Thermal behavior of metal carboxylates: III-metal acetates

NiO-Based Aerogels-Unexpected Formation of Metallic Nickel Nanoparticles during Supercritical Drying Process

The aim of the study is to investigate the influence of the solvents applied both in sol-gel process and for supercritical drying (SCD) on NiO aerogels' properties. NiO aerogels were synthesized using methanol and 2-methoxy-ethanol (MeGl) as sol solvents. SCD was performed using iso-propanol, methanol and tert-butyl-methyl ether as supercritical fluids. The obtained samples were characterized using low-temperature nitrogen adsorption, X-ray diffraction analysis, mass-spectra analysis and STEM and TEM methods. It was found that specific surface area and the phase and chemical composition strongly depend on the synthesis conditions. We revealed that Ni²⁺ cations were reduced into Ni⁰ when 2-methoxy-ethanol was applied as a sol solvent. The mechanism of the Ni²⁺ cations reduction is proposed. We consider that at the stage of sol preparation, the Ni²⁺-MeGl chelate was formed. This chelate decomposes at the SCD stage with the release of MeGl, which, in turn, eliminates methanol and leads to the formation of aldehyde. The latter is responsible for the nickel reduction. The proposed mechanism was confirmed experimentally.

Efflorescence on calcareous objects in museums: crystallisation, phase characterisation and crystal structures of calcium acetate formate phases

During the systematic investigation of the ternary system Ca(CH₃COO)₂-Ca(HCOO)₂-H₂O at room temperature, the congruent crystallisation of two solid calcium acetate formates was observed: the hitherto unknown Ca₃(CH₃COO)₄(HCOO)₂·4H₂O and the poorly characterised Ca(CH₃COO)(HCOO)·H₂O. The latter is a frequently observed efflorescence phase found on calcareous objects and it could be also identified as a corrosion phase in a natural history collection of birds' eggs. Elemental and thermal analyses were employed to determine the phase compositions and by Raman and IR spectroscopy the presence of acetate and formate anions in both solids was confirmed. Laboratory X-ray powder diffraction data were used to solve the crystal structures. Ca₃(CH₃COO)₄(HCOO)₂·4H₂O crystallises in a primitive tetragonal unit cell with space group P4₁2₁2 and lattice parameters of a = 6.8655(1) Å and c = 45.5454(6) Å, while Ca(CH₃COO)(HCOO)·H₂O crystallises in a primitive monoclinic unit cell with space group P2₁/c and lattice parameters of a = 9.2729(1) Å, b = 6.8002(1) Å, c = 11.2219(2) Å and β = 121.232(1)°. Calcium carboxylate zig-zag chains [Ca(μ₂-RCOO)⁺]_n (R = CH₃ or H) are the main motif of both crystal structures. In Ca₃(CH₃COO)₄(HCOO)₂·4H₂O these chains are exclusively composed of acetate anions, whereas in Ca(CH₃COO)(HCOO)·H₂O only formate anions are situated in the chains. The remaining places in the 7-8 fold coordination sphere of the calcium cations are filled by water molecules and additional carboxylate anions that interconnect neighbouring chains, which eventually leads to layered motifs in both structures.

A simple and room temperature sol–gel process for the fabrication of cobalt nanoparticles as an effective catalyst for carbon nanotube growth

Cobalt catalyst thin films were prepared on silicon wafers using a spin coating process.