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1.
IR optical properties of Pd nanoparticles with different size and aggregation state were studied in the current paper. The dispersed Pd nanoparticles () stabilized with poly(N-vinylpyrrolidone) (PVP) were synthesized by the seeding growth method, in which the seeds were formed step by step through reducing H2PdCl4 with ethanol. The dispersed Pd nanoparticles of much large size () were grown from the by keeping the colloid of undisturbed for 150 days at room temperature around 20 °C. The aggregates of () were prepared through an agglomeration process induced during a potential cyclic scanning between −0.25 V and 1.25 V for 20 min at a scan rate of 50 mV s−1. Scanning electron microscope (SEM) patterns confirmed such aggregation of . Fourier transform infrared (FTIR) spectroscopy together with CO adsorption as probe reaction was employed in studies of IR optical properties of the prepared Pd nanoparticles. The results demonstrated that CO adsorbed on films substrated on CaF2 IR window or glassy carbon (GC) electrode yielded two strong IR absorption bands around 1970 cm−1 and 1910 cm−1, which were assigned to IR absorption of CO bonded on asymmetric and symmetric bridge sites, respectively. Similar IR bands were observed in spectra of CO adsorbed on films, except the IR bands were much weak, whereas CO adsorbed on film produced an IR absorption band near 1906 cm−1, and an anomalous IR absorption band whose direction has been completely inverted around 1956 cm−1. The direction inversion of the IR band of CO bonded to asymmetric bridge sites on was ascribed to the interaction between Pd nanoparticles inside the aggregates. Based on FTIR spectroscopic and cyclic voltammetric results, the aggregation mechanism of Pd nanoparticles from to has been suggested that the agglomeration of Pd nanoparticles was driven by the alteration of electric field across electrode-electrolyte interface, when the PVP stabilizer was stripped via oxidation during cyclic voltammetry.  相似文献   

2.
Tar elimination and hot-gas conditioning in thermochemical conversion processes, i.e. thermal gasification, pyrolysis of heterogeneous materials involved two main classes of catalysts and/or additives: metallic and mineral oxides. This communication focused on the experimental kinetic data on catalytic steam cracking of vaporized toluene ( space-time ) as a tar-derived species and/or Volatile Organic Compound (VOC). Toluene (C7H8) has been chosen as a model formula for reactive tar-derived one-ring species determined from tar constituents. Gaseous product distribution data were obtained at atmospheric pressure steam pyrolysis temperature range of 923-1223 K and GHSV 1200-2300 Nm3 (m3 h)−1. The overall catalytic pyrolysis of toluene over a commercial available metal based catalyst NiMo/γ-Al2O3 was compared to the pyrolysis in presence of basic non-metallic mineral additives, i.e. Norwegian (Norsk Hydro) dolomitic magnesium oxide [MgO], Swedish low surface quicklime [CaO], and calcined dolomite [CaMg(O)2]. The operational conditions were applied without internal or external mass-transfer limitations. Kinetics for the pyrolysis could be described by first-order reactions for all the studied additives. The influence of hydrogen gas (30 vol%, ) and water vapor () in vaporized toluene cracking runs over low surface quicklime [CaO] was determined. A mechanistic model of the Langmuir-Hinshelwood type describing toluene decomposition was also developed.  相似文献   

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The self-diffusion coefficients of water and ions were used to study the physical (tortuosity) and electrostatic interactions of counterions in poly(perfluorosulfonic) acid membrane (Nafion-117) matrix. The self-diffusion coefficients of water were measured in the water swollen Nafion-117 membrane with Zn2+, Ca2+, Sr2+, and Fe2+ counterions by analyzing the experimental exchange rates between tritium tagged water (HTO) in membrane and equilibrating water. In order to study the effects of equilibrating solution, the HTO-desorption rate profiles between the membrane samples in H+ or Cs+ forms and equilibrating solution containing CsCl or HCl (0.25 mol/L) were measured. It was observed that the HTO-exchange rate profile was slower in case of membrane sample in Cs+-from equilibrated with salt/acid solution than that equilibrated with deionized water in same ionic form. However, HTO-exchange rate profile did not alter in case of H+-form of membrane on equilibration with salt or acid solution. The variation of ln  with polymer volume function Vp/(1 − Vp), where Vp is polymer volume fraction, indicated that: (i) in the membrane with multivalent counterions was lower than that reported for membrane with monovalent counterions at same Vp, and (ii) the linear trends observed in variation of ln  with Vp/(1 − Vp) for multivalent and monovalent counterions were significantly different. The values of in membrane normalized with at Vp = 0 were taken as an estimate of the tortuosity factor for self-diffusion of ions in the membrane matrix. The self-diffusion coefficients of ions reported in the literature along with tortuosity factor obtained from in the corresponding ionic forms of the membrane were analyzed to obtain the charge (Zi) independent electrostatic interaction parameter g(φ) of monovalent and divalent ions in the membrane. This analysis indicated that g(φ) also vary exponentially as a function of Vp/(1 − Vp) irrespective of charge on counterions. In order to study the influence of Vp on diffusional transport rates of Na+ and Cs+ ions in membrane, a permeation experiment was carried out using H+-form of membrane having high water volume fraction. The diffusional transport rates of Cs+ and Na+ in H+-form of membrane were found to be similar indicating that the water volume fraction in membrane has strong influence on the parameters that govern the diffusion across the Nafion-117 membrane.  相似文献   

