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In-Depth Information
sds remarkably enhanced the reduction rate, maybe due to the thermal decomposition that occurs at the interfacial region bet-
ween bulk solution and cavitation bubbles. A spherical particle with a geometric mean diameter of about 8 nm was obtained [52].
18.4.2
Metal oxide nanoparticles by the sonochemical route
In addition to being used for metallic and bimetallic nanoparticle synthesis, sonication was also explored for the synthesis of
metal oxide nanoparticles. In this regard, Bhatte et al. reported additive-free nanocrystalline zinc oxide synthesis using zinc
acetate and 1,4-butanediol through sonication. The solvent 1,4-butanediol played a dual role of fuel as well as capping agent,
eliminating the need for addition of any extraneous species [53].
18.5
electrocheMical synthesis of nanoparticles
electrochemistry is a branch of chemistry that deals with chemical reactions that occur in a solution at the interface of an elec-
tron conductor (the electrode: a metal or a semiconductor) and an ionic conductor (the electrolyte) and that need electron
transfer between the electrode and the electrolyte or species in solution.
chemical reactions where electrons are transferred between molecules are called redox (oxidation/reduction) reactions. In
general, electrochemistry addresses situations where oxidation and reduction reactions are separated in space or time, connected
by an external electric circuit. electrochemistry has been proven to have various applications in the field of physics and chem-
istry. In recent investigations, electrochemistry has been successfully applied for nanoparticle synthesis. electrochemical
methods have several advantages in terms of quickness, ease of operation, cost, and energy efficiency.
Reetz and helbig described an electrochemical procedure for the formation of palladium and nickel nanoparticles [54]. The
formed intermediate metal salt is reduced at the cathode, to provide metallic particles that are stabilized by tetra-alkyl ammonium
salts along with coelectrolyte acetonitrile/tetrahydrofuran.
Recently, deshmukh et al. reported a novel, one-stroke potential controllable, electrochemical method for PdNP synthesis
in the electrolyte as well as on the working electrode. In this case, ionic liquid (Il) plays the role of an electrolyte cum stabilizer.
In the typical synthesis, electrodeposition of palladium metal is carried out from a 1-butyl-3-methylimidazolium acetate Il
([BMim][oAc]), which is a common anion with a metal precursor Pd(oAc)
2
responsible for the dissolution of metal. The
presence of a common acetate anion leads to an increase in the solubility of the metal salt in Il. At a certain potential, deposition
of metallic Pd NPs took place at the working electrode; also, the formation of Pd NPs was observed in the bulk electrolyte. The
effect of various process parameters on the morphology of synthesized nanoparticles was further investigated [55].
Khaydarov et al. reported a novel electrochemical method for the synthesis of long-lived silver nanoparticles suspended in an
aqueous solution as well as silver powders. The method did not include any chemical stabilizing agents. Ag nanoparticles suspended
in water solution that were produced by the present protocol are almost spherical in the size range of 2-20 nm. Ag nanoparticles
synthesized by the proposed method were sufficiently stable for more than 7 years even under ambient conditions [56].
li et al. defined a simple, green, and controllable approach for electrochemical synthesis of nanocomposites made from
electrochemically reduced graphene oxide (eRGo) and gold nanoparticles. This material retains the specific features of both
graphene and gold nanoparticles. The obtained result reveals a homogeneous distribution of gold nanoparticles on the graphene
sheets [57].
Taleb et al. describe the electrochemical preparation of dendritic silver films with unusual wetting properties coming from
the use of a self-assembled gold nanoparticle (Au NP) template. It shows that the Au NP self-assembled monolayer on the
highly ordered pyrolytic graphite (hoPG) surface is responsible for the formation of the dendritic morphology, which is not
observed for the same deposition conditions on a bare hoPG substrate. The dendritic structure of the deposited silver film was
revealed at a later stage of the electrodeposition process. surprising wetting properties in terms of hydrophobic surface were
also revealed [58]. Mohanty reported the synthesis of various nanoscale materials, such as nanoparticles and nanowires of Au,
Pt, Ni co, Fe, Ag, and so on, by electrodeposition techniques in his article. Both potentiostatic and galvanostatic methods were
employed to carry out the electrodeposition process under different potential ranges, time durations, and current densities [59].
18.6
sonoelectrocheMical reduction
Introducing ultrasonic waves into homogeneous solutions has a considerable effect upon mass transport processes because of
macroscopic streaming and microscopic interfacial cavitation events. In electrochemical systems, cavitational erosion permits
electrode activation by continuously removing the material present at the electrode surface. In literature studies, nanoporous
