Sonochemical preparation, nanoparticles method

Abstract A convenient method to synthesize metal nanoparticles with unique properties is highly desirable for many applications. The sonochemical reduction of metal ions has been found to be useful for synthesizing nanoparticles of desired size range. In addition, bimetallic alloys or particles with core-shell morphology can also be synthesized depending upon the experimental conditions used during the sonochemical preparation process. The photocatalytic efficiency of semiconductor particles can be improved by simultaneous reduction and loading of metal nanoparticles on the surface of semiconductor particles. The current review focuses on the recent developments in the sonochemical synthesis of monometallic and bimetallic metal nanoparticles and metal-loaded semiconductor nanoparticles. 

Fig. 6.10 UV-vis absorption spectra of gold - ruthenium bimetallic nanoparticles prepared by the sonochemical co-reduction method using (a) 1 1 and (b) 1 5 gold - ruthenium compositions, respectively [45]...

A long list of oxides was prepared sonochemically. Almost all the above-mentioned oxides were synthesized in organic solvents. The other oxides that will be discussed from here on were all prepared in aqueous solutions. Submicron size spheres of silica and alumina prepared by well-known methods were coated sonochemically by nanoparticles of oxides of europium and terbium using the same concentration of ions [81]. We have also used sonochemistry to prepare nanoparticles of silica and alumina doped with the same rare-earth ions for comparison. The highest luminescence intensities were observed for europium and terbium doped in nanoparticles of alumina of dimension 20-30 run. The intensities are comparable or higher than in commercial phosphors. 

Figure 1 explains the formation mechanism of ZMP nanocontainer. ZMP nanoparticles were prepared by sonochemical irradiation method explained in figure 1. ZMP nanoparticles were functionalized by using myristic acid (C13H27COO-) with the help sonochemical micro emulsion method of to make ZMP nanoparticles hydropho-... 

The hydrazinium nickel hydrazine carboxylate complex, (N2H5)Ni (N2H3C00)3-H20, is also used as precursor for the synthesis of metallic Ni in the sonochemical preparation of Ni-Mo-S/Al203, since volatile Ni precursors such as Ni(CO)4 are exceptionally toxic and dangerous to use [24]. Similarly, copper hydrazine carboxylate is used to prepare nanoparticles of copper by the sonication method [25]. The presence of a zwitterionic surfactant in the synthesis procedure causes the formation of elongated nanoparticles of aspect ratio 10, which is of significance for electrical applications. In the absence of the zwitterionic surfactant only spherical particles result [26]. 

Kan et al. reported preparation of Au-core/Pd-shell bimetallic nanoparticles by successive or simultaneous sonochemical irradiation of their metal precursors in ethylene glycol, respectively. In the successive method, Pd clusters or nanoparticles are first formed by reduction of Pd(N03)2, followed by adding HAUCI4 solution. As a result, Au-core/Pd-shell structured particles are formed, although Pd-core/Au-shell had been expected. In their investigations, the successive method was more effective than the simultaneous one in terms of the formation of the Au-core/Pd-shell nanoparticles [143]. 

As described in this chapter, the sonochemical reduction technique appears to be a promising method for the preparation of various types of metal nanoparticles in an aqueous solution. By choosing more efficient organic additives, easily-reducible metal precursors, supports and templates with an appropriate role, more advanced functional nanoparticles could be synthesized successfully using the sonochemical reduction technique. In future, it is also possible to develop effective synthetic methods by combining the sonochemical method with other chemical methods. 

Basnayake R, Li Z, Katar S, Zhou W, Rivera H, Smotkin ES, Casadonte DJ, Korzeniewski C Jr (2006) PtRu nanoparticle electrocatalyst with bulk alloy properties prepared through a sonochemical method. Langmuir 22 10446-10450... 

Fig. 8.8 CdS nanoparticles colloid solution prepared by the sonochemical method freshly prepared (a) kept in air for 1 month (b) [63]...

Zhu Jun-Jie, Wang Hui, Xu Shu, Chen Hong-Yuan Chen (2002) Sonochemical method for the preparation of monodisperse spherical and rectangular lead selenide nanoparticles. Langmuir 18 3306-3310... 

Zho JJ, Yuri K, Gedanken A (2000) General sonochemical method for the preparation of nanophasic selenide synthesis of ZnSe nanoparticles. Chem Mater 12 73-78... 

We have prepared nanoneedles of mixed Co oxide using the sonochemical method for decomposing metal complexes. Resulted nanoparticles are rather well-ordered structures with the average size of 23 nm in length and 5 nm in diameter. Magnetic measurements revealed the ferromagnetic transition at 25 K, which can be explained by the chemical surface modification of the particles. 

