5 research outputs found
Ultralight, Flexible, and Semi-Transparent Metal Oxide Papers for Photoelectrochemical Water Splitting
Thanks
to their versatile functionality, metal oxides (MOs) constitute one
of the key family materials in a variety of current demands for sensor,
catalysis, energy storage and conversion, optical electronics, and
piezoelectric mechanics. Much effort has focused on engineering specific
nanostructure and macroscopic morphology of MOs that aims to enhance
their performances, but the design and controlled synthesis of ultrafine
nanostructured MOs in a cost-effective and facile way remains a challenge.
In this work, we have exploited the advantages of intrinsic structures
of graphene oxide (GO) papers, serving as a sacrificial template,
to design and synthesize two-dimensional (2D) layered and free-standing
MO papers with ultrafine nanostructures. Physicochemical characterizations
showed that these MO materials are nanostructured, porous, flexible,
and ultralight. The as-synthesized materials were tested for their
potential application in photoelectrochemical (PEC) energy conversion.
In terms of PEC water splitting, copper oxide papers were used as
an example and exhibited excellent performances with an extremely
high photocurrent-to-weight ratio of 3 A cm<sup>â2</sup> g<sup>â1</sup>. We have also shown that the synthesis method is
generally valid for many earth-abundant transition metals including
copper, nickel, iron, cobalt, and manganese
Nanoscale Confinement and Fluorescence Effects of Bacterial Light Harvesting Complex LH2 in Mesoporous Silicas
Many key chemical and biochemical reactions, particularly
in living
cells, take place in confined space at the mesoscopic scale. Toward
understanding of physicochemical nature of biomacromolecules confined
in nanoscale space, in this work we have elucidated fluorescence
effects of a light harvesting complex LH2 in nanoscale chemical environments.
Mesoporous silicas (SBA-15 family) with different shapes and pore
sizes were synthesized and used to create nanoscale biomimetic environments
for molecular confinement of LH2. A combination of UVâvis absorption,
wide-field fluorescence microscopy, and in situ ellipsometry supports
that the LH2 complexes are located inside the silica nanopores. Systematic
fluorescence effects were observed and depend on degree of space confinement.
In particular, the temperature dependence of the steady-state fluorescence
spectra was analyzed in detail using condensed matter band shape theories.
Systematic electronic-vibrational coupling differences in the LH2
transitions between the free and confined states are found, most likely
responsible for the fluorescence effects experimentally observed
Directed Energy Transfer in Films of CdSe Quantum Dots: Beyond the Point Dipole Approximation
Understanding of FoĚrster resonance
energy transfer (FRET)
in thin films composed of quantum dots (QDs) is of fundamental and
technological significance in optimal design of QD based optoelectronic
devices. The separation between QDs in the densely packed films is
usually smaller than the size of QDs, so that the simple pointâdipole
approximation, widely used in the conventional approach, can no longer
offer quantitative description of the FRET dynamics in such systems.
Here, we report the investigations of the FRET dynamics in densely
packed films composed of multisized CdSe QDs using ultrafast transient
absorption spectroscopy and theoretical modeling. Pairwise interdot
transfer time was determined in the range of 1.5 to 2 ns by spectral
analyses which enable separation of the FRET contribution from intrinsic
exciton decay. A rational model is suggested by taking into account
the distribution of the electronic transition densities in the dots
and using the film morphology revealed by AFM images. The FRET dynamics
predicted by the model are in good quantitative agreement with experimental
observations without adjustable parameters. Finally, we use our theoretical
model to calculate dynamics of directed energy transfer in ordered
multilayer QD films, which we also observe experimentally. The Monte
Carlo simulations reveal that three ideal QD monolayers can provide
exciton funneling efficiency above 80% from the most distant layer.
Thereby, utilization of directed energy transfer can significantly
improve light harvesting efficiency of QD devices
Three-Dimensional Graphene Matrix-Supported and Thylakoid Membrane-Based High-Performance Bioelectrochemical Solar Cell
A combination of
thylakoid membranes (TMs) as photobiocatalysts with high-surface-area
electroactive materials could hold great potential for sustainable
âgreenâ solar energy conversion. We have studied the
orientated immobilization of TMs on high-surface-area graphene electrodes,
which were fabricated by electroreduction of graphene oxide and simultaneous
electrodeposition with further aminoaryl functionalization. We have
achieved the highest performance to date under direct electron transfer
conditions through a biocompatible âwiringâ of TMs to
graphene sheets. The photobiocurrent density generated by the optimized
mediator-free TM-based bioanodes yielded up to 5.24 Âą 0.50 ÎźA
cm<sup>â2</sup>. The photobioelectrochemical cell integrating
the photobioanode in combination with an oxygen reducing enzymatic
biocathode delivered a maximum power output of 1.79 Âą 0.19 ÎźW
cm<sup>â2</sup>. Our approach ensures a simplified cell design,
a greater load of photosynthetic units, a minimized overpotential
loss, and an enhanced overall performance
Triazatriangulene as Binding Group for Molecular Electronics
The triazatriangulene (TATA) ring
system was investigated as a
binding group for tunnel junctions of molecular wires on gold surfaces.
Self-assembled monolayers (SAMs) of TATA platforms with three different
lengths of phenylene wires were fabricated, and their electrical conductance
was recorded by both conducting probe-atomic force microscopy (CP-AFM)
and scanning tunneling microscopy (STM). Similar measurements were
performed for phenylene SAMs with thiol anchoring groups as references.
It was found that, despite the presence of a sp<sup>3</sup> hybridized
carbon atom in the conduction path, the TATA platform displays a contact
resistance only slightly larger than the thiols. This surprising finding
has not been reported before and was analyzed by theoretical computations
of the transmission functions of the TATA anchored molecular wires.
The relatively low contact resistance of the TATA platform along with
its high stability and directionality make this binding group very
attractive for molecular electronic measurements and devices