BIFUNCTIONAL CAPPING OF CDS NANOPARTICLE AND BRIDGING TO TIO2

We report on the preparation of quantum-sized CdS particles capped with three bifunctional mercaptocarboxylic acids (HS-(CH2)(n)-CO2H, n = 1-3). The absorption spectra of all three colloid preparations exhibit a new band at 365 nm, assigned to a charge transfer to particle transition, probably f;om the free carboxylate head - group. Among these, mercaptobutyric acid was the most efficient acid at controlling the size of the CdS particles. TiO2 particles were attached to the CdS particles through the carboxylic end of the bifunctional caps. Bridging TiO2 to CdS through these acids leads to quenching of the blue and,enhancement of the red edges of the emission spectra of CdS. This is attributed to selective electron transfer from shallow traps, but not from deeper-traps, to the TiO2 particle. The efficiency of the quenching decreases upon increasing the alkyl chain length of the acid Presumably because of the distance dependence of the electron transfer process.