Sonochemistry theory reactions and syntheses and applications chemistry engineering methods and technology

Small gold nanoparticles size of 2.7±0.3 nm can be synthesized when ultrasound irradiation applied to a solution with the molar ratio of Au/S = 1:2 for 12 h... In another work, highly mo

CHEMICAL ENGINEERING METHODS AND TECHNOLOGY

No part of this digital document may be reproduced, stored in a retrieval system or transmitted in any form or

by any means The publisher has taken reasonable care in the preparation of this digital document, but makes no expressed or implied warranty of any kind and assumes no responsibility for any errors or omissions No liability is assumed for incidental or consequential damages in connection with or arising out of information contained herein This digital document is sold with the clear understanding that the publisher is not engaged in rendering legal, medical or any other professional services

C HEMICAL E NGINEERING M ETHODS

Additional books in this series can be found on Nova‘s website

under the Series tab

Additional E-books in this series can be found on Nova‘s website

under the E-books tab

CHEMICAL ENGINEERING METHODS AND TECHNOLOGY

Copyright © 2010 by Nova Science Publishers, Inc

All rights reserved No part of this book may be reproduced, stored in a retrieval system or

transmitted in any form or by any means: electronic, electrostatic, magnetic, tape, mechanical photocopying, recording or otherwise without the written permission of the Publisher

For permission to use material from this book please contact us:

Telephone 631-231-7269; Fax 631-231-8175

Web Site: http://www.novapublishers.com

NOTICE TO THE READER

The Publisher has taken reasonable care in the preparation of this book, but makes no expressed or implied warranty of any kind and assumes no responsibility for any errors or omissions No liability is assumed for incidental or consequential damages in connection with or arising out of information contained in this book The Publisher shall not be liable for any special, consequential, or exemplary damages resulting, in whole or in part, from the readers‘ use of, or reliance upon, this material Any parts of this book based on government reports are so indicated and copyright is claimed for those parts to the extent applicable to compilations of such works Independent verification should be sought for any data, advice or recommendations contained in this book In addition, no responsibility is assumed by the publisher for any injury and/or damage

to persons or property arising from any methods, products, instructions, ideas or otherwise contained in this publication

This publication is designed to provide accurate and authoritative information with regard to the subject matter covered herein It is sold with the clear understanding that the Publisher is not engaged in rendering legal or any other professional services If legal or any other expert assistance is required, the services of a competent person should be sought FROM A DECLARATION OF PARTICIPANTS JOINTLY ADOPTED BY A COMMITTEE OF THE AMERICAN BAR ASSOCIATION AND A COMMITTEE OF PUBLISHERS

L IBRARY OF C ONGRESS C ATALOGING - IN -P UBLICATION D ATA

Sonochemistry : theory, reactions, syntheses, and applications / [edited by]

CONTENTS

Chapter 1 Sonochemistry: A Suitable Method for Synthesis of

M F Mousavi and S Ghasemi

Chapter 2 Industrial-Scale Processing of Liquids by High-Intensity Acoustic

Cavitation: The Underlying Theory and Ultrasonic Equipment

Alexey S Peshkovsky and Sergei L Peshkovsky

Chapter 3 Some Applications of Ultrasound Irradiation in Pinacol Coupling of

Zhi-Ping Lin and Ji-Tai Li

Chapter 4 Ultrasound and Hydrophobic Interactions in Solutions 129

Ants Tuulmets, Siim Salmar and Jaak Järv

Chapter 5 Synthetic Methodologies Using Sonincation Techniques 157

Ziyauddin S Qureshi, Krishna M Deshmukh and Bhalchandra M Bhanage

Tinghe Yu and Yi Zhang

Chapter 7 Application of Ultrasound for Water Disinfection Processes 201

Vincenzo Naddeo, Milena Landi and Vincenzo Belgiorno

Chapter 8 Use Of Ultrasonication in the Production and Reaction of C60 and

Anne C Gaquere-Parker and Cass D Parker

Anne C Gaquere-Parker and Cass D Parker

PREFACE

The study of sonochemistry is concerned with understanding the effect of sonic waves and wave properties on chemical systems This book reviews research data in the study of sonochemistry including the application of sonochemistry for the synthesis of various nano-structured materials, ultrasound irradiation in pinacol coupling of carbonyl compounds, ultrasound and hydrophobic interactions in solutions, as well as the use of ultrasound to enhance anticancer agents in sonochemotherapy and the ultrasound-enhanced synthesis and chemical modification of fullerenes

Chapter 1 - Recently, sonochemistry has been employed extensively in the synthesis

of nano-structured materials Rapid reaction rate, controllable reaction conditions, simplicity and safety of the technique as well as the uniform shape, narrow size distribution, and high purity of prepared nano-sized materials are some of the main advantage of sonochemistry Sonochemistry uses the ultrasonic irradiation to induce the formation of particles with smaller size and high surface area

Because of its importance, sonochemistry has experienced a large promotion in various fields concerned with production of new nano-structured materials and improvement of their properties during the recent years However, it has encountered limitations in the case of production of some nano-materials with specific morphology, size and properties, but the growth of the number of researches and published articles in the field of sonochemistry during the recent years shows a large interest and attempt to apply sonochemistry in nanotechnology The improvement of shape, size, purity and some other chemical and physical properties of such produced materials has been the scope of the researchers recently Sonochemistry uses the powerful ultrasound irradiation (20 kHz to 10 MHz) to induce chemical reaction of molecules During the ultrasonic irradiation, the acoustic cavitations will occur which consist of the formation, growth and implosive collapse of bubbles in a liquid The implosive collapse of the bubbles generates a localized hotspot or shock wave formation within the gas phase of the collapsing bubbles (The hot-spot theory)

This chapter is planned to deal with the application of sonochemistry for the synthesis of various nano-structured materials such as metals, metal carbides, metal oxides, chalcogenides and nanocomposites with unique properties The effect of different ultrasonic parameters on the prepared structures including their size, morphology and properties are investigated Also, some applications of prepared nano-materials are introduced, e.g electrochemical energy storage, catalysis, biosensor and electrooxidation

Chapter 2 - A multitude of useful physical and chemical processes promoted by ultrasonic cavitation have been described in laboratory studies Industrial-scale

Filip M Nowak viii

implementation of high-intensity ultrasound has, however, been hindered by several technological limitations, making it difficult to directly scale up ultrasonic systems in order to transfer the results of the laboratory studies to the plant floor High-capacity flow-through ultrasonic reactor systems required for commercial-scale processing of liquids can only be properly designed if all energy parameters of the cavitation region are correctly evaluated Conditions which must be fulfilled to ensure effective and continuous operation of an ultrasonic reactor system are provided in this chapter, followed by a detailed description of

"shockwave model of acoustic cavitation", which shows how ultrasonic energy is absorbed in the cavitation region, owing to the formation of a spherical micro-shock wave inside each vapor-gas bubble, and makes it possible to explain some newly discovered properties of acoustic cavitation that occur at extremely high intensities of ultrasound After the theoretical background is laid out, fundamental practical aspects of industrial-scale ultrasonic equipment design are provided, specifically focusing on:

 electromechanical transducer selection principles;

 operation principles and calculation methodology of high-amplitude acoustic horns used for the generation of high-intensity acoustic cavitation in liquids;

 detailed theory of matching acoustic impedances of transducers and cavitating liquids in order to maximize the ultrasonic power transfer efficiency;

 calculation methodology of ―barbell horns‖, which provide the impedance matching and can help achieving the transference of all available acoustic energy from transducers into the liquids These horns are key to industrial implementation of high-power ultrasound because they permit producing extremely high ultrasonic amplitudes, while the output horn diameters and the resulting liquid processing capacity remain very large;

 optimization of the reactor chamber geometry

Chapter 3 - Carbon-carbon bond formation is one of the most important topics in organic synthesis One of the most powerful methods for constructing a carbon-carbon bond

is the reductive coupling of carbonyl compounds giving 1,2-diols Of these methods, the pinacol coupling, which was described in 1859, is still a useful tool for the synthesis of vicinal diols 1, 2-Diols obtained in the reaction were very useful synthons for a variety of organic synthesis, and were also used as intermediates for the construction of biologically important natural product skeletons and asymmetric ligands for catalytic asymmetric reaction

In particular, pinacol coupling has been employed as a key step in the construction of protease inhibitors

HIV-Generally, the reaction is effected by treatment of carbonyl compounds with an appropriate metal reagent and/or metal complex to give rise to the corresponding alcohols and coupled products, The coupling products can have two newly chiral centers formed Threo, erythro mixtures of diols are usually obtained from reactions As a consequence, efficient reaction conditions have been required to control the stereochemistry of the 1,2-diols Recent efforts have focused on the development of new reagents and reaction systems to improve the reactivity of the reagents and diastereoselectivity of the products

In some of the described methods, anhydrous conditions and long reaction time are required

to get satisfactory yields of the reaction products, some of the used reductants are expensive

or toxic; excess amounts of metal are needed Sonication can cause metal in the form of a powder particle rupture, with a consequent decrease in particle size, expose new surface and increase the effective area available for reaction It was effective in enhancing the reactivity

Preface ix

of metal and favorable for single electron transfer reaction of the aldehydes or ketones with metal to form diols Some recent applications of ultrasound in pinacol coupling reactions are reviewed The results are mostly from the author research group

