Copper (II) adsorbed on SiO(2)/SnO(2) obtained by the sol-gel processing method: application as electrochemical sensor for ascorbic acid.

With the objective of producing a material showing better conductive properties to be used as a support for electroactive species, a SiO(2)/SnO(2) mixed oxide was prepared. The procedure for SiO(2)/SnO(2) mixed oxide preparation using the sol-gel processing method, starting from tetraethylorthosilicate and SnI(4) as precursor reagents, is described. SiO(2)/SnO(2) with composition Sn=15.6 wt% and S(BET) = 525 m(2)g(-1), V(p)=0.28 mlg(-1), and D(p)= 1.5 nm, where S(BET), V(p) and D(p) are the specific surface area, the average pore volume, and the average pore diameter, respectively, was obtained. The X-ray photoelectron spectroscopy showed that the mixed oxide was thermally very stable for samples heat-treated at up to 1073 K. The Brønsted acid sites, probed with pyridine molecules for samples heat-treated at various temperatures, were chemically stable up to 473 K. Segregation of SnO(2) crystalline phase was observed at 1473 K but no crystalline phase was verified for SiO(2) at this temperature. The porous SiO(2)/SnO(2) matrix was used as base for Cu(II) immobilization and an electrode was developed for application in electrochemical detection of vitamin C in tablets.

Adsorption of metal halides from ethanol solutions by a 3-n-propylpyridiniumsilsesquioxane chloride-coated silica gel surface.

3-n-propylpyridiniumsilsesquioxane chloride polymer, abbreviated as SiPy+Cl-, was used to coat a porous silica gel, SiO2, surface to form the chemically modified solid SiO2/SiPy+Cl-. The resulting polymer film was well adhered to the surface and presented an ion exchange capacity of 0.74 mmol g(-1). Metal halides, MClz [M=Fe(III), Cu(II), and Zn(II)], were adsorbed by the modified solid from ethanol solutions as neutral species by forming the surface anionic complexes described by the equation: mSiO2/SiPy+Cl-+ MClz <=> (SiO2/SiPy+)m[MCl(z+m)]m-, where the [MCl(z+m)]m- species adsorbed on the surface are FeCl4-, ZnCl4(2-), and CuCl4(2-). Accurate estimates of the specific sorption capacities and the heterogeneous stability constants of the immobilized metal complexes were determined with the aid of computational procedures.