Enantiodifferentiation in asymmetric sonochemical hydrogenations

The effect of sonochemical pretreatment on the enantioselectivity of Pt/Al₂O₃–cinchonidine-catalyzed ethyl pyruvate hydrogenation was studied at different hydrogen pressures in various solvents, mainly in acetic acid. The sonochemical pretreatment of a commercial Pt/Al₂O₃–cinchonidine catalytic system in acetic acid resulted in enhanced enantioselectivity providing excellent ee values (97% ee) under mild and widely varied experimental conditions. Moreover, the application of ultrasonics provides a possibility of the catalyst recycling without regeneration. The catalyst was tested by transmission electron microscopy to determine the effect of the sonication on the metal particle size morphology. This revised version was published online in July 2006 with corrections to the Cover Date.     

Grafting modification of carbon black by trapping macroradicals formed by sonochemical degradation

Polymers were grafted onto the surface of carbon black (CB) by the trapping of macroradicals formed by sonochemical degradation of a polymer solution. Long chain radicals of poly(vinyl alcohol) (PVA) formed by sonochemical degradation were successfully trapped by CB and grafted onto its surface. Results showed the method to be suitable for all kinds of CB, even for furnace black with few functional groups. The crushing effect of the ultrasonic forces caused the PVA grafted CB to have a much smaller aggregate particle size and narrower particle size distribution than that of the original CB, as indicated by dynamic light scattering. The PVA grafted CB could be well dispersed in water and a polymer matrix. The compatibility between CB and polymer was significantly improved.     

The sonochemical preparation of a mesoporous NiO/yttria stabilized zirconia composite

A sonochemical process for the fabrication of the mesoporous composite NiO/yttria stabilized zirconia (YSZ) is described. Its surface area after the extraction of the surfactant is 193 m²/g for a sample containing 40 atom-% Ni. The main advantages of the sonochemical method, as compared with previous works, are the short reaction time (6 h) and that there is no requirement for the glycolation of the nickel, yttrium, and zirconium ions. The reduction of NiO/YSZ to the corresponding Ni/YSZ is also reported.     

Heterogeneous Asymmetric Reactions 20. Effect of Ultrasonic Variables on the Enantiodifferentiation in Cinchona-Modified Platinum-Catalyzed Sonochemical Hydrogenations

The effect of sonochemical variables on a cinchona alkaloid modified Pt/Al₂O₃ catalyst system and its application in -ketoester hydrogenation are described. The sonochemical pretreatment of these commercial Pt/Al₂O₃-cinchonidine catalysts resulted in excellent ee values (up to 92-98% ee) under mild experimental conditions. To gain more insight into the nature of the ultrasonic effect the reactions were screened under widely varied conditions (ultrasound source, frequency, insonation time). Besides investigating the reactions, the catalyst-modifier system was also studied. The changes in metal particle size were determined by transmission electron microscopy, while the alteration of modifier concentration in the solvent upon sonication was followed by UV-vis spectroscopy. The transformation of the modifier during the pretreatment was detected by GC-MS and verified by NMR. Summarizing the results, the major effects of the sonochemical activation on the cinchona-modified supported Pt catalyst system can be described. The ultrasonic pretreatment increased the quantity of adsorbed cinchona and blocked its hydrogenation to provide more and highly stable chiral active sites for enantioselection.     

The preparation of stable metal nanoparticles on carbon nanotubes whose surfaces were modified during production

Metal nanoparticles were synthesized by using surface-modified carbon nanotubes (m-CNTs) and pristine CNTs (p-CNTs) as stabilizing substrates. The surfaces of the m-CNTs were modified by the addition of hydrogen peroxide during the chemical vapor deposition synthesis. X-ray photoelectron spectroscopy showed oxygen peaks, which came from C-OH and C-O-C functional groups on the m-CNT walls. Unlike the p-CNTs, the m-CNTs could be used as excellent stabilizing substrates for metal nanoparticles which were produced by using resorcinol as a reducing agent via a sonochemical method. They could stabilize the nanoparticles and prevent them from agglomeration.     

