2 research outputs found
Investigation of Ligand-Stabilized Gold Clusters on Defect-Rich Titania
Chemically
synthesized atomically precise gold clusters stabilized
by triphenylphosphine ligands [Au<sub>9</sub>(PPh<sub>3</sub>)<sub>8</sub>]Â(NO<sub>3</sub>)<sub>3</sub>] were deposited onto the surface
of titania fabricated via atomic layer deposition. The titania surface
was pretreated by heating and sputtering. After deposition of the
clusters onto pretreated titania, the samples were heated at 200 °C
for 20 min under ultrahigh vacuum and subsequently investigated using
metastable-induced electron spectroscopy to study the electronic structure
of the outermost layer of the sample and X-ray photoelectron spectroscopy
to determine the chemical composition of the surface of the sample.
The former study revealed that two reference spectra are needed to
explain the electronic structure of the sample. One reference spectrum
is related to the titania substrate, while the second spectrum is
related to the presence of the Au cluster cores and the ligands removed
from the cluster cores. The latter study found that the Au 4f peak
is shifted to lower binding energy and the P 2p peak to higher binding
energy after heating. These are interpreted in the light of ligand
removal and size evolution of Au particles upon heating of the clusters
on titania. The important outcome of the present work is that defects
introduced at the ALD titania surface via sputtering and heating strongly
reduce the agglomeration of the Au clusters adsorbed to the surface
Reduction and Diffusion of Cr-Oxide Layers into P25, BaLa<sub>4</sub>Ti<sub>4</sub>O<sub>15</sub>, and Al:SrTiO<sub>3</sub> Particles upon High-Temperature Annealing
Chromium
oxide (Cr2O3) is a beneficial metal
oxide used to prevent the backward reaction in photocatalytic water
splitting. The present work investigates the stability, oxidation
state, and the bulk and surface electronic structure of Cr-oxide photodeposited
onto P25, BaLa4Ti4O15, and Al:SrTiO3 particles as a function of the annealing process. The oxidation
state of the Cr-oxide layer as deposited is found to be Cr2O3 on the surface of P25 and Al:SrTiO3 particles
and Cr(OH)3 on BaLa4Ti4O15. After annealing at 600 °C, for P25 (a mixture of rutile and
anatase TiO2), the Cr2O3 layer diffuses
into the anatase phase but remains at the surface of the rutile phase.
For BaLa4Ti4O15, Cr(OH)3 converts to Cr2O3 upon annealing and diffuses
slightly into the particles. However, for Al:SrTiO3, the
Cr2O3 remains stable at the surface of the particles.
The diffusion here is due to the strong metal–support interaction
effect. In addition, some of the Cr2O3 on the
P25, BaLa4Ti4O15, and Al:SrTiO3 particles is reduced to metallic Cr after annealing. The
effect of Cr2O3 formation and diffusion into
the bulk on the surface and bulk band gaps is investigated with electronic
spectroscopy, electron diffraction, DRS, and high-resolution imaging.
The implications of the stability and diffusion of Cr2O3 for photocatalytic water splitting are discussed