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Di Valentin C. A mechanism for the hole-mediated water photooxidation on TiO2 (1 0 1) surfaces. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2016; 28:074002. [PMID: 26808344 DOI: 10.1088/0953-8984/28/7/074002] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
The mechanism of water photooxidation on TiO2 surfaces is still controversial. Here we report a first-principles density functional study based on a hybrid functional method in which an adsorbed water molecule is found to directly interact with a self-trapped hole at a bridging oxygen site and to transform into an OH(•) radical species through a concerted proton/hole transfer. This study analyzes both the thermodynamics and kinetics of this step of the reaction, which is generally considered to be the rate determining one. The fate of the OH(•) radical is then investigated in terms of its reactivity with different surface species, with a second OH(•) radical, or with a second water molecule coming from the environment. We find that OH(•) radicals can either acquire a hydrogen from surrounding water molecules or, if they meet, couple to form hydrogen peroxide with highly associated energy gain.
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Gerosa M, Bottani CE, Caramella L, Onida G, Di Valentin C, Pacchioni G. Defect calculations in semiconductors through a dielectric-dependent hybrid DFT functional: The case of oxygen vacancies in metal oxides. J Chem Phys 2015; 143:134702. [DOI: 10.1063/1.4931805] [Citation(s) in RCA: 65] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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53
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Gerosa M, Di Valentin C, Bottani CE, Onida G, Pacchioni G. Communication: Hole localization in Al-doped quartz SiO2 within ab initio hybrid-functional DFT. J Chem Phys 2015; 143:111103. [DOI: 10.1063/1.4931405] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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54
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Ferrighi L, Píš I, Nguyen TH, Cattelan M, Nappini S, Basagni A, Parravicini M, Papagni A, Sedona F, Magnano E, Bondino F, Di Valentin C, Agnoli S. Control of the intermolecular coupling of dibromotetracene on Cu(110) by the sequential activation of C-Br and C-H bonds. Chemistry 2015; 21:5826-35. [PMID: 25711882 DOI: 10.1002/chem.201405817] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2014] [Indexed: 11/07/2022]
Abstract
Dibromotetracene molecules are deposited on the Cu(110) surface at room temperature. The complex evolution of this system has been monitored at different temperatures (i.e., 298, 523, 673, and 723 K) by means of a variety of complementary techniques that range from STM and temperature-programmed desorption (TPD) to high-resolution X-ray spectroscopy (XPS) and near-edge X-ray absorption fine structure spectroscopy (NEXAFS). State-of-the-art density-functional calculations were used to determine the chemical processes that take place on the surface. After deposition at room temperature, the organic molecules are transformed into organometallic monomers through debromination and carbon-radical binding to copper adatoms. Organometallic dimers, trimers, or small oligomers, which present copper-bridged molecules, are formed by increasing the temperature. Surprisingly, further heating to 673 K causes the formation of elongated chains along the Cu(110) close-packed rows as a consequence of radical-site migration to the thermodynamically more stable molecule heads. Finally, massive dehydrogenation occurs at the highest temperature followed by ring condensation to nanographenic patches. This study is a paradigmatic example of how intermolecular coupling can be modulated by the stepwise control of a simple parameter, such as temperature, through a sequence of domino reactions.
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55
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Basagni A, Ferrighi L, Cattelan M, Nicolas L, Handrup K, Vaghi L, Papagni A, Sedona F, Valentin CD, Agnoli S, Sambi M. On-surface photo-dissociation of C–Br bonds: towards room temperature Ullmann coupling. Chem Commun (Camb) 2015; 51:12593-6. [DOI: 10.1039/c5cc04317d] [Citation(s) in RCA: 53] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The surface-assisted synthesis of gold-organometallic hybrids on the Au(111) surface both by thermo- and light-initiated dehalogenation of bromo-substituted tetracene is reported.
