Fixation of nitrogen with cavitation

The sonochemical fixation of nitrogen to ammonia was investigated by sonolysis of liquids with nitrogen/hydrogen gas mixtures passing through them. The maximum rate (4 nmol min-1 W-1) was found in water irradiated with 900 kHz ultrasound with gas of a mole fraction 0.6 of nitrogen and the lowest temperature (278 K). Some traces of ammonia were found in the absence of external hydrogen gas, as hydrogen atoms are also formed in sonolysis of water. Thermodynamic calculations indicate that some ammonia formation should occur at the "hot spot" temperatures present in collapsing cavities. The decrease in the rate with bulk temperature suggests that kinetics, rather than thermodynamics, is the limiting condition for sonochemical synthesis of ammonia. Ammonia can be produced in organic media, but at a lower rate. A substantial portion of the ammonia in the experiments with alkanes exited with the sparging gas and was trapped in a dilute HCl solution.     

Nonlinear ultrasonic nature of organic liquid and organic liquid mixture

Based on Jacobson's molecular free length theory in liquids and the relationship between ultrasonic velocity and the molecular free length in organic liquids, this paper deduces the equations for pressure coefficient and temperature coefficient of ultrasonic velocity and nonlinear acoustic parameter B/A in both of organic liquid and organic liquid binary mixtures. These nonlinear acoustic parameters are evaluated against the measured results and data from other sources. The equations reveal the connections between the nonlinear acoustic parameters and some internal structural of the medium or mixtures e.g. the sizes of molecule, several thermodynamic physical parameters and outside status e.g. condition of pressure and temperature of the liquid or liquid mixture. With the equations the nonlinear acoustic parameter B/A of organic liquid binary mixtures, which is impossible to know without the nonlinear acoustic parameter B/A of the tow components before, can be calculated based on the structural and physical parameters of organic liquid and organic liquid binary mixtures.     

Sonochemistry in non-aqueous liquids

The chemical effects of high-intensity ultrasound on organic liquids are reported. In order to probe the factors which affect sonochemistry in non-aqueous solvents, two very different chemical dosimeters have been used: radical trapping by diphenylpicrylhydrazyl and decomposition of Fe(CO)₅. In both cases, good correlation is found between the logarithm of the sonochemical rate and the solvent vapour pressure. This result is justifiable in terms of the cavitation ‘hot-spot’ mechanism of sonochemistry. Thus, decreasing solvent vapour pressure increases the intensity of cavitational collapse, the peak temperature reached during such collapse, and, consequently, the rates of sonochemical reactions.     

Sonochemical polymerization of benzene derivatives: the site of the reaction

Sonochemical polymerization of benzene and halogen-substituted benzenes has been studied. The difference of absorption spectra of polymerization products can be explained qualitatively using bond energies of the primary products. The relative rate constant of the polymerization reaction is apparently proportional to the inverse of the vapour pressure of the liquids. Using this relation, we analysed the relative rate constant of the polymerization in benzene/chrolobenzene mixtures. From this, we conclude that sonochemical polymerization proceeds in the vapour phase of a bubble.     

Sonochemical synthesis of liquid-encapsulated lysozyme microspheres

Liquid-encapsulated lysozyme microspheres were successfully synthesized using a sonochemical method. The encapsulation of four different liquids, namely, sunflower oil, tetradecane, dodecane and perfluorohexane on the formation, stability and morphology of the lysozyme microspheres was studied. Among the four different liquids used for encapsulation, perfluorohexane-filled microspheres were found to be most stable in the dried state with a narrow size distribution. In order to explore the possibility of encapsulating biofunctional molecules (e.g., drugs) within these microspheres, liquids containing a fluorescent dye (Nile red) were encapsulated and the ultrasound-induced release of these dye-loaded liquids was studied. The fluorescence data for the liquid-filled lysozyme microspheres demonstrated the potential use of the sonochemical technique for synthesizing these “vehicles” for the encapsulation and the controlled delivery of dyes, flavours, fragrances or drugs.     

