Shape-dependent surface energetics of nanocrystalline TiO2

We report the direct determination of surface enthalpies for nanophase TiO2 anatase with different morphologies derived from drop solution calorimetry in a molten sodium molybdate (3Na(2)O center dot 4MoO(3)) solvent at 702 degrees C. The energetics of surface hydration has been measured using a Calvet microcalorimeter coupled with a gas dosing system. The surface enthalpies of hydrated surfaces for anatase TiO2 nanoparticles, nanowires and sea-urchin-like assemblies are 0.51 +/- 0.05, 1.07 +/- 0.28, and 1.29 +/- 0.16 J m(-2), respectively, whereas those of anhydrous surfaces are 0.74 +/- 0.04, 1.24 +/- 0.28, and 1.41 +/- 0.16 J m(-2), respectively. The trend in TiO2, which shows higher surface enthalpies for more complex nanostructures, is consistent with that reported in ZnO. The shape-dependent surface enthalpy at the nanoscale level is discussed in terms of exposed surface structures. The enthalpies of hydration appear to be similar for all morphologies.