4 research outputs found
Electrochemically Assisted Generation of Silica Deposits Using a Surfactant Template at Liquid/Liquid Microinterfaces
The
electrochemically assisted generation of mesoporous silica
deposits at arrays of microscopic liquid/liquid interfaces was investigated.
Ion transfer voltammetry was used in order to initiate the formation
of silica material by electrochemical transfer of template species
(cetyltrimethylammonium, CTA<sup>+</sup>), initially present in the
organic phase, to the aqueous phase containing the hydrolyzed silica
precursors (tetraethoxysilane, TEOS). The deposition mechanism was
investigated using cyclic voltammetry, based on the analysis of diffusion
layer profiles of CTA<sup>+</sup> species from the organic side of
the interface. The morphology of the deposits varied from hemispherical
to almost flat with the potential scan rate, the spacing factor of
the microinterfaces array supporting the liquid/liquid interfaces,
or the initial CTA<sup>+</sup> and TEOS concentrations, as evidenced
by scanning electron microscopy and profilometry analyses. The amount
of deposited material can be related to the amount of CTA<sup>+</sup> species passing across the liquid/liquid interfaces. Confocal Raman
spectroscopy was used to confirm the presence of surfactant-templated
silica deposits and to analyze the effectiveness of calcination in
removing the organic molecules filling the interior of the pores.
After template removal, the mesoporous network became accessible to
external reagents, as checked by interfacial alkylammonium cation
transfer, suggesting a possible analytical interest of such modified
micro-liquid/liquid interfaces
Combined Raman Microspectrometer and Shearforce Regulated SECM for Corrosion and Self-Healing Analysis
Shearforce regulated scanning electrochemical
microscopy (SECM)
has been associated with Raman microspectrometry in order to perform
combined electrochemical and spectrochemical analysis on reactive
interfaces. The interest of the method was evaluated by analyzing
local corrosion phenomena in damaged Zn(Mg, Al) self-healing coatings
deposited on steel. Despite the high aspect ratio of the analyzed
sample displaying here more than a 50 μm depth profile, the
optimized setup allowed (1) precise electrode positioning with the
help of shearforce detection, (2) electrochemical measurement at a
constant distance from the sample surface, and (3) local chemical
analysis of the solid surface by confocal Raman microspectroscopy
performed at a constant focal distance from the sample. All in all,
this new setup allows one to approach the detailed reactivity involved
in defective metal samples
Vertically Aligned and Ordered One-Dimensional Mesoscale Polyaniline
The
growth of vertically aligned and ordered polyaniline nanofilaments
is controlled by potentiostatic polymerization through hexagonally
packed and oriented mesoporous silica films. In such small pore template
(2 nm in diameter), quasi-single PANI chains are likely to be produced.
From chronoamperometric experiments and using films of various thicknesses
(100–200 nm) it is possible to evidence the electropolymerization
transients, wherein each stage of polymerization (induction period,
growth, and overgrowth of polyaniline on mesoporous silica films)
is clearly identified. The advantageous effect of mesostructured silica
thin films as hard templates for the generation of isolated polyaniline
nanofilaments is demonstrated from enhancement of the reversibility
between the conductive and the nonconductive states of polyaniline
and the higher electroactive surface areas displayed for all mesoporous
silica/PANI composites. The possibility to control and tailor the
growth of conducting polymer nanofilaments offers numerous opportunities
for applications in various fields including energy, sensors and biosensors,
photovoltaics, nanophotonics, or nanoelectronics
Mesoporous Silica Thin Films for Improved Electrochemical Detection of Paraquat
An
electrochemical method was developed for rapid and sensitive
detection of the herbicide paraquat in aqueous samples using mesoporous
silica thin film modified glassy carbon electrodes (GCE). Vertically
aligned mesoporous silica thin films were deposited onto GCE by electrochemically
assisted self-assembly (EASA). Cyclic voltammetry revealed effective
response to the cationic analyte (while rejecting anions) thanks to
the charge selectivity exhibited by the negatively charged mesoporous
channels. Square wave voltametry (SWV) was then used to detect paraquat
via its one electron reduction process. Influence of various experimental
parameters (i.e., pH, electrolyte concentration, and nature of electrolyte
anions) on sensitivity was investigated and discussed with respect
to the mesopore characteristics and accumulation efficiency, pointing
out the key role of charge distribution in such confined spaces on
these processes. Calibration plots for paraquat concentration ranging
from 10 nM to 10 μM were constructed at mesoporous silica modified
GCE which were linear with increasing paraquat concentration, showing
dramatically enhanced sensitivity (almost 30 times) as compared to
nonmodified electrodes. Finally, real samples from Meuse River (France)
spiked with paraquat, without any pretreatment (except filtration),
were analyzed by SWV, revealing the possible detection of paraquat
at very low concentration (10–50 nM). Limit of detection (LOD)
calculated from real sample analysis was found to be 12 nM, which
is well below the permissible limits of paraquat in drinking water
(40–400 nM) in various countries