Special phase transformation and crystal growth pathways observed in nanoparticles†
1 Department of Earth and Planetary Sciences, University of California, Berkeley, Berkeley, CA 94720, USA
2 Materials Science Program, University of Wisconsin - Madison, 1509 University Avenue, Madison, WI 53706-1595, USA
3 Earth Sciences Division, Lawrence Berkeley National Laboratory, MS 108B, Berkeley, CA, 94720, USA
4 Department of Environmental Science, Policy, and Management, University of California, Berkeley, Berkeley, CA 94720, USA
Geochemical Transactions 2003, 4:20 doi:10.1186/1467-4866-4-20Published: 7 November 2003
Phase transformation and crystal growth in nanoparticles may happen via mechanisms distinct from those in bulk materials. We combine experimental studies of as-synthesized and hydrothermally coarsened titania (TiO2) and zinc sulfide (ZnS) with thermodynamic analysis, kinetic modeling and molecular dynamics (MD) simulations. The samples were characterized by transmission electron microscopy, X-ray diffraction, synchrotron X-ray absorption and scattering, and UV-vis spectroscopy. At low temperatures, phase transformation in titania nanoparticles occurs predominantly via interface nucleation at particle–particle contacts. Coarsening and crystal growth of titania nanoparticles can be described using the Smoluchowski equation. Oriented attachment-based crystal growth was common in both hydrothermal solutions and under dry conditions. MD simulations predict large structural perturbations within very fine particles, and are consistent with experimental results showing that ligand binding and change in aggregation state can cause phase transformation without particle coarsening. Such phenomena affect surface reactivity, thus may have important roles in geochemical cycling.