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Abstract
We have used ab initio molecular dynamics and density-functional theory (DFT) calculations at the B3LYP/6-31G** level of theory to evaluate the energy and localisation of excess electrons at a number of representative interfaces of polymer nanocomposites.
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Affiliation(s)
- Fernan Saiz
- Department of Chemistry
- Imperial College
- London
- UK
| | - Nick Quirke
- Department of Chemistry
- Imperial College
- London
- UK
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Sternig A, Diwald O. Surface Decoration of MgO Nanocubes with Sulfur Oxides: Experiment and Theory. THE JOURNAL OF PHYSICAL CHEMISTRY. C, NANOMATERIALS AND INTERFACES 2013; 117:7727-7735. [PMID: 23616910 PMCID: PMC3632092 DOI: 10.1021/jp401432j] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 02/08/2013] [Revised: 03/15/2013] [Indexed: 06/02/2023]
Abstract
We investigated the effect of surface sulfate formation on the structure and spectroscopic properties of MgO nanocubes using X-ray diffraction, electron microscopy, several spectroscopic techniques, and ab initio calculations. After CS2 adsorption and oxidative treatment at elevated temperatures the MgO particles remain cubic and retain their average size of ∼6 nm. Their low coordinated surface elements (corners and edges) were found to bind sulfite and sulfate groups even after annealing up to 1173 K. The absence of MgO corner specific photoluminescence emission bands at 3.4 and 3.2 eV substantiates that sulfur modifies the electronic properties of characteristic surface structures, which we attribute to the formation of (SO3)2- and (SO4)2- groups at corners and edges. Ab initio calculations support these conclusions and provide insight into the local atomic structures and spectroscopic properties of these groups.
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Moreira IDP, Wojdeł JC, Illas F, Chiesa M, Giamello E. Evidence of magnetic ordering of paramagnetic surface defects on partially hydroxylated MgO nanocrystals. Chem Phys Lett 2008. [DOI: 10.1016/j.cplett.2008.07.060] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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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]
Affiliation(s)
- Gianfranco Pacchioni
- Dipartimento di Scienza dei Materiali, Università di Milano-Bicocca, Via R. Cozzi, 53 - 20125, Milano, Italy, and Dipartimento di Chimica IFM and NIS Centre of Excellence, Università di Torino, Via P. Giuria, 7 - 10125, Torino, Italy
| | - Sabrina Sicolo
- Dipartimento di Scienza dei Materiali, Università di Milano-Bicocca, Via R. Cozzi, 53 - 20125, Milano, Italy, and Dipartimento di Chimica IFM and NIS Centre of Excellence, Università di Torino, Via P. Giuria, 7 - 10125, Torino, Italy
| | - Cristiana Di Valentin
- Dipartimento di Scienza dei Materiali, Università di Milano-Bicocca, Via R. Cozzi, 53 - 20125, Milano, Italy, and Dipartimento di Chimica IFM and NIS Centre of Excellence, Università di Torino, Via P. Giuria, 7 - 10125, Torino, Italy
| | - Mario Chiesa
- Dipartimento di Scienza dei Materiali, Università di Milano-Bicocca, Via R. Cozzi, 53 - 20125, Milano, Italy, and Dipartimento di Chimica IFM and NIS Centre of Excellence, Università di Torino, Via P. Giuria, 7 - 10125, Torino, Italy
| | - Elio Giamello
- Dipartimento di Scienza dei Materiali, Università di Milano-Bicocca, Via R. Cozzi, 53 - 20125, Milano, Italy, and Dipartimento di Chimica IFM and NIS Centre of Excellence, Università di Torino, Via P. Giuria, 7 - 10125, Torino, Italy
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Berger T, Diwald O, Knözinger E, Napoli F, Chiesa M, Giamello E. Hydrogen activation at TiO2 anatase nanocrystals. Chem Phys 2007. [DOI: 10.1016/j.chemphys.2007.06.021] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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Müller M, Stankic S, Diwald O, Knözinger E, Sushko PV, Trevisanutto PE, Shluger AL. Effect of Protons on the Optical Properties of Oxide Nanostructures. J Am Chem Soc 2007; 129:12491-6. [PMID: 17892290 DOI: 10.1021/ja0736055] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Site-specific functionalization of oxide nanostructures gives rise to novel optical and chemical surface properties. In addition, it can provide deeper insights into the electronic surface structure of the associated materials. We applied chemisorption of molecular hydrogen, induced by ultraviolet (UV) light, followed by vacuum annealing to MgO nanocubes to selectively decorate three-coordinated oxygen ions (oxygen corner sites, for simplicity) with protons. Fully dehydroxylated nanocubes exhibit 3.2 +/- 0.1 eV photoluminescence induced by 4.6 eV light, where