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    Interactions between GaO4Al12(OH)24(H2O)7+12 and cellulosic materials

    Year: 2012

    Journal: Journal of Colloid and Interface Science, Volume 374, Issue 1, 15 May 2012, Pages 250–257, 20120618

    Authors: Ola Sundman a, b, Per Persson a, Dipanjan Banerjee c, Lars-Olof Öhman a

    Last authors: Lars-Olof Öhman

    Organizations: •a Department of Chemistry, Umeå University, S-901 87 Umeå, Sweden •b Department of Forest Products Technology, Aalto University School of Chemical Sciences, P.O. Box 16300, FI-02015 Aalto, Finland •c The Rossendorf Beamline at ESRF, B.P. 220, F-38043 Grenoble-Cedex, France

    Country: Sverige, Sweden, Finland, France

    The adsorption qualities of GaO4Al12(OH)24(H2O)7+12, a polycation with ε-Keggin structure, and its stability in contact with anionic cellulosic materials, was investigated under different concentration and ionic strength conditions. The cellulosic materials employed were two different fully bleached fibre materials, carboxyl methyl cellulose (CMC), and a spin-coated cellulose model surface. As analytical techniques, pH-measurements, potentiometric titrations, ICP-OES, QCM-D, equilibrium calculations and Extended X-ray Absorption Fine Structure (EXAFS) were used. The adsorption is substantial and the addition of GaO4Al12(OH)24(H2O)7+12 to a fibre suspension results in a rapid decrease in pH, followed by a small and slow increase in pH. This behaviour can be explained as due to a rapid and strong (log β > 2) equilibrium adsorption of intact GaO4Al12(OH)24(H2O)7+12 ions, followed by a slow, and minor, 3–8%, decomposition into different monomers. Alternative layer by layer adsorption of this ion, and CMC, on a spin-coated cellulose model surface constitutes further evidence for the strong interactions between the anionic cellulose materials and GaO4Al12(OH)24(H2O)7+12. It is shown that the adsorption observed could not be described as due to an unspecific Donnan adsorption behaviour, neither of GaO4Al12(OH)24(H2O)7+12 nor Ga and Al monomers, and specific surface complex formation is therefore discussed and applied. The (≡COO)7GaO4Al12(OH)24(H2O)12 species found to explain the pH- and metal adsorption data should be considered strictly as a stoichiometric entity.