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1.
《Ultrasonics sonochemistry》2014,21(2):716-721
The physical or mechanical effects induced by ultrasound were investigated through the viscosity change in degradation of polymers. The viscosity change was observed with polyethylene oxide in both aqueous and benzene solution; while polystyrene in only benzene solution. The frequency of ultrasound in these experiments varies from 20 kHz to 1 MHz, under a constant dissipated power. The viscosity ratio and the apparent degradation rate were obtained as a function of the irradiation frequency. From the analysis of these experiments, the mechanical effects are found to slow down above 100 kHz when the frequency increases. In case of the analysis of solution viscosity, since this method yields the same apparent results in both aqueous and benzene solutions, our study propose an alternative simple, cost effective method to quantify the mechanical effects in sonochemistry. 相似文献
2.
The electrochemical CO2 reduction reaction (CO2RR) on polycrystalline copper (Cu) electrode was performed in a CO2-saturated 0.10 M Na2CO3 aqueous solution at 278 K in the absence and presence of low-frequency high-power ultrasound (f = 24 kHz, PT ~ 1.23 kW/dm3) in a specially and well-characterized sonoelectrochemical reactor. It was found that in the presence of ultrasound, the cathodic current (Ic) for CO2 reduction increased significantly when compared to that in the absence of ultrasound (silent conditions). It was observed that ultrasound increased the faradaic efficiency of carbon monoxide (CO), methane (CH4) and ethylene (C2H4) formation and decreased the faradaic efficiency of molecular hydrogen (H2). Under ultrasonication, a ca. 40% increase in faradaic efficiency was obtained for methane formation through the CO2RR. In addition, and interestingly, water-soluble CO2 reduction products such as formic acid and ethanol were found under ultrasonic conditions whereas under silent conditions, these expected electrochemical CO2RR products were absent. It was also found that power ultrasound increases the formation of smaller hydrocarbons through the CO2RR and may initiate new chemical reaction pathways through the sonolytic di-hydrogen splitting yielding other products, and simultaneously reducing the overall molecular hydrogen gas formation. 相似文献
3.
Li2CO3 modified carbon microbead composites (LCO/CMB-T) with different covering amount are prepared by solvent evaporation and dipping method. LiCH3COO are first used as lithium source, which can provide a precise control of Li2CO3 amount through varying dipping times or solution concentration. The morphology, structure, and covering amount are characterized by means of X-ray diffraction (XRD), scanning electron microscope (SEM), and atomic absorption spectrometer (AAS). The dipping process can produce the samples with better surface coverage, more uniform coating, and higher Li2CO3 crystallinity, while the appropriate amount of Li2CO3 can help to decrease initial irreversible capacity and improve cell performance. Here, the sample with 1.07 % Li2CO3 prepared by dipping method shows the highest initial discharge capacity of 353.7 mAh g?1 and coulombic efficiency of 89.5 %. The capacity retention is up to 82.1 % after 30 cycles. 相似文献
4.
V. N. Solkan G. M. Zhidomirov M. Ya. Mel’nikov 《Russian Journal of Physical Chemistry B, Focus on Physics》2010,4(5):705-708
Ab initio quantum-chemical calculations of the (CF3CO2H2+…3O2) and (CF3CO2−…3O2) complexes were performed by the MP2 method. It was found that these complexes were characterized by low complex formation
energies, of 2.97 and 1.72 kcal/mol, respectively. According to the MP2(full)/6-311++G(d, p) calculation data, the bridge stabilization of oxygen by linking with both the CF3CO2H2+ cation and CF3CO2− anion is much more favorable energetically. A study of the potential energy surface of the joint molecular system (CF3CO2H2+…3O2…CF3CO2−) shows that proton experiences activationless transfer from the cation to the 3O2 molecule accompanied by electron transfer from the CF3COO− anion. An analysis of spin density distribution shows that two radicals are stabilized in the (CF3CO2….OOH….O=C(OH)CF3) complex in the triplet state observed on the potential energy surface. 相似文献
5.
