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

Abstract

We have synthesized nanoparticulate cobalt(II) hydroxide containing Co2+ in tetrahedral oxygen coordination (CoTd2+), atypical of such systems: nano- [Co(OH)2(H3O)δ+]δ+. The (CoTd2+) 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 (4A2(F)-4T1(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 (CoCl2 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(H3O)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 A (2θ = 38.8°). According to small-angle X-ray scattering data, nano-[Co(OH)2(H3O)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(H3O)δ+]δ+ for a long time.