Sub‐Bandgap Excitation‐Induced Electron Injection from CdSe Quantum Dots to TiO<sub>2</sub> in a Directly Coupled System

Yoshii, Mari; Kobayashi, Hisayoshi; Tada, Hiroaki

doi:10.1002/cphc.201500183

Cited by 13 publications

(6 citation statements)

References 41 publications

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“…A well studied and interesting approach for inducing visible-light activity in TiO 2 is to couple it with nano-structured metal chalcogenide semiconductors such as CdS, as described in [39,40]. An interesting and key feature of these metal chalcogenides is that their band edges (that determine the redox ability) can be varied over a wide range by controlling the particle size, that is the well known size quantization effect.…”

Section: Introductionmentioning

confidence: 99%

Metal oxide nanocluster-modified TiO₂as solar activated photocatalyst materials

Fronzi

Iwaszuk

Lucid

et al. 2016

J. Phys.: Condens. Matter

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In this review we describe our work on new TiO2 based photocatalysts. The key concept in our work is to form new composite structures by the modification of rutile and anatase TiO2 with nanoclusters of metal oxides and our density functional theory (DFT) level simulations are validated by experimental work synthesizing and characterizing surface-modified TiO2. We use DFT to show that nanoclusters of different metal oxides, TiO2, SnO/SnO2, PbO/PbO2, NiO and CuO can be adsorbed at rutile and anatase surfaces and can induce red shifts in the absorption edge to enable visible light absorption which is the first key requirement for a practical photocatalyst. We furthermore determine the origin of the red shift and discuss the factors influencing this shift and the fate of excited electrons and holes. For p-block metal oxides we show how the oxidation state of Sn and Pb can be used to tune both the magnitude of the red shift and also its mechanism. Finally, aiming to make our models more realistic, we present some new results on the stability of water at rutile and anatase surfaces and the effect of water on oxygen vacancy formation and on nanocluster modification. These nanocluster-modified TiO2 structures form the basis of a new class of photocatalysts which will be useful in oxidation reactions and with the suitable choice of nanocluster modifier can be applied to CO2 reduction.

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Section: Introductionmentioning

confidence: 99%

Metal oxide nanocluster-modified TiO₂as solar activated photocatalyst materials

Fronzi

Iwaszuk

Lucid

et al. 2016

J. Phys.: Condens. Matter

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“…A representative of them is the CdS QD-loaded TiO 2 (CdS/TiO 2 ) system, which has mainly been studied in particulate systems. − Also, a great deal of attention has been focused on the QD-loaded TiO 2 nanostructures such as mesoporous TiO 2 nanocrystalline film (mp-TiO 2 ) for the application as the photoanode of photoelectrochemical (PEC) cells for solar energy conversion. , The deep understanding of the mechanism on the visible-light-induced electron injection from CdS QDs to TiO 2 underpins the improvement in the performances of the photocatalysts and photoanodes. As shown in Scheme , we have shown in the CdSe/TiO 2 system that the sub-bandgap excitation-induced electron injection from the VB of CdSe to the CB of TiO 2 (path 2) occurs in addition to the inter-CB electron transfer (path 1) . However, the detailed mechanism in the CdS/TiO 2 system remains unknown.…”

Section: Introductionmentioning

confidence: 99%

“…As shown in Scheme 1, we have shown in the CdSe/TiO 2 system that the sub-bandgap excitation-induced electron injection from the VB of CdSe to the CB of TiO 2 (path 2) occurs in addition to the inter-CB electron transfer (path 1). 7 However, the detailed mechanism in the CdS/TiO 2 system remains unknown. If path 2 exists also in the CdS/TiO 2 system, the high-coverage formation of CdS QDs on TiO 2 can be expected to enhance the performance in the same manner as the CdSe/TiO 2 system.…”

Section: ■ Introductionmentioning

confidence: 99%

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

et al. 2016

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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/mp-TiO2. CdS QD-sensitized photoelectrochemical (QD-SPEC) cells with a structure of CdS/mp-TiO2 (photoanode)|aqueous sulfide solution|Ag/AgCl (reference electrode)|Pt (cathode) were fabricated. The rate of hydrogen (H2) generation in the QD-SPEC cell under illumination of simulated sunlight (AM 1.5, 1 sun, λ > 430 nm) increases with an increase in the TiO2-surface coverage by CdS QDs.

