Ultrathin Single Crystalline MgO(111) Nanosheets**

Liu, Pengxin; Abdala, Paula M.; Goubert, Guillaume; Willinger, Marc Georg; Copéret, Christophe

doi:10.1002/anie.202013196

Cited by 43 publications

(30 citation statements)

References 60 publications

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“…First, the samples were pretreated in situ in He at 450 ºC for ca. 15 min to remove adsorbed water, hydroxides and carbonates adsorbed onto the surface ( [30][31][32] and subsequently cooled down to 330 °C in He. The collected XRR data on bare MgO(100) and NaNO3-coated MgO(100) at 330 ºC under He flow are referred to as MgO(100)-He and NaNO3-MgO(100)-He, respectively.…”

Section: Changes At the Surface Of Mgo Under Co2 Capture Conditions Probed By In Situ Xrr-gixrdmentioning

confidence: 99%

Peering into buried interfaces with X-rays and electrons to unveil MgCO ₃ formation during CO ₂ capture in molten salt-promoted MgO

Bork

Rekhtina

Willinger

et al. 2021

Proc. Natl. Acad. Sci. U.S.A.

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The addition of molten alkali metal salts drastically accelerates the kinetics of CO2 capture by MgO through the formation of MgCO3. However, the growth mechanism, the nature of MgCO3 formation, and the exact role of the molten alkali metal salts on the CO2 capture process remain elusive, holding back the development of more-effective MgO-based CO2 sorbents. Here, we unveil the growth mechanism of MgCO3 under practically relevant conditions using a well-defined, yet representative, model system that is a MgO(100) single crystal coated with NaNO3. The model system is interrogated by in situ X-ray reflectometry coupled with grazing incidence X-ray diffraction, scanning electron microscopy, and high-resolution transmission electron microscopy. When bare MgO(100) is exposed to a flow of CO2, a noncrystalline surface carbonate layer of ca. 7-Å thickness forms. In contrast, when MgO(100) is coated with NaNO3, MgCO3 crystals nucleate and grow. These crystals have a preferential orientation with respect to the MgO(100) substrate, and form at the interface between MgO(100) and the molten NaNO3. MgCO3 grows epitaxially with respect to MgO(100), and the lattice mismatch between MgCO3 and MgO is relaxed through lattice misfit dislocations. Pyramid-shaped pits on the surface of MgO, in proximity to and below the MgCO3 crystals, point to the etching of surface MgO, providing dissolved [Mg2+…O2–] ionic pairs for MgCO3 growth. Our studies highlight the importance of combining X-rays and electron microscopy techniques to provide atomic to micrometer scale insight into the changes occurring at complex interfaces under reactive conditions.

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Section: Changes At the Surface Of Mgo Under Co2 Capture Conditions Probed By In Situ Xrr-gixrdmentioning

confidence: 99%

Peering into buried interfaces with X-rays and electrons to unveil MgCO ₃ formation during CO ₂ capture in molten salt-promoted MgO

Bork

Rekhtina

Willinger

et al. 2021

Proc. Natl. Acad. Sci. U.S.A.

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“…55 Additionally, we provide evidence that vacuum annealing of Mg(OH) 2 nanostructures at 473 K or 1173 K produces microfaceted surfaces with a high abundance of exposed (100) planes (Figure 7b), most likely due to the thermally induced adsorbate decomposition and surface dehydroxylation. 42 Therefore, some of the adsorption enhancement effects reported previously 56 might arise from the decomposition of the (111) surface ligand during the various sample treatments.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…Finally, our results show that MgO(111) nanostructures reconstruct into MgO(100) surfaces upon surface adsorbate removal, suggesting that these MgO(111) surfaces are not bare and thus not polar under surface science experimental conditions. We believe that the important question of how charge-compensating surface groups such as hydroxyls or methoxy groups can enhance and promote the catalytic activity and adsorption capacity as reported for MgO(111) nanosheets ,, requires further attention.…”