The present work investigates the effectiveness of application of low intensity ultrasonic irradiation for the intensification of enzymatic depolymerization of aqueous guar gum solution. The extent of depolymerization of guar gum has been analyzed in terms of intrinsic viscosity reduction. The effect of ultrasonic irradiation on the kinetic and thermodynamic parameters related to the enzyme activity as well as the intrinsic viscosity reduction of guar gum using enzymatic approach has been evaluated. The kinetic rate constant has been found to increase with an increase in the temperature and cellulase loading. It has been observed that application of ultrasound not only enhances the extent of depolymerization but also reduces the time of depolymerization as compared to conventional enzymatic degradation technique. In the presence of cellulase enzyme, the maximum extent of depolymerization of guar gum has been observed at 60 W of ultrasonic rated power and ultrasonic treatment time of 30 min. The effect of ultrasound on the kinetic and thermodynamic parameters as well as the molecular structure of cellulase enzyme was evaluated with the help of the chemical reaction kinetics model and fluorescence spectroscopy. Application of ultrasound resulted in a reduction in the thermodynamic parameters of activation energy (Ea), enthalpy (ΔH), entropy (ΔS) and free energy (ΔG) by 47%, 50%, 65% and 1.97%, respectively. The changes in the chemical structure of guar gum treated using ultrasound assisted enzymatic approach in comparison to the native guar gum were also characterized by FTIR. The results revealed that enzymatic depolymerization of guar gum resulted in a polysaccharide with low degree of polymerization, viscosity and consistency index without any change in the core chemical structure which could make it useful for incorporation in food products. 相似文献
6.
The effect of low-frequency high-power ultrasound on hydrocarbon-based ionomers, cation exchange sulfonated phenylated polyphenylene (sPPB-H+) and anion exchange hexamethyl-p-terphenyl poly(benzimidazolium) (HMT-PMBI), was studied. Ionomer solutions were subjected to ultrasonication at fixed ultrasonic frequencies (f = 26 and 42 kHz) and acoustic power (Pacous = 2.1 – 10.6 W) in a laboratory-grade ultrasonication bath, and a probe ultrasonicator; both commonly employed in catalyst ink preparation in research laboratory scale. Power ultrasound reduced the polymer solution viscosity of both hydrocarbon-based ionomers. The molecular weight of sPPB-H+ decreased with irradiation time. Changes in viscosity and molecular weight were exacerbated when ultrasonicated in an ice bath; but reduced when the solutions contained carbon black, as typically used in Pt/C-based catalyst inks. Spectroscopic analyses revealed no measurable changes in polymer structure upon ultrasonication, except for very high doses, where evidence for free-radical induced degradation was observed. Ionomers subjected to ultrasound were used to prepare catalyst layers and membrane electrode assemblies (MEA)s. Despite the changes in the ionomer described above, no significant differences in electrochemical performance were found between MEAs prepared with ionomers pre-subjected to ultrasound and those that were not, suggesting that fuel cell performance is tolerant to ionomers subjected to ultrasound. 相似文献
7.
The present work investigates the contribution of asphaltene aggregation to bitumen viscosity subject to ultrasound irradiation. A West-African bitumen with a viscosity of 12043 cP at room temperature was sonicated at low (38 kHz) and mild frequency (200 kHz) under controlled gas environment including air, nitrogen (N2) and carbon dioxide (CO2). The rheology of the bitumen, asphaltene content analyses as well as spectral studies were conducted. Herein was found that sonicating the bitumen at 200 kHz under air-environment reduces the initial viscosity up to 2079 cP, which was twice larger than that obtained when a low frequency was used. In respect of the gas environment, it was shown that ultrasound irradiation under N2 environment could lower the bitumen viscosity up to 3274 cP. A positive correlation between the asphaltene content and the viscosity reduction was established. The results from the spectral analyses including Fast Fourier Infrared and the observations from Scanned Electron Microscope were consistent with the rheological studies and led to the argument that the viscosity reduction results from either the scission of long chain molecules attached to the aromatic rings (when the applied frequency was altered under fixed gas environment) or the self-aggregation of asphaltene monomers (when gas environment was changed at fixed frequency). 相似文献
8.
