Colloidal electrochemical preparation

SERS active structures can be prepared by a variety of chemical physical and electrochemical methods described in Sect. 4.1. The chemical preparation of colloidal nanoparticles is frequently used (Sect. 4.1.1). An interesting electrochemical preparation procedure is the so-called double-pulse technique. This method is an electrochemical tool for controlling the metal deposition with respect to particle size and particle density (Sect. 4.1.2). 

Armes and coworkers have investigated the structure of both PAn colloid particles [stabilized with poly(vinyl alcohol)] and electrochemically prepared PAn films. In both cases the fundamental morphology was nanoparticles of up to 20 nm in diameter. Colloid particles were rice grain shaped. Thick films showed submicronsized features that appear to be aggregates of the smaller particles. 

The substrate is, of course, a necessary component of any SERS experiment. A wide variety of substrate surfaces have been prepared for SERS studies by an equally wide range of techniques [87]. Two important substrates are electrochemically prepared electrodes and colloidal surfaces (either deposited or in solution). 

Subsequently, this important insight led to another serendipitous discovery. We had previously shown that the electrochemical preparation of colloidal metal nanoparticles, usually carried out in organic solvents such as THF, can also be performed in water, provided H20-soluble ammonium salts of the betaine type are... 

Reetz et al. reported on catalytically active solvent-stabilized colloids in propylene carbonate, which were prepared electrochemically or by thermal decomposition of [Pd(OAc)2 assisted by ultrasound. The colloidal particles had sizes of 8 to 10 nm, as determined by TEM. After addition of aryl bromide, styrene, and base to the colloid solution, satisfactory conversions were obtained within reaction times of 5-20 h. Isolation of the particles stabilized by propylene carbonate was not possible, however [16]. The same authors also reported Suzuki and Heck reactions with electrochemically prepared Pd or Pd/Ni colloids stabilized by tetraalkylammonium, as well as polyvinylpyrrolidone (PVP)-stabilized palladium colloids prepared by hydrogen reduction (Table 1) [17]. It was assumed that the reaction occurs on the nanopartide surfaces. 

An electrohydrodynamic pol5mierization technique was introduced for the electros5mthesis of CP/insulating pol3mier nanocomposites. By this method optical active PANl colloids were prepared in a divided electrochemical flow-through cell via the polymerization of aniline in aqueous sulfuric acid/enantiomer of 10-camphorsulfon-ic acid, and polystyrenesulfonic acid as a stabilizer and codopant ... 

Barisci, J.N., et al. 1997. Electrochemical preparation of polypyrrole colloids using a flow cell. Colloids Surf A 126 (2-3) 129. 

Qu and Fredericks found that the SERS behaviour of tetrakis (3-N-methylpyridyl) porphyrin chloride and Sn(IV) tetrakis (4-A-methylpyridyl) porphyrin chloride varies with different surface concentrations. Experiments were performed on electrochemically prepared Ag surfaces. In the same sense Praus el studied, by means of the Raman correlation spectroscopy, the influence that the Ag colloid aggregation has on the SERRS spectra of 5,10,15,20-tetrakis (l-methyl-4-pyridyl) porphyrin. 

The advantages of the electrochemical pathway are that the contamination with byproducts resulting from chemical reducing agents is avoided and that the products are easily isolated from the precipitate. Further, the electrochemical preparation allows for size-selective particle formation. The electrochemical technique for preparing nanostructured mono- and bimetallic colloids has been further developed by Reetz and his group since 1994. 1... 

Reetz, M. T., Winter, M., Breinbauer, R., Thum-Albrecht, T., Vogel, W. Size-selective electrochemical preparation of surfactant-stabilized Pd-, Ni- and Pt/Pd colloids. Chem-Eur J 2001, 7, 1084-1094. 

Dubau L, Coutanceau C, Gamier E, Leger JM, Lamy C. 2003a. Electrooxidation of methanol at platinum-mthenium catalysts prepared from colloidal precursors Atomic composition and temperature effects. J Appl Electrochem 33 419-429. 

There are several bottom-up methods for the preparation of nanoparticles and also colloidal nanometals. Amongst these, the salt-reduction method is one of the most powerful in obtaining monodisperse colloidal particles. Electrochemical methods, which gained prominence recently after the days of Faraday, are not used to prepare colloidal nanoparticles on a large scale [26, 46], The decomposition of lower valent transitional metal complexes is gaining momentum in recent years for the production of uniform particle size nanoparticles in multigram amounts [47,48],... 

Transition-metal nanopartides are of fundamental interest and technological importance because of their applications to catalysis [22,104-107]. Synthetic routes to metal nanopartides include evaporation and condensation, and chemical or electrochemical reduction of metal salts in the presence of stabilizers [104,105,108-110]. The purpose of the stabilizers, which include polymers, ligands, and surfactants, is to control particle size and prevent agglomeration. However, stabilizers also passivate cluster surfaces. For some applications, such as catalysis, it is desirable to prepare small, stable, but not-fully-passivated, particles so that substrates can access the encapsulated clusters. Another promising method for preparing clusters and colloids involves the use of templates, such as reverse micelles [111,112] and porous membranes [106,113,114]. However, even this approach results in at least partial passivation and mass transfer limitations unless the template is removed. Unfortunately, removal of the template may re-... 

Zhou Y, Itoh H, Uemura T, Naka K, Chujo Y (2002) Preparation, optical spectroscopy, and electrochemical studies of novel pi-conjugated polymer-protected stable PbS colloidal nanoparticles in a nonaqueous solution. Langmuir 18 5287-5292... 

Water. A laboratory engaged in careful electrochemical work with aqueous solutions or in trace analysis will need facilities for the preparation and storage of highly purified water. Water commonly is contaminated with metals in both dissolved cationic form and in the form of colloidal or particulate matter that is not ionized appreciably.70 Frequently it also is contaminated by bacteria and by organic impurities that cannot be removed by ordinary or oxidative distillation because of the steam volatility of the impurities.71... 

One of the most attractive features of colloidal semiconductor systems is the ability to control the mean particle size and size distribution by judicious choice of experimental conditions (such as reactant concentration, mixing regimen, reaction temperature, type of stabilizer, solvent composition, pH) during particle synthesis. Over the last decade and a half, innovative chemical [69], colloid chemical [69-72] and electrochemical [73-75] methods have been developed for the preparation of relatively monodispersed ultrasmall semiconductor particles. Such particles (typically <10 nm across [50, 59, 60]) are found to exhibit quantum effects when the particle radius becomes smaller than the Bohr radius of the first exciton state. Under this condition, the wave functions associated with photogenerated charge carriers within the particle (vide infra) are subject to extreme... 

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