Chapter 4 - Sonochemistry and solution chemistry have been explicitly brought together by analyzing the effect of ultrasound on kinetics of ester hydrolysis and benzoin condensation, measured by the authors, and similar kinetic data for the solvolysis of tert-butyl chloride, compiled from literature For the first time the power ultrasound, reaction kinetics and linear free-energy relationships were simultaneously exploited to study ionic reactions in water and aqueous-organic binary solvents and the importance of hydrophobic ground-state stabilization of reagents in aqueous solutions was discussed This approach has opened novel perspectives for wider understanding of the effect of sonication on chemical reactions in solution, as well as on solvation phenomena in general

Chapter 5 - Ultrasound generates cavitation, which is "the formation, growth, and implosive collapse of bubbles in a liquid Cavitation collapse produces intense local heating (~5000 K), high pressures (~1000 atm), and enormous heating and cooling rates (>109 K/sec)" and liquid jet streams (~400 km/h), which can be used as a source of energy for a wide range of chemical processes This review will concentrate on theory, reactions and synthetic applications of ultrasound in both homogeneous liquids and in liquid-solid systems Some recent applications of ultrasound in organic synthesis, such as, Suzuki reaction, Sonogashira reaction, Biginelli reaction, Ullmann coupling reaction, Knoevenagel condensation, Claisen-Schmidt condensation, Reformatsky reaction, Bouveault reaction, Baylis-Hillman reaction, Michael addition, Curtius rearrangement, Diels-Alder reaction, Friedal-Craft acylation, Heck reaction, Mannich type reaction, Pechmann condensation and effect of ultrasound on phase transfer catalysis, oxidation-reduction reactions, ionic liquids and photochemistry are reviewed Ultrasound found to provide an alternative to traditional techniques by means of enhancing the rate, yield and selectivity to the reactions

Chapter 6 - Sonochemotherpy is the use of ultrasound to enhance anticancer agents Preclinical trials have manifested this modality is effective against cancers including chemoresistant lesions Sonochemotherapy is a target therapy, in which cavitation plays the leading role Making the occurrence and level of cavitation under control improves the safety and therapeutic efficacy Sonosensitizers and microbubbles enhance cavitation, being a measure to adjust the level of cavitation Free radicals due to cavitation have the potentials of restructuring a molecule and changing the conformation; thus the molecular structure and anticancer potency of a cytotoxic agent must be investigated, especially when sonosensitizer and microbubble are employed A potential clinical model for investigating sonochemotherapy is the residual cancer tissues when performing palliative high intensity focused ultrasound treatment

Chapter 7 - Ultrasound (US) is a sound wave of a frequency greater than the superior audibility threshold of the human hearing Sonochemistry is the application of ultrasound in chemistry It became an exciting new field of research over the past decade Some applications date back to the 1920s The 1950s and 1960s subsequently represented the first extensive sonochemical research years and significant progresses were made throughout them Then it was realized that ultrasound power has a great potential for uses in a wide variety of processes in the chemical and allied industries In these early years, experiments were often performed without any real knowledge of the fundamental physical background about the US action The situation changed in the 1980s when a new surge of activity started

Chapter 9 - In this chapter, the use of ultrasounds on carbon based nanotubes is reviewed with a focus on the English written articles The synthesis of carbon nanotubes and their surface modification such as oxidation and covalent functionalization under ultrasounds are reported The synthesis of hybrid nanocomposite materials where carbon nanotubes are added as a reinforcement agent via ultrasound-induced assembly is not described in this chapter A detailed survey of the literature concerning the purification and separation of carbon nanotubes under ultrasounds is provided The effect of sonication on carbon nanotubes suspensions which covers aqueous and organic solutions in the presence of surfactants is discussed with an emphasis being placed on the effect that ultrasounds have on non-covalent interactions between the carbon nanotubes and the components of the suspensions The effect

of ultrasounds on the physical properties of the carbon nanotubes, especially the introduction

of wall defects is analyzed Finally the advantages and shortcomings of sonochemistry described in this chapter are summarized, showing a possible trend in the direction of future research in this field

In: Sonochemistry: Theory, Reactions, Syntheses … ISBN: 978-1-61728-652-0 Editor: Filip M Nowak © 2010 Nova Science Publishers, Inc

Chapter 1

SYNTHESIS OF NANO-STRUCTURED MATERIALS

M F Mousavi1 and S Ghasemi

1 Department of Chemistry, Tarbiat Modares

University, Tehran, Iran2

Department of Chemistry, The University of Qom,

Qom, Iran

Recently, sonochemistry has been employed extensively in the synthesis of structured materials Rapid reaction rate, controllable reaction conditions, simplicity and safety of the technique as well as the uniform shape, narrow size distribution, and high purity of prepared nano-sized materials are some of the main advantage of sonochemistry Sonochemistry uses the ultrasonic irradiation to induce the formation of particles with smaller size and high surface area [1]

nano-Because of its importance, sonochemistry has experienced a large promotion in various fields concerned with production of new nano-structured materials and improvement of their properties during the recent years However, it has encountered limitations in the case of production of some nano-materials with specific morphology, size and properties, but the growth of the number of researches and published articles in the field of sonochemistry during the recent years shows a large interest and attempt to apply sonochemistry in nanotechnology The improvement of shape, size, purity and some other chemical and physical properties of such produced materials has been the scope of the researchers recently [2]

Sonochemistry uses the powerful ultrasound irradiation (20 kHz to 10 MHz) to induce chemical reaction of molecules During the ultrasonic irradiation, the acoustic cavitations will occur which consist of the formation, growth and implosive collapse of bubbles in a liquid The implosive collapse of the bubbles generates a localized hotspot or

1 Corresponding author M.F Mousavi, Department of Chemistry, Tarbiat Modares University, P.O Box

14115-175, Tehran, Iran Tel.: +98 21 82883474/9; fax: +98 21 82883455 E-mail addresses: mousavim@modares.ac.ir, mfmousavi@yahoo.com (M.F Mousavi)

M F Mousavi and S Ghasemi

When ultrasound radiations interact with molecules, chemical reactions can be initiated Sonochemistry is an interesting research area deal with the processes occurs during the application of powerful ultrasound (20 KHz–10 MHz) Sonochemistry arises from acoustic cavitations Bubbles undergo the formation, growth, and implosive collapse in a liquid under ultrasonic irradiation Bubble growth occurs through the diffusion of solute vapor into the bubble A bubble can be included evaporated water molecules and dissolved gas molecules When the bubble size reaches to a radius down to several µm, the bubbles collapse provides extreme conditions of transient high temperature(as high as 5000K) and high pressure (up to

~1800 atm) within the collapsing bubbles, shock wave generation, and radical formation The collapsing bubbles provide reaction sites, named hot spots.At this sites, sonolysis of water molecules to hydrogen radicals (H•) and hydroxyl radicals (OH•) is occurred which is responsible to sonochemical reaction Also, organic molecules in solution can form organic radicals with a reducing ability The size of a bubble depends on ultrasonic frequency and intensity Bubbles collapse occurs in very short time (nanosecond) and cooling rate of 1011 K/s is obtained The fast kinetics of such process can hinders the growth of nuclei produced during the collapse of bubbles This may be the reason of formation of nanostructured materials

Sonochemical synthesis of different types of nanostructured materials consisted of metals and their oxides, alloy, semiconductors, carbon carbonic and polymeric materials and their nanocomposite have received much attention in recent years

A number of factors can influence on cavitation efficiency and the properties of the products The dissolved gas, ultrasonic power and frequency, temperature of the bulk solution, and type of solvent are all important factors that control the yield and properties of the synthesized materials

In the field of sonochemistry, a number of book chapter and reviews have been published

4 Y Mastai and A Gedanken reviewed articles in the field of sonochemistry published before 2004 in a chapter of book entitled ―Sonochemistry and Other Novel Methods Developed for the Synthesis of Nanoparticles‖ [2] Also a review articles was published by Gedanken in 2004 entitled ―Using sonochemistry for the fabrication of nanomaterials‖ focused on the typical shape of products obtained in sonochemistry [1] Another review articles also published dealt with insertion of nanoparticles into mesoporous materials [5] and the sonochemical doping of various nanoparticles into ceramics and polymers [6]

In this chapter, we will present a literature survey on the various inorganic, organic/inorganic and inorganic/inorganic systems more recently have been synthesized by using ultrasonic method from January 2004 to January 2010s

Sonochemistry: A Suitable Method for Synthesis of Nano-Structured Materials 3

nm in 20 mM 1-propanol

This group also synthesized Gold nanorods by using sonochemical reduction (frequency,

200 kHz; power, 200 W) of gold ions in aqueous solution (60 mL) containing of HAuCl4 and CTAB including 1.2 mL of AgNO3 (4.0 mM) and 240 μL of ascorbic acid (0.050 M) with pH 3.5 [8] During the reaction, Au (III) is immediately reduced to Au (I) by reaction with the ascorbic acid CTAB and AgNO3 act as effective capping agents for the shape controlled growth of gold seeds The solution was purged with argon for 15 min and then sonicated in a water bath (at 27 ºC) by a water circulation system In the presence of ultrasonic, the following reactions are proposed:

( H H2O H2OH

Au   0    

n

Au nAu0  ( 0) (5)

1 0 0

0

) ( )