Section: Discussionmentioning

confidence: 99%

Cubes to Cubes: Organization of MgO Particles into One-Dimensional and Two-Dimensional Nanostructures

Thomele

Baumann

Schneider

et al. 2021

Crystal Growth & Design

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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 H 2 O 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 O 2– ion or Mg 2+ 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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“…Moreover, a variety of processes can occur between particles in contact and under powder compaction. These range from elastic and plastic deformation , to shearing and fracture of surface elements , such as edges and corners to coordinatively generate unsaturated surface ions of high chemical reactivity. − Our mechanistic understanding of mechanically initiated chemical surface processes at the atomistic scale is scarce. Hence, a rational connection between triboinduced chemical activation steps including their energetics and the application of processing parameters, which induce the triboelectric phenomena, is very much needed.…”

Section: Introductionmentioning

confidence: 99%

Rubbing Powders: Direct Spectroscopic Observation of Triboinduced Oxygen Radical Formation in MgO Nanocube Ensembles

et al. 2021

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Powder compaction-induced surface chemistry in metal oxide nanocrystal ensembles is important for very diverse fields such as triboelectrics, tribocatalysts, surface abrasion, and cold sintering of ceramics. Using a range of spectroscopic techniques, we show that MgO nanocube powder compaction with uniaxial pressures that can be achieved by gentle manual rubbing or pressing ( p ≥ 5 MPa) excites energetic electron–hole pairs and generates oxygen radicals at interfacial defect structures. While the identification of paramagnetic O – radicals and their adsorption complexes with O 2 point to the emergence of hole centers, triboemitted electrons become scavenged by molecular oxygen to convert into adsorbed superoxide anions O 2 – as measured by electron paramagnetic resonance (EPR). By means of complementary UV-photoexcitation experiments, we found that photon energies in the range between 3 and 6 eV produce essentially the same EPR spectroscopic fingerprints and optical absorption features. To provide insights into this effect, we performed density functional theory calculations to explore the energetics of charge separation involving the ionization of low-coordinated anions and surface-adsorbed O 2 – radicals at points of contact. For all selected configurations, charge transfer is not spontaneous but requires an additional driving force. We propose that a plausible mechanism for oxygen radical formation is the generation of significant surface potential differences at points of contact under loading as a result of the highly inhomogeneous elastic deformations coupled with the flexoelectric effect.

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Ultrathin Single Crystalline MgO(111) Nanosheets**

Cited by 43 publications

References 60 publications

Peering into buried interfaces with X-rays and electrons to unveil MgCO ₃ formation during CO ₂ capture in molten salt-promoted MgO

Peering into buried interfaces with X-rays and electrons to unveil MgCO ₃ formation during CO ₂ capture in molten salt-promoted MgO

Cubes to Cubes: Organization of MgO Particles into One-Dimensional and Two-Dimensional Nanostructures

Rubbing Powders: Direct Spectroscopic Observation of Triboinduced Oxygen Radical Formation in MgO Nanocube Ensembles

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Ultrathin Single Crystalline MgO(111) Nanosheets**

Cited by 43 publications

References 60 publications

Peering into buried interfaces with X-rays and electrons to unveil MgCO 3 formation during CO 2 capture in molten salt-promoted MgO

Peering into buried interfaces with X-rays and electrons to unveil MgCO 3 formation during CO 2 capture in molten salt-promoted MgO

Cubes to Cubes: Organization of MgO Particles into One-Dimensional and Two-Dimensional Nanostructures

Rubbing Powders: Direct Spectroscopic Observation of Triboinduced Oxygen Radical Formation in MgO Nanocube Ensembles

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Product

Resources

About

Peering into buried interfaces with X-rays and electrons to unveil MgCO ₃ formation during CO ₂ capture in molten salt-promoted MgO

Peering into buried interfaces with X-rays and electrons to unveil MgCO ₃ formation during CO ₂ capture in molten salt-promoted MgO