Hydrothermal Synthesis and Characterization of Cobalt Clays

Abstract

Abstract--Reaction of mixtures of cobalt nitrate, colloidal silica, and a metal hydroxide (MOH) under hydrothermal conditions produced a range of cobalt hydroxysilicates, the components of which depended upon the identity of M, temperature, and reactant ratios. At 250~ ifM = Na, a smectite of composition Nao o6Coa.o7Si3.95Olo(OH)2 (I) was produced. IfM = K, either a mica, KCo2.sSi4Olo(OH)2 (II), intermediate between di-and trioctahedral, or a Si-deficient mica, KCo3Si3.7sOlo(OH)2 (III), was formed depending upon the reactant ratios. Similarly, if M = Cs, either a vermiculite or a 2:1 layer silicate intermediate between a mica and a brittle mica was produced. If M = Li, only the non-clay mineral Li2CoSiO4 was formed. Tetraalkylammonium hydroxides (NR4OH, R = methyl, ethyl, or propyl) yielded chrysotile. All phases were characterized by elemental analysis, transmission electron microscopy, and X-ray powder diffraction. Further characterization of smectite I was undertaken by diffuse reflectance, infrared, and Xray photoelectron spectroscopy. The layer charge in these clays appears to stem from cation vacancies within an almost trioctahedral sheet and, possibly, within the tetrahedral sheets. Some of the cobalt present had tetrahedral coordination geometry, but its location was not determined.

Electrodes modified with synthetic clay minerals: Evidence of direct electron transfer from structural iron sites in the clay lattice

“…The spacings between the layers were of the order of 12 A. Electron diffraction from small area of the sample ( Figure 2B, Inset) gave the ring pattern expected for a layer material. The positions of the strong reflections 4.74 A, 2.71 ,~, 1.57 ,~ and 1.37 ,~ agree well with those reported by Bruce et al (1986). TEM/EDX analysis of the layers gave chemical compositions very similar to that obtained by SEM/EDX.…”

“…Results of the SEM/EDX elemental analysis of the clay gave a calculated unit cell formula of [(Si8.05)(Co5.59)O20(OH)4] Na0.66, (Based upon O20(OH)4 expected for 2:1 layer silicates (Newman 1987). Co and Si contents from SEM/EDX, Na content from the CEC) in good agreement with what is expected for trioctahedral smectites (Newman 1987 Bruce et al (1986) have previously prepared a NaCo-smectite by hydrothermal treatment of a slurry of colloidal silica, Co(NO3)2 and NaOH at 250 ~ under 3.4 MPa of H 2. Their product, described as a bright blue solid, contained more Co and slightly less Si than the clay made here.…”

“…Absorption bands between 19,000 to 20,000 cm -1 attributed to 4T1(F)---->4TI(P) transition of high-spin Co 2 § in octahedral coordination are found for many Co-containing minerals (Faye and Nickel 1968;Rossman 1988). Bruce et al (1986) attributed the blue color of their NaCo-smectites to tetrahedral Co 2+ substitutions. Acid washing of their clay gave a pink solid with an adsorption maximum at 19,400 cm -1.…”

“…The IR spectrum showed O-H stretching of the structural OH bands at 3631 cm -~ and 3510 cm -~, a broad band at 3418 cm ~ attributed to interlayer 1-120, and a band at 668 cm -~ assigned to a deformation mode of OH linked to 3 Co atoms (Bruce et al 1986).…”

“…For the first smectite sample (Co-l), the autoclave was charged with 500 psi of argon, heated at 250 ~ for 15 h with mechanical shaking, and allowed to cool for 6 h. These conditions were similar to those employed by Bruce et al (1986) for the preparation of an NaCo-smectite. The second sample (Co-2) was obtained by heating the mixture at 150 ~ for 50 h without argon.…”