4 research outputs found
Combinatorial Vibration-Mode Assignment for the FTIR Spectrum of Crystalline Melamine: A Strategic Approach toward Theoretical IR Vibrational Calculations of Triazine-Based Compounds
Although polymeric
graphitic carbon nitride (g-C<sub>3</sub>N<sub>4</sub>) has been widely
studied as metal-free photocatalyst, the
description of its structure still remains a great challenge. Fourier
transform infrared (FTIR) spectroscopy can provide complementary structural
information. In this paper, we reconsider the representative crystalline
melamine and develop a strategic approach to theoretically calculate
the IR vibrations of this triazine-based nitrogen-rich system. IR
calculations were based on three different models: a single molecule,
a 4-molecule unit cell, and a 32-molecule cluster, respectively. By
this comparative study the contribution of the intermolecular weak
interactions were elucidated in detail. An accurate and visualized
description on the experimental FTIR spectrum has been further presented
by a combinatorial vibration-mode assignment based on the calculated
potential energy distribution of the 32-molecule cluster. The theoretical
approach reported in this study opens the way to the facile and accurate
assignment for IR vibrational modes of other complex triazine-based
compounds, such as g-C<sub>3</sub>N<sub>4</sub>
Functionalization of Single-Wall Carbon Nanotubes with Chromophores of Opposite Internal Dipole Orientation
We report the functionalization of
carbon nanotubes with two azobenzene-based
chromophores with large internal dipole moments and opposite dipole
orientations. The molecules are attached to the nanotubes noncovalently
via a pyrene tether. A combination of characterization techniques
shows uniform molecular coverage on the nanotubes, with minimal aggregation
of excess chromophores on the substrate. The large on/off ratios and
the subthreshold swings of the nanotube-based field-effect transistors
(FETs) are preserved after functionalization, and different shifts
in threshold voltage are observed for each chromophore. Ab initio
calculations verify the properties of the synthesized chromophores
and indicate very small charge transfer, confirming a strong, noncovalent
functionalization
Tuning the Photocatalytic Activity of Graphitic Carbon Nitride by Plasma-Based Surface Modification
In
this study, we demonstrate that plasma treatment can be a facile and
environmentally friendly approach to perform surface modification
of graphitic carbon nitride (g-CN), leading to a remarkable modulation
on its photocatalytic activity. The bulk properties of g-CN, including
the particle size, structure, composition, and electronic band structures,
have no changes after being treated by oxygen or nitrogen plasma;
however, its surface composition and specific surface area exhibit
remarkable differences corresponding to an oxygen functionalization
induced by the plasma post-treatment. The introduced oxygen functional
groups play a key role in reducing the recombination rate of the photoexcited
charge carries. As a consequence, the oxygen-plasma-treated sample
shows a much superior photocatalytic activity, which is about 4.2
times higher than that of the pristine g-CN for the degradation of
rhodamine B (RhB) under visible light irradiation, while the activity
of nitrogen-plasma-treated sample exhibits a slight decrease. Furthermore,
both of the plasma-treated samples are found to possess impressive
photocatalytic stabilities. Our results suggest that plasma treatment
could be a conventional strategy to perform surface modification of
g-CN in forms of both powders and thin films, which holds broad interest
not only for developing g-CN-based high-performance photocatalysts
but also for constructing photoelectrochemical cells and photoelectronic
devices with improved energy conversion efficiencies
Low-Temperature, Directly Depositing Individual Single-Walled Carbon Nanotubes for Fabrication of Suspended Nanotube Devices
Single-walled
carbon nanotubes (SWNTs) grown by chemical vapor
deposition (CVD) are widely used for fabrication of high-performance
nanotube devices. However, the high-temperature growth is incompatible
with the current complementary metal-oxide semiconductor (CMOS) technology.
We demonstrate a low-temperature and direct deposition of the CVD-grown
SWNTs. The nanotubes are synthesized by floating catalytic CVD technique
and further carried by the flowing gas directly to the low-temperature
area. Individual SWNTs have been successfully deposited on Si/SiO<sub>2</sub> substrates covered with a polymethylmethacrylate layer, which
results in a suspended geometry of the nanotube in the fabricated
devices. We subsequently investigate the electrical-transport properties
of a representative small band gap nanotube, which exhibits an ambipolar
feature with <i>p</i>-channel mobility up to 1410 cm<sup>2</sup> V<sup>–1</sup> S<sup>–1</sup> at room temperature.
Furthermore, low-temperature measurements down to 4 K reveal different
transport characteristics with the gate voltage biased near zero or
at a large negative value, respectively