5.
This work presents a study on the electrochemical properties of AmCl3 in a molten LiCl-KCl eutectic, at a temperature range of 733-833 K. Transient electrochemical techniques, such as cyclic voltammetry and chronopotentiometry, on inert metallic tungsten working electrode have been used to investigate the reduction mechanism of Am3+ ions. The results show that Am3+ is reduced to Am metal by a two-step mechanism corresponding to the Am3+/Am2+ and Am2+/Am0 transitions. Formal standard potentials of Am3+/Am2+ ( versus Cl2/Cl at 733 K) and Am2+/Am0 ( versus Cl2/Cl at 733 K) redox couples as well as diffusion coefficients of Am3+ and Am2+ (2.4 × 10−5 and 1.15 × 10−5 cm2 s−1 at 733 K, respectively) have been calculated at three different temperatures. In the studied range of temperature, the DAm3+/DAm2+ ratio was found to be around 2. In addition, thermodynamic properties have been calculated for Am3+ () and Am2+ () and compared to thermodynamic reference data in order to estimate activity coefficients (Am3+ = 4.7 × 10−3 and Am2+ = 2.7 × 10−2 at 733 K) in the molten LiCl-KCl eutectic.  相似文献   

6.
《Polymer》2005,46(25):11322-11329
Poly(3-mesityl-2-hydroxypropyl methacrylate-co-N-vinyl-2-pyrrolidone) P(MHPMA-co-VP) was synthesized in 1, 4-dioxane solution using benzoyl peroxide (BPO) as initiator at 60 °C. The copolymer was characterized by 1H 13C NMR, FT-IR, DSC, TGA, size exclusion chromatography analysis (SEC) and elemental analysis techniques. According to SEC, the number-average molecular weight (Mn), weight-average molecular weight (Mw) and polydispersity index (PDI) values of PMHPMA-co-VP were found to be 58,000, 481,000 g/mol and 8.26, respectively. According to TGA, carbonaceous residue value of PMHPMA-co-VP was found to be 6% at 500 °C. Also, some thermodynamic properties of PMHPMA-co-VP such as the adsorption enthalpy, ΔHa, molar evaporation enthalpy, ΔHv, the sorption enthalpy, , sorption free energy, , sorption entropy, , the partial molar free energy, , the partial molar heat of mixing, , at infinite dilution was determined for the interactions of PMHPMA-co-VP with selected alcohols and alkanes by inverse gas chromatography (IGC) method in the temperature range of 323-463 K. According to the specific retention volumes, , the weight fraction activity coefficients of solute probes at infinite dilution, , and Flory-Huggins interaction parameters, between PMHPMA-co-VP-solvents were determined in 413-453 K. According to and , selected alcohols and alkanes were found to be non-solvent for PMHPMA-co-VP at 413-453 K. The glass transition temperature, Tg, of the PMHPMA-co-VP found to be 370 and 363 K, respectively, by IGC and DSC techniques, respectively.  相似文献   

7.
LiMn2O4 thin films were deposited on Au substrates by pulsed laser deposition (PLD). The Li-ion chemical diffusion coefficients of the films, , were measured by cyclic voltammetry (CV), galvanostatic intermittent titration technique (GITT), potentiostatic intermittent titration technique (PITT), and electrochemical impedance spectroscopy (EIS). It was found that the values by CV and PITT were in the order of 10−13 cm2 s−1, and those by EIS and GITT were in the range of 10−13 to 10−11 and 10−14 to 10−11 cm2 s−1, respectively. These data were compared with the previously reported values.  相似文献   