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56
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Favaro M, Ferrighi L, Fazio G, Colazzo L, Di Valentin C, Durante C, Sedona F, Gennaro A, Agnoli S, Granozzi G. Single and Multiple Doping in Graphene Quantum Dots: Unraveling the Origin of Selectivity in the Oxygen Reduction Reaction. ACS Catal 2014. [DOI: 10.1021/cs501211h] [Citation(s) in RCA: 145] [Impact Index Per Article: 14.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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57
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Di Valentin C, Pacchioni G. Spectroscopic properties of doped and defective semiconducting oxides from hybrid density functional calculations. Acc Chem Res 2014; 47:3233-41. [PMID: 24828320 DOI: 10.1021/ar4002944] [Citation(s) in RCA: 107] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
CONSPECTUS: Very rarely do researchers use metal oxides in their pure and fully stoichiometric form. In most of the countless applications of these compounds, ranging from catalysis to electronic devices, metal oxides are either doped or defective because the most interesting chemical, electronic, optical, and magnetic properties arise when foreign components or defects are introduced in the lattice. Similarly, many metal oxides are diamagnetic materials and do not show a response to specific spectroscopies such as electron paramagnetic resonance (EPR) spectroscopy. However, doped or defective oxides may exhibit an interesting and informative paramagnetic behavior. Doped and defective metal oxides offer an expanding range of applications in contemporary condensed matter science; therefore researchers have devoted enormous effort to the understanding their physical and chemical properties. The interplay between experiment and computation is particularly useful in this field, and contemporary simulation techniques have achieved high accuracies with these materials. In this Account, we show how the direct comparison between spectroscopic experimental and computational data for some selected and relevant materials provides ways to understand and control these complex systems. We focus on the EPR properties and electronic transitions that arise from the presence of dopants and defects in bulk metal oxide materials. We analyze and compare the effect of nitrogen doping in TiO2 and ZnO (two semiconducting oxides) and MgO (a wide gap insulator) and examine the effect of oxygen deficiency in the semiconducting properties of TiO2-x, ZnO1-x, and WO3-x materials. We chose these systems because of their relevance in applications including photocatalysis, touch screens, electrodes in magnetic random access memories, and smart glasses. Density functional theory (DFT) provides the general computational framework used to illustrate the electronic structure of these systems. However, for a more accurate description of the oxide band gap and of the electron localization of the impurity states associated with dopants or defects, we resorted to the use of hybrid functionals (B3LYP), where a portion of exact exchange in the exchange-correlation functional partly corrects for the self-interaction error inherent in DFT. In many cases, the self-interaction correction is very important, and these results can lead to a completely different physical picture than that obtained using local or semilocal functionals. We analyzed the electronic transitions in terms of their transition energy levels, which provided a more accurate comparison with experimental spectroscopic data than Kohn-Sham eigenvalues. The effects of N-doping were similar among the three oxides that we considered. The nature of the impurity state is always localized at the dopant site, which may limit their application in photocatalytic processes. Photocatalytic systems require highly delocalized photoexcited carriers within the material to effectively trigger redox processes at the surface. The nature of the electronic states associated with the oxygen deficiency differed widely in the three investigated oxides. In ZnO1-x and WO3-x the electronic states resemble the typical F-centers in insulating oxides or halides, with the excess electron density localized at the vacancy site. However, TiO2 acts as a reducible oxide, and the removal of neutral oxygen atoms reduced Ti(4+) to Ti(3+).
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Fazio G, Ferrighi L, Di Valentin C. Boron-doped graphene as active electrocatalyst for oxygen reduction reaction at a fuel-cell cathode. J Catal 2014. [DOI: 10.1016/j.jcat.2014.07.024] [Citation(s) in RCA: 111] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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59
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De Angelis F, Di Valentin C, Fantacci S, Vittadini A, Selloni A. Theoretical Studies on Anatase and Less Common TiO2 Phases: Bulk, Surfaces, and Nanomaterials. Chem Rev 2014; 114:9708-53. [DOI: 10.1021/cr500055q] [Citation(s) in RCA: 321] [Impact Index Per Article: 32.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
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60
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Gionco C, Paganini MC, Giamello E, Burgess R, Di Valentin C, Pacchioni G. Cerium-Doped Zirconium Dioxide, a Visible-Light-Sensitive Photoactive Material of Third Generation. J Phys Chem Lett 2014; 5:447-451. [PMID: 26276590 DOI: 10.1021/jz402731s] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
The dispersion of small amounts of Ce(4+) ions in the bulk of ZrO2 leads to a photoactive material sensitive to visible light. This is shown by monitoring with EPR the formation and the reactivity of photogenerated (λ > 420 nm) charge carriers. The effect, as confirmed by DFT calculations, is due to the presence in the solid of empty 4f Ce states at the mid gap, which act as intermediate levels in a double excitation mechanism. This solid can be considered an example of a third-generation photoactive material.
