Supercapacitance of Single-Walled Carbon Nanotubes-Polypyrrole Composites

The composites based on carbon nanotubes (CNTs) and conducting polymers (CPs) are promising materials for supercapacitor devices due to their unique nanostructure that combines the large pseudocapacitance of the CPs with the fast charging/discharging double-layer capacitance and excellent mechanical properties of the CNTs. Here, we report a new electrochemical method to obtain polypyrrole (PPY)/single-walled carbon nanotube (SWCNT) composites. In the first step, the SWCNTs are covalently functionalized with monomeric units of pyrrole by esterification of acyl chloride functionalized SWCNTs and N-(6-hydroxyhexyl)pyrrole. In the second step, the PPY/SWCNTs composites are obtained by copolymerizing the pyrrole monomer with the pyrrole units grafted on SWCNTs surface using controlled potential electrolysis. The composites were further characterized by cyclic voltammetry and electrochemical impedance spectroscopy. The results showed good electrochemical charge storage properties for the synthesized composites based on PPY and SWCNTs covalently functionalized with pyrrole units making them promising electrode materials for high power supercapacitors

A simple model of ac hopping surface conductivity in ionic liquids

The boundary conditions proposed to discuss the charge exchange taking place in an ionic liquid in contact with non-blocking electrodes are reconsidered in a dynamic situation. Assuming that the variation of the bulk ionic current density depends linearly on the surface value of the ionic current density, the frequency dependence of the phenomenological parameter is determined. The analysis has been performed in the framework where the relaxation times are smaller than a maximum relaxation time τM, and that the response function is independent on the value of the relaxation time. Using simple physical considerations, an expression for the surface conductivity describing the ionic charge exchange at the electrode is obtained. According to our calculations, its frequency dependence is similar to that predicted for the electric conductivity in disordered materials when the mechanism is of the hopping type. From measurements of impedance spectroscopy, by the best fit of the experimental data, the temperature dependence of the hopping time, of the dc surface conductivity, and of the diffusion coefficient are derived. They are in good agreement with the theoretical predictions obtained with the random distribution of surface energy barrier. Keywords: Ionic liquids, Non-blocking electrodes, Electrical impedance spectroscopy, AC hopping surface conductivit

The Role of Aryldiazonium Chemistry in Designing Electrochemical Aptasensors for the Detection of Food Contaminants

Food safety monitoring assays based on synthetic recognition structures such as aptamers are receiving considerable attention due to their remarkable advantages in terms of their ability to bind to a wide range of target analytes, strong binding affinity, facile manufacturing, and cost-effectiveness. Although aptasensors for food monitoring are still in the development stage, the use of an electrochemical detection route, combined with the wide range of materials available as transducers and the proper immobilization strategy of the aptamer at the transducer surface, can lead to powerful analytical tools. In such a context, employing aryldiazonium salts for the surface derivatization of transducer electrodes serves as a simple, versatile and robust strategy to fine-tune the interface properties and to facilitate the convenient anchoring and stability of the aptamer. By summarizing the most important results disclosed in the last years, this article provides a comprehensive review that emphasizes the contribution of aryldiazonium chemistry in developing electrochemical aptasensors for food safety monitoring

Supercapacitance of Single-Walled Carbon Nanotubes-Polypyrrole Composites

The composites based on carbon nanotubes (CNTs) and conducting polymers (CPs) are promising materials for supercapacitor devices due to their unique nanostructure that combines the large pseudocapacitance of the CPs with the fast charging/discharging double-layer capacitance and excellent mechanical properties of the CNTs. Here, we report a new electrochemical method to obtain polypyrrole (PPY)/single-walled carbon nanotube (SWCNT) composites. In the first step, the SWCNTs are covalently functionalized with monomeric units of pyrrole by esterification of acyl chloride functionalized SWCNTs and N-(6-hydroxyhexyl)pyrrole. In the second step, the PPY/SWCNTs composites are obtained by copolymerizing the pyrrole monomer with the pyrrole units grafted on SWCNTs surface using controlled potential electrolysis. The composites were further characterized by cyclic voltammetry and electrochemical impedance spectroscopy. The results showed good electrochemical charge storage properties for the synthesized composites based on PPY and SWCNTs covalently functionalized with pyrrole units making them promising electrode materials for high power supercapacitors