M F Mousavi and S Ghasemi

From the obtained results, it was demonstrated that longer gold nanorods would be obtained if the synthesis was performed in solution with acidic pH

Li et al reported the synthesis of single-crystal Au nanoprisms with triangular or hexagonal shape, 30-40 nm planar dimensions, and 6-10 nm thickness from solution of HAuCl4 and PVP in ethylene glycol solution [9] Ethylene glycol, the surfactant poly(vinylpyrrolidone), and ultrasonic irradiation play important roles in the formation of Au nanoprisms

Single-crystalline gold nanobelts have been prepared sonochemically from aqueous solution of HAuCl4 in the presence of α-D-glucose, a biological directing agent, under ambient conditions (Figure 2)

Figure 1 TEM images of gold nanorods and nanoparticles formed in different pH solutions of (a) pH 3.5, (b) pH 5.0, (c) pH 6.5, (d) pH 7.7, and (e) pH 9.8 after 180 min irradiation under argon (f) TEM image of gold nanoparticles formed in pH 9.8 without ultrasonic irradiation

Sonochemistry: A Suitable Method for Synthesis of Nano-Structured Materials 5

Figure 2 a,b) SEM images and c,d) high-magnification SEM images of as-synthesized gold nanobelts; [HAuCl4]=50 mgmL-1, [α-D-glucose]= 0.2 m, ultrasound time=1 h

The formation of gold nanobelts depends on the concentration of α-D-glucose When its concentration was as low as 0.05 M, only gold particles with a size of approximately 40 nm were obtained [10] In the dilute solution, the glucose can not provide effective coverage or passivation of gold facets The gold nanobelts have a width of 30–50 nm and a length of several micrometers with highly flexibility Nanobelts have thickness of approximately 10

nm Authors also showed that only spherical particles with a diameter of approximately 30

nm were obtained in the presence of β-cyclodextrin It was mentioned that ultrasound irradiation can enhance the entanglement and rearrangement of the α-D-glucose molecules on gold crystals

Park et al showed the effects of concentration of stabilizer (sodium dodecylsulfate: SDS) and ultrasonic irradiation power on the formation of gold nanoparticles (Au-NPs) [11] The multiple shapes and size distribution of Au-NPs are observed by different ratio of Au (III) ion/SDS and ultrasonic irradiation power

A sonochemical method in preparation of gold nanoparticles capped by functionalized ionic liquid (TFIL) in the presence of hydrogen peroxide as a reducing agent reported by Jin et al [12] It was demonstrated that the molar ratio of gold atom in chloroauric acid to thiol group in TFIL (Au/S) has great effects on the particles size and distribution of gold nanoparticles Small gold nanoparticles size of 2.7±0.3 nm can be synthesized when ultrasound irradiation applied to a solution with the molar ratio of Au/S = 1:2 for 12 h

thiol-M F Mousavi and S Ghasemi

of palladium nanoparticles with a slight increase in particle size For the highest Pd (II)/PVP value, 0.53 × 10-3, the reduction reaction leads to the unexpected smallest aggregated nanoparticles

2 3 Tellurium

Crystalline tellurium nanorods and nanorod branched structures are successfully prepared

at room temperature via an ultrasonic-induced process in alkaline aqueous solution containing tellurium nitrate, D-glucose and polyethylene glycol (PEG-400,CP) for 2 h treatment in an ultrasonic bath [14] A yellow sol was produced and was kept in darkness for 24 h to allow the growth of Te nanocrystals The as-obtained nanorods are single crystalline with [0 0 1] growth orientation, and have 30–60 nm in diameter with 200–300 nm in length Some branched architectures, consisting of several nanorods, are also found in the products The formation of the branched structures is suggested to be the result of multi-nuclei growth in monomer colloid

2.4 Tin

Metallic tin nanorods were synthesized by a sonochemical method employing the polyol process [15] In the reaction a solution of SnCl2 in ethylene glycol was exposed to high-intense ultrasound irradiation The crystallized metallic tin nanorods have diameters of 50–

100 nm and lengths of up to 3 µm were synthesized In the absence of the high-intensity ultrasonic irradiation, no reduction of tin ions occurs even at temperatures as high as 500 ºC

in a closed cell

Sonochemistry: A Suitable Method for Synthesis of Nano-Structured Materials 7

2.5 Ruthenium

Ruthenium nanoparticles have been prepared by sonochemical reduction of a ruthenium chloride solution in 0.1 M perchloric acid containing propanol and SDS foralmost 13 h [16] The effects of different ultrasound frequencies in the range 20–1056 kHz were investigated The Ru particles have diameters between 10 and 20 nm The rate of Ru (III) reduction by the sonochemical method is very slow The sonochemical reduction rate has been found to influence by ultrasound frequency An optimum reduction rate was determined in the frequency range 213–355 kHz

2.6 Germanium

Wu et al reported a method based on ultrasonic solution reduction of GeCl4 by metal hydride (LiAlH4 and NaBH4) or alkaline (N2H4·H2O) in tetrahydrofuran (THF) and in ambient condition [17] The germanium nanocrystals have narrow size distribution with average grain sizes ranging from 3 to 10 nm Octanol was used as capping agent To prevent the formation of GeO2 formed in the presence of water, the anhydrous salt is added to form a transparent ionic solution in THF

2.7 Selenium

Single crystalline trigonal selenium (t-Se) nanotubes with diameters of less than 200 nm and nanowires with diameters of 20-50 nm have been synthesized by the reduction of H2SeO3 in different solvents with a sonochemical method [18] The morphology of the products depends on the reaction conditions including ultrasonic parameters (e.g., frequency, power, and time), aging time, and solvent Hydrazine hydrate was dissolved in ethylene glycol, water, etc to form solutions The solution was added dropwise to the corresponding selenious acid solution At the same time, ultrasound was preceded to the solution, and the ultrasonic time is 30-60 min Selenium nanotube and nanowire formation involved several stage:

) (

) ( )

(

)))

))) )))

4 2 3

2

Se t Nanowires

Se t like Spherical Se

Spherical H

N SeO

M F Mousavi and S Ghasemi

The irradiation time, the concentration of Ag+ and the molar ratio of PEG to AgNO3 are parameters can influence the morphology of silver nanostructured The low molar ratio of PEG400 to AgNO3 (1:4 ~ 1:1) result in the formation of silver dendritic nanostructures but the molar ratio of 10:1 will cause to formation of silver nanoparticles (in the range of 40–100

nm) instead of dendritic nanostructures Only silver spheroidal nanoparticles were obtained at the beginning of the reaction but silver dendrites were observed with 1 h sonication.These dendritic nanostructures transform to hexagonal compact crystals after 6 h later

In another work, highly monodispersed Ag nanoparticles (NPs) were prepared by a sonochemical reduction in which Ag+ in an ethanol solution of AgNO3 was reduced by ultrasound irradiation in the presence of benzyl mercaptan without the additional step of introducing other reducing reagents or protective reagents [20]

The nanoalloys are formed when two or more kinds of metals are melted together Nanoalloy materials can exhibit many novel properties, including electronic, catalytic, magnetic and corrosion-resistant properties The sonochemical method has been used as a new technique for preparing alloy nanoparticles Bimetallic nanoalloys show different

Sonochemistry: A Suitable Method for Synthesis of Nano-Structured Materials 9

properties such as high catalytic activity and catalytic selectivity in comparison with the corresponding monometallic counterparts so that they can be used as catalysts and gas sensors

3.1 Sn–Bi

Sn–Bi alloy nanoparticles were prepared by sonicating bulk Sn–Bi alloy directly in paraffin oil under ambient pressure and room temperature [21] Twenty grams Sn and 30 g Bi were melted together in a vessel to obtain the bulk Sn–Bi alloy Then 0.5 g bulk Sn–Bi alloy was added to 30 ml paraffin oil in a horniness test tube and the system was irradiated for two hours at 1000Wcm−2 with a high intensity ultrasonic probe The product was centrifuged after cooled to room temperature and washed with chloroform and dried to get some gray-black powder They show that when the ultrasonic power was increased from 700 to 1000 Wcm-2, the size distribution reduced from 60-80 nm to 10-25 nm They also show that the sonication time had little impact on the size of the nanoparticles

3.2 Pd–Sn

Kim et al prepared Pd–Sn nanoparticles from aqueous ethanol solution of Pd(NH4)2Cl4 and SnCl2 in the presence of citric acid by applying ultrasonic irradiation and investigate the Pd–Sn nanoparticles for the oxygen reduction reaction (ORR) in alkaline media [22] The average size of Pd–Sn nanoparticles thus prepared was about 3–5 nm The initial concentrations of Pd and Sn and their molar ratio, the concentration of ethanol and the concentration of citric acid affect the size distribution of the Pd–Sn nanoparticles The Pd in Pd–Sn nanoparticles is mostly in the metallic form

3.3 Pt-Ru

Bimetallic catalysts comprised of Pt and Ru (Pt-Ru) are important in the development of low temperature (<~120 ºC) H2-air and direct methanol fuel cells Korzeniewski et al prepared Pt-Ru nanoparticles with diameters in the range of 2–6 nm as catalyst materials to investigate the electrochemical oxidation of CH3OH and CO [23] In Pt-Ru catalyst, Pt provides sites for C-H bond cleavage and CO adsorption, and Ru activates water to produce reactive oxides that enable conversion of carbon containing fragments to CO2