Sonochemically activated solid-state synthesis of BaTiO3 powders

We report the sonochemically activated solid-state synthesis of BaTiO₃ powders. Unlike conventional ball-mill mixing, coarse BaCO₃ and fine TiO₂ powders were sonochemically mixed in ethanol, requiring only 5 min for full mixing and activation. Significantly accelerated phase conversion to BaTiO₃ via a solid-state reaction was achieved by the sonochemical mixing, and the process exhibited almost Arrhenius-type activation behavior depending on the ultrasonic power. The sonochemical activation was attributed to the preferential fragmentation of BaCO₃ by the ultrasonic irradiation, which led to the particle size reduction and homogeneous mixing in the sonochemical mixtures. Based on the structural, dielectric, and ferroelectric characterizations, we suggest that the sonochemical mixing can replace the time-consuming ball-mill mixing for the solid-state synthesis of BaTiO₃ powders and can also be applied to develop a time-saving, contamination-free, and cost-effective process for various ceramic industries.     

Organic reactions in water or biphasic aqueous systems under sonochemical conditions. A review on catalytic effects

Catalysis in aqueous systems under sonochemical conditions has become an irreplaceable method in green synthetic chemistry after more than two decades of studies in this domain. The present review has the aim of describing the state-of-the-art with a comprehensive view of advantages and limitations as well as new potential applications. Catalytic procedures in water assisted by ultrasound and/or hydrodynamic cavitation are environmentally friendly with milder conditions, shorter reaction times and higher yields. Sonochemical processes can reduce the formation of hazardous by-products, the generation of waste and also produce energy savings. Cavitational implosion generates mechanical and chemical effects such as cleaning of catalyst surface and formation of free radicals by sonolysis of water. The present overview of sonochemical reactions in water (oxidation, bromination, aza-Michael, C–C couplings, MCR and aldol reactions) should provide useful models for furthering the progress of organic synthesis using harmless and greener sound energy.     

工艺因素对水热电泳沉积硅酸钇涂层显微结构的影响

采用水热电泳沉积法在C/C-SiC复合材料表面制备了硅酸钇抗氧化外涂层.研究了沉积电流密度和低温热处理对硅酸钇涂层的影响.采用X-射线衍射仪(XRD)和扫描电子显微镜(SEM)对涂层的相组成和显微结构进行了表征.结果表明:采用声化学法制备的硅酸钇微晶颗粒尺寸为25～40nm.随着沉积电流密度增加,硅酸钇涂层均匀性、致密性先逐渐增加后降低.当电流密度超过0.04 A/cm2时会导致涂层表面开裂.进行低温热处理,涂层表面硅酸钇纳米晶出现熔融现象;随热处理温度增加,涂层表面呈现玻璃化趋势.当热处理温度达1200℃时,表面完全熔融,形成致密的硅酸钇玻璃层.涂层在1500℃静态空气中,经过氧化10 h后,失重仍然小于2%.     

平行与交叉双声束声场中的声化学反应研究

给描述超声空化效应动力学过程的Noltingk-Napprias方程增加了一个表征外界随机微扰的修正项,通过对这个方程的解发现,声场施加微扰后,可使空化的空化泡数量增加。在此理论基础上,设想采用交叉双声束声场实现对声场施加微扰。实验结果证实,采用交叉双声束声场后声场中的声化学产额(分别以溶液pH值改变,电导率改变表征)较平行双声束声场增加约11%~13%不等。这一结果对于声化学反应器提高声化学产额有意义。     

超声化学法制备高纯钛酸钡的工艺研究

以氯化钡和钛酸丁酯为原料,采用超声化学法制备高纯钛酸钡（BaTiO3）粉体。利用X衍射分析、扫描探针、激光粒度仪等检测方法对样品进行表征。研究超声化学法制备高纯钛酸钡的方法和影响因素,对比研究了超声化学法与传统化学沉淀法制备对粉体粒度的影响。结果表明,将反应的pH控制在3左右,反应物的n（钡）/n（钛）控制在1∶（1～1.02）时,超声化学法制备的钛酸钡为立方相,且为均匀的球形,粒度为100 nm,纯度为99.82%。     