In this study, a high-molecular-weight polysaccharide PL-N isolated from the alkaline extract of Phellinus linteus mycelia was degraded by ultrasound. Results showed that ultrasound treatment at different ultrasonic intensities decreased the intrinsic viscosity and molecular weight of PL-N, as well as narrowed the molecular weight distribution. A larger reduction in intrinsic viscosity and molecular weight was caused by a higher ultrasonic intensity. The degradation kinetics model was fitted to (1/Mt − 1/M0) = k·t, and the reaction rate constant (k) increased with increasing ultrasonic intensity. Ultrasound degradation did not change the primary structure of PL-N, and scanning electron microscopy analysis indicated that the morphology of the original PL-N was different from that of degraded PL-N fractions. Antioxidant activity assays in vitro indicated that the degraded PL-N fraction with low molecular weight had stronger hydroxyl radical scavenging capacity and higher TEAC and FRAP values. 相似文献
9.
The removal of organic compounds from aqueous solutions has been tackled by a novel integrated heterogeneous system. The efficacy of the different systems has been assessed using Fenton-like processes (H2O2/Fe2O3–SBA-15) and phenol as model pollutant. Sono- and photo-Fenton processes separately applied as well as combined systems were studied in order to evaluate of possible beneficial effects on the use of coupled systems. The sequential system evidences an enhancement in terms of phenol and TOC conversions compared to the ultrasound or UV–light irradiation processes. A total phenol degradation and ca. 90% TOC reduction are achieved by sequentially ultrasound followed by UV–visible light irradiation. These effects are ascribed cavitation effect of ultrasound producing a reduction of particle size that provides a higher amount of available active sites due to an increased surface area for the subsequent photo-Fenton system. These encouraging results open new paths for the existing oxidation technologies for potable water and wastewater treatment. 相似文献
10.
V. I. Gerasimova A. A. Antoshkov Yu. S. Zavorotny D. A. Lemenovskii 《Journal of Applied Spectroscopy》2012,79(2):203-210
Optical properties (photoluminescence and absorption) of Eu(bta)3(B) n (B = H2O or 1,10-phenanthroline) polycrystalline powders and fluoroacrylate polymers (FAPs) impregnated with these compounds using supercritical CO2 (SC CO2) were investigated. It was established that impregnation of Eu(bta)3phen into the FAPs using an SC CO2 solution was difficult to achieve. The type of B (ancillary ligand) and the polymer matrix were shown to influence the temperature quenching of photoluminescence of Eu3+ ions in the range 25–100°C. A comparative analysis of quantum yields (λex = 300 and 380 nm) and photoluminescence decay times (λex = 337.1 nm) for Eu(bta)3B n and for Eu(bta)3B n -doped FAPs was performed. 相似文献
11.
Ling Zhu Qin Li Jiayan Li Xiangdong Liu Jian Meng Xueqiang Cao 《Journal of nanoparticle research》2007,9(2):261-268
A simple and efficient method has been established for the selective synthesis of mesoporous and nanorod CeVO4 with different precursors by sonochemical method. CeVO4 nanorod can be simply synthesized by ultrasound irradiation of Ce(NO3)3 and NH4VO3 in aqueous solution without any surfactant or template. While mesoporous CeVO4 with high specific surface area can be prepared with Ce(NO3)3, V2O5 and NaOH in the same way. Mesoporous CeVO4 has a specific surface area of 122 m2 g−1 and an average pore size of 5.2 nm; CeVO4 nanorods have a diameter of about 5 nm, and a length of 100–150 nm. The ultrasound irradiation and ammonia in the reactive
solution are two key factors in the formation of such rod-like products. X-ray diffraction (XRD), transmission electron microscopy
(TEM), X-ray photoelectron spectroscopy (XPS), thermogravimetric (TG) and differential thermal analyses (DTA), UV/vis absorption
spectroscopy and Brunauer–Emmett–Teller (BET) were applied for characterization of the as-prepared products. 相似文献
12.