Pt-Ru Nanoparticle bimetallic electrocatalysts with XRu ≈0.1 and XRu ≈ 0.5 were

synthesized and its response toward the electrochemical oxidation of CO and CH3OH in 0.1

M H2SO4 was investigate [24] Syntheses were carried out in tetrahydrofuran (THF) containing Ru3+ and Pt4+ in a fixed mole ratio of either 1:10 or 1:1 using high-intensity sonochemistry

M F Mousavi and S Ghasemi

10

3.4 Co-B

Uniform spherical Co-B amorphous alloy nanoparticles were prepared by assisted reduction of Co(NH3)2+6 with BH−4 in aqueous solution which the particle size distribution was controlled by changing the ultrasound power and the ultrasonication time [25] During liquid-phase cinnamaldehyde (CMA) hydrogenation, the as-prepared Co-B catalyst exhibited much higher activity and better selectivity to cinnamyl alcohol (CMO) than the regularCo-B in the absence of ultrasonic waves

ultrasound-3.5 Au-Ag

Au-Ag nanoalloys were prepared sonochemically form solution containing gold nanoparticles and silver nitrate in the presence of different surfactant (sodium borohydride in water; poly(vinyl pyrrolidone) in ethylene glycol; poly(ethylene glycol); sodium dodecyl sulfate in water or propanol) [26] It was suggested that the degradation of the surfactants occurred during the ultrasonic treatment and allowed modification of the shape of gold nanoparticles in their interaction with silver ions Monodisperse gold-silver nanocomposite of triangular or polygonal structure was obtained with reduction of the silver by NaBH4 on the gold surface in the presence of ultrasonic irridation Uniformly distributed gold-silver with round shapes was resulted after sonication in poly (ethylene glycol) Multiangular Au-Ag nanocomposites of larger size appeared after ultrasonic irradiation of the gold-silver mixture

in the presence of poly (vinyl pyrrolidone) in ethylene glycol due to the capping effect and the relatively low rate of degradation of PVP With SDS, worms or netlike gold-silver nanostructures obtained after 1 h of ultrasonic irradiation of AgNO3 in propanol and water, respectively

3.6 Bimetallic Nanoparticles with Core-Shell Morphology

Sonochemically assisted synthesis of bimetallic nanoparticles with core-shell morphology have been reported for materials such as Co/Cu [27], Au/Pd 28 and Pt-Ru [29]

A sequential sonolysis method was used to synthesis of Pt-Ru core shell (Pt@Ru) structure [29] Pt-Ru has been used as a methanol oxidation catalyst in direct methanol fuel cells (DMFC) A potassium tetrachloroplatinate (K2PtCl4) solution containing 8 mM SDS,

200 mM propanol, and 0.1 M HClO4 were sonicated to reduce the Pt (II) to colloidal Pt (0) during 3h at 20 °C When all of the Pt (II) has been reduced, the RuCl3 solution was added to the Pt colloidal solution and sonication continued TEM image of the nanoparticles showed that the ruthenium formed a layer around the platinum particles and Pt-Ru core-shell particles

in the range of 5-10 nm were formed (Figure 4) The platinum particle sizes are ~7 nm, while the thickness of the ruthenium shell was estimated to be between 2 and 3 nm

When 1mg/mL of polyvinyl-2-pyrrolidone, PVP (MW =55000) is used as the stabilizer, the formation of colloidal platinum is very rapid and become complete within 1 h of sonication At the end of 1 h, when all of the Pt (II) was reduced, the RuCl3 solution was added to the Pt colloidal solution and sonication continued

Sonochemistry: A Suitable Method for Synthesis of Nano-Structured Materials 11

Figure 4: (a) TEM of Pt-Ru nanoparticles synthesized by sonocation of a solution containing 1 mM PtCl4

in 200 mM propanol, 0.1 M HClO4, and 8 mM SDS followed by the reduction of 1 mM RuCl3

under argon atmosphere The RuCl3 solution was added after the PtCl4

Figure 4b shows the change in absorption spectra of the colloidal solutions with time

Curve a shows the absorption spectrum of PtCl4 2- solution at time t = 0 and continuing

through the addition of the RuCl3 and its reduction Curve e shows the absorption spectrum immediately upon addition of the ruthenium chloride Only one prominent peak at 400 nm appears in the curve indicating an instantaneous partial reduction of Ru (III) upon addition to the solution

As mentioned above, Vinodgopal et al used a sequential reduction method to prepare

Pt-Ru core-shell nanoparticles but Anandan and his coworker prepared Au-Ag bimetallic

nanoparticles by the sonochemical co-reduction of Au(III) and Ag(I) ions in aqueous solutions containing polyethylene glycol (0.1 wt %) and ethylene glycol (0.1 M) [30] The average diameter of the bimetallic clusters prepared by the simultaneous reduction is about 20

nm The stabilizing polymers can coordinate to metal ions before the reduction This interaction between the polymer and the metal ions lead to the formation of smaller size core-

M F Mousavi and S Ghasemi

12

shell nanoparticles with a narrow size distribution They also suggested that the formation of core-shell morphology is most likely due to the difference in the reduction rates of the individual metal ions and the involvement of a polymer-Ag ion complex Gold ions are firstly reduced under the sonochemical conditions followed by the reduction of Ag+ ions on the surface of the gold particles

4 METAL OXIDE

During the last years, the ultrasonically assisted synthesis of metallic oxides and hydroxides has been considered by some of researchers Due to their importance in various area of science, some of them are investigated in the following paragraph

4.1 ZnO

ZnO is one of the most important multifunctional semiconductors with wide direct energy band gap of 3.37 eV and large exciton binding energy (about 60 meV) Sonochemical synthesis of ZnO nanostructures with different shapes such as nanowires, nanotubes, nanoparticles have been considers by some of authors The effects of various parameters on the morphology of ZnO nanostructures were investigated ZnO nanostructure with morphologies such as flower-like clusters [31], cauliflower-like [32], nanorods [33], needle-shape [34], trigonal-shaped [35], nanosheet [36] and Hollow ZnO microspheres [37]

Jung et al fabricated ZnO nanorods, nanocups, nanodisks, nanoflowers, and nanospheres

in a horn-type reaction vessel using an ultrasonic technique at a power of 50 W (intensity of 39.5 W/cm2) and frequency of 20 kHz (Figure 5) [38] The kind of hydroxide anion-generating agents, concentration of reactants, sonication time and additives are dominant factor affect on preparation of different morphology of ZnO For the production of ZnO nanorods and ZnO nanocups, different concentration of Zn(NO3)2 and hexamethylenetetramine (HMT, (CH2)6N4 as well as different sonication time (30 min for nanorods in comparison with 2h for nanocups) were used An increase in ultrasonication time provides such energy indicates to the reaction System that hinders the ZnO nanorod growth Triethyl citrate was used as an additional chemical additive to synthesize ZnO nanodisks ZnO nanocrystals grow preferentially along the [0001] direction to form nanorods The growth rate of the ZnO crystal along the [0001] direction decreases dramatically due to the addition of triethyl citrate

For the synthesis of ZnO nanoflowers and nanospheres, ammonia–water (28–30 wt %) solution were used as hydroxide anion precursors In the case of ZnO nanospheres, triethyl citrate was added to the mixture of zinc acetate dihydrate solution (90 mL) and ammonia–water (10 mL) The sonochemical growth mechanism of ZnO nanostructures was suggested

by authors as follows:

HCHO NH

O H N

Sonochemistry: A Suitable Method for Synthesis of Nano-Structured Materials 13





4 2

) (

2 2

The sonolysis of water produces O2 radicals in solution

Figure 5 SEM (left) and TEM (right) images of ZnO nanostructures (a,b) Nanorods (c,d) Nanocups (e,f) Nanodisks (g, h) Nanoflowers (i, j) Nanospheres (Insets: HRTEM image)

The same authors presented in another paper a sonochemical method for fabricating vertically aligned ZnO nanorods arrays on various substrates such as a large-area Zn sheet, Si

M F Mousavi and S Ghasemi

4.2 CuO

The synthesis of one-dimensional (1D) Cu(OH)2 nanowires [45] in a aqueous solution of CuCl2 and NaOH was done under ultrasound irradiation with 40 kHz ultrasonic waves at the output power of 100% at 70 ºC for 5-60 min The morphology of products is highly depends

on time of ultraonication Under continuous ultrasonic irradiation, Cu(OH)2 nanowires integrated into nanoribbons, then parts of nanoribbons crosswise grew to form 3D Cu(OH)2 nanostructures; finally, 3D nanostructures disrupted and transformed into 3D CuO microstructures The effect of ultrasonic irradiation time on conversion process of Cu(OH)2

to CuO was investigated A color change of the product from the pale-blue to the black was observed in the range of 15 to 45 min of irradiation implied the gradual conversion of Cu(OH)2 to CuO The XRD analyses of the products confirmed the conversion process It was demonstrated that the ultrasound plays two roles besides dispersion: shortening the conversion time from Cu(OH)2 to CuO and inducing the formation of 3D CuO microstructures The CuO microstructures showed better electrochemical property than Cu(OH)2

