| 1. |
- B. Brant Carvalho, Paulo H., et al.
(författare)
-
Elucidating the guest disorder in structure II argon hydrate : A neutron diffraction isotopic substitution study
- 2020
-
Ingår i: Journal of Solid State Chemistry. - : Elsevier. - 0022-4596 .- 1095-726X. ; 285
-
Tidskriftsartikel (refereegranskat)abstract
- Clathrate hydrates with the cubic structure II (CS-II) form typically with large guest molecules, such as tetrahydrofuran, trimethylamine oxide, or propane. However, CS-II is also realized for argon hydrate despite the comparatively small van der Waals diameter of the guest (around 3.8 angstrom). Here, the structure of deuterated argon hydrate was studied at ambient pressure in the temperature range 20-95 K using neutron diffraction and comparing natural Ar with Ar-36, which scatters neutrons more than 13 times more efficiently. The procedure allowed to unambiguously establish the positional disorder within the large cages of CS-H, while simultaneously refining host and guest structures. These cages are singly occupied and off-centered argon atoms distribute on two tetrahedron-shaped split positions with a ratio 3:1. Molecular dynamics (MD) simulations revealed that the crystallographic positional disorder structure is due to mobile argon atoms even at 20 K. The MD potential energy distribution confirmed the diffraction model. It is noted that the unit cell volumes of argon hydrate in the investigated temperature range are virtually identical to N-2 hydrate, which has a similar composition at ambient pressure, indicating a very similar (slightly attractive) host-guest interaction.
|
|
| 2. |
- Gordeeva, Alisa, et al.
(författare)
-
Layered Zinc Hydroxide Dihydrate, Zn-5(OH)(10)center dot 2H(2)O, from Hydrothermal Conversion of epsilon-Zn(OH)(2) at Gigapascal Pressures and its Transformation to Nanocrystalline ZnO
- 2020
-
Ingår i: ACS Omega. - : AMER CHEMICAL SOC. - 2470-1343. ; 5:28, s. 17617-17627
-
Tidskriftsartikel (refereegranskat)abstract
- Layered zinc hydroxides (LZHs) with the general formula (Zn2+)(x)(OH-)(2x-my ),(A(m-))(y)center dot nH(2)O (A(m-) = Cl- , NO3- , ac(-) , SO42-, etc) are considered as useful precursors for the fabrication of functional ZnO nanostructures. Here, we report the synthesis and structure characterization of the hitherto unknown "binary" representative of the LZH compound family, Zn-5(OH)(10)center dot 2H(2)O, with A(m-) = OH- , x = 5, y = 2, and n = 2. Zn-5(OH)(10)center dot 2H(2)O was afforded quantitatively by pressurizing mixtures of epsilon-Zn(OH)(2) (wulfingite) and water to 1-2 GPa and applying slightly elevated temperatures, 100-200 degrees C. The monoclinic crystal structure was characterized from powder X-ray diffraction data (space group C2/c, a = 15.342(7) angstrom, b = 6.244(6) angstrom, c = 10.989(7) angstrom, beta = 100.86(1)degrees). It features neutral zinc hydroxide layers, composed of octahedrally and tetrahedrally coordinated Zn ions with a 3:2 ratio, in which H2O is intercalated. The interlayer d(200) distance is 7.53 angstrom. The H-bond structure of Zn-5(OH)(10)center dot 2H(2)O was analyzed by a combination of infrared/Raman spectroscopy, computational modeling, and neutron powder diffraction. Interlayer H2O molecules are strongly H-bonded to five surrounding OH groups and appear orientationally disordered. The decomposition of Zn-5(OH)(10)center dot 2H(2)O, which occurs thermally between 70 and 100 degrees C, was followed in an in situ transmission electron microscopy study and ex situ annealing experiments. It yields initially 5-15 nm sized hexagonal w-ZnO crystals, which, depending on the conditions, may intergrow to several hundred nm-large two-dimensional, flakelike crystals within the boundary of original Zn-5(OH)(10)center dot 2H(2)O particles.
|
|
| 3. |
- Gordeeva, Alisa, et al.
(författare)
-
Layered Zinc Hydroxide Dihydrate, Zn5(OH)10·2H2O, from Hydrothermal Conversion of ε-Zn(OH)2 at Gigapascal Pressures and its Transformation to Nanocrystalline ZnO
- 2020
-
Ingår i: ACS Omega. - : American Chemical Society (ACS). - 2470-1343. ; 5:28, s. 17617-17627
-
Tidskriftsartikel (refereegranskat)abstract
- Layered zinc hydroxides (LZHs) with the general formula (Zn2+)x(OH–)2x−my(Am–)y·nH2O (Am– = Cl–, NO3–, ac–, SO42–, etc) are considered as useful precursors for the fabrication of functional ZnO nanostructures. Here, we report the synthesis and structure characterization of the hitherto unknown “binary” representative of the LZH compound family, Zn5(OH)10·2H2O, with Am– = OH–, x = 5, y = 2, and n = 2. Zn5(OH)10·2H2O was afforded quantitatively by pressurizing mixtures of ε-Zn(OH)2 (wulfingite) and water to 1–2 GPa and applying slightly elevated temperatures, 100–200 °C. The monoclinic crystal structure was characterized from powder X-ray diffraction data (space group C2/c, a = 15.342(7) Å, b = 6.244(6) Å, c = 10.989(7) Å, β = 100.86(1)°). It features neutral zinc hydroxide layers, composed of octahedrally and tetrahedrally coordinated Zn ions with a 3:2 ratio, in which H2O is intercalated. The interlayer d(200) distance is 7.53 Å. The H-bond structure of Zn5(OH)10·2H2O was analyzed by a combination of infrared/Raman spectroscopy, computational modeling, and neutron powder diffraction. Interlayer H2O molecules are strongly H-bonded to five surrounding OH groups and appear orientationally disordered. The decomposition of Zn5(OH)10·2H2O, which occurs thermally between 70 and 100 °C, was followed in an in situ transmission electron microscopy study and ex situ annealing experiments. It yields initially 5–15 nm sized hexagonal w-ZnO crystals, which, depending on the conditions, may intergrow to several hundred nm-large two-dimensional, flakelike crystals within the boundary of original Zn5(OH)10·2H2O particles.
|
|