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61
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Sezen H, Buchholz M, Nefedov A, Natzeck C, Heissler S, Di Valentin C, Wöll C. Probing electrons in TiO2 polaronic trap states by IR-absorption: evidence for the existence of hydrogenic states. Sci Rep 2014; 4:3808. [PMID: 24448350 PMCID: PMC3898047 DOI: 10.1038/srep03808] [Citation(s) in RCA: 71] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2013] [Accepted: 12/30/2013] [Indexed: 01/19/2023] Open
Abstract
An important step in oxide photochemistry, the loading of electrons into shallow trap states, was studied using infrared (IR) spectroscopy on both, rutile TiO2 powders and single-crystal, r-TiO2(110) oriented samples. After UV-irradiation or n-doping by exposure to H-atoms broad IR absorption lines are observed for the powders at around 940 cm(-1). For the single crystal substrates, the IR absorption bands arising from an excitation of the trapped electrons into higher-lying final states show additional features not observed in previous work. On the basis of our new, high-resolution data and theoretical studies on the polaron binding energy in rutile we propose that the trap states correspond to polarons and are thus intrinsic in nature. We assign the final states probed by the IR-experiments to hydrogenic states within the polaron potential. Implications of these observations for photochemistry on oxides will be briefly discussed.
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Di Valentin C, Botti S, Cococcioni M. The development of ever more advanced technologies depends very critically on the definitions of materials with appropriate characteristics. Top Curr Chem (Cham) 2014; 347:v-ix. [PMID: 25392865] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
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63
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Di Valentin C, Fittipaldi D. Hole Scavenging by Organic Adsorbates on the TiO2 Surface: A DFT Model Study. J Phys Chem Lett 2013; 4:1901-1906. [PMID: 26283127 DOI: 10.1021/jz400624w] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Understanding the interfacial hole transfer between photoirradiated anatase TiO2 nanoparticles and organic adsorbates at the surface is a crucial step toward the full comprehension and control of the photooxidation processes, which are fundamental in photocatalytic applications for energy production, environmental care, and medical cancer phototherapy. In this density functional study, we use the hybrid functional B3LYP in order to investigate how the hole transfer process takes place at the anatase (101) surface when a series of organic alcohols and acids are adsorbed. The results allow us to propose a mechanism of photoinduced proton dissociation and a scale of scavenging power of the different organic adsorbates (glycerol > tert-butanol > iso-propanol > methanol > formic acid). We observe that the surface dipole originated by the molecular adsorption causes a reduction in the cost to form a hole at a surface oxygen. This can then be trapped by the organic adsorbate only if proton dissociation takes place. In the case of glycerol, the hole transfer triggers further photoinduced chemical reactivity than the simple proton dissociation. Only in the case of cathecol, which is an excellent hole scavenger, the proton dissociation is not a required step.
