Electron spin resonance study on the vanadium adsorption by persimmon tannin gel Electron Spin Resonance Study on the Vanadium Adsorption by Persimmon Tannin Gel

http://www.elsevier.com/wps/find/journaldescription.cws_home/525438/descriptionThe persimmon tannin gel can adsorb vanadium highly effectively from aqueoussolutions containing VOCl2 and NH4VO3, respectively. The adsorption of vanadiumfrom the VOCl2 solution had a broad maximum at around pH 5 - 6, while that from theNH4VO3 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 VOCl2 and NH4VO3 solutions was rapid, and was obeyed the Langmuir adsorption isotherm. The ESR spectrum of VO2+ 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⊥ = 2.005, |A//| = 552MHz, and |A⊥| = 168 MHz, suggesting a square pyramidal coordination structure ofVO2+-persimmon tannin complex. The ESR analysis of vanadium adsorption from the NH4VO3 solution (pH 6) indicated the reduction of VO3- to VO2+. The highvanadium-adsorption ability of the persimmon tannin gel from the VOCl2 solution was attributed to the stable complex formation of VO2+ with catechol and pyrogallol groups in the gel, while the vanadium adsorption from the NH4VO3solution can be explained as the combination of H3VO4 and VO2+ adsorptions.