Metal colloid synthesis microemulsions

Barnickel P, Wokaun A (1990) Synthesis of Metal Colloids in Inverse Microemulsions. Mol Phys 69 1-9... 

P. Bamickel and A. Wokaun, Synthesis of metal colloids in inverse microemulsions. Mol. Phys. 

The environmentally benign, nontoxic and nonflammable fluids water and carbon dioxide (CO2) are the two most abundant and inexpensive solvents on earth. Vater-in-CO2 (W/C) or C02-in-water (C/W) dispersions in the form of microemulsions and emulsions offer new possibilities in waste minimization for the replacement of organic solvents in fields including chemical processing, pharmaceuticals, and microlectronics for solubilization and separations (e.g., proteins, ions, heavy metals), particle formation, enzymatic catalysis, organometallic catalysis, and synthesis of polymer colloids and inorganic nanoparticles (2,13,11). 

Two systems were used by Chen et al. [428] for synthesis of cobalt metal nanoparticles. One of them was the well-known system AOT/isooctane/aqueous solution. Two reverse microemulsions (w = 11) were prepared with 0.3M C0CI2 or 0.6M NaBH4 dissolved in water as the aqueous phase. The microemulsions, when mixed, yielded a black colloid. Removal of the isooctane led to the formation of a paste containing Co particles in AOT. The surfactant was removed by washing with water. The product in this form, or as a powdery material, yielded 3-4 nm sized Co particles. Heating at 550°C/2 h produced crystalline Co. 

W/o microemulsions have been used for many years as microreactors for the synthesis of ultrafine metallic particles [78, 79]. Since the pioneer works of Boutonnet et al. [80], who studied the production of colloidal Pt, Pd, Rh, and Ir particles by hydrogen or hydrazine (N2H4) reduction in w/o microemulsions, many studies have been made on the synthesis of this type of material. A reverse micelle (microemulsion) method, as a kind of soft technique, is a suitable way for obtaining the uniform and size controllable nanoparticles. The droplet dimension was modulated by various parameters, in particular W [81]. Some studies indicated that with the assistant of cosurfactant, the size of nanoparticles prepared in quaternary reverse micelle system is more controllable [82]. For example, compared with the anionic (AOT) ternary reverse micelle system, the droplet dimension of the quaternary cationic (cetyltrimethyl-ammonium bromide, CTAB) reverse micelles can be elaborately adjusted by changing W with the additional modulation of cosurfactant at the interface of water and oil. The microstmcture and djmamic exchange process are dominated by the influence of cosuifactant on the curvature radius and interface rigidity of the droplets in the quaternary reverse miceUe [82]. 

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