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“…The discrepancy between the photocurrent onset wavelength ( λ on ) and the absorption edge originates from the electron transition from the VB of CdS or CdSe QD to the CB of TiO 2. The CdSe photodeposition on CdS/mp‐TiO 2 extends the λ on value to 680 nm, and the IPCE is comparable with that for CdSe/mp‐TiO 2 at 500< λ <600 nm and that for CdS/mp‐TiO 2 at 400< λ <500 nm. Evidently, CdS and CdSe QDs cooperatively act as the photosensitizer in the CdS@CdSe( t p1 =1 h, t p2 =2 h)/mp‐TiO 2 photoanode cell.…”

Section: Methodsmentioning

confidence: 64%

“…Figure B shows the Tauc plots for the samples. CdS/mp‐TiO 2 and CdSe/mp‐TiO 2 have band gaps ( E g ) of 2.68 eV and 1.81 eV, respectively, which are near the bulk values of 2.5 eV for CdS and 1.7 eV for CdS . Thus, the E g value of CdS@CdSe/mp‐TiO 2 can be controlled in a wide range from 1.7 and 2.5 eV due to the size quantization of CdSe by changing t p1 and t p2 .…”

Section: Methodsmentioning

confidence: 99%

Photocatalytic Synthesis of CdS(core)–CdSe(shell) Quantum Dots with a Heteroepitaxial Junction on TiO₂: Photoelectrochemical Hydrogen Generation from Water

et al. 2017

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A major challenge in chemistry for the synthesis of hetero-nanostructures is to build up atomically commensurate interfaces for smooth interfacial charge transfer. Photodeposition of CdSe on a CdS-preloaded mesoporous TiO nanocrystalline film yields CdS(core)-CdSe(shell) quantum dots (CdS@CdSe/mp-TiO ) with a heteroepitaxial nanojunction at 298 K. Two-electrode quantum-dot-sensitized photoelectrochemical (QD-SPEC) cells with the structure photoanode |0.25 M Na S, 0.35 M Na SO (solvent=water)| cathode were fabricated. The CdS@CdSe QD-SPEC cell affords a solar-to-current efficiency (STCE) of 0.03 % without external bias under illumination of simulated sunlight (λ>430 nm, AM 1.5, one sun). By applying 0.1 V between the electrodes, the STCE increases up to 0.048 %, far surpassing the CdS/mp-TiO and CdSe/mp-TiO photoanode cells. The CdS-CdSe interfacial analysis by high-resolution transmission electron microscopy and the band energy analysis taking the size quantization and the electrolyte effect indicate that the excellent performance of the CdS@CdSe/mp-TiO photoanode originates from the effective charge separation due to the cascade-like band edge alignment and the heteroepitaxial junction between CdS and CdSe QDs. In addition, high surface coverage of TiO with QDs can contribute to the reduction in the loss of the electron transport from TiO to the electron collecting electrode.

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Sub‐Bandgap Excitation‐Induced Electron Injection from CdSe Quantum Dots to TiO₂ in a Directly Coupled System

Cited by 13 publications

References 41 publications

Metal oxide nanocluster-modified TiO₂as solar activated photocatalyst materials

Metal oxide nanocluster-modified TiO₂as solar activated photocatalyst materials

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

Photocatalytic Synthesis of CdS(core)–CdSe(shell) Quantum Dots with a Heteroepitaxial Junction on TiO₂: Photoelectrochemical Hydrogen Generation from Water

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Sub‐Bandgap Excitation‐Induced Electron Injection from CdSe Quantum Dots to TiO2 in a Directly Coupled System

Cited by 13 publications

References 41 publications

Metal oxide nanocluster-modified TiO2as solar activated photocatalyst materials

Metal oxide nanocluster-modified TiO2as solar activated photocatalyst materials

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

Photocatalytic Synthesis of CdS(core)–CdSe(shell) Quantum Dots with a Heteroepitaxial Junction on TiO2: Photoelectrochemical Hydrogen Generation from Water

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Sub‐Bandgap Excitation‐Induced Electron Injection from CdSe Quantum Dots to TiO₂ in a Directly Coupled System

Metal oxide nanocluster-modified TiO₂as solar activated photocatalyst materials

Metal oxide nanocluster-modified TiO₂as solar activated photocatalyst materials

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

Photocatalytic Synthesis of CdS(core)–CdSe(shell) Quantum Dots with a Heteroepitaxial Junction on TiO₂: Photoelectrochemical Hydrogen Generation from Water