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1.
Modelling of proton and metal exchange in the alginate biopolymer   总被引:1,自引:0,他引:1  
Acid–base behaviour of a commercial sodium alginate extracted from brown seaweed (Macrocystis pyrifera) has been investigated at different ionic strengths (0.1≤I/mol l?1≤1.0) and in different supporting electrolytes (Et4NI, NaCl, KCl, LiCl, NaCl+MgCl2), with the aim of examining the influence of ionic medium on the proton-binding capacity and of quantifying the strength of interaction with light metal ions in the perspective of speciation studies in natural aqueous systems. Potentiometric ([H+]-glass electrode) and titration calorimetric data were expressed as a function of the dissociation degree (α) using different models (Henderson–Hasselbalch modified, Högfeldt three parameters and linear equations). The dependence on ionic strength of the protonation constants was taken into account by a modified specific interaction theory model. Differences among different media were explained in terms of the interaction between polyanion and metal cations of the supporting electrolytes. Quantitative information on the proton-binding capacity, together with the stabilities of different species formed, is reported. Protonation thermodynamic parameters, at α=0.5, are log K H=3.686±0.005, ΔG 0=?21.04±0.03 kJ mol?1, ΔH 0=4.8±0.2 kJ mol?1 and TΔS 0=35.7±0.3 kJ mol?1, at infinite dilution. Protonation enthalpies indicate that the main contribution to proton binding arises from the entropy term. A strict correlation between ΔG and TΔS was found, TΔS=?9.5–1.73 ΔG. Results are reported in light of building up a chemical complexation model of general validity to explain the binding ability of naturally occurring polycarboxylate polymers and biopolymers. Speciation profiles of alginate in the presence of sodium and magnesium ions, naturally occurring cations in natural waters, are also reported.  相似文献   

2.
Adsorption of the gadolinium from H2O and HCl solutions on the ion-exchange resin C100 is investigated. The experiments were carried out by varying the acidity of the liquid phase, the amount of sorbent, and the temperature. The maximal sorption of the ions Gd3+ is observed from the solution 0–0.2 M HCl under optimal conditions, the sorption reaches more than 99.5%. Sorption of Gd3+ on C100 from H2O solution occurs most intensively during the first 3 min then for 30 min the system smoothly comes to equilibrium. The maximal sorption capacity of the resin C100 amounted to 1.2 ± 0.1 mmol g?1. The thermodynamic parameters of sorption: ΔG = ? 24.20 kJ mol?1, ΔS = ? 90.27 J mol?1 K?1, ?H = ? 50.93 kJ mol?1 were evaluated. It is shown that the sorption of gadolinium on the ion-exchange resin C100 is described by models of kinetically pseudo-first and pseudo-second order. It is established that the Gd3+ sorption on the C100 resin is reversible second order chemical reaction.  相似文献   

3.
The thermodynamic activation parameters of hindered rotation of the CF3 group in the 4-nitrophenyltrifluoromethylsulfone radical anion in DMF were determined from the temperature dependence of the EPR line widths and spin density distributions calculated by the U-B3LYP method in the 6-31+G* basis set. In the range 293 > T > 199 K, the activation energy of hindered rotation E F depends on the temperature and changes in the range 9.67 < E F < 18.95 kJ·mol?1; the changes in the activation enthalpy and entropy are 7.23 < ΔH < 17.30 kJ·mol?1 and ?53.45 < ΔS < ?11.37 J·(mol·K)?1, respectively. Based on the suggested method for evaluating the inner product of the g tensor and the tensor of anisotropic hfi with the 14N nucleus for nitrobenzene radical anions in the liquid state we calculated the correlation time and determined the activation energy of rotational diffusion of the 4-nitrophenyltrifluoromethylsulfone radical anion in DMF, E r = 20.175±0.54 kJ·mol?1.  相似文献   

