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Effects of Defects on Photocatalytic Activity of Hydrogen-Treated Titanium Oxide Nanobelts

Cushing, Scott K. and Meng, Fanke and Zhang, Junying and Ding, Bangfu and Chen, Chih Kai and Chen, Chih-Jung and Liu, Ru-Shi and Bristow, Alan D. and Bright, Joeseph and Zheng, Peng and Wu, Nianqiang (2017) Effects of Defects on Photocatalytic Activity of Hydrogen-Treated Titanium Oxide Nanobelts. ACS Catalysis, 7 (3). pp. 1742-1748. ISSN 2155-5435. https://resolver.caltech.edu/CaltechAUTHORS:20180627-102850462

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Abstract

Previous studies have shown that hydrogen treatment leads to the formation of blue to black TiO_2, which exhibits photocatalytic activity different from that of white pristine TiO_2. However, the underlying mechanism remains poorly understood. Herein, density functional theory is combined with comprehensive analytical approaches such as X-ray absorption near edge structure spectroscopy and transient absorption spectroscopy to gain fundamental understanding of the correlation among the oxygen vacancy, electronic band structure, charge separation, charge carrier lifetime, reactive oxygen species (ROS) generation, and photocatalytic activity. The present work reveals that hydrogen treatment results in chemical reduction of TiO_2, inducing surface and subsurface oxygen vacancies, which create shallow and deep sub-band gap Ti(III) states below the conduction band. This leads to a blue color but limited enhancement of visible light photocatalytic activity up to 440 nm at the cost of reduced ultraviolet photocatalytic activity. The extended light absorption spectral range for reduced TiO_2 is ascribed to both the defect-to-conduction band transitions and the valence band-to-defect transitions. The photogenerated charge carriers from the defect states to the conduction band have lifetimes too short to drive photocatalysis. The Ti(III) deep and shallow trap states below the conduction band are also found to reduce the lifetime of photogenerated charge carriers under ultraviolet light irradiation. The ROS generated by the reduced TiO_2 are less than those generated by pristine TiO_2. Consequently, the reduced TiO_2 exhibits ultraviolet-responsive photocatalytic activity worse than that of pristine TiO_2. This report shows that increasing the light absorption spectral range of a semiconductor by doping or introduction of defects does not necessarily guarantee an increase in photocatalytic activity.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1021/acscatal.6b02177DOIArticle
https://pubs.acs.org/doi/suppl/10.1021/acscatal.6b02177PublisherSupporting Information
ORCID:
AuthorORCID
Cushing, Scott K.0000-0003-3538-2259
Liu, Ru-Shi0000-0002-1291-9052
Wu, Nianqiang0000-0002-8888-2444
Additional Information:© 2017 American Chemical Society. Received: July 31, 2016. Revised: December 30, 2016. Published: January 19, 2017. The resources used in this work were partially supported by the National Science Foundation (Grant CBET-1233795). S.K.C. was supported by an NSF Graduate Research Fellowship under Grant 1102689. R.-S.L. is grateful for the financial support from the Ministry of Science, Technology of Taiwan (Contract MOST 104-2113-M-002-012-MY3), Academia Sinica (Contract AS-103-TP-A06), and National Taiwan University (Grant 104R7563-3). The authors declare no competing financial interest.
Funders:
Funding AgencyGrant Number
NSFCBET-1233795
NSF Graduate Research FellowshipDGE-1102689
Ministry of Science and Technology (Taipei)104-2113-M-002-012-MY3
Academia SinicaAS-103-TP-A06
National Taiwan University104R7563-3
Subject Keywords:band structure; charge dynamics; oxygen vacancy; photocatalyst; titanium oxide
Issue or Number:3
Record Number:CaltechAUTHORS:20180627-102850462
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20180627-102850462
Official Citation:Effects of Defects on Photocatalytic Activity of Hydrogen-Treated Titanium Oxide Nanobelts Scott. K. Cushing, Fanke Meng, Junying Zhang, Bangfu Ding, Chih Kai Chen, Chih-Jung Chen, Ru-Shi Liu, Alan D. Bristow, Joeseph Bright, Peng Zheng, and Nianqiang Wu ACS Catalysis 2017 7 (3), 1742-17
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:87390
Collection:CaltechAUTHORS
Deposited By: George Porter
Deposited On:27 Jun 2018 17:50
Last Modified:03 Oct 2019 19:55

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