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Thomele D, Baumann SO, Schneider J, Sternig AK, Shulda S, Richards RM, Schwab T, Zickler GA, Bourret GR, Diwald O. Cubes to Cubes: Organization of MgO Particles into One-Dimensional and Two-Dimensional Nanostructures. CRYSTAL GROWTH & DESIGN 2021; 21:4674-4682. [PMID: 34381312 PMCID: PMC8343528 DOI: 10.1021/acs.cgd.1c00535] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/07/2021] [Revised: 06/22/2021] [Indexed: 05/29/2023]
Abstract
Developing simple, inexpensive, and environmentally benign approaches to integrate morphologically well-defined nanoscale building blocks into larger high surface area materials is a key challenge in materials design and processing. In this work, we investigate the fundamental surface phenomena between MgO and water (both adsorption and desorption) with particles prepared via a vapor-phase process (MgO nanocubes) and a modified aerogel process (MgO(111) nanosheets). Through these studies, we unravel a strategy to assemble individual MgO nanoparticles into extended faceted single-crystalline MgO nanosheets and nanorods with well-defined exposed surfaces and edges. This reorganization can be triggered by the presence of H2O vapor or bulk liquid water. Water adsorption and the progressive conversion of vapor-phase grown oxide particles into hydroxides give rise to either one-dimensional or two-dimensional (1D or 2D) structures of high dispersion and surface area. The resulting Mg(OH)2 lamella with a predominant (001) surface termination are well-suited precursor structures for their topotactic conversion into laterally extended and uniform MgO(111) grain surface configurations. To understand the potential of polar (111) surfaces for faceting and surface reconstruction effects associated with water desorption, we investigated the stability of MgO(111) nanosheets during vacuum annealing and electron beam exposure. The significant surface reconstruction of the MgO(111) surfaces observed shows that adsorbate-free (111)-terminated surfaces of unsupported MgO nanostructures reconstruct rather than remain as charged planes of either three-fold coordinated O2- ion or Mg2+ ions. Thus, here we demonstrate the role water can play in surface formation and reconstruction by bridging wet chemical and surface science inspired approaches.
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Affiliation(s)
- Daniel Thomele
- Department
of Chemistry and Physics of Materials, Paris-Lodron
University Salzburg, Jakob Haringerstrasse 2a, Salzburg, 5020, Austria
- Institute
of Particle Technology (LFG), Friedrich-Alexander-Universität
Erlangen-Nürnberg, Cauerstraße 4, Erlangen, 91058, Germany
| | - Stefan O. Baumann
- Institute
of Particle Technology (LFG), Friedrich-Alexander-Universität
Erlangen-Nürnberg, Cauerstraße 4, Erlangen, 91058, Germany
| | - Johannes Schneider
- Department
of Chemistry and Physics of Materials, Paris-Lodron
University Salzburg, Jakob Haringerstrasse 2a, Salzburg, 5020, Austria
- Institute
of Particle Technology (LFG), Friedrich-Alexander-Universität
Erlangen-Nürnberg, Cauerstraße 4, Erlangen, 91058, Germany
| | - Andreas K. Sternig
- Institute
of Particle Technology (LFG), Friedrich-Alexander-Universität
Erlangen-Nürnberg, Cauerstraße 4, Erlangen, 91058, Germany
| | - Sarah Shulda
- Department
of Chemistry, Colorado School of Mines, Golden, Colorado 80401, United States
| | - Ryan M. Richards
- Department
of Chemistry, Colorado School of Mines, Golden, Colorado 80401, United States
| | - Thomas Schwab
- Department
of Chemistry and Physics of Materials, Paris-Lodron
University Salzburg, Jakob Haringerstrasse 2a, Salzburg, 5020, Austria
| | - Gregor A. Zickler
- Department
of Chemistry and Physics of Materials, Paris-Lodron
University Salzburg, Jakob Haringerstrasse 2a, Salzburg, 5020, Austria
| | - Gilles R. Bourret
- Department
of Chemistry and Physics of Materials, Paris-Lodron
University Salzburg, Jakob Haringerstrasse 2a, Salzburg, 5020, Austria
| | - Oliver Diwald
- Department
of Chemistry and Physics of Materials, Paris-Lodron
University Salzburg, Jakob Haringerstrasse 2a, Salzburg, 5020, 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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3
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Chiesa M, Giamello E, Annino G, Massa C, Murphy D. Multi-frequency high-field EPR study of (H+)(e−) pairs localized at the surface of polycrystalline MgO. Chem Phys Lett 2007. [DOI: 10.1016/j.cplett.2007.03.024] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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Stankic S, Sterrer M, Hofmann P, Bernardi J, Diwald O, Knözinger E. Novel optical surface properties of Ca2+ -doped MgO nanocrystals. NANO LETTERS 2005; 5:1889-93. [PMID: 16218704 DOI: 10.1021/nl0511418] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
Surface doping of oxide nanoparticles is important in fields ranging from heterogeneous catalysis to optoelectronics. Here, we report the solvent-free synthesis of mixed calcium-magnesium oxide nanocrystals in the size range between 5 and 40 nm. Although CaMgO mixtures are thermodynamically forbidden on a macroscopic scale, Calcium ions can be distributed homogeneously in MgO using chemical vapor deposition (CVD) as a nonequilibrium technique. Subsequent thermal activation leads to calcium ion segregation into the nanocrystal surface which, in addition to the synthesis parameters, provides efficient means for manipulating the optical surface properties of insulating oxide nanocrystals. A novel material with unexpected photonic behavior, such as enhanced photoluminescence emission which is also red-shifted with respect to those of CaO and MgO, was found.
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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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Sterrer M, Berger T, Diwald O, Knözinger E. Energy transfer on the MgO surface, monitored by UV-induced H2 chemisorption. J Am Chem Soc 2003; 125:195-9. [PMID: 12515522 DOI: 10.1021/ja028059o] [Citation(s) in RCA: 99] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Surface anions on edges (4-coordinated = 4C) and on corners (3-coordinated = 3C) of cubic MgO nanoparticles exhibit UV resonance absorptions around 5.5 and 4.6 eV, respectively. After monochromatic excitation of either site the electron paramagnetic resonance (EPR) spectrum exhibits exclusively signal components related to 3-coordinated O- radicals (O-(3C), electron hole centers), which are perfectly bleached by H(2) addition. The disappearance of the O-(3C) EPR signal components is paralleled by a depletion of the UV resonance absorption of the 3-coordinated O(2-) only and the appearance of one single band in the OH stretching region of the IR spectrum. Obviously the sites of UV excitation and subsequent UV induced surface reaction with H(2) are not the same. This may coherently be explained in terms of mobility of the exciton (O(2-)(4C)* or--after ionization--of the corresponding electron hole O-(4C) along the edge where it was created. Finally the mobile state is trapped at a corner site where the O(3C)H group is formed.
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Affiliation(s)
- Martin Sterrer
- Institut für Materialchemie, Technische Universität Wien, c/o Veterinärplatz 1/GA, A-1210 Vienna, Austria
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Knözinger E, Diwald O, Sterrer M. Chemical vapour deposition — a new approach to reactive surface defects of uniform geometry on high surface area magnesium oxide. ACTA ACUST UNITED AC 2000. [DOI: 10.1016/s1381-1169(00)00323-x] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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