4.
Differential scanning calorimetry (DSC) was used to investigate the thermal behavior and non-isothermal crystallization kinetics of the Fe67Nb5B28 metallic glasses prepared by melt-spinning method. DSC traces exhibit that the crystallization takes place through a single exothermic reaction, and it processes a good thermal stability in thermodynamics. The activation energies for nucleation and grain growth processes were calculated to be 536 ± 22 and 559 ± 20 kJ mol?1 by Kissinger equation, respectively, and 551 ± 24 and 574 ± 20 kJ mol?1 by Ozawa equation, respectively. It means that the grain growth process is more difficult than the nucleation process. The variation of local Avrami exponent n(x) with crystallized fraction x demonstrates that the crystallization mechanism varies at different stages. The n(x) is larger than 2.5 at the initial stage of 0 < x < 0.3, implying a mechanism of diffusion-controlled three-dimensional growth with increasing nucleation rate. The n(x) decreases from 2.5 to 1.5 in the range of 0.3 < x < 0.65, suggesting that the crystallization belongs to three-dimensional nucleation and grain growth with decreasing nucleation rate. And n(x) lies between 1.0 and 1.5 in the range of 0.65 < x < 0.95, indicating that the crystallization corresponds to the growth of particles with an appreciable initial volume. Low-temperature annealing corresponds to the precipitation of α-Fe, Fe2B, and Fe23B6 phases, and further annealing leads to the formation of α-Fe, Fe2B, and FeNbB phases. The magnetic properties in relation to microstructure change of the Fe67Nb5B28 metallic glasses are discussed.  相似文献   

5.
Dimethylgold(III) complexes with 8-hydroxyquinoline Me2Au(Ox) (I) and 8-mercaptoquinoline Me2Au(Tox) (II) were synthesized and studied. Complex II obtained for the first time was identified from the elemental analysis, IR, 1H NMR, and mass spectrometry data. The thermal properties of complexes I, II in condensed state were investigated by thermography. The temperature dependences of the saturated vapor pressure over crystals were measured by the Knudsen effusion method with mass spectrometric recording of the gas phase composition and the thermodynamic characteristics of the sublimation process were determined: for I, log P[Torr] = (14.6 ± 0.3) ? (6.34 ± 0.10) × 103/(T, K), Δ H subl o = 121.2 ± 1.9 kJ?1, Δ S subl o = 224.1 ± 4.6 J mol?1 K?1 (the temperature interval under study 80–115°C); for II, log P [Torr] = (13.3 ± 0.2) ? (6.30 ± 0.09) × 103/(T, K), Δ H subl o = 120.5 ± 1.7 kJmol?1, ΔS subl o = 199.3 ± 3.0 J mol?1 K?1 (86–145°C).  相似文献   

6.
7.
The kinetics of 1,1-dimethylpropyl peroxy radicals recombination in polar solvents—water, methanol, and their mixtures—was studied by EPR spectroscopy in combination with the stopped-flow method, and the rate constants of this reaction were determined. Peroxyl radicals were generated by mixing solutions of Ce4+ sulfate and 1,1-dimethylpropyl hydroperoxide. The observed EPR signal of the peroxyl radical is a singlet with a g-factor of 2.015 ± 0.001, and a line width of ΔH = (1.36 ± 0.02) × 10?3 T for methanol and ΔH = (9.7 ± 0.2) × 10?4 T for water. The measured rate constants of (CH3)2C(O2·)CH2CH3 radical recombination at 298 K are 2kt = (3.9 ± 0.4) × 104 L mol?1 s?1 for water and 2kt = (5.2 ± 0.5) × 103 L mol?1 s?1 for methanol. A linear relationship between ln(2kt) and the Kirkwood function (ε?1)/(2ε + 1), where e is the dielectric constant of the medium, has been established, indicating an important role of nonspecific solvation in the recombination of tertiary peroxyl radicals.  相似文献   

