Molar Enthalpy of Ion Exchange Comparisons Between Bulk and Nanocrystalline TiO2.

One of nanoscience’s tenet is that the properties of materials change as their size approaches the nano-scale and as the percentage of atoms at the surface becomes significant. This high surface area to volume ratio of nanoparticles imparts them with unique properties that renders them advantageous in novel applications. Due to the quantum size effect which is an electronic modification , nanosized Titanium oxide (TiO₂) show significant enhancement of its photocatalytic properties over that of  bulk TiO₂ powders. The aim of this study is to examine whether the nano-scale size has any effect on the charge properties of TiO₂ surfaces, specifically the energetics of outer- sphere ion exchange reactions. To that end two different sizes of TiO₂ were selected: a nanocrystalline Ti(IV) oxide aeroxide ® P25 and bulk TiO₂ (Sigma Aldrich). Both products were characterized using X-ray diffraction, transmission electron microscopy and N₂ gas adsorption for surface area determination. The heats of exchange were obtained using a flow adsorption calorimeter. Solutions of 50 mM NaCl and KCl adjusted to pH 7.5 using an MES buffer were used to measure the heats of Na and K exchange. The heats of exchange (in KJ) will be normalized to surface area and mole of charge and compared for both the bulk and nanocrystalline TiO₂.

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