NiO-Based Aerogels—Unexpected Formation of Metallic Nickel Nanoparticles during Supercritical Drying Process
Elena A. Straumal,
Andrey A. Mazilkin,
Inna O. Gozhikova,
Lyudmila L. Yurkova,
Sergey Yu. Kottsov,
Sergey A. Lermontov
Affiliations
Elena A. Straumal
Institute of Physiologically Active Compounds at Federal Research Center of Problems of Chemical Physics and Medicinal Chemistry, Russian Academy of Sciences, 1 Severnij Pr., Chernogolovka, 142432 Moscow, Russia
Andrey A. Mazilkin
Institute of Solid State Physics, Russian Academy of Sciences, 2 Academician Ossipyan Str., Chernogolovka, 142432 Moscow, Russia
Inna O. Gozhikova
Institute of Physiologically Active Compounds at Federal Research Center of Problems of Chemical Physics and Medicinal Chemistry, Russian Academy of Sciences, 1 Severnij Pr., Chernogolovka, 142432 Moscow, Russia
Lyudmila L. Yurkova
Institute of Physiologically Active Compounds at Federal Research Center of Problems of Chemical Physics and Medicinal Chemistry, Russian Academy of Sciences, 1 Severnij Pr., Chernogolovka, 142432 Moscow, Russia
Sergey Yu. Kottsov
Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences, 31 Leninsky Prosp., 119991 Moscow, Russia
Sergey A. Lermontov
Institute of Physiologically Active Compounds at Federal Research Center of Problems of Chemical Physics and Medicinal Chemistry, Russian Academy of Sciences, 1 Severnij Pr., Chernogolovka, 142432 Moscow, Russia
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.
