4 research outputs found
Improving Carbon Nitride Photocatalysis by Supramolecular Preorganization of Monomers
Here
we report a new and simple synthetic pathway to form ordered,
hollow carbon nitride structures, using a cyanuric acid–melamine
(CM) complex in ethanol as a starting product. A detailed analysis
of the optical and photocatalytic properties shows that optimum hollow
carbon nitride structures are formed after 8 h of condensation. For
this condensation time, we find a significantly reduced fluorescence
intensity and lifetime, indicating the formation of new, nonradiative
deactivation pathways, probably involving charge-transfer processes.
Enhanced charge transfer is seen as well from a drastic increase of
the photocatalytic activity in the degradation of rhodamine B dye,
which is shown to proceed via photoinduced hole transfer. Moreover,
we show that various CM morphologies can be obtained using different
solvents, which leads to diverse ordered carbon nitride architectures.
In all cases, the CM-C<sub>3</sub>N<sub>4</sub> structures exhibited
superior photocatalytic activity compared to the bulk material. The
utilization of CM hydrogen-bonded complexes opens new opportunities
for the significant improvement of carbon nitride synthesis, structure,
and optical properties toward an efficient photoactive material for
catalysis
<i>In Situ</i> Formation of Heterojunctions in Modified Graphitic Carbon Nitride: Synthesis and Noble Metal Free Photocatalysis
Herein, we report the facile synthesis
of an efficient roll-like
carbon nitride (C<sub>3</sub>N<sub>4</sub>) photocatalyst for hydrogen
production using a supramolecular complex composed of cyanuric acid,
melamine, and barbituric acid as the starting monomers. Optical and
photocatalytic investigations show, along with the known red shift
of absorption into the visible region, that the insertion of barbituric
acid results in the <i>in situ</i> formation of in-plane
heterojuctions, which enhance the charge separation process under
illumination. Moreover, platinum as the standard cocatalyst in photocatalysis
could be successfully replaced with first row transition metal salts
and complexes under retention of 50% of the catalytic activity. Their
mode of deposition and interaction with the semiconductor was studied
in detail. Utilization of the supramolecular approach opens new opportunities
to manipulate the charge transfer process within carbon nitride with
respect to the design of a more efficient carbon nitride photocatalyst
with controlled morphology and optical properties
Polyelectrolyte Layer-by-Layer Assembly on Organic Electrochemical Transistors
Oppositely
charged polyelectrolyte multilayers (PEMs) were built up in a layer-by-layer
(LbL) assembly on top of the conducting polymer channel of an organic
electrochemical transistor (OECT), aiming to combine the advantages
of well-established PEMs with a high performance electronic transducer.
The multilayered film is a model system to investigate the impact
of biofunctionalization on the operation of OECTs comprising a poly(3,4-ethylenedioxythiophene)
polystyrenesulfonate (PEDOT:PSS) film as the electrically active
layer. Understanding the mechanism of ion injection into the channel
that is in direct contact with charged polymer films provides useful
insights for novel biosensing applications such as nucleic acid sensing.
Moreover, LbL is demonstrated to be a versatile electrode modification
tool enabling tailored surface features in terms of thickness, softness,
roughness, and charge. LbL assemblies built up on top of conducting
polymers will aid the design of new bioelectronic platforms for drug
delivery, tissue engineering, and medical diagnostics
Fluorinated Copolymer PCPDTBT with Enhanced Open-Circuit Voltage and Reduced Recombination for Highly Efficient Polymer Solar Cells
A novel fluorinated copolymer (F-PCPDTBT) is introduced
and shown
to exhibit significantly higher power conversion efficiency in bulk
heterojunction solar cells with PC<sub>70</sub>BM compared to the
well-known low-band-gap polymer PCPDTBT. Fluorination lowers the polymer
HOMO level, resulting in high open-circuit voltages well exceeding
0.7 V. Optical spectroscopy and morphological studies with energy-resolved
transmission electron microscopy reveal that the fluorinated polymer
aggregates more strongly in pristine and blended layers, with a smaller
amount of additives needed to achieve optimum device performance.
Time-delayed collection field and charge extraction by linearly increasing
voltage are used to gain insight into the effect of fluorination on
the field dependence of free charge-carrier generation and recombination.
F-PCPDTBT is shown to exhibit a significantly weaker field dependence
of free charge-carrier generation combined with an overall larger
amount of free charges, meaning that geminate recombination is greatly
reduced. Additionally, a 3-fold reduction in non-geminate recombination
is measured compared to optimized PCPDTBT blends. As a consequence
of reduced non-geminate recombination, the performance of optimized
blends of fluorinated PCPDTBT with PC<sub>70</sub>BM is largely determined
by the field dependence of free-carrier generation, and this field
dependence is considerably weaker compared to that of blends comprising
the non-fluorinated polymer. For these optimized blends, a short-circuit
current of 14 mA/cm<sup>2</sup>, an open-circuit voltage of 0.74 V,
and a fill factor of 58% are achieved, giving a highest energy conversion
efficiency of 6.16%. The superior device performance and the low band-gap
render this new polymer highly promising for the construction of efficient
polymer-based tandem solar cells