A GREEN APPROACH FOR THE SELECTIVE REDUCTION OF AROMATIC CARBONYL COMPOUNDS USING RANEY Ni-Al ALLOY

Given the significant environmental risk associated with the use of organic solvents and catalysts in the classic reduction reaction catalysts, we are interested in adapting the reaction medium and in developing an eco-friendly methodology for the synthesis of corresponding alcohols in reasonably yields. In this study, the reduction of some aromatic carbonyl compounds with Ni-Al alloy in aqueous alkaline medium was carried out in two versions: with 20 wt% aq NaOH and with 1 wt% aq NaOH without organic solvent. The structures of the reaction products are rigorously proven by gas chromatography-mass spectrometry (GC-MS). There was observed an increase of the reduction reaction rate when we used 1 wt% aq NaOH without addition of organic solvent. For a good part of the studied substrates high conversion and selectivity were achieved by employing mild reaction conditions, minimal environmental pollution and simple work up procedure, foreshadowing yields above 90 % and representing candidates for convenient preparative applications

Critical Design Factors for Electrochemical Aptasensors Based on Target-Induced Conformational Changes: The Case of Small-Molecule Targets

Nucleic-acid aptamers consisting in single-stranded DNA oligonucleotides emerged as very promising biorecognition elements for electrochemical biosensors applied in various fields such as medicine, environmental, and food safety. Despite their outstanding features, such as high-binding affinity for a broad range of targets, high stability, low cost and ease of modification, numerous challenges had to be overcome from the aptamer selection process on the design of functioning biosensing devices. Moreover, in the case of small molecules such as metabolites, toxins, drugs, etc., obtaining efficient binding aptamer sequences proved a challenging task given their small molecular surface and limited interactions between their functional groups and aptamer sequences. Thus, establishing consistent evaluation standards for aptamer affinity is crucial for the success of these aptamers in biosensing applications. In this context, this article will give an overview on the thermodynamic and structural aspects of the aptamer-target interaction, its specificity and selectivity, and will also highlight the current methods employed for determining the aptamer-binding affinity and the structural characterization of the aptamer-target complex. The critical aspects regarding the generation of aptamer-modified electrodes suitable for electrochemical sensing, such as appropriate bioreceptor immobilization strategy and experimental conditions which facilitate a convenient anchoring and stability of the aptamer, are also discussed. The review also summarizes some effective small molecule aptasensing platforms from the recent literature

Investigation of the conduction properties of ionic liquid crystal electrolyte used in dye sensitized solar cells

To investigate the conduction properties of ionic liquid crystal electrolytes and to correlate them to their molecular structure, two electrolytes based on imidazolium iodides have been chosen for a comparative study: one ionic liquid crystal (1-dodecy1-3-methylimidazolium iodide) (C12) and one ionic liquid (1-hexyl-3-methylimidazolium iodide) (C6). For the electrical characterization of the samples the electrochemical impedance spectroscopy technique (EIS) has been used in the frequency range 1 MHz divided by 10 mHz. For both electrolytes three frequency domains have been singled out. At large frequencies a hopping mechanism ensures the relative high conductivity of ionic liquids. A good fit of the conductivity data with respect to temperature with a Vogel-Tamman-Fulcher (VTF) equation has been done. The interesting result is that although C12 has a higher viscosity than C6 and thus a smaller conductivity was expected the observed conductivity is actually larger, this fact being attributed to the smectic A liquid crystal order of C12. At medium frequencies and especially at low frequencies the buildup of double layers by the electrodes is well observed. Assuming that in this region (10 Hz divided by 10 mHz) the cell is equivalent to an electric circuit formed by the parallel of a resistance, R-0, and a capacitance, C-0, the simple Debye relaxation model, characterized by one relaxation time, has been modified taking into account the adsorption phenomenon in the Langmuir approximation. A theoretical interpretation of the experimental results based on the double layer model is presented