A different approach was taken by Kumar and associates [61]. Fie also embedded metals in polymers, but used as his precursor the polymer and not the monomer. In his first study a composite material containing amorphous Cu nanoparticles and nanocrystalline CU2O embedded in polyanUine matrices was prepared by a sonochemical method. These composite materials were obtained from the soni-cation of copper (II) acetate when aniline or 1% v/v aniline-water was used as the solvent. Mechanisms for the formation of these products are proposed and discussed. The physical and thermal properties of the as-prepared composite materials are presented. A band gap of 2.61 eV is estimated from optical measurements for the as-prepared CU2O in polyaniline. 

In a similar work, ultrasound radiation was used to prepare EU2O3 doped in zir-conia and yttrium-stabilized zirconium (YSZ) nanoparticles [83]. Europium oxide was also coated sonochemically on the surface of submicron spherical zirconia and YSZ, which were fabricated by wet chemical methods. Time decay measurements of the doped and coated materials were conducted using a pulsed laser source. Lifetimes < 1.1 ms radiative lifetime of the Eu+ ions were detected for the doped and coated as-prepared materials. When the doped and coated samples were an-... 

Another III-V semiconductor was prepared by Li and coworkers [143]. A room temperature sonochemical method for the preparation of GaSb nanoparticles using less hazardous Ga and antimony chloride (SbClj) as the precursors has been described. TEM and SAED results show that the as-prepared solid consists of nanosized GaSb crystals with sizes in the 20-30 run range. The photoacoustic spectrum result reveals that the GaSb nanopartides have a direct band gap of about 1.21 eV. On the basis of the control experiments and the extreme conditions produced by ultrasound, an ultrasound-assisted in situ reduction/combination mechanism has been proposed to explain the reaction. 

Recently it was proposed that PEMLC electrocatalysts may also be prepared by water-in-oil microemulsions. These are optically transparent, isotropic, and thermodynamically stable dispersions of two nonmiscible liquids. The method of particle preparation consists of mixing two microemulsions carrying appropriate reactants (metal salt + reducing agent), to obtain the desired particles. The reaction takes place during the collision of water droplets, and the size of the particles is controlled by the size of the droplets. Readers are referred to the early work of Boutonnet et al. [149], the review paper of Capek [150] and refs. [128,151], and 152 for fuel cell apphcations. The carbonyl route has the ability to control the stoichiometry between bimetallic nanoparticles, but also the particle size. The reader is referred to review papers for more details [106,107]. Other methods, including sonochemical and radiation-chemical, have been used successfully for the preparation of fuel cell catalysts (see, e.g., review articles 100 and 153). 

Various approaches were developed to prepare silver nanoparticles with the size less than 100 nm photolytic [7] and radiolytic reduction [8], the sonochemical method [9], solvent extraction reduction [10]. Among these methods, chemical reduction is the most common one. One could control the intrinsic properties of synthesized silver nanoparticles during chemical synthesis [11] by reducing the concentration of silver salts and using larger amount of stabilizer to avoid aggregation of the nanoparticles. 

Nanocomposites are materials in which nanoparticles (in this case, nanorods) are dispersed in a continuous matrix. The matrix may be a polymer, nanorods, or other nanoparticles. Nanorod composites find applications in diverse areas such as efficient charge storage, removal of contaminants (e.g. surfactant) from water, emissivity control devices, and metallodielectrics, and so on. A number of methods such as electroless deposition, the sol-gel method, the hydrothermal method, solution casting, carbother-mal reduction, the template-based method, the sonochemical method, and electrospinning can be used to prepare composite nanorods. Nanorod composites are different from core-shell nanorods. In core-shell nanorods, the coating is uniform, whereas in the nanorod composite (consisting of a nanorod and a nanoparticle on a surface), fine nanoparticles are dispersed on the surface of the nanorods. Some specific examples of the preparation of nanocomposites consisting of nanorods are described below. 

Sonochemical methods for the preparation of nanoparticles were pioneered by Suslick et al. in 1991.[ They prepared Fe nanoparticles by sonication of Fe(C0)5 in a decaline solution, which gave them 10-20 nm amorphous iron nanoparticles. Sonochemical decomposition methods have been further developed by Suslick et al.h3°i and Gedanken and coworkersi and have produced Fe, MojC, Ni, Pd, and Ag nanoparticles in various stabilizing environments. 

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