International audienceChemically-prepared gold nanoparticles (AuNPs) were drop-casted onto bare glassy carbon (GC) and on GC functionalized by two different diazonium salts bearing either nitro (NO2) or thiol (SH) groups. The resulting interfaces were characterized by field emission gun scanning electron microscopy (FEG-SEM) and cyclic voltammetry in H2SO4. The micrographs evidenced different densities of AuNPs depending on the substrate, bare GC affording denser deposits than diazonium-functionalized GC. The stability of the interfaces was evaluated over one month and showed higher recovery of active surface area (up to 91% depending on the storage conditions) for AuNPs deposited on diazonium-functionalized GC than on bare GC. The three electrodes were also tested for Hg(II) trace detection by using Square Wave Anodic Stripping Voltammetry (SWASV) and a preconcentration time shortened from 300 s to 30 s. In such conditions, a linear response was obtained in the range 1-10 nmol l-1 together with a normalized sensitivity up to 17 times higher than that reported in our previous works dealing with electrodeposited AuNP

For the purpose of preparing well-organized functional surfaces, carbon and gold substrates were modified using electroreduction of a tetrahedral-shape preorganized tetra-aryldiazonium salt, leading to the deposition of ultrathin organic films. Characterization of the modified surfaces has been performed using cyclic voltammetry, X-ray photoelectron spectroscopy, infrared absorption spectroscopy, ellipsometry, atomic force microscopy, and contact angle measurements. The specific design of the tetra-aryldiazonium salts leads to an intrinsic structuring of the resulting organic films, allowing molecular sieving and current rectification properties toward redox probes in solution.

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Electrochemical properties of functionalized carbons with ferrocene-alkyl monolayer were evaluated with different electrolytes and solvents for charge storage applications. Investigations were performed both by cyclic voltammetry and impedance spectroscopy using edge plane pyrolytic graphite (PG) electrodes, being a good example of fragile and porous carbon material. The functionalization method is based on the electrografting of protected aryldiazonium ions that leads after deprotection to the formation of a covalently attached mono-layer. In a second step, C 11 -long chain alkyl ferrocene is attached on the platform. The functionalization considerably increases the charge density by a factor of 5-10 depending on the electrolyte with the advantage that it does not alter the structure of the carbon surface. The grafted layer presents a very fast electron transfer kinetics providing an easy way for increasing the charge density in devices like supercapacitors, the charging time being limited by the resistance of the electrolyte.

We report the use of poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) as a transducing material in the fabrication of mechanical-to-electrical conversion devices based on the flexoelectric-like response of this polymer. Devices are made in a cantilever-based three-layer stainless-steel/PEDOT:PSS/top metal electrode configuration to assess the effective transverse flexoelectric coefficient μ12′. We investigated the influence of the nature of the top electrode in the flexoelectric response comparing samples with gold and aluminum top electrodes and demonstrated the huge impact of adding a small fraction of a second dopant such as xylitol to the PEDOT:PSS polymer blend and the benefits of a post-treatment of the polymer film with ethanol and methanol on the flexoelectric coefficient. The combination of xylitol addition and the rinsing of the polymer films with ethanol and methanol, along with the use of gold as a top electrode, led to a significant improvement of μ12′ to ca. 24 μC m−1, which is in the range of those reported for high permittivity oxide materials. These findings support the use of conjugated polymers as an alternative to inorganic materials in flexoelectric-based applications, where large flexibility is required.

The antioxidant protective properties of polyaromatic organic layers were evaluated towards Reactive Oxygen Species (ROS) using Scanning Electrochemical Microscopy (SECM) in a foot-printing strategy. The layers were prepared by electrografting of aryldiazonium salts. Where p-(methyl)phenyl films show only weak protective properties towards ROS, p-(ethynyl)phenyl films evidence an efficient protection of the covered surfaces. Applied potentials and electrolytes used during ORR are critical parameters to control, to prevent or reduce the influence of ROS production and hence enhancing devices lifetime.

Diffraction patterns observed in surface plasmon resonance imaging (SPRI) microscopy measurements of single gold nanorods (AuNRs) exhibit a complex behavior at wavelengths near the longitudinal plasmonic resonance band. SPRI microscopy measurements at 814 nm from AuNRs in three samples with resonance extinction maxima at 670, 816, and 980 nm reveal a variety of diffraction patterns with central peaks that are either positive, negative, or biphasic. A unitless ratio parameter M R (−1 ≤ M R ≤ 1) is created to describe the distribution of diffraction patterns. A purely negative (M R = −1) central peak is observed for 30%, 57%, and 98% of the diffraction patterns in the 670, 816, and 980 nm samples, respectively. These results along with a theoretical modeling of the diffraction patterns with an anisotropic complex scattering coefficient suggests that this behavior only occurs for AuNRs when the laser wavelength used in SPRI experiments is shorter than the AuNR plasmonic resonance maxima, that is, in the anomalous dispersion region.

Layer-by-layer assembly of thin films have received growing interest in a variety of applications worldwide. Methods for depositing films, patterning, unconventional assemblies, and approaches are gaining immense scientific advancements. The porous structures, tunable surface areas, remarkable thermal and mechanical stabilities, abundant reserves, and cost-effectiveness makes clays one of the most sought-after materials for plethora of applications. Interestingly, several naturally occurring silicates, viz. clay minerals have layered structure with possibility of interchangeable intercalated ions and tunable chemical properties. Among these clay minerals, Bentonite is very promising owing to its abundance, low cost, high surface area, porosity, and unique layered structure. Clay is composed of alternating tetrahedral silica (T) and octahedral alumina (O) sheets arranged in 1:1 ratio (T-O). The tetrahedral sheets are formed from Si4+ ions coordinated with oxygen, however in the octahedral sheet Al3+ metal ion is the central atom. Notably, naturally occurring Bentonite have some of the octahedral sites occupied by the Mg2+ and Fe2+ ions. The presence of these ions shows the tunable property of the octahedral layer that can concomitantly widen its applicability in the energy fields. Herein, we have put a focused effort in developing a sustainable, cost-effective, environmental benign, and biocompatible clay films having unique physical and chemical properties. We present a unique approach to develop clay galleries infused with intercalating quaternary ammonium salts. The insertion of such zwitter ions enhances the interlayer spacing, while simultaneously allowing to form durable clay films. The hybrid clay films have been characterized using the powder X-ray diffraction, X-ray photoelectron spectra, ATR-FTIR spectra, DSC-TGA, dynamic mechanical analyses, and imaging techniques. Effect of varying the carbon chain length in these zwitter ions have been verified to have a significant impact in controlling the interlayer spacing in the clay films. Further, the intercalation using zwitter ions led to the alternations in the electron environment of the dielectric silicate layers that has been confirmed using electrochemical and impedance spectroscopy studies. Owing to the high electronic resistance and high ionic conductivity present in the films, a series of impedance spectroscopy experiments were conducted in variety of electrolytes. The ionic conductivity of the hybrid clay films is remarkable, and a correlation have been established with the ionic size of the conducting ions. In metal ion batteries, where dendritic growth causes thermal degradation of the batteries, the hybrid clay films possess high thermal and mechanical stability that makes them versatile for energy materials. can provide The abundance and sustainability of clay minerals and a cost-effective approach to engineer these hybrid films may provide efficient avenues to develop new generation of battery separators and capacitors for future.