PNNL-13501 - Pacific Northwest National Laboratory

Study Control Number: PN00084/1491
The Discovery of New Nanocrystalline Metal Oxide Materials
Yali Su, Scott H. Elder, Glenn Fryxell, John Fulton
A new field of materials chemistry and physics is synthesis of nanocrystalline materials. Nanomaterials often exhibit
novel properties that have potential applications in catalysis, electronics, optical-electronics, artificial photosynthesis, and
nanoparticles (as biosensors). The synthetic route discovered as a result of this project is one of the first examples where
stable nanocrystalline metal oxide powders have been synthesized and tailored to approximate size by controlling crystal
growth.
Project Description
The focus of this project was to develop new moleculeby-molecule
synthetic routes for preparing
nanocrystalline metal oxide powders. The objective is to
systematically control nanoparticle size and
nanoarchitecture through a rational chemical approach,
and determine how size quantization and unique
nanostructural features influence photophysical and
magnetic properties. We discovered a synthetic route to
make stable nanocrystalline metal oxide powders with
tailorable size and architecture. We studied and
elucidated the reaction mechanism for the synthesis of
nanoarchitectured transition metal oxides. We studied the
thermochemical properties of nanoarchitectured transition
metal oxides to fundamentally understand the key
thermodynamic features that contribute to their stability.
Our fundamental investigation enabled us to understand
the critical nanoscopic issues that govern the
photophysical and magnetic properties of nanoparticle
metal oxides.
Introduction
Considering the technological importance of bulk metal
oxides in catalysis, magnetic information storage, and
electronics, it is surprising that very little synthetic work
has been reported on nanocrystalline metal oxides (with
the exception of titanium oxide [TiO2]) with physical and
chemical properties that can be tailored though size
quantization and nanoarchitecturing. The primary
difficulty faced in preparing nanocrytalline oxides of the
early first, second, and third row transition metals is their
propensity for crystal growth due to their large lattice
energies. For example, these oxides have large heats of
crystallization because of the electropositive nature of the
early transition metals and the electronegative character
of oxygen and their reactive hydroxylated surfaces.
Our approach was to prevent or retard crystal growth by
chemically modifying the surface of nanocrytalline metal
oxides as they are nucleated. Thus, we control
crystallization using interfacial chemistry at the
nanoscopic level. In addition, we expect the
functionalization of nanoparticle surfaces to provide us
with another viable route to tailor the physical and
chemical properties of nanoparticle metal oxides since
interfacial interactions tend to dominate such systems
(i.e., a large fraction of the atoms are located at the
surface/interface). To this end, we investigated a new
class of solid-state metal oxide nanocomposite materials,
whose crystallite size, chemical composition, surface
structure, and electronic properties can be systematically
modified through a molecular-chemistry synthetic
approach.
Results and Accomplishments
We completed experiments to demonstrate our ability to
synthesize core-shell TiO2-(MoO3) powders with
tailorable nanoarchitecture and electronic properties. We
elucidated the reaction mechanism of heterogeneous
nucleation of nanocrystalline metal oxides from
homogeneous micellar solutions. We also developed an
understanding of the thermodynamic properties of
nanoarchitectured metal oxides.
TiO2-(MoO3) Core-Shell Materials
We successfully synthesized a series of TiO2-(MoO3)x
core-shell powders. This is the first example of a coreshell
metal oxide system with tailorable nanoarchitecture
and electronic properties. Figure 1 shows
photoabsorption energy as a function of TiO2-(MoO3)x
core-shell diameter and architecture.
Materials Science and Technology 327