4.3 V2O5

A sonochemical method has been developed to preparation self-assemble V2O5

nanowires with spindle-like morphology (Figure 6) Vanadium oxide (V2O5, 0.46 g, 2.5 mmol) and sodium fluoride (NaF, 0.21 g, 5 mmol) were dissolved in 50 mL of distilled water

in a 100-mL round-bottom flask and exposed to high-intensity ultrasound irradiation (20 kHz,

100 W/cm2) under ambient air for 2 h The organization of 1D V2O5 nanostructured subunits into spindle -like V2O5 bundles was occurred

Each bundles composed of several tens of homogeneous nanowires with diameters of

30-50 nm and lengths of 3-7 µm Also, a sensitive resonance light scattering (RLS) method was

developed to detect bovine serum albumin (BSA) based on the ultrasonically V2O5 bundles [46] An increase in the scattered light signals of V2O5 bundles were observed by the addition of BSA The enhanced RLS intensity at 468 nm of V2O5 bundles-BSA varies

linearly with the concentration of BSA in the range from 0.5 to 20 µg mL-1

Synthesis of self-assembled nanorod vanadium oxide bundles by sonochemical technique were reported by a Malaysian group [47]

Sonochemistry: A Suitable Method for Synthesis of Nano-Structured Materials 15

Figure6 FE-SEM images of the V2O5 bundles with spindle-like morphology (a) low-magnification SEM image of V2O5 bundles; (b) low-magnification TEM image

The morphologies of the nanorod vanadium oxides are depended on the time of sonication so that a uniform, well defined shapes and smaller size nanorod vanadium oxide bundles were obtained with higher ultrasound irradiation times Vanadium oxide bundles showed higher

activity to anaerobic oxidation of n-butane than the bulk material

4.4 Iron oxide

Suslick and Bang used carbon nanoparticles as a spontaneously removable template for synthesis of crystalline hollow hematite (α-Fe2O3) [48] A mixture of Spherical carbon nanoparticles (0.1 g) (4- 12 nm diameter) and Fe(CO)5 (0.5 mL) in 40 mL of hexadecane was irradiated by a high-intensity ultrasound horn (operated at 20 kHz and 50 W/cm2 at 20 °C for

3 h under argon flow) The decomposition of Fe(CO)5 form high-surface-area iron shells around the core carbon nanoparticles The high-surface-area iron shells rapidly oxidize in contact with air and release such heat that ignites the carbon particles The combustion of the nanosized carbon particles generates enough heat to crystallize the iron oxide shells to hollow cores α-Fe2O3 (Figure 7) Mössbauer spectra confirm the presence of hematite as the only iron species Under the same condition, the sonication of precursor solution in the absence of carbon nanoparticles produce agglomerated nanoparticles of ~ 6 nm

M F Mousavi and S Ghasemi

16

Figure 7 (a) Bright-field and (b) dark-field TEM image of nanosized hollow hematit

Any organic residues were completely removed by annealing the as-produced hollow hematite at 450 °C for 2 h under air TEM image and EDS (energy dispersve X-ray spectroscopy) reveal that the morphology and composition of the hollow hematite remained unchanged after the heat-treatment The hollow hematite nanoparticles shows hysteresis loops for at 5 and 298 K Also, the hollow hematite nanoparticles are weakly ferromagnetic down to

5 K

Another work has been reported to sonochemically synthesis of monodispersed magnetit nanoparticles [49] Dang et al used an FeCl2 ethanol–water mixed solvent and a 2 N NaOH aqueous solution to from a Fe(OH)2 precipitate The Fe(OH)2 precipitate was irradiated by an ultrasonic horn in air at 50 ºC to synthesize magnetite nanoparticles It was demonstrated that the formation of magnetite was accelerated in ethanol–water solution in the presence of ultrasonic irradiation

Monodisperse iron oxide nanoparticles with 5–20 nm can be synthesized by an inexpensive and simple ultrasonic-assisted method at low temperature [50] This is based on the decomposition of iron pentacarbonyl in cis–trans decalin They found that ultrasonic irradiation could greatly enhance the crystallization of iron oxide nucleus at 190 °C, after the react solution was refluxed at this temperature; monodisperse γ-Fe2O3 nanocrystals were obtained

4.5 Manganese Oxide

An ultrasonic technique was used to prepare MnO2 nanoparticles inside the pore channels of ordered mesoporous CMK-3 [51] MnO2 nanoparticles were anchored in pores of carbon CMK-3 The size of MnO2 incorporated in CMK-3 is between 0.5 nm and 3.0 nm In the pores, KMNO4 reduce to MnO2 Ultrasonic technique controls the amount of loading MnO2 inside CMK-3 CMK-3 with 20 wt % loading of MnO2 inside CMK-3 produced an improved discharge capacity of 223 mAhg-1 at 1 Ag-1

Sonochemistry: A Suitable Method for Synthesis of Nano-Structured Materials 17

Colloidal Mn3O4 nanoparticles with diameters of about 5-10 nm has been pepared by an ultrasonic-assisted method in the absence of any additional nucleation and surfactant at normal temperature and pressure [52] It was shown that reveal the size and the crystallinity

of Mn3O4 nanoparticles depends on the growth temperature so that the smaller the average diameter and the poorer the crystallinity of Mn3O4 nanoparticles was observed at lower reaction temperature The magnetic properties of the samples showed that Mn3O4 nanoparticles exhibited ferromagnetic behavior at low temperature (40 K)

Kumar et al prepared sonochemically a highly dispersed and non-agglomerated α-MnO2 nano-needles of dimensions 20–30 nm from aqueous solution consisting of manganese Mn(acetate)3 and LiOH with a pH value of 7.2 [53]

The sonochemical preparation of MnO2 was reported through the reduction of MnO4- in water under Ar atmosphere The effect of H2O2 formed in the sonolysis of water on the rates

of reduction of MnO4- was investigated [54] It was shown that the rate of the sonochemical reduction of MnO4- depend on the amount of sonochemically formed H2O2 molecules

Mn3O4 nanoparticles were prepared by reacting MnCl2 and NaOH in water at room temperature through a sonochemical method, operated at 20 kHz and 220 W for 20 min [55] Also, the LiMn2O4 nanoparticles were also prepared A thin film of the LiOH with the thickness of about 4.5–5.5 nm was coated onto the surface of Mn3O4 under the same sonochemical conditions and the LiOH-coated Mn3O4 particles sample was heated at the relatively low temperature of 300–500 °C The thickness of coated LiOH on Mn3O4 obtained from the reaction ratio of 3:1 between LiOH and Mn3O4 was about 4.5–5.5 nm range Then,

by heating LiOH-coated Mn3O4 particles at the relatively low temperature of 300–500 °C for

1 h, they were transformed into phase-pure LiMn2O4 nanoparticles of about 50 to 70 nm size

in diameter

4.6 In2O3

The synthesis of monodispersed In2O3 nanoparticles and doped with rare earth ions ((Eu3+ and Dy3+)) is another work considered to investigate their photoluminescence properties [56] To a solution of indium ethoxide, In(OEt)3, in 20 ml ethanol containing 0.36

g cetyltrimethyl ammonium bromide (CTAB), 60 ml water was added and pH of solution was adjusted to 10 by adding NH4OH The irradiation of solution with a high-intensity (100 W/cm2) ultrasonic radiation operating at 20 kHz, under air at room temperature resulted in In(OH)3 nanoparticles After 1 h sonication, In(OH)3 nanocubes are obtained in the range of 30-35 nm The In2O3 nanoparticles were formed by heating the In(OH)3 nanoparticles in furnace under air at 350 °C for 1 h On exciting at 235 nm, emission peaks around 460 nm (blue) and two relatively less intense peaks centered around 548 nm (yellow) and 618 nm (orange) were observed possibly due to the presence of shallow defect levels in the annealed samples With Eu3+/Dy3+ incorporation, the In2O3 diffraction peaks broads with respect to diffraction peaks of undoped In2O3 With Eu3+/Dy3+ incorporation, Eu3+/Dy3+ has gone into the In2O3 lattice and lattice undergoes distortion In2O3 doped Dy3+ nanoparticles did not show any luminescence due to the highly strained and distorted environment around the dysprosium ions in the In2O3 lattice A similar strain causes tothe low emission intensity in the In2O3 doped Eu3+ particles

M F Mousavi and S Ghasemi

ultrasonic-of TiO2 and formation ultrasonic-of mesopore TiO2.The as-prepared products by the ultrasonic method were composed of anatase and brooktie phases Photocatalytic decomposition was investigated for formaldehyde and acetone Mesopore TiO2 prepared by ultrasonic method showed better photocatalytic activities than the samples prepared by conventional hydrolysis method Wang et al prepared mixed-crystal TiO2 powder with high sonocatalytic activity under ultrasonic irradiation in hydrogen peroxide solution [58] The nano-sized rutile phase TiO2 powder (10.0 g) and 30% hydrogen peroxide solution (30 mL) were mixed into a glass reactor and suspension was treated under ultrasonic irradiation for 4.0 h A white powder was obtained after washing and drying This powder was heat-treated at 400 °C for 40 min The XRD and the FT-IR spectra of treated mixed-crystal showed both nano-sized rutile phase and anatase phase TiO2 powders The sonocatalytic degradation of methylene blue in aqueous solution was investigated under ultrasonic irradiation in the presence of treated mixed-crystal TiO2 powder Effect of different parameters such as heat-treated temperature and heat-treated time on degredation of methylen blue was studied It was shown by the UV–vis spectra that the methylene blue in aqueous solution can be obviously degraded under ultrasonic irradiation

in the presence of treated mixed-crystal TiO2 powder

Guo et al prepared the mesoporous TiO2 nanorods using industrial bulk Ti powder [59] The as prepared materials contained numerous irregular olive-like nanorods aggregates The nanorods were 8–12 nm in width and 15–100 nm in length The products showed higher photocatalytic activity to toluene than Degussa P25 TiO2