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A gel polymer electrolyte (GPE) was prepared using tetra(ethylene glycol) diacrylate monomer, benzoyl peroxide, and (). The LiCoO2/GPE/graphite cells were prepared and their electrochemical properties were evaluated at various current densities and temperatures.The viscosity of the precursor containing the tetra(ethylene glycol) diacrylate monomer was around . The ionic conductivity of the gel polymer electrolyte at 20°C was around . The gel polymer electrolyte had good electrochemical stability up to vs. Li/Li+. The capacity of the LiCoO2/GPE/graphite cell at rate was 63% of the discharge capacity at rate. The capacity of the cell at −10°C was 81% of the discharge capacity at 20°C. Discharge capacity of the cell with gel polymer electrolyte was stable with charge-discharge cycling.  相似文献   

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The normal potential of the Ce(IV)/Ce(III) redox couple was determined by square wave voltammetry (SWV) at different temperatures in solutions with a constant ratio [CO32−]/[HCO3] ≈10 for high ionic strengths (3.29 mol dm−3 at 4.39 mol dm−3): varies from 259.5 to 198.0 mV/S.H.E. in the 15-50 °C range. Linear variations were found for versus (RT/F)ln(mCO32−), leading to the stoichiometry, Ce(CO3)68− for the Ce(IV) limiting complex. But the slopes of these linear variations were actually found in the range 1.8-1.9, not exactly 2. This was interpreted as dissociation of the Ce(IV) limiting complex following the reaction: Ce(CO3)56− + CO32− → Ce(CO3)68− and as dissociation of the Ce(III) limiting complex following the reaction: Ce(CO3)33− + CO32− → Ce(CO3)45−; for which maximum possible values of log10 KIV,6 and log10 KIII,4 were estimated via fitting in the 15-50 °C temperature range (log10 KIV,6 = 0.42 (0.97) and log10 KIII,4 = 0.88 (7.00) at 15 °C (50 °C). The normal potential was found to decrease linearly with T, these variations correspond to , with T0 = 298.15 K and . The apparent diffusion coefficient of Ce(IV) was determined by direct current polarography (DCP), cyclic voltammetry (CV) and square wave voltammetry. It was found to depend on the ionic strength and to be proportional to T.  相似文献   

12.
The effect of iron on the precipitation behaviour of nickel powder was investigated. Reduction experiments were conducted on a 0.5 L laboratory autoclave fitted with a Teflon reaction beaker and a double impeller configuration consisting of an upper axial impeller and lower Rushton turbine. Reduction was conducted in the presence of a morphology modifier at a temperature between 180 and and 2800 kPa pressure using a synthetic nickel ammine sulphate solution (, free NH3:Ni2+ and (NH4)2SO4:Ni2+ molar ratios of 2.0-2.1 and 2.2, respectively). Nickel seed was used to initiate reduction and iron was added to the reduction solution as ferrous sulphate solution (acidified to pH 2.5 to prevent oxidation) to give a reduction solution with Fe2+ concentration of 6, 20 and 200 mg/L. The effect of iron was investigated by studying the evolution of the moments, volume or mass moment mean D(4.3), number based mean size , nickel depletion rate and population balance in the absence of sampling between batch reductions. Iron was found to act as a growth promoter and nucleation agent through reversible adsorption and hydrolysis on the surface of the seed particles. Growth was preferentially favoured over nucleation up to a Fe2+ concentration of 6 mg/L, thereafter the extent of nucleation increased with increasing Fe2+ concentration up to 200 mg/L. Nucleation and growth promotion in the presence of high shear rates gave rise to rapid aggregation, which ceased at a critical size of approximately and in the presence of iron and without. However, the sharp increase in the D(4.3) towards the end of the cycle and the general decrease in surface area shows that aggregation of larger particles plays a major role in size enlargement. Comparison of the scanning electron microscopy (SEM) micrographs of the powder with undesirable morphology produced in industrial practice and that produced in the laboratory in the presence of iron showed that iron was one of the factors responsible for the production of powder with undesirable morphology. Based on these laboratory scale experiments, iron levels in reduction solutions should not exceed 6 mg/L for effective control of particle morphology.  相似文献   

