The present experiment describes an easy procedure for obtaining SiO2/ZrO2 by reacting ZrOCl2 with SiO2 with the following characteristics: S BET = 500 m² g-1 and an average pore diameter of 6 nm. The material obtained presented 1.3 wt% ZrO2 content corresponding to 140 mumol g-1. The average density of ZrO2 onto SiO2/ZrO2 matrix is 2.8x10-11 mol cm-2. The adsorption isotherm for Cr(VI) showed a maximum of adsorption value (200 mumol g-1) at pH 2. The adsorption can be described by the reaction: =Zr(OH)2 + 2HCrO4- + 2H+ <IMG SRC="http:/img/fbpe/qn/v25n3/9346fr1.gif">[(=Zr(OH2+)2) (HCrO4-)2]. Above the zero point of charge, i.e. pH > 5.5 due to the surface charge inversion, desorption of Cr(VI) occurs according to the reaction: [(=Zr(OH2+)2) (HCrO4-)2] + 6OH- <IMG SRC="http:/img/fbpe/qn/v25n3/9346fr1.gif">(=ZrO2)2- + 6H2O + 2CrO4(2-).

This work describes the preparation and characterization of a cellulose acetate fiber coated with Al2O3, resulting in the organic-inorganic hybrid Cella/Al2O3. Furthermore, it was modified by attaching organofunctional groups, by reaction with the precursor reagents (RO)3Si(CH2)3L (L = -NH2, NH(CH2)2NH2, NH(CH2)2NH(CH2) 2NH2 and NC3H3N), resulting in Cella/Al2O3/Si(CH2 )3NH2 (1), Cella/Al2O3/Si(CH2 )3NH(CH2)2NH2 (2), Cella/Al2O3/Si(CH 2)3NH(CH2)2 NH(CH2)2NH2 (3) and Cella/Al2O3/Si(CH2 )3NC3H3N (imidazole) (4). The amount of attached organofunctional groups were (in mmol per gram of the material): 1 = 1.90, 2 = 1.89, 3 = 1.66 and 4 = 1.35. The adsorption isotherms from ethanol solutions of FeCl3, CuCl2 and ZnCl2 by Cella/Al2O3/Si(CH2 )3L were obtained at 298 K. The results obtained in flow experiments showed a retention and recovery of ca. 100% of the metal ions by Cella/Al2O3/Si(CH2 )3L packed in a column, for a solution containing either one or mixture of the ions.

The present experiment describes the preparation, characterization of n-butyl(pyridil)cobaloxime complex and its electrochemical property. The infrared and uv-visible absorption spectra were used to characterize the complex obtained. The infrared spectrum of the compound showed characteristics bands that indicated the formation of the Co-C chemical bond formation. The electronic absorption spectrum in acetonitrile showed transition bands attributed to p-p*, metal-to-ligand charge transfer, d-d transitions and charge transfer Co-C. The electrochemical property was investigated by the pulse differential voltammetry technique. Two oxidation processes: Co(I)/Co(II) at -423 mV and Co(II)/Co(III) at 752 mV were observed.

Highly dispersed zirconium phosphate was prepared by reacting celullose acetate/ZrO2 (ZrO2 = 11 wt%, 1.0 mmol g-1 of zirconium atom per gram of the material) with phosphoric acid. High power decoupling magic angle spinning (HPDEC-MAS) 31P NMR and X-ray photoelectron spectroscopy data indicated that HPO4(2-) is the species present on the membrane surface. The specific concentration of acidic centers, determined by ammonia gas adsorption, is 0.60 mmol g-1. The ion exchange capacities for Li+, Na+ and K+ ions were determined from ion exchange isotherms at 298 K and showed the following values (in mmol g-1): Li+= 0.05, Na+= 0.38 and K+= 0.57. Due to the strong cooperative effect, the H+/Na+ and H+/K+ ion exchange is of non ideal nature. These ion exchange equilibria were treated with the use of models of fixed tridentate centers, which consider the surface of the sorbent as polyfunctional sorption centers. Both the observed ion exchange capacities with respect to the alkaline metal ions and the equilibrium constants are discussed by taking into consideration the sequence of the ionic hydration radii for Li+, Na+ and K+. The matrix affinity for the ions decreases with increasing the cations hydration radii from K+ to Li+. The high values of the separation factors S Na+/Li+ and S K+/Li+ (up to several hundreds) support the application of this material for the quantitative separation of Na+ and K+ from Li+ from a mixture containing these three ions.