多元有机混合液声速特性与非线性声参量B/A的数值计算

根据Jacobson的液体分子自由程理论和液体声速与分子自由程的关系,推导出多元有机混合液声速的温度系数、压力系数和非线性声参量B/A的计算公式,并根据组成多元有机混合液各组分特性参量(密度、自由程、非线性声参量B/A、等压膨胀系数、等温压缩系数等),利用给出的公式对声速的温度系数、压力系数、非线性声参量B/A进行了数值计算,并将计算结果与实验结果进行了比较.     

Electrochemical,luminescent and photographic characterisation of cavitation

The characterisation of a small sonochemical reactor has been performed using electrochemical, luminescent and photographic techniques. The electrochemical experiments have employed a novel flow system to determine the formation of sonochemical products (in this case hydrogen peroxide) in semi-real time with high sensitivity. The rate of production of hydrogen peroxide is reported as a function of driving pressure amplitude. The degradation of an organic molecule, specifically the organic dye amaranth, within the sonochemical cell is also reported.     

二元有机混合液声速压力系数(C/P)T

依据Jacobson液体分子自由程理论及液体声速与分子自由程关系,推导出二元有机混合液的声速压力系数表达式.由此计算出的二元有机混合液的声速压力系数值与实验值符合较好. 关键词：     

Ultrasonic study on organic liquid and binary organic liquid mixtures by using Schaaffs＇ collision factor theory

Based on Schaaff's collision factor theory (CFT) in liquids, the equations for nonlinear ultrasonic parameters in both organic liquid and binary organic liquid mixtures are deduced. The nonlinear ultrasonic parameters, including pressure coefficient, temperature coefficients of ultrasonic velocity, and nonlinear acoustic parameter B/A in both organic liquid and binary organic liquid mixtures, are evaluated for comparison with the measured results and data from other sources. The equations show that the coefficient of ultrasonic velocity and nonlinear acoustic parameter B/A are closely related to molecular interactions. These nonlinear ultrasonic parameters reflect some information of internal structure and outside status of the medium or mixtures. From the exponent of repulsive forces of the molecules, several thermodynamic parameters, pressure and temperature of the medium, the nonlinear ultrasonic parameters and ultrasonic nature of the medium can be evaluated. When evaluating and studying nonlinear acoustic parameter B/A of binary organic liquid mixtures, there is no need to know the nonlinear acoustic parameter B/A of the components. Obviously, the equation reveals the connection between the nonlinear ultrasonic nature and internal structure and outside status of the mixtures more directly and distinctly than traditional mixture law for B/A, e.g. Apfel's and Sehgal's laws for liquid binary mixtures.     

Investigations on the energy conversion in sonochemical processes

In the present work the energy transformation in sonochemical processes is studied by using electrical power measurement techniques and calorimetry. The influence of the ultrasonic amplitude and the properties of the irradiated medium on the efficiency of the equipment is shown. With increasing temperature and increasing solvent vapor pressure less energy can be brought into the fluid. More energy is consumed in high viscous media than in low viscous liquids. Finally the quality of calorimetry is discussed and a new energy-based efficiency factor for sonochemical processes is introduced.     

Acoustic emission spectra and sonochemical activity in a 36 kHz sonoreactor

During ultrasound-induced cavitation in liquids, acoustic emissions at fundamental and harmonic frequencies can be detected. The effect of acoustic emissions at harmonic frequencies on the sonochemical and sonophysical activities has not been explored, especially in large-scale sonoreactors. In this study, the acoustic emissions in the range, 0-250 kHz in a 36 kHz sonoreactor with varying liquid heights were studied and compared with the sonochemical activities. The acoustic pressures at both fundamental and harmonics decreased drastically as the liquid height was increased due to the attenuation of sound energy. It was observed that the increase in input power resulted in only an increase in the acoustic emissions at derivative frequencies such as, harmonics and subharmonics. The sonochemical activity, evaluated in terms of sonochemiluminescence and H₂O₂ yield, was not significantly enhanced at higher input power levels. This suggests that at higher power levels, the “extra” acoustic energy is not effectively used to generate primary cavitation activity; rather it is converted to generate acoustic emissions at harmonic and subharmonic frequencies. This is an important observation for the design of energy efficiency large-scale sonochemical reactors.     

