Photodeposition of CdS Quantum Dots on TiO2: Preparation, Characterization, and Reaction Mechanism

Ultraviolet light irradiation (lambda(ex) > 300 nm) to a mixed ethanol solution of cadmium perchlorate and elemental sulfur (S-8) under deaerated conditions has led to deposition of CdS quantum dots on the surfaces of TiO2 particles and films (CdS/TiO2). High-resolution transmission electron rnicroscopy (HRTEM) confirmed that the hexagonal CdS crystals are in good contact with TiO2. The loading amount and band gap of CdS can be controlled by irradiation time. Photoelectrochemical measurements using cyclic voltammetry and photochronopotentiometry indicated the photodeposition of CdS on TiO2 preferentially proceeds via an atomic route (Cd-0 + S -> CdS), whereas that on An nanoparticle-loaded TiO2 (Au/TiO2) follows an ionic route (Cd2+ + S2- -> CdS). This difference was revealed to result from the predominant adsorption of Cd2+ over S-8 on TiO2 (adsorbent-selective adsorption) in the former system and the selective adsorption Of S-8 and Cd2+ ions on Au and TiO2, respectively, (site-selective adsorption) in the latter system.