Studies of the binding sites of silica using centrifugation of the colloid are less straightforward than those in which the free adsorbate concentration is determined in situ1. In our previous work, a pulse radiolysis technique was utilized in order to avoid problems associated with silica precipitation2. However, the high cost of specialized equipment lessens the practicability of this method. In the present study, the adsorption of 1-ethylpyridinium, EP+, methyl viologen, MV2+, and triparaquat-2, (TPQ-2)3+, onto colloidal silica nanoparticles suspended in an aqueous solution was studied in situ using a pulse laser photolysis technique, which is more accessible and by far less expensive. The luminescent probe 1-pyrenemethanol is quenched efficiently by the free adsorbates in solution but not by adsorbates bound to silica particles. The decrease in the extent of the luminescence quenching observed with the addition of particles was used to determine the concentration of free adsorbate in solution. The adsorption equilibrium constants and number of binding sites were determined for two different colloidal silica solutions obtained from Sigma – Aldrich; the AS-30 sample (surface area = ~230 m2/g, stabilized with an ammonium counterion) and the SM-30 sample (surface area = 320 – 400 m2/g, stabilized with a sodium counterion). It was determined for both samples that the equilibrium constant increases with the size and charge of the ion, while the number of binding sites decreases with size. Literature: 1. Ralph K. Iler, The Chemistry of Silica: Solubility, Polymerization, Colloid and Surface Properties and Biochemistry of Silica, Wiley, 1979 2. B. H. Milosavljevic and D. Meisel, J. Phys. Chem. B 2004, 108, 1827-1830

Charge effect on adsorption onto colloidal silica surfaces: An in situ laser photolysis study

251st National Meeting (2016)

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