Characterization and activity of sonochemically-prepared BSA microspheres containing Taxol--an anticancer drug

Proteinaceous microspheres of BSA (Bovine Serum Albumin) containing an anticancer drug, Taxol (paclitaxel) were fabricated using a sonochemical procedure and then assayed for chemical and biological activity. The sonochemical reaction did not compromise the drug, which became encapsulated in the BSA microspheres. The amount of the anticancer drug in the microspheres was determined by HPLC. Anticancer activity of the proteinaceous microspheres encapsulating the Taxol was tested on Mouse Multiple Myeloma cell line MPC-11. The influence of the Taxol microspheres on the cancer cells was different from pristine Taxol. It was found that Taxol in combination with the organic solvent causes the death of cancer cells.     

Sonochemical cycloadditions in ionic liquids. Lessons from model cases involving common dienes and carbonyl dienophiles

This contribution describes a series of sonochemical cycloadditions involving either cyclopentadiene or 1,3-cyclohexadiene with carbonyl dienophiles in an imidazolium-based ionic liquid as reaction medium. In general, ultrasound does effectively improve these processes in terms of higher yields and/or shorter reaction times when compared with the corresponding silent reactions. Stereoselectivities, however, remain practically unaffected by sonication. The role of ionic liquids under ultrasonic activation is also discussed.     

Kinetics analysis for development of a rate constant estimation model for ultrasonic degradation reaction of methylene blue

Ultrasound has been used as an advanced oxidation method for wastewater treatment. Sonochemical degradation of organic compounds in aqueous solution occurs by pyrolysis and/or reaction with hydroxyl radicals. Moreover, kinetics of sonochemical degradation has been proposed. However, the effect of ultrasonic frequency on degradation rate has not been investigated. In our previous study, a simple model for estimating the apparent degradation rate of methylene blue was proposed. In this study, sonochemical degradation of methylene blue was performed at various frequencies. Apparent degradation rate constant was evaluated assuming that sonochemical degradation of methylene blue was a first-order reaction. Specifically, we focused on effects of ultrasonic frequency and power on rate constant, and the applicability of our proposed model was demonstrated. Using this approach, maximum sonochemical degradation rate was observed at 490 kHz, which agrees with a previous investigation into the effect of frequency on the sonochemical efficiency value evaluated by KI oxidation dosimetry. Degradation rate increased with ultrasonic power at every frequency. It was also observed that threshold power must be reached for the degradation reaction to progress. The initial methylene blue concentration and the apparent degradation rate constant have a relation of an inverse proportion. Our proposed model for estimating the apparent degradation rate constant using ultrasonic power and sonochemical efficiency value can apply to this study which extended the frequency and initial concentration range.     

From crystal phase mixture to pure metal-organic frameworks – Tuning pore and structure properties

In this study, a sonochemical route for the preparation of a new Hf-MIL-140A metal–organic framework from a mixture of UiO-66/MIL-140A is presented. The sonochemical synthesis route not only allows the phase-pure MIL-140A structure to be obtained but also induces structural defects in the MIL-140A structure. The synergic effect between the sonochemical irradiation and the presence of a highly acidic environment results in the generation of slit-like defects in the crystal structure, which increases specific surface area and pore volume. The BET-specific surface area in the case of sonochemically derived Zr-MIL-140A reaches 653.3 m²/g, which is 1.5 times higher than that obtained during conventional synthesis. The developed Hf-MIL-140A structure is isostructural to Zr-MIL-140A, which was confirmed by synchrotron X-ray powder diffraction (SR-XRD) and by continuous rotation electron diffraction (cRED) analysis. The obtained MOF materials have high thermal and chemical stability, which makes them promising candidates for applications such as gas adsorption, radioactive waste removal, catalysis, and drug delivery.     

Recent trends in the applications of sonochemical reactors as an advanced oxidation process for the remediation of microbial hazards associated with water and wastewater: A critical review

