5 research outputs found
Photophysical Study of Electron and Hole Trapping in TiO<sub>2</sub> and TiO<sub>2</sub>/Au Nanoparticles through a Selective Electron Injection
The photophysics surrounding the electron and hole trapping
in
TiO2 do not have a scientific consensus. Herein, we studied
the steady-state photoluminescence and time-resolved spectroscopy
features from TiO2 and TiO2/Au nanoparticles
(NPs). In TiO2/Au NPs, time-resolved photoluminescence
indicates that the electrons from bandgap excitation decay slower
(∼30 ps) than in TiO2 (<24 ps). We conclude this
as a result of the band bending passivation effect on the surface
electron traps. Meanwhile, electron trapping is proved as the dominant
surface depopulation process because of the easy-fill characteristics
of surface hole traps even under low excitation density, which also
interprets the slow surface hole trapping (∼2 ns) in TiO2. Through plasmon-assisted electron injection, we distinguished
the electron and hole behaviors at varied photon fluences and then
obtained the intrinsic bulk trapping of electrons and holes in the
∼50 and ∼400 ps time range, respectively
Organic Thiol Modified Pt/TiO<sub>2</sub> Catalysts to Control Chemoselective Hydrogenation of Substituted Nitroarenes
The quest for selective heterogeneous hydrogenation catalysts
is
state of the art research. We present a simple surface modification
method for Pt/TiO<sub>2</sub> catalysts employing organic thiols for
the liquid phase selective hydrogenation of 4-nitrostyrene. Our modified
catalyst shows a 100% switch of selectivity to 4-aminostyrene at conversion
levels close to 100%
Real Time Determination of the Electronic Structure of Unstable Reaction Intermediates during Au<sub>2</sub>O<sub>3</sub> Reduction
Chemical
reactions are always associated with electronic structure changes
of the involved chemical species. Determining the electronic configuration
of an atom allows probing its chemical state and gives understanding
of the reaction pathways. However, often the reactions are too complex
and too fast to be measured at in situ conditions due to slow and/or
insensitive experimental techniques. A short-lived Au<sub>2</sub>O
compound has been detected for the first time under in situ conditions
during the temperature-programmed reduction of Au<sub>2</sub>O<sub>3</sub>. A time-resolved resonant inelastic X-ray scattering experiment
(RIXS) allowed the determination of changes in the Au electronic structure,
enabling a better understanding of the reaction mechanism of Au(III)
reduction. On the basis of time-resolved RIXS data analysis combined
with genetic algorithm methodology, we determined the electronic structure
of the metastable Au<sub>2</sub>O intermediate species. The data analysis
showed a notably larger value for the lattice constant of the intermediate
Au as compared to the theoretical predictions. With support of DFT
calculations, we found that such a structure may indeed be formed
and that the expanded lattice constant is due to the termination of
Au<sub>2</sub>O on the Au<sub>2</sub>O<sub>3</sub> structure
Redispersion of Gold Supported on Oxides
Although many gold heterogeneous catalysts have been
shown to exhibit
significant activity and high selectivity for a wide range of reactions
in both the liquid and gas phases, they are prone to irreversible
deactivation. This is often associated with sintering or loss of the
interaction of the gold with the support. Herein, we report on the
use of methyl iodide as a method of dispersing gold nanoparticles
supported on silica, titania, and alumina supports. In the case of
titania- and alumina-based catalysts, the gold was transformed from
nanometer particles into small clusters and some atomically dispersed
gold. In contrast, although there was a drop in the gold particle
size on the silica support following CH<sub>3</sub>I treatment, the
size remained in the submicrometer range. The structural changes were
correlated with changes in the selectivity and activity for ethanol
dehydration and benzyl alcohol oxidation. From these observations,
it is clear that this treatment provides a method by which deactivated
gold catalysts can be reactivated via redispersion of the gold
Direct Determination of Metal Complexes’ Interaction with DNA by Atomic Telemetry and Multiscale Molecular Dynamics
The lack of molecular mechanistic
understanding of the interaction
between metal complexes and biomolecules hampers their potential medical
use. Herein we present a robust procedure combining resonant X-ray
emission spectroscopy and multiscale molecular dynamics simulations,
which allows for straightforward elucidation of the precise interaction
mechanism at the atomic level. The report unveils an unforeseen hydrolysis
process and DNA binding of [Pt{N(p-HC<sub>6</sub>F<sub>4</sub>)CH<sub>2</sub>}<sub>2</sub>py<sub>2</sub>] (Pt103), which showed potential
cytotoxic activity in the past. Pt103 preferentially coordinates to
adjacent adenine sites, instead of guanine sites as in cisplatin,
because of its hydrogen bond ability. Comparison with previous research
on cisplatin suggests that selective binding to guanine or adenine
may be achieved by controlling the acidity of the compound