Synthesis, electronic state, and particle size stabilization of nanoparticulate [Co(OH)2(H3O)δ+]δ

• Published in: Inorganic materials Vol. 45; no. 12; pp. 1355 - 1361
• Main Authors: Krivoruchko, O. P., Larina, T. V., Anufrienko, V. F., Molina, I. Yu, Paukshtis, E. A.
• Format: Journal Article
• Language: English
• Published: Dordrecht SP MAIK Nauka/Interperiodica 01.12.2009
• Subjects: Chemistry; Chemistry and Materials Science; Industrial Chemistry/Chemical Engineering; Inorganic Chemistry; Materials Science; Nanoparticulate Cobalt; Mother Liquor; Narrow Particle Size Distribution; Cobalt Hydroxide; Positive Surface Charge
• ISSN: 0020-1685; 1608-3172
• DOI: 10.1134/S0020168509120097

We have synthesized nanoparticulate cobalt(II) hydroxide containing Co 2+ in tetrahedral oxygen coordination (Co Td 2+ ), atypical of such systems: nano- [Co(OH) 2 (H 3 O) δ + ] δ+ . The (Co Td 2+ ) coordination in the hydroxide is inferred from its electronic diffuse reflectance spectrum, which shows a multiplet of strong absorption bands at 14500, 15000, and 16000 cm −1 ( 4 A 2 ( F )- 4 T 1 ( P ) transition). Nanoparticulate cobalt(II) hydroxide forms in a weakly acidic medium under essentially nonequilibrium conditions due to supersaturation (by three to four orders of magnitude) with the starting reagents (CoCl 2 and LiOH) at the instant of the formation of the poorly soluble phase Co(OH) 2 . Presumably, colloidal particles of nanoparticulate cobalt(II) hydroxide in a weakly acidic aqueous medium have a positive surface charge, compensated by a counter-ion (Cl − ) layer: nano-[Co(OH) 2 (H 3 O) δ + ] δ+ · δCl − . The XRD patterns of pastes (gels) containing this hydroxide show three broad-ened lines with d = 5.31 (2θ = 16.7°), 2.77 (2θ = 32.3°), and 2.32 Å (2θ = 38.8°). According to small-angle X-ray scattering data, nano-[Co(OH) 2 (H 3 O) δ + ] δ+ has a narrow particle size distribution (1.0–2.0 nm). Synthesis and storage conditions are identified which ensure stabilization of the electronic state and particle size of nano-[Co(OH) 2 (H 3 O) δ + ] δ+ for a long time.