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SCIENCE CHINA Materials, Volume 61, Issue 6: 851-860(2018) https://doi.org/10.1007/s40843-017-9170-6

Constructing CdS/Cd/doped TiO2 Z-scheme type visible light photocatalyst for H2 production

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  • ReceivedOct 18, 2017
  • AcceptedNov 27, 2017
  • PublishedDec 15, 2017

Abstract

Constructing Z-scheme type photocatalyst is an efficient way to improve the charge separation efficiency and enhance the photocatalytic activity. In this report, the Cd:TiO2 nanoparticles are prepared via the sol-gel route and employed as a starting material. When it was reduced by NaBH4 at 300°C, the surface oxygen vacancies were produced and Cd2+ was reduced into metal Cd0 nanoparticle (denoted as R-Cd:TiO2). Subsequently, the formed R-Cd:TiO2 was treated with thioureain the hydrothermal reaction. Through the decomposition of thiourea, the oxygen vacancies were refilled by S2− from thiourea to form S:TiO2/TiO2 (d-TiO2) and Cd was partially converted into CdS to form CdS/Cd/d-TiO2 composite. The formed CdS/Cd/d-TiO2 composite exhibits improved photocatalytic activity. Under visible light irradiation (λ>400 nm), the H2 production rate of CdS/Cd/d-TiO2 reaches 119 μmol h−1 with 50 mg of photocatalyst without any cocatalyst, which is about 200 and 60 times higher than that of S:TiO2/TiO2(0.57 μmol h−1), CdS (2.03 μmol h−1) and heterojunction CdS/d-TiO2 (2.17 μmol h−1) materials, respectively. The results illustrate that metal Cd greatly promotes the charge separation efficiency due to the formation of Z-scheme type composite. In addition, the photocatalytic activity in the visible light region was dramatically enhanced due to the contribution of both CdS and d-TiO2. The method could be easily extended to other wide bandgap semiconductors for constructing visible light responsive Z-scheme type photocatalysts.


Funded by

the National Natural Science Foundation of China(21671011)

Beijing High Talent Program

Beijing Natural Science Foundation(KZ201710005002)

China Postdoctoral Science Foundation

Beijing Postdoctoral Research Foundation

Dongguan Program for International S&T Cooperation

and the National Science Foundation of USA(DMR-1506661,Feng,P)


Acknowledgment

Sun Z thanks the financial support from the National Natural Science Foundation of China (21671011), Beijing High Talent Program, Beijing Natural Science Foundation (KZ201710005002). The authors thank China Postdoctoral Science Foundation, Beijing Postdoctoral Research Foundation, and Dongguan Program for International S&T Cooperation. Zhao Z thanks the support from China Scholarship Council. This research was also supported by the National Science Foundation (DMR-1506661, Feng P).


Interest statement

The authors declare that they have no conflict of interest.


Contributions statement

Zhao Z designed and engineered the samples; Zhao Z, Xing Y and Li H performed the experiments. Zhao Z, Sun Z and Feng P wrote the paper. All authors contributed to the general discussion.


Author information

Zhao Zhao received his PhD degree from Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, Changchun, China. He is currently a lecturer in the Key Laboratory of Functional Materials Physics and Chemistry of the Ministry of Education, Jilin Normal University. His main research area includes photocatalyst based on inorganic semiconductors.


Zaicheng Sun is a professor of Beijing Key Lab for Green Catalysis and Separation, Department of Chemistry and Chemical Engineering, College of Environmental and Energy Engineering, Beijing University of Technology, Beijing. China. His research interests are mainly on the photocatalytic nano materials for water splitting, H2 production, and self-cleaning optical coating, fluorescent carbon dots for theragnostics.


Pingyun Feng is a professor of the Department of Chemistry, University of California, Riverside, CA, USA. She received her PhD degree from the Department of Chemistry, University of California, Santa Barbara. Her research interest centers on the development of synthetic methodologies to prepare novel materials for energy conversion and storage. These materials integrate uniform porosity, high surface area, semi conductivity, optical property, photocatalytic, acid- or base-catalytic properties and have a variety of applications.


Supplement

Supplementary information

Experimental details are available in the online version of the paper.


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  • Figure 1

    Characterization of Cd:TiO2 and reduced Cd:TiO2. (a) HR-TEM graph of Cd:TiO2 (inset is a low magnitude TEM image of Cd:TiO2). (b) UV-vis spectra of TiO2 NPs, Cd:TiO2 and Cd:TiO2 after NaBH4 treatment for 30 min (R-Cd:TiO2). (c) HR-TEM of R-Cd:TiO2 NPs; (d) XRD patterns of Cd:TiO2, R-Cd:TiO2 treated for 30 and 60 min.

  • Scheme 1

    The synthesis route of CdS/Cd/d-TiO2 core/shell type heterostructure composite.

  • Figure 2

    Optical properties and XRD of TiO2 and S:TiO2. (a) Diffuse reflectance UV-vis spectra of TiO2, R:TiO2 and S:TiO2 represented as d-TiO2(S:TiO2/TiO2). (b) Transformed Kubelka-Munk function vs. photon energy plot of TiO2 and S:TiO2. (c) Full XPS spectra of S:TiO2 (inset is the high resolution S 2p XPS spectra).

  • Figure 3

    (a) XRD patterns of R-Cd:TiO2 and hydrothermally treated R-Cd:TiO2 with different amounts of thiourea. (b) HR-TEM image of CdS/Cd/d-TiO2. (c) UV-vis spectra of TiO2, CdS, and CdS/Cd/d-TiO2 obtained with different amounts of thiourea treatment. (d) High resolution Cd XPS of the as-prepared Cd:TiO2, R-Cd:TiO2 and CdS/Cd/d-TiO2 NPs.

  • Figure 4

    H2 evolution rate of S:TiO2, CdS, CdS/Cd/d-TiO2 and CdS/TiO2 under AM 1.5 (a) and visible light (λ>400 nm) (b) irradiation in the 0.35 mol L−1 Na2SO3-0.35 mol L−1 Na2S aqueous solution. The inset of (b) is the H2 production rate of TiO2 and S:TiO2 under visible light. (c) H2 production dependence of CdS/Cd/d-TiO2 and CdS/TiO2 on the wavelength under different band pass, the curves are the UV-vis spectra of S:TiO2 (dash) and CdS/Cd/d-TiO2 (solid). (d) Transient photocurrent responses of TiO2, R-Cd:TiO2 and CdS/Cd/d-TiO2.

  • Figure 5

    The proposed work mechanism of CdS/Cd/d-TiO2 composites.

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