Crystalline anatase TiO2 nanoparticles was synthesized from titanium tetraisopropoxide

in the ionic liquid 1-(3-hydroxypropyl)-3-methylimidazolium-bis(trifluoromethan esul- fonyl)amide by ultrasound assisted synthesis [60].The spherical shaped TiO2 particles have a small size (~5 nm) with narrow size distribution TiO2 nanoparticles have high surface area

of 177m2 g−1 with bandgap of 3.3 eV The spherical TiO2 nanocrystals have good photocatalytic activity in the degradation of methylorange

Zhou reported the preparation of nanocrystalline mesoporous Fe-doped TiO2 powders red by the ultrasonic-induced hydrolysis reaction of tetrabutyl titanate (Ti(OC4H9)4) in a ferric nitrate aqueous solution [61] The photocatalytic activities of Fe-doped TiO2 powders were investigated by the photocatalytic oxidation of acetone in air The high activities of the Fe-doped TiO2 powders was observed due to synergetic effects of Fe-doping and large specific surface area of catalyst

Sonochemistry: A Suitable Method for Synthesis of Nano-Structured Materials 19

4.8 PbO2

Our research group synthesized β-PbO2 nano-powder by the ultrasonic irradiation of an aqueous suspension of dispersed β-PbO (Pure yellow orthogonal phase), as precursor, in the presence of ammonium peroxydisulfate as an oxidant [62] The effect of pararmeters such as oxidant concentration, temperature and ultrasonic wave amplitude on the morphology, reaction rate and composition of products were investigated The reaction rate increased with

an increase in temperature and ammonium peroxydisulfate concentration It was found that the applied ultrasonic wave determines the particle size PbO2 samples prepared under optimized experimental conditions have lead dioxide particles in the range of 50–100 nm

It was observed that the use of Pb(NO3)2, instead of the lead precursor β-PbO, resulted in the formation of PbSO4, which precipitated out at the end of the reaction Thus, the oxidation process should be initiated with β-PbO When ultrasonic waves were applied to β-PbO particles, only mechanical milling occurred and the particles were cracked β-PbO was not oxidized under these conditions, even with an increase in the duration of ultrasonication In fact, a proper oxidant is necessary to convert β-PbO to PbO2 In the presence of ammonium peroxydisulfate, the increased concentration of hydroxyl radical facilitated the oxidation of β-PbO to PbO2 under ultrasonic irradiation The XRD results reveal that only β-PbO2 is formed under optimum conditions When the reaction mixture was stirred instead of ultrasonically irradiated, only a fraction of the lead oxide was converted to lead dioxide, and lead sulfate was the main reaction product

4.9 Other Metallic Oxide

Other metallic oxides such as bismuth oxide [63], lead oxide [64 65], magnesium oxide66, molybdenum oxide [67], mercury oxide [68], Tungsten oxide [69] and tin oxide[70] have been synthesized by sonochemistry methods in the past several years

Figure 8 SEM of lead dioxide (β-PbO2) samples prepared from a solution containing 0.2 g β-PbO and 5

g (NH4)2S2O8 at 60 ºC and ultrasonic amplitude of 84µm (Diffrent magnification)

M F Mousavi and S Ghasemi

20

4.10 Rare-Earth Oxide

Wang et al in 2002 used a sonochemical method to prepare CeO2 nanoparticles [71] After that, Miao et al succeed to synthesis of CeO2 nanotubes by a sonochemical method under ambient air in alkali aqueous solution without any template [72] The CeO2 nanotubes had diameters of 10–15nm and length of 150–200 nm They also showed that when 3 M KOH aqueous solutions is used, only rod-like assemblies composed of CeO2 nanoparticles with the size of 5 nm were appeared The CeO2 nanotubes were obtained only at concentration higher than 5 M KOH

In 2007, Zhang et al proposed a sonochemical method to synthesis of Polycrystalline CeO2 nanorods with 5-10 nm in diameter and 50-150 nm in length at room temperature [73] Polyethylene glycol (PEG) was used as a structure-directing agent In the absence of PEG, the agglomerated nanoparticles was formed instead nanorods To a solution of Ce(NO3)3 containing 1 g of PEG600, NaOH solution (0.005 g/mL) was added gradually (5 mL/min) under ultrasonication for ~1 h at room temperature until the pH value was 10 TEM images of the CeO2 showed nanorods with the clear (111) and (220) lattice fringes with the interplanar spacing of 0.31 and 0.19 nm, respectively The UV-vis absorption spectrum of the CeO2 nanorods exhibits a strong absorption band at the UV region due to the charge transfer transitions from O 2p to Ce 4f bonds The BET specific surface area of CeO2 nanorods was calculated 154.5 m2 g-1 in comparison with 5.7 m2 g-1 of commercial CeO2

Nanoparticles of the single (Eu3+, Dy3+, Tb3+), double(Eu3+/Dy3+, Eu3+/Tb3+,

Dy3+/Tb3+), and triple (Eu3+/Dy3+/Tb3+) doped Gd2O3 (gadolinium oxide) nanoparticles were prepared via a sonochemical technique [74] The particles sizes were in the range of 15

to 30 nm The triple doped samples showed multicolor emission on single wavelength excitation

5 THE SONOCHEMICAL SYNTHESIS OF MIXED OXIDES

Mixed Oxides such as aluminates, molybdates, manganates and etc have been found many applications in sensors, electrooptic and electromagnetic devices because of their prominent properties The sonochemical method is one of the simple route have been used during the last years to prepare nanostructure mixed oxides

5.1 MVO4

Much of work on metal vanadate is focused on bismuth vanadate (BiVO4) because BiVO4 has been recently recognized as a strong photocatalyst for water water decomposition and organic pollutant decomposing under visible light irradiation due to its narrow band gap

75

A facile sonochemical approach has been developed for the synthesis of BiVO4 photocatalyst by Zhou and his coworkers In a typical preparation, aqueous solutions of Bi(NO3)3 and NH4VO3 were mixed together in 1:1 molar ratio and exposed to high-intensity ultrasound irradiation for 60 min The average crystal size of as-prepared BiVO4 particles is

ca 50 nm and samples exhibited surface areas of ca 4.16 m2/g The as-prepared BiVO4

Sonochemistry: A Suitable Method for Synthesis of Nano-Structured Materials 21

nanocrystals had strong absorption in visible light region with an obvious blue-shift compared with that of the bulk sample The band gap was estimated to be ca 2.45 eV BiVO4 nanocrystals showed high photocatalytic activities to decolorization of methyl orange under

visible light (λ > 400 nm)

Shang et al used polyethylene glycol (PEG 20000) as surfactant[76] An aqueous solutions of Bi(NO3)3 and NH4VO3 in 1:1 molar ratio as well as polyethylene glycol (1 g) was exposed to high-intensity ultrasonic irradiation (6 mm diameter Ti-horn, 600W, 20 kHz) for 30 min in ambient condition The pH value was adjusted to about 7 by NH3 Nanosized

BiVO4 consisted of small nanoparticles with the size of ca 60 nm The nanosized BiVO4

exhibited excellent visible-light-driven photocatalytic efficiency for degrading Rhodamine B (RhB) with good stability When the RhB solution was irradiated with visible-light (λ > 420 nm) in the presence of calcinated well-crystallized BiVO4 sample, about 95% of RhB was degraded after being irradiated for 30min and the spectral maximum shifted from 552 to 500

nm

The lanthanide orthovanadate LnVO4 (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er,

Tm, Yb, Lu) nanoparticles had been prepared from an aqueous solution of Ln(NO3)3 and NH4VO3 without any surfactant under ultrasonic irradiation[77] It was observed that the morphology of the LnVO4 nanoparticles was affected strongly by ultrasonic irradiation The as-formed LnVO4 particles have a spindle-like shape with an equatorial diameter of 30-70

nm and a length of 100-200 nm Each particles (as aggregates) are composed of smaller nanoparticles of 10-20 nm

The sonochemical synthesis of Lanthanide orthovanadates RVO4 ( R = La, Ce, Nd, Sm,

Eu and Gd) was reported in the presence of Polyethylene glycol (PEG-900) and amphiphilic triblock copolymer Pluronic P123 as structure-directing agents at room temperature [78] When the P123 surfactant was used, the Lanthanide orthovanadates with nanorod shape was observed With the surfactant PEG, nanorods of NdVO4, nanospindles of GdVO4 and nanoparticles of other orthovanadates were obtained

5.2 MTiO3

The metal tiatanates, BaTiO3, PbTiO3, and PbTiO3 have been reported to be synthesized

by sonochemical methods [79] Wang and his coworker prepared PbTiO3 fine powders with narrow size distribution (40–60 nm) by a sol-gel method with lead acetate Pb(OCOCH3)2, tetrabutyl titanate Ti(OBu)4 as precursors via ultrasound irradiation

