4.8% for eight successive determinations of 5.0×10−7 mol dm−3 Mb. 相似文献
14.
The influence of TiOSO4 and free sulphuric acid concentrations in the starting solution on the degree of titanyl sulphate conversion to hydrated
titanium dioxide and post-hydrolytic sulphuric acid was studied. Titanyl sulphate solution, an intermediate product in the
commercial preparation of titanium dioxide pigments by sulphate route, was used. It was found that the degree of hydrolysis
markedly depends on the studied parameters. The lower was the content of TiOSO4 in the starting solution, the higher conversion was achieved. The degree of hydrolysis at the final stage varied between
81 % (420 g TiOSO4 dm−3, 216 g H2SO4 dm−3) and 92 % (300 g TiOSO4 dm−3, 216 g H2SO4 dm−3). The same relation was obtained when changing the concentration of free H2SO4 in the starting solution. The degree of hydrolysis at the final stage varied between 49 % (261 g H2SO4 dm−3, 340 g TiOSO4 dm−3) and 96 % (136 g H2SO4 dm−3, 340 g TiOSO4 dm−3). The particle size of the obtained hydrated titanium dioxide (HTD) also depends on the initial solution composition.
Presented at the 34th International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 21–25 May
2007. 相似文献
15.
Rates of oxidation of dimethyl sulphoxide (DMSO) by HOBr producedin situ from sodium bromate-sodium bisulphite reagent have been studied iodometrically in aqueous medium. The order in [DMSO] is
one when [DMSO] < 001 mol dm-3, fractional when [DMSO] is between 0.01 and 0.5mol dm-3 and zero when (DMSO) > 0.5 mol dm-3. Different rate laws are operative under these three conditions though HOBr is the effective oxidizing species in all the
cases. A mechanism involving an intermediate four-membered cyclic transition state between DMSO and HOBr (formation constantK), which decomposes in a slow step with a rate constant(k) has been proposed. Thermodynamic parameters for the adduct formation step and activation parameters for the first-order decomposition
of the adduct step have been evaluated in the temperature range 308–323 K. Activation parameters have also been determined
while the orders in [DMSO] are unity and zero. The reaction product has been identified as dimethyl sulphone (DMSO2). 相似文献
16.
The removal of Ce(III) from aqueous solutions by hydrous manganese oxide (HMO) and hydrous stannic oxide (HSO) was studied
as a function of concentrations (10−2−10−7 mol·dm−3) and pH (1.2–10.0) by using the radiotracer technique. The effects of co-ions and irradiation of HMO and HSO were also studied.
The uptake of Ce(III) fitted well with the Freundlich adsorption isotherm. No significant desorption of pre-adsorbed Ce(III)
in the studied temperature range (303–333 K) indicates that both the solids may be good adsorbents for the removal of Ce(III). 相似文献
17.
G. Horányi 《Journal of Solid State Electrochemistry》2000,4(3):153-158
The specific adsorption of anions (HSO4
−, Cl−) present in low concentration (c < 10−3 mol dm−3) was studied by radiotracer techniques in the course of the reduction of dichromate (chromate) species in 1 mol dm−3 HClO4 supporting electrolyte. In accordance with the results of preliminary studies reported earlier, enhancement of the anion
adsorption was found, induced by some adsorbed intermediates of the reduction process. Potential dependence of the induced
adsorption and its correlation with the reduction rate was investigated. The role of adsorption competition between various
anions is discussed. It is concluded that study of the induced anion adsorption could be a tool for the investigation of the
sorption of intermediates formed in the course of the reduction.
Received: 3 May 1999 / Accepted: 10 June 1999 相似文献
18.
An electrochemical quartz crystal microbalance (EQCM) is employed for monitoring the growth of poly(neutral red) films on
platinum in the electrolytic solution containing 5.0 mmol dm−3 neutral red, 0.3 mol dm−3 H2SO4, and 0.5 mol dm−3 Na2SO4. The in situ measurement of the frequency changes of the EQCM reveals that both the adsorption/desorption of neutral red
and the formation of poly(neutral red) film can be observed together with anion sorption/desorption during the redox transformation
of the polymer, and that the polymerization rate of neutral red increases slowly before the 11th cycle and then increases
quickly with increasing number of potential cycles.
Published in Russian in Elektrokhimiya, 2007, Vol. 43, No. 3, pp. 284–289.
The text was submitted by the authors in English. 相似文献
19.
Arun K. Prasad P. Giridhar Visalakshi Ravindran V. Muralidharan 《Journal of Solid State Electrochemistry》2001,6(1):63-68
Zinc-cobalt alloy electrodeposits offer enhanced corrosion protection to steel, compared to zinc deposits. A near neutral
zinc-cobalt alloy sulfate bath was developed. In the absence of β-naphthol and sodium lauryl sulfate (SLS), only a light grey
and non-uniform deposit was obtained. Addition of boric acid yielded a grey and uniform deposit. To obtain the grey uniform
alloy deposit, the optimum bath composition was: 0.5 M ZnSO4, 0.5 M CoSO4, 40 g/L H3BO3, 0.865 g/L SLS and 0.345 g/L β-naphthol. The current efficiency for alloy deposition was 50% in the current density range
0.5–2.5 A/dm2. X-ray fluorescence studies on the alloy deposit formed on steel revealed 58–75% zinc on the surface. Anodic stripping voltammetric
studies were carried out on zinc-cobalt alloy films formed on glassy carbon to identify the phases formed in the alloy. Zn-Co
alloy film dissolution peaks suggested the existence of β, β1 and γ phases of the alloy.
Electronic Publication 相似文献
20.
Wiesława Ferenc Agnieszka Walków-Dziewulska Maria Wojciechowska J. Sarzyński 《Journal of Thermal Analysis and Calorimetry》2006,86(2):359-364
Physico-chemical properties of 4-chloro-2-nitrobenzoates of Co(II),
Ni(II), and Cu(II) were studied. The complexes were obtained as mono- and
trihydrates with a metal ion to ligand ratio of 1:2. All analysed 4-chloro-2-nitrobenzoates
are polycrystalline compounds with colours depending on the central ions:
pink for Co(II), green for Ni(II), and blue for Cu(II) complexes. Their thermal
decomposition was studied only in the range of 293–523 K, because it
was found that on heating in air above 523 K 4-chloro-2-nitrobenzoates decompose
explosively. Hydrated complexes lose crystallization water molecules in one
step and anhydrous compounds are formed. The final products of their decomposition
are the oxides of the respective transition metals. From the results it appears
that during dehydration process no transformation of nitro group to nitrite
takes place. The solubilities of analysed complexes in water at 293 K are
of the order of 10–4–10–2
mol dm–3. The magnetic moment values of Co2+,
Ni2+ and Cu2+ ions in
4-chloro-2-nitrobenzoates experimentally determined at 76–303 K change
from 3.89 to 4.82 μB for Co(II) complex, from 2.25
to 2.98 μB for Ni(II) 4-chloro-2-nitrobenzoate,
and from 0.27 to 1.44 μB for Cu(II) complex. 4-chloro-2-nitrobenzoates
of Co(II), and Ni(II) follow the Curie–Weiss law. Complex of Cu(II)
forms dimer. 相似文献