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Cano I, Martínez-Prieto LM, van Leeuwen PWNM. Heterolytic cleavage of dihydrogen (HCD) in metal nanoparticle catalysis. Catal Sci Technol 2021. [DOI: 10.1039/d0cy02399j] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Supports, ligands and additives can promote heterolytic H2 splitting by a cooperative mechanism with metal nanoparticles.
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Affiliation(s)
- Israel Cano
- Applied Physics Department
- University of Cantabria
- 39005 Santander
- Spain
| | - Luis M. Martínez-Prieto
- Instituto de Tecnología Química
- Universitat Politècnica de València-Consejo Superior de Investigaciones Científicas (UPV-CSIC)
- 46022 Valencia
- Spain
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2
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Anicˇić N, Vukomanović M, Koklicˇ T, Suvorov D. Fewer Defects in the Surface Slows the Hydrolysis Rate, Decreases the ROS Generation Potential, and Improves the Non-ROS Antimicrobial Activity of MgO. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2018; 14:e1800205. [PMID: 29782697 DOI: 10.1002/smll.201800205] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/16/2018] [Revised: 03/21/2018] [Indexed: 06/08/2023]
Abstract
Magnesium oxide (MgO) is recognised as exhibiting a contact-based antibacterial activity. However, a comprehensive study of the impact of atomic-scale surface features on MgO's antibacterial activity is lacking. In this study, the nature and abundance of the native surface defects on different MgO powders are thoroughly investigated. Their impacts on the hydrolysis kinetics, antibacterial activity against Escherichia coli (ATCC 47076), Staphylococcus epidermidis and Pseudomonas aeruginosa and the reactive oxygen species (ROS) generation potential are determined and explained. It is shown that a reduction in the abundance of low-coordinated oxygen atoms on the surface of the MgO improves its resistance to both hydrolysis and antibacterial activity. The ROS generation potential, determined in-situ using a fluorescence microplate assay and electron paramagnetic resonance spectroscopy, is not an inherent property of the studied MgO, rather it is a side product of hydrolysis (only for the most highly defected MgO particles) and/or a consequence of the MgO/bacteria interaction. The evaluation of the mutual correlations of the hydrolysis, the antibacterial activity and the ROS generation, with their origin in the surface defects' peculiarities, led to the conclusion that the acid/base reaction between the MgO surface and the bacterial wall contributes considerably to the MgO's antibacterial activity.
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Affiliation(s)
- Nemanja Anicˇić
- Advanced Materials Department, Jozef Stefan Institute, Jamova 39, 1000, Ljubljana, Slovenia
| | - Marija Vukomanović
- Advanced Materials Department, Jozef Stefan Institute, Jamova 39, 1000, Ljubljana, Slovenia
| | - Tilen Koklicˇ
- Laboratory for Biophysics, Jozef Stefan Institute, Jamova 39, 1000, Ljubljana, Slovenia
| | - Danilo Suvorov
- Advanced Materials Department, Jozef Stefan Institute, Jamova 39, 1000, Ljubljana, Slovenia
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4
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Sternig A, Stankic S, Müller M, Siedl N, Diwald O. Surface exciton separation in photoexcited MgO nanocube powders. NANOSCALE 2012; 4:7494-7500. [PMID: 23100068 DOI: 10.1039/c2nr31844j] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
In MgO nanocube powders surface excitons can separate and the resulting charge carriers provide reactive adsorption sites at well-defined surface elements. We employed photoluminescence (PL) emission bands originating from the photoexcitation of nanocube corners and edges as quantitative probes to explore their chemical reactivity towards molecular hydrogen. Surface excitons which form at corners and edges exhibit similar cross-sections for separation in vacuum. The separation of edge excitons, however, is significantly enhanced in hydrogen atmosphere when hydrogen adsorption occurs as a simultaneous surface process. The electronic structure of MgO nanocube edges which split hydrogen heterolytically upon generation of surface hydroxyls and hydrides is unaffected by the photoexcitation of corners. Respective edges, however, are efficient absorption sites for UV photons. Transfer of exciton energy to oxygen ions in corners is followed by exciton separation which transforms corner ions into surface radicals leading to a well-defined starting point for the site selective functionalization of metal oxide nanostructures.
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Affiliation(s)
- Andreas Sternig
- Cluster of Excellence - Engineering of Advanced Materials (EAM), Friedrich-Alexander University Erlangen-Nuremberg, Cauerstrasse 4, 91058 Erlangen, Germany
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5
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Pacchioni G, Freund H. Electron Transfer at Oxide Surfaces. The MgO Paradigm: from Defects to Ultrathin Films. Chem Rev 2012; 113:4035-72. [DOI: 10.1021/cr3002017] [Citation(s) in RCA: 241] [Impact Index Per Article: 20.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Affiliation(s)
- Gianfranco Pacchioni
- Dipartimento di Scienza dei
Materiali, Università di Milano-Bicocca, Via R. Cozzi, 53−20125,
Milano, Italy
| | - Hajo Freund
- Fritz-Haber-Insitut
der MPG,
Department of Chemical Physics, Faradayweg 4-6, 14195 Berlin, Germany
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Sternig A, Müller M, McCallum M, Bernardi J, Diwald O. BaO clusters on MgO nanocubes: a quantitative analysis of optical-powder properties. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2010; 6:582-8. [PMID: 20029851 DOI: 10.1002/smll.200901662] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
Abstract
Uniformly sized and shaped nanoparticles are well suited for the quantitative characterization of optical-powder properties. For the first time, quantum yields related to photoluminescence emissions that originate from the photoexcitation of MgO nanocube corners and edges are measured. In addition, the surfaces of these nanoparticles are doped with submonolayer barium, which oxidizes during adsorption onto the MgO nanocrystal surfaces and transforms in O(2) atmosphere into BaO. UV-Vis diffuse reflectance and photoluminescence spectroscopy is employed to explore whether 10(-3) monolayer equivalents of these dopants affect the MgO specific optical properties. Surface-admixed BaO produces additional absorption and photoluminescence emission features but does not significantly affect those specific to MgO nanocubes. On this basis the number of optically active sites that can be sampled inside a powder of alkaline earth oxide nanoparticles using a standard spectrometer system is estimated.
