Metallic colloidal characterization

Although much remains to be learned about the chemistry of the catalyst particles in this important application, in light of the advandng state of the art in metal colloid characterization (see Section 6.3) there is good reason to expect... 

Bonnemann, H. and Brijoux, W. (1996) Catalytically active metal powders and colloids, in Active Metals Preparation, Characterization, Applications (ed A. Fiirstner,), VCH Verlag GmbH, Weinheim, pp. 339-379. 

Bonnemann, H. et al., Preparation, characterization, and application of fine metal particles and metal colloids using hydrotriorganoborates, J. Mol. Catal., 86, 129,1994. 

In a few studies sonochemistry was used to coat polymers with nanosized par-tides [48-50]. Of these three reports one [50] dealt with metals, more specifically with noble metals (Pt, Pd, and Au). In this research, metal colloids are adsorbed to the surface of neutral functionalized polystyrene microspheres, PSMS. The authors report on the synthesis and characterization of catalytically important noble monometallic colloids using various chemical and sonochemical methods. These metal colloids are then adsorbed onto suitably functionalized PSMS. The metal-immobilized microspheres are reacted with a linker such as 4-mercaptobutyl phosphonic acid and subsequently used to grow multilayers. 

The authors gratefully acknowledge the valuable support of Prof. H. Bonnemann from MPI Germany, for kindly supplying stabilized metal colloids and Prof. P. Grange, Belgium, for XPS and DRIFT characterizations. 

As for all catalysts, well-characterized samples are necessary to be able to relate the catalytic performance to physico-chemical properties. Transmission electron microscopy (TEM) and X-ray absorption spectroscopy (XAFS) were used in this study to characterize the stabilized metal colloid. The necessity of such extensive characterization of particle size has been outlined by Harada et al. [6,7] showing that the formation of aggregates may be overlooked and misinterpreted as large metal particles when using TEM alone. The actual availability of the polymer stabilized surface has been probed by hydrogen/oxygen titration adopted from the description of Bernard et al. [8]. 

Kim K.J., Chen V., Fane A.G. (1994b), Characterization of clean and fouled membranes using metal colloids. Journal of Membrane Science, 88, 93-101. 

During the last 2-3 decades a vast amount of knowledge regarding the preparation and characterization of nanostructured transition metal colloids in the zerovalent form has accumulated [1, 2]. The emphasis has been largely on the development of methods for the control of size and, more recently, even of shape [3]. In the majority of cases application in catalysis was not pursued systematically, i.e., generally only a simple model reaction such as the hydrogenation of cyclohexene was studied. 

In this work different deposition teehniques were evaluated for the addition of metal nanoparticles to a contaminated area for in situ surface enhanced Raman spectroscopy. Also metallic colloids were added to solutions for Raman characterization at 7 meters of standoff distance. The goal was to combine SERS and a Raman telescope for remote detection of materials at trace levels. 

With these considerations in mind, the goals of contemporary metal colloid research, the approaches to whidi will be covered in this chapter, may be stated as the search for synthetic methods for metal particles which are stabilized in the 1-20 nm size range, the application of characterization methods to identify the potential novelty of the partides (structural methods, electronic properties, surface chemistry), and finally the ap cation of these properties to various fields of chemistry and physics. Perhaps the field for which the renaissance in transition metal colloid chemistry has the most potential impact is catalyds. It has been... 

The properties of metal colloids whidi are of interest in the context of this diap-ter are those of dze, structure, and compodtion. The questions to be answered in characterizing these partides are those which would occur both to the molecular chemist and to the solid state chemist, namely ... 

Several techniques are commonly used to measure the size distributions of metal colloid particles. Electron microscopy. X-ray diffi ction, and small angle X-ray scattering are the most commonly used, although dassical methods such as sedimentation rates are sometimes reported. The techniques whidi have been extensively applied to the sizing of polymer colloids and emulsions, [183] such as light scattering and neutron scattering, have been only rarely applied to the characterization of metal sols. [103, 151, 153, 184]... 

Antonietti M, Wenz E, Bronstein LM, Seregina MS (1995) Synthesis and characterization of noble metal colloids in block copolymer micelles. Adv Mater 7 1000-1005... 

Bonnemann, H., Brijoux, W., Brinkmann, R., Fretzen, R., Joussen, T., Koppler, R., Korall, B., Neiteler, P., Richter, J. Preparation, characterization, and application of fine metal particles and metal colloids using hydrotriorganoborates. J Mol Catal 1994, 86, 129-177. 

This is only the beginning of a process which ultimately results in the formation of solid state hydroxides or oxides. Actually, the solution species present in neutral or alkaline solutions of transition-metal ions are relatively poorly characterized. The formation of numerous hydroxy- and oxy-bridged polynuclear species makes their investigation very difficult. However, it is clear that there is a near-continuous transition from mononuclear solution species, through polynuclear solution species to colloidal and solid state materials. By the way, the first example of a purely inorganic compound to exhibit chirality was the olated species 9.11. 

---