PREPARATION AND PROPERTIES OF TAILORED MORPHOLOGY, MONODISPERSE COLLOIDAL SILICA CADMIUM-SULFIDE NANOCOMPOSITES

We have developed a new synthetic methodology for preparing ca. 40-300-nm monodisperse silica-cadmium sulfide nanocomposite spheres. This methodology uses water-in-oil microemulsions in which monodisperse silica colloids are produced by the controlled hydrolysis of tetraethyl orthosilicate (TEOS) in water nanodroplets. The resulting pure silica spheres can be grown to between 40 and 80 nm in diameter and can be used as seed particles for production of larger silica colloids upon further reactions with TEOS in the microemulsion. Cadmium sulfide quantum dots are incorporated into the silica colloids during the silica sphere synthesis by the simultaneous coprecipitation of cadmium nitrate and ammonium sulfide in the water nanodroplets. The CdS can be introduced as a homogeneous dispersion of CdS quantum dots (ca. 25 Angstrom diameter), as large inclusions, as surface caps, as the central core of a silica particle, or as shells of CdS interleaved between silica shells. These different nanoscale complex morphologies in silica are created by controlling the coprecipitation of CdS. Techniques including TEM, SEM/EDS, X-ray diffraction, and light scattering were used to characterize the elemental analysis as well as particle morphology. In addition, we have prepared doublet and triplet spheres which are connected by welds of CdS. This silica-CdS nanocomposite is a new material with potential utility for nonlinear optics. Further processing makes this material useful for a new class of high surface area catalytic supporting materials.