Ultraviolet light irradiation (λex > 300 nm) to a mixed ethanol solution of cadmium perchlorate and elemental sulfur (S8) 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 microscopy (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 (Cd0 + S → CdS), whereas that on Au 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 S8 on TiO2 (adsorbent-selective adsorption) in the former system and the selective adsorption of S8 and Cd2+ ions on Au and TiO2, respectively, (site-selective adsorption) in the latter system.
UV light irradiation of TiO(2) (λ > 320 nm) in a mixed solution of AgNO(3) and S(8) has led to the formation of Ag(2)S quantum dots (QDs) on TiO(2), while Ag nanoparticles (NPs) are photodeposited without S(8). Photoelectrochemical measurements indicated that the Ag(2)S photodeposition proceeds via the preferential reduction of Ag(+) ions to Ag(0), followed by the chemical reaction with S(8). The application of this in situ photodeposition technique to mesoporous (mp) TiO(2) nanocrystalline films coated on fluorine-doped SnO(2) (FTO) electrodes enables formation of Ag(2)S QDs (Ag(2)S/mp-TiO(2)/FTO). Ag(2)S/mp-TiO(2)/FTO has the interband transition absorption in the whole visible region, while in the spectrum of Ag/mp-TiO(2)/FTO, a localized surface plasmon resonance absorption of Ag NPs is present centered at 490 nm. Ag(2)S QD-sensitized photoelectrochemical cells using the Ag(2)S/mp-TiO(2)/FTO and Ag/mp-TiO(2)/FTO photoanodes were fabricated. Under illumination of one sun, the Ag(2)S photoanode cell yielded H(2) at a rate of 0.8 mL·h(-1) with a total conversion efficiency of 0.29%, whereas the Ag/mp-TiO(2)/FTO photoanode is inactive.
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