Mechanochemistry and sonochemistry

The paper is devoted to mutual problems in mechanochemistry and sonochemistry and their interconnection.     

Asymmetric reactions in sonochemistry.

Sonochemical processes involved in asymmetric synthesis are reviewed. The goal of this overview is to provide a comprehensive picture about the fields of both enantioselective and diastereoselective reactions accelerated or initiated by ultrasounds. Since the most, in many cases comparative, data are available in heterogeneous metal catalysis, the emphasis will be placed on these enantioselective hydrogenations, however, other applications such as phase transfer catalysis etc. will also be cited.     

Educational aspects of sonochemistry: The role of sonochemistry at high school level

The applications of sonochemistry have attracted a great deal of attention. However, conventional chemistry textbooks used in universities and high schools cover traditional chemistry plus thermo,- photo- and electrochemistry. The effect of sound on chemical systems has completely been ignored. Although the mechanisms of many sonochemical reactions remain unresolved, the rapid expansion of knowledge in sonochemistry has already justified its inclusion in present chemistry curricula. Moreover, the interesting and unusual phenomena encountered under sonication conditions can be used for motivation purposes. Furthermore, exploring and equipping students with a new tool for investigating chemistry is also important based on educational principles. This paper examines some chemical systems (in a high school chemistry syllabus) which are affected by sound energy. It is hoped that these sonochemical applications will facilitate the learning of chemistry in terms of cognitive, psychomotor and affective domains.     

Numerical simulations for sonochemistry

Numerical simulations for sonochemistry are reviewed including single-bubble sonochemistry, influence of ultrasonic frequency and bubble size, acoustic field, and sonochemical synthesis of nanoparticles. The theoretical model of bubble dynamics including the effect of non-equilibrium chemical reactions inside a bubble has been validated from the study of single-bubble sonochemistry. By the numerical simulations, it has been clarified that there is an optimum bubble temperature for the production of oxidants inside an air bubble such as OH radicals and H₂O₂ because at higher temperature oxidants are strongly consumed inside a bubble by oxidizing nitrogen. Unsolved problems are also discussed.     

Importance of hydrodynamic shielding for the dynamic behavior of short polyelectrolyte chains

The dynamic behavior of polyelectrolyte chains in the oligomer range is investigated with coarse-grained molecular dynamics simulation and compared to data obtained by two different experimental methods, namely, capillary electrophoresis and electrophoresis NMR. We find excellent agreement of experiments and simulations when hydrodynamic interactions are accounted for in the simulations. We show that the electrophoretic mobility exhibits a maximum in the oligomer range and for the first time illustrate that this maximum is due to the hydrodynamical shielding between the chain monomers. Our findings demonstrate convincingly that it is possible to model dynamic behavior of polyelectrolytes using coarse-grained models for both the polyelectrolyte chains and the solvent induced hydrodynamic interactions.     

腐植酸溶液的声化学降解研究

采用频率为1.8MHz的超声波在固定式声化学反应器内研究了声化学降解腐植酸的自由基氧化历程。通过采用TA溶液作为OH自由基捕获剂,吡啶溶液作HO2自由基捕获剂,以及KI溶液的I2释放法分别确定出实验条件下反应溶液中OH自由基的浓度为10^-7M,HO2自由基浓度为10^-5M及H2O2浓度为10^-5M。在此基础上研究了均相与多相催化条件下声化学降解腐植酸溶液的TOC削减情况。发现CeO2和Cu2O催化作用下腐植酸的降解效率分别较均相条件下提高40％和20％。并就反应机理和反应动力学过程进行了描述。     

Fundamental problems of sonochemistry and cavitation

This paper discusses the problems of cavitation which are associated with sonochemistry. It is concluded that the hot-spot theory is not sufficient to accommodate all experimental data and the alternative is a new electrical theory of cavitation phenomena.     

Applications of sonochemistry in Russian food processing industry

In food industry, conventional methodologies such as grinding, mixing, and heat treatment are used for food processing and preservation. These processes have been well studied for many centuries and used in the conversion of raw food materials to consumable food products. This report is dedicated to the application of a cost-efficient method of energy transfer caused by acoustic cavitation effects in food processing, overall, having significant impacts on the development of relatively new area of food processing such as food sonochemistry.     

