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Williams OBJ, Katsiev K, Baek B, Harrison G, Thornton G, Idriss H. Direct Visualization of a Gold Nanoparticle Electron Trapping Effect. J Am Chem Soc 2022; 144:1034-1044. [PMID: 34985273 DOI: 10.1021/jacs.1c12197] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
A new atomic-scale anisotropy in the photoreaction of surface carboxylates on rutile TiO2(110) induced by gold clusters is found. STM and DFT+U are used to study this phenomenon by monitoring the photoreaction of a prototype hole-scavenger molecule, benzoic acid, over stoichiometric (s) s-TiO2, Au9/s-TiO2, and reduced (r) Au9/r-TiO2. STM results show that benzoic acid adsorption displaces a large fraction of Au clusters from the terraces toward their edges. DFT calculations explain that Au9 clusters on stoichiometric TiO2 are distorted by benzoic acid adsorption. The influence of sub-monolayers of Au on the UV/visible photoreaction of benzoic acid was explored at room temperature, with adsorbate depletion taken as a measure of activity. The empty sites, observed upon photoexcitation, occurred in elongated chains (2 to 6 molecules long) in the [11̅0] and [001] directions. A roughly 3-fold higher depletion rate is observed in the [001] direction. This is linked to the anisotropic conduction of excited electrons along [001], with subsequent trapping by Au clusters leaving a higher concentration of holes and thus an increased decomposition rate. To our knowledge this is the first time that atomic-scale directionality of a chemical reaction is reported upon photoexcitation of the semiconductor.
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Affiliation(s)
- Oscar Bentley Jerdmyr Williams
- Department of Chemistry and London Centre for Nanotechnology (LCN), University College London (UCL), WC1H 0AH, London, U.K
| | - Khabiboulakh Katsiev
- Surface Science and Advanced Characterisation, SABIC-CRD at King Abdullah University for Science and Technology (KAUST), Thuwal, 23955, Saudi Arabia
| | - Byeongjin Baek
- SABIC Global Corporate Research, Sugar Land, Texas 77478, United States
| | - George Harrison
- KAUST Solar Center (KSC), Physical Sciences and Engineering Division (PSE), King Abdullah University for Science and Technology (KAUST), Thuwal, 23955, Saudi Arabia
| | - Geoff Thornton
- Department of Chemistry and London Centre for Nanotechnology (LCN), University College London (UCL), WC1H 0AH, London, U.K
| | - Hicham Idriss
- Department of Chemistry and London Centre for Nanotechnology (LCN), University College London (UCL), WC1H 0AH, London, U.K.,Surface Science and Advanced Characterisation, SABIC-CRD at King Abdullah University for Science and Technology (KAUST), Thuwal, 23955, Saudi Arabia
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Tanner AJ, Kerr R, Fielding HH, Thornton G. Chemical Modification of Polaronic States in Anatase TiO 2(101). THE JOURNAL OF PHYSICAL CHEMISTRY. C, NANOMATERIALS AND INTERFACES 2021; 125:14348-14355. [PMID: 34267854 PMCID: PMC8273885 DOI: 10.1021/acs.jpcc.1c03684] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 04/24/2021] [Revised: 06/02/2021] [Indexed: 06/13/2023]
Abstract
Two polymorphs of TiO2, anatase and rutile, are employed in photocatalytic applications. It is broadly accepted that anatase is the more catalytically active and subsequently finds wider commercial use. In this work, we focus on the Ti3+ polaronic states of anatase TiO2(101), which lie at ∼1.0 eV binding energy and are known to increase catalytic performance. Using UV-photoemission and two-photon photoemission spectroscopies, we demonstrate the capability to tune the excited state resonance of polarons by controlling the chemical environment. Anatase TiO2(101) contains subsurface polarons which undergo sub-band-gap photoexcitation to states ∼2.0 eV above the Fermi level. Formic acid adsorption dramatically influences the polaronic states, increasing the binding energy by ∼0.3 eV. Moreover, the photoexcitation oscillator strength changes significantly, resonating with states ∼3.0 eV above the Fermi level. We show that this behavior is likely due to the surface migration of subsurface oxygen vacancies.
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Affiliation(s)
- Alex J. Tanner
- Department
of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, United Kingdom
- London
Centre for Nanotechnology, University College
London, 17-19 Gordon Street, London WC1H 0AH, United Kingdom
| | - Robin Kerr
- Department
of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, United Kingdom
- London
Centre for Nanotechnology, University College
London, 17-19 Gordon Street, London WC1H 0AH, United Kingdom
| | - Helen H. Fielding
- Department
of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, United Kingdom
| | - Geoff Thornton
- Department
of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, United Kingdom
- London
Centre for Nanotechnology, University College
London, 17-19 Gordon Street, London WC1H 0AH, United Kingdom
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Tanner AJ, Wen B, Ontaneda J, Zhang Y, Grau-Crespo R, Fielding HH, Selloni A, Thornton G. Polaron-Adsorbate Coupling at the TiO 2(110)-Carboxylate Interface. J Phys Chem Lett 2021; 12:3571-3576. [PMID: 33819053 PMCID: PMC8054240 DOI: 10.1021/acs.jpclett.1c00678] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2021] [Accepted: 03/31/2021] [Indexed: 06/12/2023]
Abstract
Understanding how adsorbates influence polaron behavior is of fundamental importance in describing the catalytic properties of TiO2. Carboxylic acids adsorb readily at TiO2 surfaces, yet their influence on polaronic states is unknown. Using UV photoemission spectroscopy (UPS), two-photon photoemission spectroscopy (2PPE), and density functional theory (DFT) we show that dissociative adsorption of formic and acetic acids has profound, yet different, effects on the surface density, crystal field, and photoexcitation of polarons in rutile TiO2(110). We also show that these variations are governed by the contrasting electrostatic properties of the acids, which impacts the extent of polaron-adsorbate coupling. The density of polarons in the surface region increases more in formate-terminated TiO2(110) relative to acetate. Consequently, increased coupling gives rise to new photoexcitation channels via states 3.83 eV above the Fermi level. The onset of this process is 3.45 eV, likely adding to the catalytic photoyield.
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Affiliation(s)
- Alex J. Tanner
- Department
of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, United Kingdom
- London
Centre for Nanotechnology, University College
London, 17-19 Gordon
Street, London WC1H 0AH, United Kingdom
| | - Bo Wen
- Department
of Chemistry, Princeton University, Princeton, New Jersey 08540, United States
| | - Jorge Ontaneda
- Department
of Chemistry, University of Reading, Whiteknights, Reading RG6 6AX, United Kingdom
| | - Yu Zhang
- Department
of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, United Kingdom
- London
Centre for Nanotechnology, University College
London, 17-19 Gordon
Street, London WC1H 0AH, United Kingdom
| | - Ricardo Grau-Crespo
- Department
of Chemistry, University of Reading, Whiteknights, Reading RG6 6AX, United Kingdom
| | - Helen H. Fielding
- Department
of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, United Kingdom
| | - Annabella Selloni
- Department
of Chemistry, Princeton University, Princeton, New Jersey 08540, United States
| | - Geoff Thornton
- Department
of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, United Kingdom
- London
Centre for Nanotechnology, University College
London, 17-19 Gordon
Street, London WC1H 0AH, United Kingdom
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