如今碳捕获和储存技术已得到了迅速发展以减少对环境的二氧化碳排放. 研究发现胺基有机分子溶剂能有效地吸收二氧化碳,并通过氢键和二氧化碳形成的碳酸氢盐相互作用. 最近,实验报道了一种1,3-二苯基胍溶液,在室温条件下能捕获环境中的二氧化碳并将其转化为有价值的化学品. 然而,1,3-二苯基胍分子在溶液状态下如何与二氧化碳相互作用的机理仍不清楚. 在这项工作中,利用分子动力学方法模拟研究了溶液相中1,3-二苯基胍分子与二氧化碳的复杂作用细节. 模拟结果表明,质子化的1,3-二苯基胍分子和碳酸氢根离子倾向通过不同的双氢键模式作用形成稳定的复合物. 精确的密度泛函方法计算表明,这些双氢键复合物在热力学上相当稳定. 本研究有助于理解溶液相中1,3-二苯基胍分子中催化转化二氧化碳的机理. 相似文献
13.
The solvation of carbon dioxide in sea water plays an important role in the carbon circle and the world climate. The salting-out/salting-in mechanism of CO2 in electrolyte solutions still remains elusive at molecule level. The ability of ion salting-out/salting-in CO2 in electrolyte solution follows Hofmeister Series and the change of water mobility induced by salts can be predicted by the viscosity B-coefficients. In this work, the chemical potential of carbon dioxide and the dynamic properties of water in aqueous NaCl, KF and NaClO4 solutions are calculated and analyzed. According to the viscosity B-coefficients, NaClO4 (0.012) should salt out the carbon dioxide relative to in pure water, but the opposite effect is observed for it. Our simulation results suggest that the salting-in effect of NaClO4 is due to the strongly direct anion-CO2 interaction. The inconsistency between Hofmeister Series and the viscosity B-coefficient suggests that it is not always right to indicate whether a salt belongs to salting-in or salting-out just from these properties of the salt solution in the absence of solute. 相似文献
14.
Several olivine phosphates were investigated in the last years as cathode materials for secondary lithium ion batteries. Among
these compounds, LiFe
x
Co1 − x
PO4 solid solutions might be interesting candidates because they should combine the high potential value of Co3+/Co2+ (higher than 4.5 V vs Li+/Li) with the relatively high charge–discharge rate of LiFePO4. Solid solutions were prepared by solid-state route and characterised by X-ray powder diffraction, cyclic voltammetry, impedance
spectroscopy and the Hebb–Wagner method. The results show that also low amount of iron induces high electronic conductivity
in the solid solutions. 相似文献
15.
《Ultrasonics sonochemistry》2014,21(3):1108-1116
The present work deals with achieving viscosity reduction in polymer solutions using ultrasound-based treatment approaches. Use of simple additives such as salts, or surfactants and introduction of air at varying flow rates as process intensifying parameters have been investigated for enhancing the degradation of polyvinyl pyrrolidone (PVP) using ultrasonic irradiation. Sonication is carried out using an ultrasonic horn at 36 kHz frequency at an optimized concentration (1%) of the polymer. The degradation behavior has been characterized in terms of the change in the viscosity of the aqueous solution of PVP. The intrinsic viscosity of the polymer has been shown to decrease to a limiting value, which is dependent on the operating conditions and use of different additives. Similar extent of viscosity reduction has been observed with 1% NaCl or 0.1% TiO2 at optimized depth of horn and 27 °C, indicating the superiority of titanium dioxide as an additive. The combination of ultrasound and ultraviolet (UV) irradiation results in a significantly faster viscosity reduction as compared to the individual operations. A kinetic analysis for the degradation of PVP has also been carried out. The work provides a detailed understanding of the role of the operating parameters and additives in deciding the extent of reduction in the intrinsic viscosity of PVP solutions. 相似文献
16.