The formation of BaTiO3 particles was reported by a Japanese group [80] They used ultrasonic irradiation to form narrow size distribution of aggregated particles This method caused to formation of the aggregation of the original 5–10 nm BaTiO3 particles It is thought that under ultrasonic irradiation, Ti-based sol forms by the hydrolysis of TiCl4 in Ba2+ aqueous solution Ti ions dissolve form the Ti-based sol to form Ti(OH)62-octahedron and the nucleation of BaTiO3 occurs around the Ti-based sol.Ultrasound influences the synthesis

of BaTiO3 particles mainly throughacceleration the dissolution of Ti ion from Ti-based sol and the nucleation of BaTiO3 particles

Xu et al developed a sonochemical method for the synthesis of spherical BaTiO3 nanoparticles by sonicating a strong alkaline solution including BaCl2 and TiCl4 [81] They

M F Mousavi and S Ghasemi

of the methyl orange degradation was measured to be as high as 98% in 2 h

They reported another work that investigate the effect of processing conditions on preparation of nanosized copper aluminate (CuAl2O4) spinel using Cu(NO3)2 and Al(NO3)3

as starting materials and urea as a precipitation agent at a concentration of 9 M [83] The reaction was carried out under ultrasound irradiation at 80 ºC for 4 h and a calcination temperature of 900 ºC for 6 h

High surface area MgAl2O4 has been synthesised by a sonochemical method Two kinds

of precursors were used, alkoxides and aluminium nitrates/magnesium acetates in the presence and absence of cetyl trimethyl ammonium bromide (CTAB) In the case of alkoxides precursors the as-made product is a mixture of hydroxides of aluminium and magnesium, and after heating at 500 ºC pure MgAl2O4 phase was not obtained [84] While with nitrates/acetates a gel is obtained after sonication, containing the metal hydroxides and ammonium nitrate Heating at 500 ºC transforms the as-made products into MgAl2O4 spinel phase with the surface area of 267 m2/g In the case of nitrates/acetates precursors, the CTAB reduces the formation of large stable aggregates

Zinc Aluminate ZnAl2O4 and Zinc Gallate ZnGa2O4 doped with Mn2+ and some of lanthanide ions such as Dy3+, Tb3+, Eu3+ were synthesized through a sonochemical process

85 Photoluminescence studies were done on prepared samples The doped samples showed multicolor emission on single wavelength excitation

5.4 MWO4

PbWO4 nanostructures with different morphologies, such as polyhedral, spindle-like, and dot-shaped, have been synthesized via a mild sonochemical route from an aqueous solution of lead acetate and sodium tungstate (Na2WO4) in the presence of complexing reagent nitrilotriacetate acid (NTA) [86] H3NTA is a precursor of a multidentate organic ligand (NTA3-), incorporating carboxylic acid groups and one N-donor atom, capable of coordinating to several metal centers The mechanism of the formation of PbWO4 nanocrystals is probably related to the coordination of Pb2+ and NTA3- to form Pb-NTA complex To explain what has been occurred in the reaction vessel, it was suggested that Pb-NTA complex is formed due to coordination of Pb2+ and NTA3- In the presence of

Sonochemistry: A Suitable Method for Synthesis of Nano-Structured Materials 23

ultrasound irradiation (20 kHz, 60 W/cm2), the dissociation of the complex was occurred and PbWO4 was formed The mechanism is summerised as follow:





NTA Pb

4 2

4 2

PbWO WO

Pb   

(17)

Different shapes of PbWO4 nanocrystals, i.e polyhedral, spindle-like, and dot-shaped morphologies were obtained with controlling the pH value and the amount of complexing reagent A pH range of 5-9 is optimal Figure 9a shows that the products prepared at pH 9.0 are polyhedrons with dimension of (400-500) nm × (600-700) nm At the pH value was decreased of 7.0, the homogeneous spindle-like nanorods with diameters of 50-60 nm at the center and lengths of about 200-250 nm (Figure 9b) was obtained Figure 9c shows the dot-shaped product prepared with a pH value of 5.0 The average size of these polycrystalline particles is about 10 nm

Under pH 7-9, nitrilotriacetic acid exists as NTA3- and the predominant species in solution remains a 1:1 complex of PbNTA- With pH decreasing, NTA3- would partly combine H+ in the solution When pH was lower than 5, NTA3- would exist as HxNTAx-3 and its complexing ability with metal ions would therefore decrease At the pH > 11, another complex, Pb(OH)x2-x, was formed instead of PbWO4 due to the strong complexing ability between Pb2+ and OH- Room-temperature photoluminescence of PbWO4 nanocrystals showed green emissions at 480-500 nm with different luminescence intensity The optical properties of these PbWO4 nanocrystals differ from those of the bulk crystals

In another work, Geng et al prepared nanosized lead tungstate (PbWO4) hollow spindles via a sonochemical process by using triblock copolymer Pluronic P123- (EO20PO70EO20) as

a structure directing agent [87] The concentration of polymer had vital role in preparation of PbWO4 Hollow PbWO4 nanospindles were obtained in the polymer concentration of 4 gL-1 PbWO4 hollow spindles can be formed by templating the P123 micellar aggregates induced

by the ultrasonic irradiation Pb2+ ions in the solution are easily attracted on the micellar surfaces by forming Pb-(PEO-PPO-PEO) units and provide nucleation domains for the subsequent reaction between Pb2+ and WO42- to form PbWO4 nanoparticles

Figure 9 TEM images of samples prepared at pH values of (a) 9.0, (b) 7.0, and (c) 5.0 The initial concentrations of Pb2+, WO2-, and HNTA were 20, 20, and 40 mM, respectively

M F Mousavi and S Ghasemi

24

The same procedure was used to preparation of ZnWO4 nanorods [88] ZnWO4 nanorods were successfully synthesized via powerful ultrasonic irradiation An aqueous solution of sodium tungstate (Na2WO4) was slowly added to a solution of zinc acetate, 3 g P123, 20mL ethanol and 200mL deionized and Ultrasound irradiation was applied to solution by a high-intensity ultrasonic probe, 20 kHz, 250 W/cm2 The photocatalytic activity of ZnWO4 in degradation of rhodamine-B (RhB) under 365nm UV light illumination was investigated Also, Metal tungstates (MWO4, M = Ba, Sr and Ca) were synthesized using the corresponding M(NO3)2 and Na2WO4 in ethylene glycol by ultrasonic irradiation [89] Their average sizes of round shaped nanoparticles of metal tungstates were 42.0 ± 10.4, 18.5 ± 5.1 and 13.1 ± 3.3 nm for M = Ba, Sr and Ca, respectively

5.5 MoO4

Lead molybdate (PbMoO4) and lead tungstate nanoparticles were synthesized from solution of Pb(NO3)2 and Na2MO4 dissolved in 50 ml ethylene glycol by applying ultrasound waves for 1 h [90] The particle sizes were 29.09 ± 5.22 nm and 21.05 ± 2.68 nm for PbMoO4 and PbWO4, respectively

Bismuth molybdate (α-Bi2Mo3O12 phase) nanorods were synthesized by pyridine intercalative sonochemical method [91] Spherically α-Bi2Mo3O12 powder was dissolved in pyridine and sonicated at 30–40°C under nitrogen atmosphere, for varying time periods (2, 4,

6, 8, and 10 h) The diameter of the α-Bi2Mo3O12 nanorods were about 10 nm and length in few hundreds of nanometer to μm after sonicating in pyridine for 6 h The controlled heating

of pyridine-intercalated nanorods to 450 °C was resulted in a-Bi2Mo3O12 phase nanorods free of pyridine

5.6 Ferrites

Ferrites are widely used in ferrofluid technology, magnetic resonance imaging, drug delivery and data storage The synthesis of spinel ferrites MFe2O4 ((M = Mn, Co, Ni, Cu and Zn)) such as copper ferrite (CuFe2O4) [92] and zinc ferrite (ZnFe2O4) [93a] were reported Sivakumar et al [93b] used a ultrasound assisted emulsion (consisting of rapeseed oil and aqueous solution of Zn2+ and Fe2+ acetates) and evaporation protocol to synthesize zinc ferrite (ZnFe2O4) nanoparticles (Figure 10) The as-synthesized sample consisted of crystalline zinc ferrite particles with an average diameter of ~4 nm and the heat-treated ferrite particles (350 °C for 3 h) with ~12 nm

The small amount of oil present on the surface of the as-synthesized ferrite sample was removed by heat treatment at 350 °C for 3 h

Ferrites with formula MFeO3 also were reported Das et al reported the preparation of nanosized BiFeO3 powders by sonochemical technique [94]

Nanocrystalline rare earth orthoferrites MFeO3 (M=Gd, Er, Tb and Eu) were prepared by Sivakumar et al using Fe(CO)5 and rare earth carbonates precursor through sonochemical method [95] A distinct advantage of the sonochemical method is the preparation of nanocrystalline orthoferrites at a remarkably reduced calcination temperature The magnetic properties of different orthoferrites were reported

Sonochemistry: A Suitable Method for Synthesis of Nano-Structured Materials 25

Figure 10 TEM of as-prepared and heat-treated ZnFe2O4 nanocrystals (scale bar is 20 nm)