8.
The heat capacities of 1-butyl-3-methylimidazolium lactate ionic liquids ([C4mim][Lact]) were measured with a highly accurate automatic adiabatic calorimeter over the temperature range from 79 to 406 K. And the experimental values of molar heat capacities were fitted to a polynomial equation using least square method in the appropriate temperature ranges. The standard molar heat capacity was determined to be 1734.46?±?5.12 J K?1 mol?1 at 298.15 K. The molar enthalpy and molar entropy of the transition were determined to be 15.575?±?0.045 and 64.44?±?0.14 J K?1 mol?1. Other thermodynamic properties, such as (HT???H298.15) and (ST???S298.15), were also calculated. Furthermore, when the temperature reaches 241.87 K, the strongest peaks appeared by analysis of the heat capacity curve. This phenomenon could be explained from the interionic interaction, which is the hydrogen bond between the anions and cations.  相似文献   

9.
Interaction of ammonia with H-MCM-22 zeolite (Si/Al = 24.5) was investigated by temperature-programmed desorption technique in order to obtain information on thermodynamics of the process. Average activation energy for desorption of ammonia from Brønsted acid sites of H-MCM-22 zeolite was estimated from the data obtained under conditions varying in heating rate and also flow rate of carrier gas. It resulted in value of E d = 127 kJ mol?1 for heat rate variation method, whereas flow rate variation led to E d value of 111 kJ mol?1. Obtained E d values are compared with those reported in the literature for other zeolitic materials and discussed in the broader context of zeolite acidity. Comparison of E d values estimated here for H-MCM-22 zeolite with corresponding data for other protonic zeolites shows that H-MCM-22 displays mediocre/lower activation energy for ammonia compared with other high-silica zeolites.  相似文献   

10.
A dimethylgold(III) compound with an acetate fragment [(CH3)2AuOCOCH3]2 has been synthesized. The complex was identified from the melting point, IR, 1H NMR, and mass spectrometry data. The temperature dependence of saturated vapor pressure over crystals has been measured and the thermodynamic parameters of sublimation have been determined by Knudsen’s effusion method with mass spectrometric measurements of the composition of the gas phase: ΔH subl = 100.87 kJ·mol?1, ΔS subl = 216.67 J·mol?1·K?1. The thermal behavior of the solid compound was investigated by differential thermal analysis. The compound was studied by X-ray diffraction. Crystal data for C8H18Au2O4: a = 12.214(5) Å, b = 14.307(3) Å, c = 7.6635(15) Å; β = 103.39(3)°, Z = 4, d calc = 2.917 g/cm3, space group P2(1)/c, R = 0.0261. The [(CH3)2AuOCOCH3]2 dimer complex with an Au...Au distance of 2.989 Å is the structural unit. The gold atom has a square plane environment of two carbon and two oxygen atoms; the Au-O distances vary from 2.118 Å to 2.139 Å. The molecules are arranged in chains linked by van der Waals interactions.  相似文献   

11.
A comparative electrooxidation of Eg in the alkaline solution was investigated over Pt, Pd and Au nanoparticle-modified carbon-ceramic electrode. The kinetic parameters of Eg oxidation, i.e., Tafel slope and activation energy (E a), were determined on the modified electrodes. The lowest E a value of 8.9 kJ mol?1 was calculated on Pt|CCE. In continuation, the reaction orders with respect to the Eg and NaOH concentrations on Pd|CCE were found to be 0.4–0.2 and 0.6, respectively. An adsorption equilibrium constant (b) of 22.36 M?1 and the adsorption Gibbs energy change (ΔG°) of ?7.7 kJ mol?1 were obtained on Pd|CCE. The chronopotentiometry (CP) and chronoamperometry (CA) results showed that Pd|CCE and then Au|CCE have better performance stability than Pt|CCE for Eg electrooxidation. Additionally, the electrochemical impedance spectroscopy (EIS) suggested faster electron-transfer kinetics on Pt than that on the Pd and Au electrocatalysts.  相似文献   