both emission and absorption are associated with three-coordinated oxygen sites. We find that partially hydroxylated nanocubes show an additional photoluminescence feature at 2.9 +/- 0.1 eV. Interestingly, the excitation spectra of the 2.9 and 3.2 eV emission bands, associated with protonated and nonprotonated oxygen corner sites, respectively, nearly coincide and show well-pronounced maxima at 4.6 eV in spite of a significant difference in their local atomic and electronic structures. These observations are explained with the help of ab initio calculations, which reveal that (i) the absorption band at 4.6 eV involves four-coordinated O and Mg ions in the immediate vicinity of the corner sites and (ii) protonation of the three-coordinated oxygen ions eliminates the optical transitions associated with them and strongly red-shifts other optical transitions associated with neighboring atoms. These results demonstrate that the optical absorption bands assigned to topological surface defects are not simply determined by the ions of lowest coordination number but involve contributions due to the neighboring atoms of higher coordination. Thus, we suggest that the absorption band at 4.6 eV should not be regarded as merely a signature of the three-coordinated O2- ions but ought to be assigned to corners as multiatomic topological features. Our results also suggest that optical absorption signatures of protonated and nonprotonated sites of oxide surfaces can be remarkably similar.
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Affiliation(s)
- Markus Müller
- Institute of Materials Chemistry, Vienna University of Technology, Veterinärplatz 1/GA, A-1210 Vienna, Austria
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Chiesa M, Paganini MC, Giamello E, Di Valentin C, Pacchioni G. Electron Traps on Oxide Surfaces: (H+)(e−) Pairs Stabilized on the Surface of 17O Enriched CaO. Chemphyschem 2006; 7:728-34. [PMID: 16477669 DOI: 10.1002/cphc.200500564] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
(H+)(e-) pairs generated at the surface of polycrystalline CaO are analyzed for the first time in terms of the interaction of the unpaired electron spin with the nuclear spin of the 17O anions of the surface. CaO crystals enriched in the 17O isotope are prepared and the corresponding hyperfine coupling constants are measured in electron paramagentic resonance (EPR) spectra. The results are analyzed on the basis of cluster model density functional theory calculations. The computed hyperfine coupling constants for (H+)(e-) pairs formed on the edge, corner, and reverse corner sites of the CaO surface allow a tentative assignment of two observed spectral features to specific morphological surface sites.
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Affiliation(s)
- Mario Chiesa
- Dipartimento di Chimica IFM, Università di Torino and NIS, Nanostructured Interfaces and Surfaces Center of Excellence, Via P. Giuria 7, 10125 Torino, Italy.
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Sterrer M, Berger T, Diwald O, Knözinger E, Sushko PV, Shluger AL. Chemistry at corners and edges: Generation and adsorption of H atoms on the surface of MgO nanocubes. J Chem Phys 2005; 123:64714. [PMID: 16122342 DOI: 10.1063/1.1997108] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We used UV light to generate site-selective O- hole centers at three-coordinated corner oxygen sites on MgO nanocubes. These highly reactive O- radicals split H2 homolytically and, in the course of this reaction, become hydroxylated and produce hydrogen atoms. The hydrogen atoms adsorb predominantly at cube edges and dissociate into surface-trapped electrons and protons. We propose that the experimentally observed (H+)(e-) centers are formed adjacent to the hydroxyl groups generated in the homolytic splitting process and can be defined as (H+)3C...(e-)(H+)NC centers where 3C and NC refer to the coordination numbers of the corresponding hydroxylated oxygen sites. Our ab initio embedded cluster calculations reveal that the electronic properties of (H+)3C...(e-)(H+)4C centers situated along MgO nanocube edges are consistent with both the electron-paramagnetic-resonance signal parameters and the reported optical-absorption properties. The transformation of corner O- centers into the (H+)3C...(e-)(H+)NC-type centers prevents their recombination with electronic surface centers and, hence, significantly alters the electronic structure of MgO nanocubes by introducing shallow electron traps.
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Affiliation(s)
- Martin Sterrer
- Department of Chemical Physics, Fritz-Haber-Institute of the Max-Planck-Society, Faradayweg 4-6, D-14195 Berlin, Germany
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