November 13, 2007
Journal Article

Surface Enthalpies of Nanophase ZnO with Different Morphologies

Abstract

A direct calorimetric measurement of the dependence of the surface enthalpy of nanophase ZnO on morphology is reported. Nanoparticles, nanoporous composites, nanorods, and nanotetrapods were prepared with various sizes and their surface enthalpies were derived from their drop solution enthalpies in molten sodium molybdate. Water adsorption calorimetry for nanoparticles and nanorods was carried out to characterize the stabilization effect of surface hydration. The surface enthalpies of hydrated surfaces for nanoparticles, nanoporous composites, nanorods and nanotetrapods are 1.31±0.07, 1.42±0.21, 5.19±0.56, and 5.77±2.50 J/m2, respectively, while those of the anhydrous surfaces are 2.55±0.23, 2.74±0.16, 6.67±0.56, and 7.28±2.50 J/m2. The surface enthalpies of nanoparticles are the same as those of nanoporous composites, and are much lower than those of nanorods and nanotetrapods, which are also close to each other. The dependence of surface enthalpy on morphology is discussed in terms of exposed surface structures. This is the first time that calorimetry on nanocrystalline powders bas been able to detect differences in surface energetics of materials having different morphologies.

Revised: January 24, 2008 | Published: November 13, 2007

Citation

Zhang P., F. Xu, A. Navrotsky, J.S. Lee, S. Kim, and J. Liu. 2007. Surface Enthalpies of Nanophase ZnO with Different Morphologies. Chemistry of Materials 19, no. 23:5687-5693. PNNL-SA-58404. doi:10.1021/cm0711919