TOC and THMFP reduction by ultrasonic irradiation in wastewater effluent

Humic substances (HS) are amorphous organic macromolecules that are responsible for the color of natural water and wastewater effluents. They play an important role in the formation of disinfection by-products. The ultrasonic process is applied as a treatment method to investigate its effect on the TOC removal and the formation of trihalomethanes (THMs) during chlorination. It was observed that the metal ions such as Fe(II) and Mn(II) showed catalytic effects while Al(III), Ca(II), and Mg(II) had inhibitory effects on the TOC removal of humic substances in sonochemical reaction with hydrogen peroxide. Experimental results also showed hydrogen peroxide dose affected the formation of disinfection by-products. Chloroform and dichlorobromomethane were formed as major THMs during chlorination.     

声化学技术处理有机废水的研究进展

对近年来国内外兴起的超声波降解技术作了较为全面的概述,主要针对有机废水的处理,分别就超声波工作原理、超声降解机理、超声波降解技术的研究成果及技术优化和超声降解技术的展望及今后研究方向等作了较为系统的介绍。     

近场型声化学反应器中的化学反应

引　言声化学是 2 0世纪 80年代兴起的一门新化学学科[1～ 3] .声化学均相合成[4 ] 、声化学反应机理[5] 、声化学用于水处理[6 ,7] 是当前主要的研究方向 .近年 ,声化学反应的工业化也初露头角[8] ,而工业化所涉及到的一个重要问题是声化学反应器的设计理论 .Ｍａｒｔｉｎ[9] ,Ｈｏｆｆｍａｎｎ[10 ] ,Ｂｅｒｌａｎ[11] ,作者[12～ 15] 等对声化学反应器设计的一般原理进行过论述 .但是 ,直到目前 ,人们对空化泡数量与声化学产额之间定量关系的描述还很缺乏 .本研究采用近场型声化学反应器研究ＫＩ水溶液中的声化学产额与声场中空化泡数量…     

Sonochemical synthesis of conducting polymer-metal nanoparticles nanocomposite

Colloidal dispersions of hybrid nanocomposite composed of polypyrrole (PPy) and gold nanoparticles (Au-NPs) or platinum nanoparticles (Pt-NPs) were prepared by a sonochemical method, in which Au ion and pyrrole monomer in an aqueous solution were reduced and oxidized, respectively, by ultrasonic irradiation in the presence of sodium dodecyl sulfate (SDS). The formation of PPy on the surface of Au-NPs or Pt-NPs is confirmed by UV-vis and transmission electron microscopy (TEM) images.     

Sonochemical synthesis of LaMnO3 nano-powder

We report the preparation of LaMnO₃ nanosized powder by the sonochemical process. Sodium dodecyl sulphate (SDS) was used as surfactant, to prevent agglomeration. The particle size obtained in this method was 19–55 nm. The phase formation temperature of LaMnO₃ was 700 °C which is lower than other conventional processes. So sonochemical process is cost effective and it is more acceptable considering its ease of preparation in comparison to other conventional processes. Powder synthesized was characterized by measuring crystallite size, specific surface area, morphology and by thermal analysis. The particle sizes of the powders were controlled by calcinations schedule. Narrow size distribution and core and shell structure of the prepared powder was revealed by transmission electron microscopy.     