Water is one of the major sources that spread human diseases through contamination with bacteria and other pathogenic microorganisms. This review focuses on microbial hazards as they are often present in water and wastewater and cause various human diseases. Among the currently used disinfection methods, sonochemical reactors (SCRs) that produce free radicals combined with advanced oxidation processes (AOPs) have received significant attention from the scientific community. Also, this review discussed various types of cavitation reactors, such as acoustic cavitation reactors (ACRs) utilizing ultrasonic energy (UE), which had been widely employed, involving AOPs for treating contaminated waters. Besides ACRs, hydrodynamic cavitation reactors (HCRs) also effectively destroy and deactivate microorganisms to varying degrees. Cavitation is the fundamental phenomenon responsible for initiating many sonochemical reactions in liquids. Bacterial degradation occurs mainly due to the thinning of microbial membranes, local warming, and the generation of free radicals due to cavitation. Over the years, although extensive investigations have focused on the antimicrobial effects of UE (ultrasonic energy), the primary mechanism underlying the cavitation effects in the disinfection process, inactivation of microbes, and chemical reactions involved are still poorly understood. Therefore, studies under different conditions often lead to inconsistent results. This review investigates and compares other mechanisms and performances from greener and environmentally friendly sonochemical techniques to the remediation of microbial hazards associated with water and wastewater. Finally, the energy aspects, challenges, and recommendations for future perspectives have been provided.     

Kinetics of nitrous acid formation in a two-phase tri-n-butylphosphate-diluent/aqueous nitric acid extraction system under the effect of power ultrasound

The kinetics of nitrous acid formation were investigated in two-phase tri-n-butylphosphate (TBP)-diluent/HNO3 (1.5-6.0 mol l-1) systems, where diluent is n-C16H34, n-C12H26, n-C9H20 and i-C8H18, under the effect of power ultrasound at 20 kHz frequency under Ar atmosphere. The rate of HNO2 sonochemical formation decreases with the rise in diluent vapor pressure. The HNO2 formed is distributed between the aqueous and organic phases due to its extraction with TBP. The kinetics of HNO2 sonochemical formation in the two-phase system exhibits induction periods due to NOx (NO + NO2) gas reactions in the HNO3 medium. This induction period decreases with increasing HNO3 concentration and ultrasound intensity. The HNO2 steady-state concentration was obtained under long-time sonication as the result of HNO2 sonochemical decomposition. HNO2 decomposes faster under sonication in the aqueous phase than in the organic phase.     

Mesophilic alcohol dehydrogenase behavior in imidazolium based ionic liquids

The use of ionic liquids to replace organic solvents in biocatalytic processes has recently gained much attention. Despite the wide applications of oxidoreductases, there are few reports of their catalyzed reaction in ionic liquid. We have investigated the influence of four water miscible ionic liquids on the activity, stability and structure of the mesophilic alcohol dehydrogenase from yeast. Upon changes in ionic liquids concentration, both activity and stability of the enzyme were affected. As the concentration of ionic liquids increased, K_m increased while k_cat decreased. Associated conformational changes caused by ILs (150 mM) were monitored using fluorescence technique. Finally, the effects of ILs cations and anions on the enzyme activity and stability in aqueous IL mixtures were discussed.     

Characteristics of adsorption phase with water/organic mixtures at a surface of activated carbons possessing intraparticle and textural porosities

The behaviour of water and water/organic mixtures adsorbed onto activated microporous carbons or a carbon adsorbent with narrow intraparticle micropores and broad mesopores and macropores between nanoparticles was studied using low-temperature adsorption method and ¹H NMR spectroscopy with layer-by-layer freezing-out of liquids at 190-273 K. These investigations revealed concentration-dependent effects of benzene, DMSO, acetone, chloroform, methane and acetonitrile on the characteristics of adsorbed water and the influence of this water on the interfacial behaviour of adsorbed organics. The influence of organics causes the structural and energetic differentiations of adsorbed water. The latter can be displaced by organics from micropores into broader pores and/or form mixture with polar solvents in meso and macropores. Freezing of adsorbed water can affect the adsorbent structure because ice crystallites have a larger size than that of liquid water droplets that lead to changes in the behaviour of adsorbed water/organic mixtures observed by the ¹H NMR and adsorption methods.     

Recent advances in organic synthesis utilizing ultrasound

This review describes the recent applications of ultrasound in organic synthesis. Oxidation processes, N-C and C-C bond formation (encompassing the Wittig, Ullman and acyloin reactions), cycloaddition reactions (including the first example of an ultrasonically promoted Diels-Alder reaction), bond cleavage reactions and biological examples are discussed. The important area of sonochemical switching is reviewed and comments are made on the relationship between ionic and radical sonochemical reactions.