Using sonochemistry for the fabrication of nanomaterials

One of the reasons for the huge interest in nanomaterials originated because of the prohibitive price that commercial companies have to pay for introducing new materials into the market. Nanotechnology enables these companies to obtain new properties using old and recognized materials by just reducing their particle size. For these known materials no government approval has to be obtained. Thus, the interest in nanomaterials has led to the development of many synthetic methods for their fabrication. Sonochemistry is one of the earliest techniques used to prepare nanosized compounds. Suslick, in his original work, sonicated Fe(CO)5 either as a neat liquid or in a decalin solution and obtained 10-20 nm size amorphous iron nanoparticles. A literature search that was conducted by crossing Sono* and Nanop* has found that this area is expanding almost exponentially. It started with two papers published in 1994, two in 1995, and increased to 59 papers in 2002. A few authors have already reviewed the fields of Sono and Nano. It should be mentioned that in 1996, Suslick et al. published an early review on the nanostructured materials generated by ultrasound radiation. Suslick and Price have also reviewed the application of ultrasound to materials science. This review dealt with nanomaterials, but was not directed specifically to this topic. The review concentrated only on the sonochemistry of transition metal carbonyls and catalytic reactions that involve the nanoparticles resulting from their sonochemical decomposition. Grieser and Ashokkumar have also written a review on a similar topic. A former coworker, Zhu, has recently submitted for publication a review article entitled "Novel Methods for Chemical Preparation of Metal Chalcogenide Nanoparticles" in which he reviews three synthetic methods (sonochemistry, sonoelectrochemistry, and microwave heating) and their application in the synthesis of nanosized metal chalcogenides. Although still unpublished, I myself have recently written a review discussing novel methods (sonochemistry, microwave heating, and sonoelectrochemistry) for making nanosized materials. The current review will: (1) Present the four main advantages that sonochemistry has over other methods related to materials science and nanochemistry; (2) concentrate on the more recent (2003) literature that was not reviewed in the previously-mentioned reviews, and (3) focus on a specific question, such as what is the typical shape of products obtained in sonochemistry? This review will not survey the literature related to sonoelectrochemistry.     

水处理用声化学反应器研究进展

介绍了在水处理中采用的液哨式、清洗槽式、变幅杆式、杯式、平行板、管型等声化学反应器的研究进展和应用现状。指出要在实际水处理工程中采用超声技术，必须尽快开展高效、大批量处理或流水式连续运行的声学反应器的基础研究与应用开发。     

On the frequency and isotope effect in sonochemistry

In the first part of the work, it was observed, by a relative method, that the Weissler reaction and the Br2-catalysed isomerisation of maleic acid into fumaric acid are faster at 20 kHz than at 1.7 MHz. The difference between the relative reaction rates can be considered as small when the two order magnitude difference between the two frequencies is taking into account. In the second part of the work, the frequency effect associated to an isotope effect was studied. The Weissler reaction was performed in H2O and D2O at 20 kHz and 1.7 MHz. The isotope effect is not the same at the two frequencies.     

On the origin of sonoluminescence and sonochemistry

Recent experimental results on the origins of sonoluminescence and sonochemistry are reviewed and the conclusion reached that most observed effects originate from thermal processes associated with a localized hot-spot created by acoustic cavitation. Sonoluminescence is definitively due to chemiluminescence from species produced thermally during cavitational collapse and is not attributable to electric microdischarge. Homogenous sonochemistry follows the behaviour expected for high temperature thermal reactions. Ultrasonic irradiation of liquids containing solid powders dramatically increases their chemical reactivity and improves chemical yields for a wide range of synthetically useful heterogenous reactions. Shock waves generated from the cavitational hot-spot cause high velocity interparticle collisions in such slurries. Brittle solids are shock fragmented, which increases surface area. This increase in reactive surface provides for substantial increases in chemical reactivity. For malleable metal powders, these collisions are sufficiently violent to remove surface oxide coatings and to induce local melting at the site of impact for most metals.     

