5 research outputs found
Bipolar Spectroelectrochemistry
Bipolar
electrochemistry is receiving growing attention in the
last years, not only because it is an important tool for studying
electron transfer processes, but also because it is really fruitful
in the development of new analytical sensors. Bipolar electrodes show
promising applications as a direct analytical tool since oxidation
and reduction reactions take place simultaneously on different parts
of a single conductor. There are several electrochemical devices that
provide information about electron transfer between two immiscible
electrolyte solutions, but to the best of our knowledge, this is the
first time that a bipolar device is able to record two spectroelectrochemical
responses concomitantly at two different compartments. It allows deconvolving
the electrochemical signal into two different optical signals related
to the electron transfer processes occurring at two compartments that
are electrically in contact. The combination of an electrochemical
and two spectroscopic responses is indeed very useful, providing essential
advantages in the study of a huge variety of systems. The study of
three different electrochemical systems, such as reversible redox
couples, carbon nanotubes, and conducting polymers has allowed us
to validate the new cell and to demonstrate the capabilities of this
technique to obtain valuable time-resolved information related to
the electron transfer processes
Simultaneous UV–Visible Absorption and Raman Spectroelectrochemistry
The
development of a new device based on the use of UV–vis
bare optical fibers in a long optical path length configuration and
the measurement of the Raman response in normal arrangement allows
us to perform UV–vis and Raman spectroelectrochemistry simultaneously
in a single experiment. To the best of our knowledge, this is the
first time that a spectroelectrochemistry device is able to record
both spectroscopic responses at the same time, which further expands
the versatility of spectroelectrochemistry techniques and enables
us to obtain much more high-quality information in a single experiment.
Three different electrochemical systems, such as ferrocyanide, dopamine,
and 3,4-ethylenedioxythiophene, have been studied to validate the
cell and to demonstrate the performance of the device. Processes that
take place in solution can be properly distinguished from processes
that occur on the electrode surface during the electrochemical experiment,
providing a whole picture of the reactions taking place at the electrode/solution
interface. Therefore, this device allows us to study a larger number
of complex electrochemical processes from different points of view
taking into account not only the UV–vis spectral changes in
the solution adjacent to the electrode but also the Raman signal at
any location. Furthermore, complementary information, which could
not be unambiguously extracted without considering together the two
spectroscopic signals and the electrochemical response, is obtained
in a novel way
Study of Adenine and Guanine Oxidation Mechanism by Surface-Enhanced Raman Spectroelectrochemistry
Metal
nanoparticles are systems largely employed in surface-enhanced
Raman spectroscopy (SERS). In particular, gold nanoparticles are one
of the best substrates used in this field. In this work, the optimal
conditions for gold nanoparticles electrodeposition on single-walled
carbon nanotubes electrodes have been established to obtain the best
SERS response. Using this substrate and analyzing the changes of in
situ Raman spectra obtained at different potentials, we have been
able to explain simultaneously the oxidation mechanism of purine bases,
differentiating the oxidation intermediates and their orientation
during the different oxidation steps. Adenine orientation hardly changes
during the whole oxidation; the molecule maintains a parallel configuration
and only shows a slightly tilted orientation after the first oxidation
step. On the other hand, guanine orientation changes completely during
its oxidation. Initially, guanine is perpendicular respect to gold
nanoparticles, changing its orientation after the first oxidation
process when the molecule shows a slightly tilted orientation, and
it finishes parallel respect to the electrode surface after the second
oxidation step
Janus Electrochemistry: Asymmetric Functionalization in One Step
Janus
structures represent an overwhelming member of materials with adaptable
chemical and physical properties. Development of new synthesis routes
has allowed the fabrication of Janus architectures with specific characteristics
depending on the final applications. In the case of the membranes,
the improvement of wet routes has been limited to the capillary effect,
in which the solution can gradually penetrate through the membrane,
avoiding a double modification different at each face of the membrane.
In this work, we propose a new electrochemical methodology to circumvent
the capillary limitation and obtain a double electrochemical functionalization
in only one step in a controlled way. This innovative methodology
has been validated using a tridirectional spectroelectrochemistry
setup. Moreover, the information provided by this optical arrangement
should be especially useful for the study of the different processes
(ion transfer, assisted ion transfer, and electron transfer) that
can take place at liquid/liquid interfaces. Janus electrochemistry
allows us to modify the two faces of a free-standing single-walled
carbon nanotube electrode in a single experiment. As proof of concept,
the free-standing films have been functionalized with two different
conducting polymers, polyaniline and poly(3-hexylthiophene), in one
electrochemical experiment. According to the obtained results, this
new electrochemical methodology will open new gates for the design
and functionalization of Janus materials
In-situ Evidence of the Redox-State Dependence of Photoluminescence in Graphene Quantum Dots
Changes
in the optical properties of graphene quantum dots (GQD)
during electrochemical reduction and oxidation were investigated by
photoluminescence (PL) spectroelectrochemistry, which provided direct
in situ evidence of the dependence of GQD luminescence on their redox
state. We demonstrated that GQD PL intensity was enhanced upon reduction
(quantum yield increased from 0.44 to 0.55) and substantially bleached
during oxidation (quantum yield ∼0.12). Moreover, PL emission
blue/red-shifted upon GQD reduction/oxidation, rendering information
about electronic transitions involved in the redox processes, namely,
the π → π* and the <i>n</i> →
π* transitions between energy levels of the aromatic sp<sup>2</sup> domains and the functional groups, respectively. PL intensity
changes during GQD reduction/oxidation resulted from a variation in
structural changes in GQD as a result of charge injection, as corroborated
by in situ Raman spectroelectrochemistry