Simulation of adsorption equilibria on hybrid materials: binding of metal chlorides with 3-n-propylpyridinium silsesquioxane chloride ion exchanger.

The quantitative description of cooperativity effects at binding of low-molecular reagents with active reactive centers of hybrid materials requires the elaboration of convenient and reliable meaningful models and calculation procedures. The model of fixed polydentate centers was analyzed as a prospective tool for simulation of adsorption equilibria. The model was shown to be flexible and adaptive. At the theoretic foundations, it is equivalent or more general as compared with another approaches. The procedure for constructing the models fitting the experimental data within their errors and the corresponding calculation tools were discussed. The special attention was paid to the problem of simultaneous determination of sorption capacities and equilibrium constants. To overcome this difficulty the strategy involving the fuzzy sets theory was proposed. The elaborated methods were used to characterize a new material, 3-n-propylpyridinium silsesquioxane chloride ion exchanger. Adsorption of Fe(III), Cu(II), Zn(II), Cd(II), and Hg(II) chlorides by the material from ethanol solutions was studied at 298 K. The material was found to possess a high affinity to metal chlorides. The sorption capacities of the material and the constants of adsorption equilibria were determined. The material demonstrates the following order of affinity: FeCl(3) > CuCl(2), HgCl(2) > CdCl(2) > ZnCl(2). On the base of simulation, the negative cooperativity in the case of the CuCl(2) adsorption was concluded, while adsorption of other chlorides is accompanied by the positive cooperativity.

Structure and property studies of hybrid xerogels containing bridged positively charged 1,4-diazoniabicycle[2.2.2]octane dichloride.

The compound di-3-n-propyltrimethoxysilane (1,4-diazoniabicycle[2.2.2]octane) dichloride, [(MeO)3Si(CH2)3N+ (CH2CH2)3N+ (CH2)3Si(OME)3]Cl2 was obtained and was used as a precursor reagent to obtain hybrid xerogels where the organic molecule was bonded to a silica framework by reacting the ends of both sides of the precursor reagent. That is, both -Si(OME)3 groups react with tetraethylorthosilicate (TEOS) by hydrolysis-condensation reactions. The resulting hybrid xerogels with variable C/Si mole ratios were prepared and analyzed and their textural characteristics determined. The samples prepared presented micropores with diameter 1.5 nm, the chain length of which matched with the estimated length of the organic bridging group. The charged organic bridging groups allow the immobilization of hexacyanoferrate ions by an ion exchange process. The electron transfer process of the hexacyanoferrate anionic complex confined in the pores of the matrices was studied by cyclovoltammetry.

Al2O3-coated 3-N-propylpyridinium chloride silsesquioxane polymer film: preparation and electrochemical property study of adsorbed cobalt tetrasulfophthalocyanine.

Porous Al2O3 presenting a specific surface area of SBET = 105 m2 g(-1) was coated with 3-N-propylpyridinium chloride silsesquioxane polymer. The ion exchange capacity of this polymer grafted onto an Al2O3 surface, resulting in a material designated as AlSiPy(+)Cl-, was 1.09 mmol g(-1). Furthermore, a cobalt(II) tetrasulfophthalocyanine anionic complex was immobilized on the chemically modified surface by an ion exchange reaction with a yield of 40 micromol g(-1) (the surface density of the electroactive species is 3.80 x 10(-11) mol cm(-2)). The electrochemical properties of the material obtained, AlSiPy/CoTsPc, were tested for the catalytic oxidation of oxalic acid at 0.77 V vs SCE in 1.0 mol l(-1) KCl solution. Furthermore, a chronoamperometric technique was used with the electrode to test its potential use as a sensor for oxalic acid. The electrode response to oxalic acid concentrations between 1.0 and 3.5 mmol l(-1) was linear with an estimated detection limit of 0.5 mmol l(-1). The charge transfer resistance of the material, measured using the electrochemical impedance spectroscopy technique, was 43 Omega cm2.

Anilinepropylsilica xerogel used as a selective Cu (II) adsorbent in aqueous solution.

The metal ion adsorption properties of the microporous hybrid anilinepropylsilica xerogel were studied using divalent copper, zinc, and cadmium ions in aqueous solutions in concentrations ranging from 10(-4) up to 5x10(-3) moll(-1). At low concentrations the surface of the solid phase presents selectivity for Cu (II), even in competitive conditions. This preferential sorption ability for copper in relation to zinc and cadmium ions was interpreted by considering the xerogel morphology.