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Jianhua Huang  Zhaofeng Mao 《Polymer》2006,47(8):2928-2932
The effect of nanoparticles on the dynamic and configurational properties of a single polymer chain has been studied by using dynamic Monte Carlo simulation. An attractive potential, ε, is considered between fixed nanoparticles and polymer beads. The diffusion coefficient of the polymer D remains constant for weak interactions, i.e. small β=−ε/kBT, and then gradually drops to zero at a critical value . However, the mean square end-to-end distance 〈R2〉 shows a different behavior with an increase in the attractive interaction. 〈R2〉 decreases at small β and reaches a minimum at , then goes up slowly and at last saturates at strong interaction. The values and scale with the concentration of nanoparticles. Interesting findings are: (1) a chain has its minimum size before the chain stops its diffusion, and (2) a chain continues its configuration adjustment even for .  相似文献   

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The precipitation of different forms of magnesium carbonate has been studied at temperatures between 25 and and at a partial pressure of CO2 between 1 and 100 bar. These conditions are relevant for mineral carbonation applications. Precipitation was triggered by the supersaturation created by mixing Na2CO3 solutions in equilibrium with a CO2 atmosphere with MgCl2 solutions. Experiments were monitored using attenuated total reflection Fourier transform infrared (ATR-FTIR) and Raman spectroscopy as well as a focused beam reflectance measurement (FBRM) probe and a turbidimeter. Solubility and supersaturation were calculated using the software package EQ3/6. Solids were identified using X-ray diffraction (XRD) analysis and scanning electron microscope (SEM) images. At and , only the hydrated carbonate nesquehonite (MgCO3·3H2O) precipitates, as it has previously been observed. Solutions undersaturated with respect to nesquehonite did not form any precipitates in experiments lasting 16 h. Induction times increased with decreasing supersaturation with respect to nesquehonite. At and , hydromagnesite ((MgCO3)4·Mg(OH)2·4H2O) was formed which transformed within 5-15 h into magnesite (MgCO3). Solutions undersaturated with respect to brucite (Mg(OH)2) did not form any precipitates in experiments lasting 19 h. At and , direct formation of magnesite and, at elevated levels of supersaturation, the co-precipitation of magnesite and hydromagnesite has been observed. In the latter case, hydromagnesite transformed within a few hours into magnesite. Solutions undersaturated with respect to hydromagnesite did not form any precipitates in experiments lasting 20 h.  相似文献   

18.
Dimitri R. Kioussis 《Polymer》2005,46(22):9342-9347
Ion exchange systems for the removal of nutrient pollutants, even at extremely low concentrations, from wastewater effluents are a major environmental need. This work reports on the features of batch sorption processes for the ultimate removal and recovery of reactive phosphorus, nitrogen, and sulfur anions from aquaculture production wastewater effluents. The sorbent used was a crosslinked polyamine (PAA·HCl) polymeric hydrogel. The PAA·HCl hydrogels were prepared by chemically crosslinking aqueous solutions of linear PAA·HCl chains with epichlorohydrin (EPI). The nutrient anion binding capacity of the gels was studied as a function of various processing parameters. Lab scale batch and experiments showed maximum anion removal, from aquaculture wastewater, with regard to by 99%, by 70%, and by 95%. diffusivities of 16, 10, and 8×10−6 cm2/s were measured at pH levels of 5.5, 7.0, and 8.5.  相似文献   

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Specific selectivity toward different heavy metal ions could be introduced into self-assembled monolayers (SAMs) by ion imprinting. In the mixed solution, good response toward mercury ions could be obtained on mercury ions imprinted SAMs, the copper ions imprinted SAMs presented good selectivity toward copper ions, while on lead ions imprinted SAMs, significantly higher insertion of lead ions than mercury and copper ions were observed. Linear calibration plots were obtained for each heavy metal ion and the regression equations were: [Hg(II)]/(10−6 M), [Cu(II)]/(10−6 M) and [Pb(II)]/(10−6 M) for mercury, copper and lead ions, respectively. The detection limits were determined to be: 1.46×10−8 M for Hg(II), 3.73×10−8 M for Cu(II) and 4.34×10−8 M Pb(II). The decreases in current response for mercury, copper and lead ions in the presence of 100-fold interferential ions were: 3.37%, 9.16% and 7.60%, respectively. Acceptable recoveries were obtained in mixed solutions at both high and low concentrations.  相似文献   

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