V2O5-SiO2 hybrid material was fabricated by heat-treating a mixture of H2SiO3 and V2O5. SEM, TEM, XRD, and N2 isotherm analyses were performed to characterize the morphology and structure details of the as-prepared V2O5-SiO2. The possibility of using the as-prepared V2O5-SiO2 as anode material for aqueous lithium-ion batteries was investigated. Potentiostatic and galvanostatic results indicated that the intercalation/de-intercalation of Li+ in this material in aqueous electrolyte was quasi-reversible. It was also found that a discharge capacity of up to 199.1 mAh g?1 was obtained at a current density of 50 mA g?1 in aqueous solution of 1 M Li2SO4, a value which is much higher than the available reported capacities of vanadium (+5) oxides in aqueous electrolytes. 相似文献
17.
The optical technology based on Mach-Zehnder interferometry was successfully applied to a high-pressure liquid CO2 and water system to measure CO2 solution density. Experiments were carried out at a pressure range of from 5.0 to 12.5 MPa, temperatures from 273.25 to 284.15 K, and CO2 mass fraction in solution up to 0.061. CO2 solution density data were obtained from two sets of experiments. These data were calculated through the fringe shifts induced by density changes inside of the high-pressure vessel, which were directly recorded during the experiments, and a modified version of Lorentz-Lorenz formulation. The experimental results indicated that the density ratio of CO2 solution to that of pure water at the same pressure and temperature is monotonically linear with the CO2 concentration in the solution. The slope of this linear function, calculated by the experimental data fitting, is 0.275. 相似文献
18.
Hui Ming Zhang Jing Bing Liu Hao Wang Wen Xiong Zhang Hui Yan 《Journal of nanoparticle research》2008,10(5):767-774
Pure tetragonal and monoclinic phases BiVO4 were prepared from aqueous Bi (NO3)3 and NaVO3 solutions by a rapid microwave-assisted method that employed accurate controlling of microwave irradiation time and power.
The highly crystalline phase converted irreversibly from tetragonal to monoclinic BiVO4 with gradually elongated irradiation time gradually, which is further proved by X-ray diffraction, UV–vis and Raman measurements.
These variations of phase structures led to different photocatalytic properties under visible light. 相似文献
19.
The excitonic absorption spectra of thin films of ferroelectric Cs2CdI4 and Cs2ZnI4 solid solutions are studied for the first time. It is found that, within the whole range of molar concentrations x, the spectra of Cs2(Cd1 − x
Zn
x
)I4 comprise two bands that originate from the bands of the two compounds. It is shown that the exciton transfer occurs most
efficiently between the tetrahedrons CdI4 and ZnI4 along the b axis of the crystal. Unusual behavior of the concentration with regards to the maxima of long-wavelength excitonic bands
E
m
(x) agrees well with the developed theory that takes into account dependence on x of the matrix element of the intertetrahedron exciton transfer and that is similar to the theory of Davydov’s splitting in
molecular crystals. 相似文献
20.
Due to the tunability in mass transfer, solvation and solubility, gas-expanded liquids show advantages over traditional organic solvents in many characteristics. Ultrasonication is a commonly used method to promote heat and mass transfer. The introduction of ultrasonic technology into the gas-expanded liquid system can promote the polymerization of polymer monomers, enhance extraction efficiency, and control the growth size of nanocrystals, etc. Although acoustic cavitation has been extensively explored in aqueous solutions, there are still few studies on cavitation in organic liquids, especially in gas-expanded liquid systems. In this article, the development of cavitation bubble cloud structure in CO2-expanded N, N-dimethylformamide (DMF) was observed by a high-speed camera, and the cavitation intensity was recorded using a spherical hydrophone. It was found that the magnitude of the transient cavitation energy was not only related to input power, but also closely related to CO2 content. The combination of ultrasound (causing a rapid alternation of gas solubility) and gas-expanded liquid system (causing a decrease in viscosity and surface tension of liquids) is expected to provide a perfect platform for high-speed mass transfer. 相似文献