12.
The nanosized LiNiPO4 was successfully synthesized by a solid-state reaction between the new Ni3(PO4)2·8H2O precursor and Li3PO4 at 700 °C in air atmosphere. The formation of LiNiPO4 was generated via three thermal decomposition steps. The samples were characterized by Fourier transform infrared, X-ray diffraction, scanning electron microscopy, atomic absorption/atomic emission spectrophotometers, and thermogravimetric/differential thermal gravimetric/differential thermal analysis techniques. The activation energy (Eα) values of the three steps were calculated by Vyazovkin method and determined to be 90.39?±?5.79, 197.81?±?7.46, and 308.66?±?12.03 kJ mol?1, respectively. The average Eα values from this method are very close to Eα from KAS method. The most probable mechanism functions g(α) of three steps were evaluated by using the masterplots method and found to be the F1/3 (first step), F3/2 (second step), and D4 (final step), respectively. The pre-exponential factors (A) values of three steps were obtained based on the Eα and g(α). The kinetic triplet parameters of the formation of LiNiPO4 from the new precursor are reported in the first time.  相似文献   

13.
The chemisorption of CO2 by aqueous-hindered amines has been investigated experimentally and theoretically. Negative-ion ESI–MS analysis of solutions containing a sterically hindered amine and a source of 13CO2 reveals peaks corresponding to [M–H + 45]?. These ions readily lose 45 Da when subjected to collisional activation, and together with other key fragments confirms the generation of the 13C-labelled carbamate derivatives. The thermochemistry of the two key capture reactions: $$2.{\text{amine }} + {\text{ CO}}_{ 2} { \leftrightarrows }{\text{amine}} - {\text{CO}}_{ 2}^{ - } + {\text{ amine}} - {\text{H}}^{ + } {\kern 1pt} \quad 1:{\text{carbam}}$$ $${\text{amine }} + {\text{ CO}}_{ 2} + {\text{ H}}_{ 2} {\text{O}}{ \leftrightarrows }{\text{HCO}}_{ 3}^{ - } + {\text{ amine}} - {\text{H}}^{ + } \quad 2:{\text{ bicarb}}$$ at 298 K was modelled using composite chemistry methods, CCSD(T), DFT, and SM8 free energies of solvation. The aqueous reaction free energies (ΔG 298) for reaction 1 are predicted to be more negative than ΔG 298 for reaction 2 when amine = ammonia, 2-aminoethanol (MEA), 2-amino-2-methyl-1-propanol (AMP), 2-amino-2-hydroxymethyl-propane-1,3-diol (tris), and 2-piperidinemethanol (2-PM). For AMP, tris, and 2-PM, activation free energies ΔG 298 ? for reaction 1 (SM8 + CCSD(T)/6-311 ++G(d,p)//M08-HX/MG3S: 38–67 kJ mol?1) are smaller than the corresponding values for 2 (109–113 kJ mol?1). For 2-PM, the computed carbamate ΔG 298 ? (38 kJ mol?1) is comparable to the MEA value (45 kJ mol?1), whereas the primary amines with tertiary alpha carbons have slightly larger values (60–70 kJ mol?1). The organic amine values are much lower than the value for ammonia (93 kJ mol?1). The results indicate CO2 chemisorption proceeds via a carbamate intermediate for all aqueous primary and secondary amines. Hindered carbamates are susceptible to further chemical transformations following their formation.  相似文献   

