Anionic clay-like behaviour of alpha-nickel hydroxide: chromate sorption studies

While the sorption capacity of alpha-nickel hydroxide for the chromate ion is comparable with that of hydrotalcite-like anionic clays, the control samples of beta- and beta(bc)(bc: badly crystalline)-nickel hydroxide show negligible sorption. This provides direct evidence for the clay-like nature of alpha-nickel hydroxide. (C) 2002 Elsevier Science B.V. All rights reserved

On the existence of a nickel hydroxide phase which is neither alpha nor beta

A novel phase of nickel hydroxide with an average interlayer spacing 5.4-5.6 Angstrom has been synthesized which is neither ct nor beta type but is an interstratification of both. It ages to the beta form in strong alkali. These observations have implications on the dissolution-reprecipitation mechanism suggested for the alpha-->beta transformation of nickel hydroxide

Chemical synthesis of alpha-cobalt hydroxide

Precipitation reactions using ammonia yield a novel cobalt hydroxide phase that is structurally and compositionally similar to alpha-nickel hydroxide. The use of other synthetic methods yields the well-known beta-Co(OH)(2). The slab composition, mode of anion inclusion, and thermal behavior of the hydroxides obtained by ammonia precipitation are similar to those of alpha-nickel hydroxide; however, the materials are poorly ordered. A DIFFaX simulation of the powder X-ray diffraction patterns offers the best visual march with the observed patterns for a 50% stacking disorder and a disc radius between 100 and 1000 Angstrom. (C) 2000 Elsevier Science Ltd, All rights reserved

Anion mediated polytype selectivity among the basic salts of Co(II)

Basic salts of Co(II) crystallize in the rhombohedral structure. Two different polytypes, 3R1 and 3R2, with distinct stacking sequences of the metal hydroxide slabs, are possible within the rhombohedral structure. These polytypes are generated by simple translation of successive layers by (2/3, 1/3, z) or (1/3, 2/3, z). The symmetry of the anion and the mode of coordination influences polytype selection. Cobalt hydroxynitrate crystallizes in the structure of the 3R2 polytype while the hydroxytartarate, hydroxychloride and α-cobalt hydroxide crystallize in the structure of the 3R1 polytype. Cobalt hydroxysulfate is turbostratically disordered. The turbostratic disorder is a direct consequence of the mismatch between the crystallographically defined interlayer sites generated within the crystal and the tetrahedral symmetry of the SO4 2- ions. © 2006 Elsevier Inc. All rights reserved

Transformation of β-Ni(OH)2to NiO nano-sheets via surface nanocrystalline zirconia coating: Shape and size retention

Shape and size of the synthesized NiO nano-sheets were retained during transformation of sheet-like β-Ni(OH)2to NiO at elevated temperatures via nano-sized zirconia coating on the surface of β-Ni(OH)2. The average grain size was 6.42 nm after 600 °C treatment and slightly increased to 10 nm after 1000 °C treatment, showing effective sintering retardation between NiO nano-sheets. The excellent thermal stability revealed potential application at elevated temperatures, especially for high temperature catalysts and solid-state electrochemical devices

Probing catalytic surfaces by correlative scanning photoemission electron microscopy and atom probe tomography

The chemical composition and the electronic state of the surface of alloys or mixed oxides with enhanced electrocatalytic properties are usually heterogeneous at the nanoscale. The non-uniform distribution of the potential across their surface affects both activity and stability. Studying such heterogeneities at the relevant length scale is crucial for understanding the relationships between structure and catalytic behaviour. Here, we demonstrate an experimental approach combining scanning photoemission electron microscopy and atom probe tomography performed at identical locations to characterise the surface's structure and oxidation states, and the chemical composition of the surface and sub-surface regions. Showcased on an Ir-Ru thermally grown oxide, an efficient catalyst for the anodic oxygen evolution reaction, the complementary techniques yield consistent results in terms of the determined surface oxidation states and local oxide stoichiometry. Significant chemical heterogeneities in the sputter-deposited Ir-Ru alloy thin films govern the oxide's chemistry, observed after thermal oxidation both laterally and vertically. While the oxide grains have a composition of Ir0.94Ru0.06O2, the composition in the grain boundary region varies from Ir0.70Ru0.30O2 to Ir0.40Ru0.60O2 and eventually to Ir0.75Ru0.25O2 from the top surface into the depth. The influence of such compositional non-uniformities on the catalytic performance of the material is discussed, along with possible engineering levers for the synthesis of more stable and reactive mixed oxides. The proposed method provides a framework for investigating materials of interest in the field of electrocatalysis and beyond

Synthesis of (cinnamate-zinc layered hydroxide) intercalation compound for sunscreen application

Background: Zinc layered hydroxide (ZLH) intercalated with cinnamate, an anionic form of cinnamic acid (CA), an efficient UVA and UVB absorber, have been synthesized by direct method using zinc oxide (ZnO) and cinnamic acid as the precursor. Results: The resulting obtained intercalation compound, ZCA, showed a basal spacing of 23.9 Å as a result of cinnamate intercalated in a bilayer arrangement between the interlayer spaces of ZLH with estimated percentage loading of cinnamate of about 40.4 % w/w. The UV–vis absorption spectrum of the intercalation compound showed excellent UVA and UVB absorption ability. Retention of cinnamate in ZLH interlayers was tested against media usually came across with sunscreen usage to show low release over an extended period of time. MTT assay of the intercalation compound on human dermal fibroblast (HDF) cells showed cytotoxicity of ZCA to be concentration dependent and is overall less toxic than its precursor, ZnO. Conclusions: (Cinnamate-zinc layered hydroxide) intercalation compound is suitable to be used as a safe and effective sunscreen with long UV protection effect

Hexacyanoferrate-intercalated nickel zinc hydroxy double salts

When anionic clay like nickel zinc hydroxyacetate was subjected to anion exchange reaction with either hexacyanoferrate(II) or hexacyanoferrate(III) ions, the complex anion intercalation was accompanied by auto redox reactions. In both the cases a mixture of hexacyanoferrate(II) and hexacyanoferrate(III) ions was found to be intercalated in the anionic clay. The mixed anion intercalated anionic clays could be oxidized by hydrogen peroxide to get pure hexacyanoferrate(III) intercalated anionic clay. Thermal decomposition of the intercalated anionic clays yields mixed oxides of Ni, Zn and Fe. © 2009 Elsevier Masson SAS. All rights reserved

High coercivity stellated cobalt metal multipods through solvothermal reduction of cobalt hydroxide nanosheets

Solvated 2D nanosheets of dodecylsulphate intercalated [small alpha]-cobalt hydroxide in 1-butanol are solvothermally reduced to hexagonal close packed (hcp) Co metal multipods in the presence of oleylamine. 1-Butanol,} being a reducing solvent{,} facilitates the formation of Co metal. In addition to being a reducing agent{,} oleylamine also acts as a base which converts the metastable [small alpha]-cobalt hydroxide nanosheets into [small beta]-hydroxide sheets. These sheets yield face centered cubic (fcc) CoO spheres which eventually grow into hcp Co metal multipods. All the pods are single crystalline with growth direction being [001]{,} making the multipods resemble stellated polyhedra with overgrown branches. The stellated Co metal multipods exhibit high coercivity (Hc){,} of 880 and 552 Oe at 2 K and 300 K respectively{, due to shape anisotropy