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65
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Di Valentin C, Rosa M, Pacchioni G. Radical versus Nucleophilic Mechanism of Formaldehyde Polymerization Catalyzed by (WO3)3 Clusters on Reduced or Stoichiometric TiO2(110). J Am Chem Soc 2012; 134:14086-98. [DOI: 10.1021/ja304661g] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
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66
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Gallino F, Di Valentin C. Copper impurities in bulk ZnO: A hybrid density functional study. J Chem Phys 2011; 134:144506. [DOI: 10.1063/1.3575198] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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67
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Maurelli S, Livraghi S, Chiesa M, Giamello E, Van Doorslaer S, Di Valentin C, Pacchioni G. Hydration Structure of the Ti(III) Cation as Revealed by Pulse EPR and DFT Studies: New Insights into a Textbook Case. Inorg Chem 2011; 50:2385-94. [DOI: 10.1021/ic1021802] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
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68
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Qiu H, Gallino F, Di Valentin C, Wang Y. Shallow donor states induced by in-diffused Cu in ZnO: a combined HREELS and hybrid DFT study. PHYSICAL REVIEW LETTERS 2011; 106:066401. [PMID: 21405480 DOI: 10.1103/physrevlett.106.066401] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/13/2010] [Indexed: 05/30/2023]
Abstract
A combined experimental and first principles study of Cu defects in bulk ZnO is presented. Cu particles are epitaxially deposited on the polar O-ZnO(0001) surface at room temperature. Upon heating, a broadening of the quasielastic peak in high resolution electron energy loss spectra is observed, corresponding to an electronic doping effect of Cu atoms in bulk ZnO with an ionization energy of 88 meV. Cu impurities in ZnO, although commonly acting as acceptors, are presently observed to induce shallow donor states. We assign these to interstitial Cu species on the basis of a hybrid density functional study.
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69
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Gallino F, Di Valentin C, Pacchioni G. Band gap engineering of bulk ZrO2 by Ti doping. Phys Chem Chem Phys 2011; 13:17667-75. [DOI: 10.1039/c1cp21987a] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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70
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Gallino F, Pacchioni G, Di Valentin C. Transition levels of defect centers in ZnO by hybrid functionals and localized basis set approach. J Chem Phys 2010; 133:144512. [DOI: 10.1063/1.3491271] [Citation(s) in RCA: 91] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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71
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Napoli F, Chiesa M, Giamello E, Preda G, Di Valentin C, Pacchioni G. Formation of superoxo species by interaction of O(2) with Na atoms deposited on MgO powders: a combined continuous-wave EPR (CW-EPR), hyperfine sublevel correlation (HYSCORE) and DFT study. Chemistry 2010; 16:6776-85. [PMID: 20514645 DOI: 10.1002/chem.201000546] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The formation of O(2) (-) radical anions by contact of O(2) molecules with a Na pre-covered MgO surface is studied by a combined EPR and quantum chemical approach. Na atoms deposited on polycrystalline MgO samples are brought into contact with O(2). The typical EPR signal of isolated Na atoms disappears when the reaction with O(2) takes place and new paramagnetic species are observed, which are attributed to different surface-stabilised O(2) (-) radicals. Hyperfine sublevel correlation (HYSCORE) spectroscopy allows the superhyperfine interaction tensor of O(2) (-)Na(+) species to be determined, demonstrating the direct coordination of the O(2) (-) adsorbate to surface Na(+) cations. DFT calculations enable the structural details of the formed species to be determined. Matrix-isolated alkali superoxides are used as a standard to enable comparison of the formed species, revealing important and unexpected contributions of the MgO matrix in determining the electronic structure of the surface-stabilised Na(+)-O(2) (-) complexes.
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72
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Valentin CD, Pacchioni G, Onishi H, Kudo A. Cr/Sb co-doped TiO2 from first principles calculations. Chem Phys Lett 2009. [DOI: 10.1016/j.cplett.2008.12.086] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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73
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Finazzi E, Di Valentin C, Pacchioni G, Selloni A. Excess electron states in reduced bulk anatase TiO2: Comparison of standard GGA, GGA+U, and hybrid DFT calculations. J Chem Phys 2008; 129:154113. [DOI: 10.1063/1.2996362] [Citation(s) in RCA: 431] [Impact Index Per Article: 26.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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74
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Pacchioni G, Sicolo S, Valentin CD, Chiesa M, Giamello E. A Route toward the Generation of Thermally Stable Au Cluster Anions Supported on the MgO Surface. J Am Chem Soc 2008; 130:8690-5. [DOI: 10.1021/ja710969t] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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75
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Di Valentin C. Scanning tunneling microscopy image simulation of the rutile (110) TiO2 surface with hybrid functionals and the localized basis set approach. J Chem Phys 2007; 127:154705. [DOI: 10.1063/1.2790430] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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