14.
The research shows theoretical calculations on the thermodynamics of digestion/gasification processes where glucose is used as a surrogate for biomass. The change in Enthalpy (?H) and Gibbs Free Energy (?G) is used to obtain the Attainable Region (AR) that shows the overall thermodynamic limits for digestion/gasification from 1 mol of glucose. Gibbs Free Energy and Enthalpy (GH) plots were calculated for the temperature range 25–1500 °C. The results show the effect of temperature on the AR for the processes when water is in both liquid and gas states using 25 °C, 1 bar as the reference state. The AR results show that the production of CO, H2, CH4 and CO2 are feasible at all temperatures studied. The minimum Gibbs Free Energy becomes more negative from ?418.68 kJ mol?1 at 25 °C to ?3024.34 kJ mol?1 at 1500 °C while the process shifts from exothermic (?141.90 kJ mol?1) to endothermic (1161.80 kJ mol?1) for the respective temperatures. Methane and carbon dioxide are favoured products (minimum Gibbs Free Energy) for temperatures up to about 600 °C, and this therefore includes Anaerobic Digestion. The process is exothermic below 500 °C, and thus Anaerobic Digestion requires heat removal. As the temperature continues to increase, hydrogen production becomes more favourable than methane production. The production of gas is endothermic above 500 °C, and it needs a supply of heat that could be done, either by combustion or by electricity (plasma gasification). The calculations show that glucose conversion at temperatures around 700 °C favours the production of carbon dioxide and hydrogen at minimum G. Generally, the results show that the gas from high-temperature gasification (>~800 °C) typically carries the energy mainly in syngas components CO and H2, whereas at low-temperature gasification (<500 °C) the energy is carried in CH4. The overall analysis for the temperature range (25–1500 °C) also suggests a close relationship between biogas production/digestion and gasification as biogas production can be referred to as a form of low-temperature gasification.  相似文献   

15.
Leachate samples from a sanitary landfill of Araraquara city and composting usine of Vila Leopoldina, São Paulo, Brazil were lyophilized to remove the water content. TG/DTG curves at different heating rates were recorded. The second step of the thermal decomposition of leachate from the Araraquara landfill (CB1), from the composting usine from Vila Leopoldina (CB2) from the organic phase extracted (FO) and aqueous phase (FA) were all kinetically evaluated using the non-isothermal method.By Flynn-Wall isoconversional method the following values were obtained: E=234±3.65 kJ mol?1 and logA=29.7±0.58 min?1 for CB1; E=129±1.66 kJ mol?1 and logA=11.8±0.10 min?1 for CB2; E=51.6±1.35 kJ mol?1 and logA=6.09±0.09 min?1 for FO and E=76.91±6.33 kJ mol?1 and logA=8.88±0.7 min?1 for FA with 95% confidence level. Applying the procedures of Málek and Koga, SB kinetic model (?esták-Berggren) is the most appropriate to describe the decomposition of CB1, CB2, FO and FA.  相似文献   

16.
Thermal decomposition measurements for lithium borohydride (LiBH4) are performed at non-isothermal and non-equilibrium conditions by means of differential thermal analysis (DTA). A simplified alternative procedure is introduced for evaluating thermodynamic and kinetic parameters simultaneously using a single set of measurements. Rate constant (k) and enthalpy (ΔH = ?102.1 ± 0.7 kJ mol?1 LiBH4) are archived. Temperature dependence for activation energy (E a) is found taking advantage of Guggenheim–Arrhenius method; the mean activation energy is $ \overline{E}_{a} $  93.9 ± 0.9 kJ mol?1 LiBH4 in the range of heating rate β 1–50 K min?1.  相似文献   

17.
Molecular structure, conformational stability and vibrational wave numbers for the rotational isomers of 2-furoyl chloride and 3-furoyl chloride have been computed using the B3LYP method with the 6-311++G(d,p) basis set. From computations, 2-furoyl chloride was predicated to exist predominantly in cis conformation with cistrans rotational barrier 40.40 kJ·mol?1, and 3-furoyl chloride was predicated to exist predominantly in the trans conformation with cistrans rotational barrier 30.17 kJ·mol?1. The effects of solvents on the conformational stability of all the molecules in nine different solvents (heptane, chloroform, tetrahydrofuran, dichloroethane, acetone, ethanol, methanol, dimethylsulfoxide and water) were investigated. The integral equation formalism of the polarizable continuum model was used for all solution phase computations. The vibrational wave numbers and the corresponding vibrational assignments of the molecules in C1 symmetry were examined and the simulated infrared spectra of the molecules are reported. The geometrical parameters, highest occupied and lowest unoccupied molecular orbitals, Infrared intensities, and molecular electrostatic potentials results are reported.  相似文献   

