CAPPED SEMICONDUCTOR COLLOIDS - SYNTHESIS AND PHOTOELECTROCHEMICAL BEHAVIOR OF TIO2-CAPPED SNO2 NANOCRYSTALLITES

In our continuing efforts to surface-modify semiconductor colloids, we have succeeded in preparing TiO2-capped SnO2 (SnO2@TiO2) and TiO2-cap ped SiO2 (SiO2@TiO2) colloids. The SnO2@TiO2 colloids are 80-100 Angst rom in diameter and exhibit improved photochromic and photocatalytic e fficiencies compared to the native colloids. The improved charge separ ation in this system was confirmed from the enhanced efficiency of hol e trapping monitored from the absorption peak at 360 nm. The photocata lytic properties of SiO2@TiO2 colloids are similar to that of native T iO2 colloids. The capped semiconductor systems are useful for the oxid ation of I- and SCN-. For example, the quantum efficiency for I- oxida tion can be improved by a factor of 2-3 upon capping the SnO2 colloids with TiO2. The distinction between the capped and coupled semiconduct or systems has been made by preparing nanocrystalline thin films in tw o different geometries and studying their photoelectrochemical behavio r.