title: Electron spin resonance study on the vanadium adsorption by persimmon tannin gel.
abstract: The persimmon tannin gel can adsorb vanadium highly effectively from aqueous solutions containing VOCl(2) and NH(4)VO(3), respectively. The adsorption of vanadium from the VOCl(2) solution had a broad maximum at around pH 5-6, while that from the NH(4)VO(3) solution, a sharp maximum at around pH 3.75 and a broad one at around pH 5-6. The adsorption of vanadium by the gel from both VOCl(2) and NH(4)VO(3) solutions was rapid, and was obeyed the Langmuir adsorption isotherm. The ESR spectrum of VO(2+) in the persimmon tannin gel showed a typical powder pattern with g-anisotropy and anisotropic hyperfine structure (I=7/2), with g(//)=1.937, g( perpendicular)=2.005, mid R:A(//)mid R:=552 MHz, and mid R:A( perpendicular)mid R:=168 MHz, suggesting a square pyramidal coordination structure of VO(2+)-persimmon tannin complex. The ESR analysis of vanadium adsorption from the NH(4)VO(3) solution (pH 6) indicated the reduction of VO(3)(-) to VO(2+). The high vanadium-adsorption ability of the persimmon tannin gel from the VOCl(2) solution was attributed to the stable complex formation of VO(2+) with catechol and pyrogallol groups in the gel, while the vanadium adsorption from the NH(4)VO(3) solution can be explained as the combination of H(3)VO(4) and VO(2+) adsorptions.
authors.affiliation: Department of Chemistry, Miyazaki Medical College, Kiyotake, Miyazaki 889-1692, Japan.
authors.forename: Akira
authors.initials: A
authors.lastname: Nakajima