COLLOIDAL CDS PREPARATION VIA FLOW TECHNIQUES - ULTRASMALL PARTICLES AND THE EFFECT OF A CHROMATOGRAPHIC COLUMN

A fast flow technique is described in which two solutions containing Cd2+ and SH- ions are mixed, and the absorption spectrum of the resulting CdS sol is rapidly recorded using a diode array detector. Experiments were also performed in which the sol passed through a high-performance liquid chromatography column between the mixing chamber and diode array. The colloidal particles formed with and without the column had practically the same absorption spectrum (very small particles with a diameter down to 1.3 nm, strongly quantized). However, the particles formed using the column grew thermally much more slowly. The effect is attributed to the existence of "active" particles after the precipitation which promote the thermal growth. The active particles are filtered out by the column. With increasing Cd2+/SH- concentration ratio in the mixing chamber, smaller CdS particles are formed. In the most extreme cases studied, new species with a strong absorption maximum at 211 nm were obtained and their size (1.5 nm) was determined by size exclusion chromatography, the calibration of which was carried out by transmission electron microscopy. The flow technique is useful for rapid optimization of the precipitation conditions as well as for easy preparation of very small particles with extremely narrow size distribution.