Angélica M. Lazarin

The ion exchange properties and equilibrium constants of Li+, Na+ and K+ on zirconium phosphate highly dispersed on a cellulose acetate fibers surface

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 HPO42- 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 SNa+/Li+ and SK+/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.

Methylene blue-zirconium phosphate-cellulose acetate hybrid membrane film attached to a platinum electrode and its application in electrocatalytic oxidation of NADH

Highly dispersed zirconium phosphate was prepared by reacting a cellulose acetate membrane film containing zirconium oxide (ZrO2 ¼ 6:3 wt.%; 0.50 mmol g � 1 of the zirconium atom per gram of the material) with phosphoric acid. The resulting membrane film was reacted with methylene blue (MB) by an ion exchange reaction. The amount of the dye bonded to the surface was 0.15 mmol g � 1 . High power decoupling magic angle spinning (HPDEC-MAS) 31 P NMR data indicated that Zr(HPO4)2 is the species present on the membrane surface. Cyclic voltammetry experiments of the MB dye adsorbed onto CelZrP, carried out on a thin membrane of the material fixed on a platinum disk electrode, were obtained. The midpoint potential (Em) of CelZrP/MB was � 0.15 V. The solution pH practically did not affect the midpoint potential of the adsorbed dye between pH 3 and 7. The modified electrode presented a reproducible response and it was chemically stable under various oxidation–reduction cycles. The electrode proved to be efficient to mediate the transfer for NADH oxidation. The apparent Michaelis–Menten constant, K app M , for the modified electrode showed an efficient interaction between dye and NADH. # 2002 Elsevier Science B.V. All rights reserved.

Nitrogen Containing Organosilicon Bonded an Al2O3-Cellulose Acetate Hybrid Material: Preparation, Characterization and Use for Adsorption of Fe(III), Cu(II) and Zn(II) from Ethanol Solutions

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.

Adsorção do complexo H[Ru(III)Cl2(H2EDTA)] sobre a superfície da sílica gel modificada com [3-(2-aminoetil) aminopropil]trimetoxissilano em soluções etanólicas

Silica gel was functionalized with [3-(2-aminoethyl)aminopropyl]trimethoxysilane group (SF-AEATS) and the characterization by chemical analysis (N) and infrared spectroscopy confirmed the functionalization. The capacity of the modified silica to adsorb the complex Ru(III)-EDTA from ethanolic solution was studied. The selectivity coefficients of the complex formed on the support obtained was (Gn), 2,07 x 104 L/mol and the average number of ligand bonded by one metal ion on the support (n) was ~ 1.

Filme Fino de ZrO 2 Enxertado sobre a Superfície de Sílica Gel: Preparação e Propriedade de Adsorção de Cr(VI)

The present experiment describes an easy procedure for obtaining SiO2/ZrO2 by reacting ZrOCl2 with SiO2 with the following characteristics: SBET = 500 m2 g-1 and an average pore diameter of 6 nm. The material obtained presented 1.3 wt% ZrO2 content corresponding to 140 mmol 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 mmol g-1) at pH 2. The adsorption can be described by the reaction: =Zr(OH)2 + 2HCrO4- + 2H+ [(=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- (=ZrO2)2- + 6H2O + 2CrO42-.

Preparação e caracterização do complexo cobaloxima e sua utilização na construção de um eletrodo modificado: um experimento eletroquímico no curso de graduação

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.

Adsorption of a copper (II) complex on calcium phosphate intercalated with 4-aminobenzoic acid: synthesis and electrochemical investigation

In this study, the adsorption isotherm of copper (II) on a calcium phosphate host intercalated with 4-aminobenzoic acid in an ethanol solution was investigated. This gave a maximum adsorption capacity of 1.74 mmol g-1. The material was incorporated into a carbon-paste electrode, and its electrochemical properties were investigated. However, for a dopamine solution, the anodic peak current increased owing to the electrocatalytic oxidation. The electrode presented the same response for at least 150 successive measurements, showing good repeatability. The modified electrode is very stable and reproducible. The electrode sensor was successfully applied for dopamine determination in pharmaceutical preparations.