Particle synthesis: mechanisms supersaturation

The wet synthesis of CdS nanoparticles used in this work is based on the reaction between a dissolved cadmium salt (CdCl2) and a S-containing compound (thiourea (NH2)2CS) in an aqueous solution. Chemical deposition of CdS nanoparticles in the CdCl2 - NH3 - NaOH - (NH2)2CS - H2O bath was described elsewhere [3]. In the present work all the baths had the same composition and were prepared from solutions of cadmium chloride CdCl2 (0.005 mold-1), ammonia NH3-H2O (1.5 moll"1), sodium hydroxide NaOH (0.074 mold-1) and thiourea (NH2)2CS (0.025 mol-F1) using distilled water. The synthesis temperature was varied from 294 to 325 K. The primary concentrations of the precursors have been chosen according to the thermodynamic analysis [4]. A supersaturation of the solution with Cd(OH)2 takes place in the baths. It means that the mechanism of the cadmium sulfide formation could involve the stage of Cd(OH)2 formation. When the deposition process of CdS particles in the solution completed, the residue was filtered at an ambient pressure and dried at room temperature. 

This chapter deals with the synthesis of nanoscale particles from supersaturated vapors generated by laser vaporization under controlled condensation conditions. The synthesis of nanoscale particles has received considerable attention in view of the potential for new materials with novel properties and the design of catalysts with specific dimensions and compositions (1-10). The reduced size and dimensionality of these atomically engineered materials are responsible for their unique electronic, magnetic, chemical and mechanical properties. The characterization of these properties can ultimately lead to identifying many potential uses, particularly in the field of catalysis. For example, particles of metal oxides and mixed oxides such as Si02/Ti02 exhibit unusual acidic properties and can be used as acidic catalysts (11). 

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