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.
Highlights
Layered zinc hydroxides (LZHs) are considered interesting materials for intercalation and anion exchange, as well as precursors toward porous ZnO nanostructures.[1−4]LZHs are part of a larger family of layered hydroxide salts with the chemical formula M(II)x(OH−)2x−myAm−y·nH2O, whereCMO(I3I2)−.=2−M5 Tg,hMe lna−yeZrnstarnudctuArme−isisr,eela.gt.e,dCtlo−,bNruOci3t−e, SO42−, and Mg(OH)[2], and features edge-sharing sheets of octahedral zinc hydroxide units where two tetrahedrally coordinated Zn ions are situated above and below vacant octahedral sites
We show that the hydrothermal conversion of ε-Zn(OH)[2] at high pressures, 1−2 GPa, and moderate temperatures, 100−200 °C, quantitatively produces the zinc hydroxide dihydrate Zn5(OH)8(OH)2· 2H2O
The powder X-ray diffraction (PXRD) pattern of the product obtained at 1 GPa and 100 °C (“1− 100” product) revealed a new and unknown phase
Summary
Layered zinc hydroxides (LZHs) are considered interesting materials for intercalation and anion exchange, as well as precursors toward (functional) porous ZnO nanostructures.[1−4]LZHs are part of a larger family of layered hydroxide salts with the chemical formula M(II)x(OH−)2x−myAm−y·nH2O, whereCMO(I3I2)−.=2−M5 Tg,hMe lna−yeZrnstarnudctuArme−isisr,eela.gt.e,dCtlo−,bNruOci3t−e,, SO42−, and Mg(OH)[2], and features edge-sharing sheets of octahedral zinc hydroxide units where two tetrahedrally coordinated Zn ions are situated above and below vacant octahedral sites. Layers are terminated by an additional ligand, which coordinates the apical site of the tetrahedra. LZH layers may be (positively) charged or neutral, depending on whether the terminating ligand is water or. ·2H2O cases, 6a 1/4 nd of the octahedrally coordinated Zn within a layer is replaced by pairs of tetrahedra, i.e., the Zno/Znt ratio is 3:2; their distribution is different, resulting in orthorhombic and trigonal layer symmetries for the nitrate and chloride, respectively. For the former, the terminating ligand is H2O, and NO3− ions are intercalated. Interlayer spacings are comparatively small for LZHs with neutral layers (i.e., for which layers are held together only by a hydrogen-bond network).[5,7]
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