Same authors reported a sonochemical method for preparation of strontium hexaferrite by

a sonochemical method employing Fe(CO)5 and SrCO3 [96] A SrCO3 hexagonal rod was synthesized using strontium nitrate and urea in the presence of ultrasonic irradiation Stoichiometric amounts of SrCO3 and Fe(CO)5 was dissolved in decalin and irradiated with ultrasound (using the titanium horn tip with power of 29.7W/cm2) in an air atmosphere at 0°C for 4 h to get the strontium hexaferrite powder The resultant precursor was then calcined

at 900°C for 14 h in air atmosphere, which is lower than the conventional solid-state reaction (1300°C) It was suggested that the application of ultrasound on the Fe(CO)5 generates amorphous Fe2O3 The amorphous Fe2O3 was then dispersed or coated on SrCO3 during the ultrasound irradiation SrFe12O19 exhibited an intrinsic coercivity field (Hc) of ~4600 Oe and a saturation magnetization (Ms) of ~60 emu/g at 20 K and ~32 emu/g at 300 K The Hc value remains more or less temperature independent over the 20–300K range The magnetization vs temperature pattern exhibits strong temperature dependence over a range of 300–800 K probably due to the presence of single-domain nanoparticles and consequent superparamagnetism

Sonochemistery is one of the techniques have been used to synthesis different categories

of nanocomposites such as inorganic/inorganic and inorganic/organic materials [97]

6.1 Metal Oxide-Metal (Oxide) Nanocomposite

Perkas and et al used sonochemical irradiation of iron (II) acetate aqueous solution in presence of silver nanopowder to deposite magnetite nanoparticles on silver nanocrystals [97] The crystalline size of silver nanoparticles was calculated as 50 nm and magnetite nanoparticles ~ as 10 nm Ag-Fe3O4 composite was well arranged in the series of chains (Figure 11 a and b)

M F Mousavi and S Ghasemi

26

Figure 11 (a) initial nanosilver powder (b) TEM images of Ag–Fe3O4 composite obtained by

sonochemical method and (C) HRTEM image of Ag–Fe3O4 composite

The characterization of the product reveals the presence of two phases of the silver and the magnetite without any chemical interaction between them It was suggested that local melting of silver occur when the magnetite nucleus is thrown at the silver surface by high speed sonochemical microjets and this is probably the phenomenon causes the anchoring of magnetite to the nanosilver surface The total saturation magnetization of the composite is rather low – 1.8 Emu/g However, it most considered that only 5.2 wt% of the nanocomposite

is corresponded to Fe3O4 and its magnetization would be about 35 Emu/g Fe3O4 The Fe3O4 nanocomposite showed superparamagnetic behavior in a magnetic field

Ag-Pradhan et al also synthesized gold-magnetite nanocomposite materials via sonochemical methods (Figure 12) [98] Magnetite nanoparticles (1 mg suspended in 100 μL of methanol) with diameter of ca 30 nm were added to a 50 mL solution of 0.1 mM HAuCl4 (aq) containing methanol (100 μL), diethylene glycol (100 μL), or oleic acid (100 μL) as solvent modifiers sparged with argon during the experiment [99] The solution was then sonicated in

a jacketed, water cooled (20 C) reaction vessel under an argon atmosphere for 10 min at 50% amplitude using an ultrasonic processor The resulting solution was then transferred into a test tube and kept in front of a magnet The gold–magnetite nanocomposite material was pulled against the wall of the test tube by the magnet

The coercivity of the treated magnetite was 75 Oe, while the gold–magnetite nanocomposite material exhibited a coercivity of 200 Oe The changes in magnetic properties are likely due to changes in the surface characteristics of the magnetite Gold could contribute

to changes in the surface states and magnetic properties

Sonochemistry: A Suitable Method for Synthesis of Nano-Structured Materials 27

Figure 12 TEM images of gold–magnetite nanocomposite material formed by sonication of magnetite

in aqueous HAuCl4 with added (a) methanol (b) oleic acid additives Dark particles are gold, grey particles are magnetite

Also, during sonication, the capping ligands can be removed and cause a change in the surface charge or magnetic domains The additives were also found to change the gold particle loading and the Fe/Au ratio in the composite materials With oleic acid added, substantially smaller gold particles were observed, and the Fe/Au ratio was intermediate between that of the materials prepared with methanol and diethylene glycol

Mizukoshi et al reported immobilization of noble metal nanoparticles (Au, Ptand Pd) on the surface of maghemite with irradiation of aqueous solutions containing noble metal ions (HAuCl4, Na2PdCl4, H2PtCl6), polyethyleneglycol monostearate (PEG-MS), and magnetic maghemite nanoparticles [100] The noble metal ions were reduced by the effects of ultrasound, and uniformly immobilized on the surface of the maghemite XRD patterns of prepared nanocomposites showed peaks originated from 111 planes of noble metals with peaks of maghemite TEM images showed that the diameters noble metal particles depended upon the concentration of PEG-MS, pH of the solution and the concentration of noble metal ions, but not upon the maghemite concentration The average diameter of immobilized Au was 7–13 nm, and the diameters of Pd and Pt were several nm It was suggested that the nucleation of noble metal occurred in the homogeneous bulk solution and then the nuclei were immobilized on the surface of the Maghemite Then, the growth of noble metal nuclei were continuing on the surface of the maghemite

Another work was reported by Mizukoshi et al which prepared the magnetically retrievable palladium/Maghemite nanocomposite catalysts by sonochemical reduction method [101] Such a catatalyst show high catalytic activities for the reduction of nitrobenzene and could be readily retrieved by magnets and verified the durability of the catalytic performance Mizukoshi et al also introduced Au/γ-Fe2O3 composite nanoparticles which could selectively adsorb sulfur-containing amino acids [102] Adsorbed amino acids were successfully manipulated by applying all external magnetic fields

Nanocomposites of Ag nanoparticles/mesoporous γ-Al2O3 were synthesized by

sonochemical method [103] The as prepared product consisted of Ag nanoparticles dispersed

in the bayerite [Al(OH)3]/boehmite [AlO(OH)] matrix The Ag nanoparticles were

incorporated in a mesoporous structure of γ-Al2O3 upon calcination of product under Ar

atmosphere at 700 °C for 4 h For a nanocomposite containing 3.7 wt % Ag nanoparticles, the

BET surface area is more than that of γ-Al2O3 because the Ag nanoparticles remained on the

M F Mousavi and S Ghasemi

28

surface of mesoporous alumina whereas for 10.5 wt % Ag nanoparticles, the BET surface area decreased In this case, the Ag nanoparticles blocked the pores, and also increased the diameter of the pores of mesoporous alumina

Insertion of Pt nanoparticles into Mesoporous (MSP) CeO2 reported by an assisted reduction procedure [104] With incorporation of highly dispersed Pt into the CeO2 (MSP) by the sonochemical method, the specific surface area, pore volume and size of the CeO2 support decreased The observed changes could be attributed to incorporation of the metallic Pt particles in the CeO2 interparticle volume Pt/CeO2 nanoparticles have excellent properties in EA combustion at low temperature The catalytic activity of these catalysts was higher than that of the Pt catalysts on the CeO2 support prepared by the classic incipient wetness- impregnation method It was demonstrated that the higher the dispersion of the CeO2 support and the Pt phase, the better the catalyst properties Ultrasonic technique causes

ultrasound-to the homogeneity and better dispersion of the Pt in CeO2 support

The best results with 100% selectivity to CO2 at the lowest temperature were achieved with the Pt catalysts sonochemically incorporated into the mesoporous CeO2 support previously synthesized by the ultrasound method

ZnO nanorod/Ag nanoparticle composites was synthesized by ultrasonic irradiation of a mixture of ZnO nanorods, Ag(NH3)2+, and formaldehyde in a aqueous solution 105 TEM images of ZnO/Ag composites reveal that the ZnO nanorods are coated with spherical Ag nanoparticles with a mean size of several tens nanometer and fcc structure

The sonochemically synthesized Pt (Pd) nano-particles (~2 nm) were impregnated into zirconia (3 mol% yttria-stabilized zirconia, 3Y-TZP) nano-aggregates (20–45 nm) (Figure 13)

106

Figure 13 TEM of 3Y-TZP porous nano-aggregates impregnated with 1.5 wt.% of platinum

As shown in Figure 13, the primary crystallites with an average size of ~5nm are aggregated and nanoaggregates with a mean aggregate size of 20–40 nm are formed With low temperature sintering (1150 °C for 30 h), it can be possible to produce the Pt–3Y-TZP

Sonochemistry: A Suitable Method for Synthesis of Nano-Structured Materials 29

and Pd–3Y-TZP (0.5–2 wt % of platinum) nano-composites with uniform distribution of the

Pt (Pd) grains (in the range of 20–60 nm) and with a zirconia average grain size of 120 nm

Bhattacharyya and Gedanken reported [107] the preparation of γ-Al2O3-doped porous ZnO nanocomposite by sonochemistry The nanoparticles of γ-Al2O3 partially or fully block

the pores of porous ZnO

Figure 14 (a) HR-SEM images of pristine cotton fabric coated with CuO nanoparticles (magnification

×20,000) (Inset: magnified image (×100,000) of the nanoparticles coated the fiber)

In a similar work, silver nanoparticles were deposited on the surface of natural wool fibers under ultrasonic irradiation [109] The sonochemical irradiation of slurry containing wool fibers, silver nitrate, and ammonia in an aqueous medium for 120 min under an argon