声化学微反应器降解亚甲基蓝废水试验研究

为提高Fe²⁺活化过硫酸钠（SPS）降解亚甲基蓝（MB）的效率，设计了一种声化学微反应器。首先研究了静置系统、磁力搅拌系统、毛细管微反应器系统和声化学微反应器系统中MB和硫酸亚铁（FeSO₄）混合液pH值、FeSO₄浓度、SPS浓度对MB降解率的影响。其次，在声化学微反应器系统和毛细管微反应器系统中研究了流道结构和流速对MB降解率的影响。结果表明：在不同的MB和FeSO₄混合液pH值、FeSO₄浓度下，声化学微反应器系统中MB降解率均高于其他反应系统。随着SPS浓度的增加，MB降解率呈上升趋势，但在声化学微反应器系统中增加SPS浓度会影响MB降解。相比于直线形、三角波形和半圆波形流道结构，MB在矩形波形流道结构中降解效率更高。溶液在管道内停留时间相同时，增加流速更有利于氧化降解反应的进行。实验表明：当MB浓度为0.2 mmol·L^-1，MB和FeSO₄混合液pH值为3、FeSO₄浓度为1.4 mmol·L^-1、SPS浓度为1.8 mmol·L^-1，流道结构为矩形波形，流速为13.16 cm·s^-1时，声化学微反应系统中MB降解率达到85.45%。     

Sonochemical synthesis of ZnO‐ZnS core‐shell nanorods for enhanced photoelectrochemical water oxidation

The ultrasonic‐assisted synthesis method provides a fast, simple, and large‐scale route for synthesizing desired materials under ambient conditions. In this work, we report on the facile preparation of ZnO‐ZnS core‐shell nanorods on a fluorine‐doped tin oxide (FTO) substrate. The core‐shell nanorods were synthesized by sequential nanoscale reactions involving the preparation of ZnO nanorods and conversion of the ZnO surface into a ZnS shell on the FTO substrate, using an in situ sonochemical method. The ZnO‐ZnS core‐shell nanorods showed improved photocurrents compared with ZnO nanorods for the water oxidation reaction. During the water oxidation reaction, the ZnS shell passivates the surface‐defects of the ZnO, which results in enhanced charge separation in the ZnO nanorods and higher performance.     

超声化学法快速原位制备形貌可选择的硫化银

利用超声化学技术,在金属Ag片表面快速原位合成不同形貌的Ag2S晶体。借助扫描电子显微镜(SEM)和X-射线衍射仪(XRD)对硫化银晶体的形貌和晶型进行表征和分析。结果表明:生成的Ag2S薄膜致密而牢固;通过改变反应条件(包括:超声照射时间、硫粉的浓度、超声功率、溶剂以及表面活性剂),可以很好地调控产物Ag2S的形貌。该方法简便易行,可望为其他半导体材料的快速原位制备提供一种参考。     

A Sonochemical‐Assisted Synthesis of Pure Nanocrystalline Tetragonal Zirconium Dioxide Using Tetramethylethylenediamine

Pure nanocrystalline zirconia has been successfully synthesized by sonochemical‐assisted route from zirconyl nitrate and tetramethylethylenediamine (TMED) as starting materials. Here, TMED for the first time was used as precipitating agent to generate nanocrystalline tetragonal zirconia via a sonochemical‐assisted route. The effect of solvent and concentration of TMED on the morphology and crystallite size was studied. It was found that these parameters have significant influence on the morphology and crystallite size of the products. The products were characterized by SEM, UV–vis absorption and TEM images, XRD patterns, PL, FTIR, and EDS spectroscopy.     

超声清洗石油污染海滨土的效果与影响因素

土壤的石油类有机污染物污染是近几年继农药和重金属之后的又一大污染。石油主要是由烷烃、环烷烃和芳香烃组成的混合物,具有致癌、致畸、致突变的潜在性。常规技术净化酸性的落地油泥的效果并不理想,而声化学处理以前就被认为是修复碳氢化合物污染土的一个有效方法。基于此,本研究对石油污染的海滨土开展了以声化学为技术手段的修复实验。在本实验研究中,泥浆浓度、清洗时间、温度、泥浆pH值、投加碱性添加剂与微量自由基试剂H₂O₂等因素对石油烃从细粒海滨土中的解吸效果的影响得到考虑。根据实验结果,在采用声化学工艺净化海滨细粒土时,建议工艺操作参数控制在液固比6∶1、超声作用时间5 min、常温20℃、pH值9、Na₂CO₃的投加量为0.15%。另外,在处理过程中有必要采取措施及时避免清洗过程油泥造成的固结现象。