气幕对潜艇声屏蔽作用的数值计算

本文利用惠更斯-菲涅尔原理和虚源方法建立了均匀海水中障碍物后声传播损失的计算模型,对模型进行了数值实验验证,并与海上试验数据对比,得到了较为合理的结果。     

Industrial applications of sonochemistry in the syntheses of vitamin-building blocks

In this article, the application of ultrasound in syntheses of vitamins and fine chemicals is presented. Based on selected examples, the use of ultrasound in dehydration, isomerisation, and decarboxylation reactions is described.     

A few questions on the sonochemistry of solutions

Sonochemical reactions in solution have an underexploited synthetic potential. Most of the obstacles to expand this attractive domain come from unanswered questions on, for example, the importance of the radiomimetic effect, the implication of the solvent as a relay in the reaction mechanism, the existence of redox processes, and concerning cavitation, the structure of the bubble interface and the pressure effects associated to the collapse.     

Qualitative characterization of ultrasound reactors for heterogeneous sonochemistry

Several measurement methods (thermocouple probe, perforation of aluminium foils by cavitation, chemical dosimeter) are used to characterize the sound fields of low and high intensity ultrasound reactors and to find optimal conditions for the ultrasonic irradiation of heterogeneous reaction mixtures. In this Paper it is shown that, due to the formation of standing waves, the local ultrasound intensity in a flask fixed in an ultrasonic cleaner is strongly susceptible to small changes in experimental conditions. It is also shown that high intensity ultrasound sources, such as an ultrasonic horn, tend to uncouple: that is, cavitation only occurs at the radiating surface and only marginal ultrasound intensity can be detected elsewhere in the surrounding liquid.     

A study on effect of sonochemistry in a reverberation field

In this paper,an ultrasound with frequency of 815 kHz was used to re-search the sonochemical yield in a small-size reverberation field by the methodof fluorescent spectrum analysis.There are two characteristics on the effect ofsonochemistry in the reverberation field:First,the cavitation threshold wasabout 0.3W/cm~2(it was 0.7W/cm~2 in travelling field);Second,when thesound intensity was larger than the threshold,the sonochemical yield increasedas the intensity increased and increased rapidly after the intensity was at1.69-2.13W/cm~2,so that there was a upturned point in the curve of the result(which would tend to saturation in the travelling field).The theoretical analysisshows that the reason of the threshold decrease is that the sound energy densitybecomes high in the reverberation field,and the upturned point results from thedisturbance of the radiation pressure on the liquid surface.Therefore,by exper-iment and theory this paper shows that a reverberation field has to be built forthe higher sonoche     

Organometallic sonochemistry: Successes,problems and by-products

This review summarizes a part of the work undertaken by a group in Grenoble in the area of organometallic sonochemistry. Organolithium and organozinc reactions promoted by ultrasonic waves offer synthetic advantages over the classical methods with regard to the selectivity, yields and rates. Tentative interpretations of the ultrasonic effects on such reactive systems are discussed. New trends in organometallic chemistry resulting from the sonochemical studies have become apparent, especially new reactions occurring in aqueous media.     

我国的声化学应尽快大力开展实用化工作

声化学在实验室的研究在我国正在迅速发展。面对国内外大量的、已证实有效的声化学实例,让声化学尽早尽快在化学工业、绿色化学、制药工业、食品工业、纳米材料等新技术等等方面在我国实用起来,应该是不可多得的机遇。当前急务,一方面是大力进行深入的技术准备,让声化学能在多个环节从实验室高能效地走向社会;另一方面是,利用现有的技术,现在就慎重选择部分有条件实现的实验室成果,因陋就简地推广起来,工作中再逐步提高能效。     

Using sonochemistry for the fabrication of hollow ZnO microspheres

Hollow ZnO microspheres assembled by nanoparticles have been prepared by a sonochemical synthesis at room temperature using carbon spheres as template. The growth process of the precursor was investigated. The prepared hollow spheres were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HRTEM). The diameter of the obtained hollow spheres is about 500 nm, and the walls are composed of numerous ZnO aggregate nanocrystallines with diameters of 90 nm. A possible growth mechanism for the formation of ZnO microspheres has been proposed, in which carbon spheres play a crucial role in the formation of the wurtzite hollow ZnO microspheres. The specific structure of the hollow spheres may find applications in nanoelectronics, nanophotonics and nanomedicine.