18.
A mixed oxide-covered mesh electrode composed of NiCo2O4 (MOME-NiCo2O4) was prepared on a stainless-steel substrate using thermal decomposition (slow-cooling rate method). Surface, bulk and electrochemical properties of MOME were studied using different techniques, namely scanning electron microscopy (SEM), X-ray diffraction (XRD), cyclic voltammetry (CV) with determination of the electrochemical porosity (?) and morphology factor (φ) parameters, quasi-stationary polarisation curves (PC) and electrochemical impedance spectroscopy (EIS). SEM images revealed a good coverage of the metallic wires by a compact oxide layer (absence of cracks). XRD analysis confirmed the formation of the spinel NiCo2O4 with the presence of NiO. The ‘in situ’ surface parameters denoted as ? and φ exhibited values of 0.39 and 0.33, respectively, revealing that the electrochemically active surface area is mainly confined to the ‘outer/external’ surface regions of the oxide layer. The PC was characterised by two Tafel slopes distributed in the low (b 1 = 46 mV dec?1) and high (b 2 = 59 mV dec?1) overpotential domains. The corresponding apparent exchange current densities were j 0(1) = (3.43 ± 0.11) × 10?6 A cm?2 and j 0(2) = (6.70 ± 0.08) × 10?6 A cm?2, respectively. The EIS study accomplished in the low-overpotential domain revealed a Tafel slope (b 1) of 51 mV dec?1. According to the spin-trapping reaction using N,N-dimethyl-p-nitrosoaniline (RNO), the MOME-NiCo2O4 electrode exhibited good performance for the generation of weakly adsorbed hydroxyl radicals (HO?) during the OER in electrolyte-free water.  相似文献   

19.
A novel peroxy group-containing silane coupling agent was synthesized and anchored on the surface of titanium dioxide nanoparticles (nano-TiO2) to form an immobilized-initiator-modified nano-TiO2 species. In this study, the kinetic parameters of the peroxy group-containing silane were tested and assessed using DSC. The pre-exponential factor (Ad) was 8.973?×?108 and the activation energy (Ea) was 80.736 kJ mol?1. Moreover, the empirical Arrhenius equation was determined to be ln Kd?=???80.736/RT?+?ln(8.973?×?108). To obtain continuous polymers, acrylonitrile (AN) and methyl methacrylate (MMA) were polymerized using the novel peroxy group-containing silane and FeSO4 as an initiator system. The number average molecular weights (Mn of PAN?=?3×104 and Mn of PMMA?=?1.4?×?105) and polydispersity indexes (PDI of PAN?=?2.76 and PDI of PMMA?=?1.65) were determined by GPC. It was suggested that the redox initiation system can generate highly reactive species on the surfaces of inorganic nanoparticles. The nano-TiO2-grafted polymers were successfully obtained.  相似文献   

20.
A new high-nitrogen complex [Cu(Hbta)2]·4H2O (H2bta = N,N-bis-(1(2)H-tetrazol-5-yl) amine) was synthesized and characterized by elemental analysis, single crystal X-ray diffraction and thermogravimetric analyses. X-ray structural analyses revealed that the crystal was monoclinic, space group P2(1)/c with lattice parameters a = 14.695(3) Å, b = 6.975(2) Å, c = 18.807(3) Å, β = 126.603(1)°, Z = 4, D c = 1.888 g cm?3, and F(000) = 892. The complex exhibits a 3D supermolecular structure which is built up from 1D zigzag chains. The enthalpy change of the reaction of formation for the complex was determined by an RD496–III microcalorimeter at 25 °C with the value of ?47.905 ± 0.021 kJ mol?1. In addition, the thermodynamics of the reaction of formation of the complex was investigated and the fundamental parameters k, E, n, \( \Updelta S_{ \ne }^{{{\uptheta}}} \), \( \Updelta H_{ \ne }^{{{\uptheta}}} \), and \( \Updelta G_{ \ne }^{{{\uptheta}}} \) were obtained. The effects of the complex on the thermal decomposition behaviors of the main component of solid propellant (HMX and RDX) indicated that the complex possessed good performance for HMX and RDX.  相似文献   

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