High Coverage Formation of CdS Quantum Dots on TiO2 by the Photocatalytic Growth of Preformed Seeds

Abstract

Photoelectrochemical experiments and density functional theory calculations indicated that visible-light irradiation of the CdS quantum dots (QDs)–TiO2 direct coupling system (CdS/TiO2) causes the electron injection from the valence band (VB) of CdS into the conduction band (CB) of TiO2 (path 2) in addition to the inter-CB electron transfer from CdS to TiO2 (path 1). Path 2 can be induced by the sub-bandgap excitation of CdS QDs to extend the spectral response of the CdS/TiO2 system. For path 2 as well as path 1 to effectively work, CdS QDs should be directly deposited on the TiO2 surface with high coverage. According to the guideline, a photocatalytic growth of the preformed seed (PCGS) technique has been developed. Transmission electron microscopy observation and X-ray photoelectron spectroscopy measurements of the CdS/TiO2 prepared by the PCGS technique indicated that the TiO2 surface is highly covered by CdS QDs. The technique was applied to mesoporous TiO2 nanocrystalline films (mp-TiO2) to yield CdS...