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Affiliation(s)
- Andreas Sternig
- Institute of Materials Chemistry, Vienna University of Technology, Veterinärplatz 1/GA, Vienna 1210, Austria
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Stankic S, Bernardi J, Diwald O, Knözinger E. Optical surface properties and morphology of MgO and CaO nanocrystals. J Phys Chem B 2007; 110:13866-71. [PMID: 16836335 DOI: 10.1021/jp061741a] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Optical absorption and photoluminescence emission properties of dehydroxylated MgO and CaO nanocrystals are discussed with respect to particle morphology and size. On MgO nanocubes with pronounced corner and edge features two emission bands at 3.4 and 3.3 eV result from the excitation of 4-coordinated surface O(4C)(2-) anions in edges at 5.4 eV and of regular oxygen-terminated corners at 4.6 eV, respectively. Morphologically ill-defined CaO particles are a factor of 5 larger, do not display regular corner features, and show only one photoluminescence emission band at 3.0 eV. The associated excitation spectrum indicates electronic excitations above the energy required to excite regular oxygen-terminated CaO corners. It is concluded that in the case of morphologically well-defined MgO nanocubes variations in the next coordination of oxygen-terminated corners can effectively be probed by photoluminescence spectroscopy and thus allows for discrimination between 3-coordinated surface O(2-) in regular corner sites and kinks.
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Affiliation(s)
- Slavica Stankic
- Institute of Materials Chemistry, Vienna University of Technology, Veterinärplatz 1/GA, A-1210 Vienna, Austria
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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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Sterrer M, Berger T, Diwald O, Knözinger E, Allouche A. Ozonide ions on the surface of MgO nanocrystals. Top Catal 2007. [DOI: 10.1007/s11244-007-0321-9] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Sterrer M, Fischbach E, Heyde M, Nilius N, Rust HP, Risse T, Freund HJ. Electron Paramagnetic Resonance and Scanning Tunneling Microscopy Investigations on the Formation of F+ and F0 Color Centers on the Surface of Thin MgO(001) Films. J Phys Chem B 2006; 110:8665-9. [PMID: 16640421 DOI: 10.1021/jp060546t] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The formation of surface color centers (F(S) centers) by electron bombardment of thin MgO(001) films is investigated using electron paramagnetic resonance and low-temperature scanning tunneling microscopy. At low electron doses both techniques indicate the formation of singly occupied color centers (F(S)(+)), whereas at high electron doses the doubly occupied type (F(S)(0)) is dominant. It is suggested that with increasing electron dose F(S)(+) centers are transformed into F(S)(0). Tunneling spectra of individual F(S)(0) centers reveal a large distribution of energetic positions of occupied and unoccupied states, which is caused by local variations of the coordination number of the defects and explains the broad signals usually detected with integrating spectroscopic techniques.
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Affiliation(s)
- Martin Sterrer
- Department of Chemical Physics, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, D-14195 Berlin, Germany. sterrer@ fhi-berlin.mpg.de
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11
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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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12
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Sterrer M, Heyde M, Novicki M, Nilius N, Risse T, Rust HP, Pacchioni G, Freund HJ. Identification of Color Centers on MgO(001) Thin Films with Scanning Tunneling Microscopy. J Phys Chem B 2005; 110:46-9. [PMID: 16471496 DOI: 10.1021/jp056306f] [Citation(s) in RCA: 130] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Localized electronic defects on the surface of a 4 monolayer (ML) thin MgO(001) film deposited on Ag(001) have been investigated by low-temperature scanning tunneling microscopy and spectroscopy. Depending on the location of the defect, we observe for the first time different defect energy levels in the band gap of MgO. The charge state of defects can be manipulated by interactions with the scanning tunneling microscope tip. Comparison with ground state energy levels of color centers on the MgO surface obtained from embedded cluster calculations corroborates the assignment of the defects to singly and doubly charged color centers.
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Affiliation(s)
- Martin Sterrer
- Fritz-Haber-Institut der Max-Planck-Gesellschaft, Department of Chemical Physics, Faradayweg 4-6, D-14195 Berlin, Germany.
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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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Sterrer M, Fischbach E, Risse T, Freund HJ. Geometric characterization of a singly charged oxygen vacancy on a single-crystalline MgO(001) film by electron paramagnetic resonance spectroscopy. PHYSICAL REVIEW LETTERS 2005; 94:186101. [PMID: 15904384 DOI: 10.1103/physrevlett.94.186101] [Citation(s) in RCA: 87] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/11/2005] [Indexed: 05/02/2023]
Abstract
Electron paramagnetic resonance spectra of singly charged surface oxygen vacancies (F or color centers) formed by electron bombardment on a single-crystalline MgO film under UHV conditions are reported. The embedding of the defect in a well-defined geometrical environment allows not only for the determination of the magnetic quantities but also, in conjunction with STM studies, for the geometrical assignment of the observed signal to color centers located on the edges of the MgO film.
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Affiliation(s)
- Martin Sterrer
- Department of Chemical Physics, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, D-14195 Berlin, Germany
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