Mohammed Boujtita

Development of a disposable ethanol biosensor based on a chemically modified screen-printed electrode coated with alcohol oxidase for the analysis of beer

A disposable amperometric biosensor for the measurement of ethanol has been developed. It comprises a screen-printed carbon electrode doped with 5% cobalt phthalocyanine (CoPC-SPCE), and coated with alcohol oxidase; a permselective membrane on the surface acts as a barrier to interferents. The measurement of ethanol is based on the signal produced by H2O2, the product of the enzymatic reaction. Optimisation studies were performed using amperometry in stirred solution and the magnitude of the signal was found to be dependent on pH, enzyme loading, type of membrane and applied potential. The same technique was used to evaluate the biosensor for the determination of ethanol in samples. The results obtained compared well with the manufacturers specifications. In order to test the possibility of using the devices in the field, chronoamperometry was also used to determine ethanol in the same beer samples. The precision and recovery data again indicated that the biosensor should give reliable results under the conditions described.

CuGaO2: a promising alternative for NiO in p-type dye solar cells

CuGaO2 is used here as photocathode in place of NiO for a p-type dye-sensitized solar cell with iodide/triiodide (I−/I3−) or tris(4,4′-bis-tert-butyl-2,2′-bipyridine)cobalt (Co2+/Co3+) as redox mediator, and PMI or PMI-NDI as sensitizer. Both photovoltaic characteristics and flat band potentials suggest that CuGaO2 can be viewed as a promising substitute for NiO.

P-Type Nitrogen-Doped ZnO Nanoparticles Stable under Ambient Conditions

Zinc oxide is considered as a very promising material for optoelectronics. However, to date, the difficulty in producing stable p-type ZnO is a bottleneck, which hinders the advent of ZnO-based devices. In that context, nitrogen-doped zinc oxide receives much attention. However, numerous reviews report the controversial character of p-type conductivity in N-doped ZnO, and recent theoretical contributions explain that N-doping alone cannot lead to p-typeness in Zn-rich ZnO. We report here that the ammonolysis at low temperature of ZnO(2) yields pure wurtzite-type N-doped ZnO nanoparticles with an extraordinarily large amount of Zn vacancies (up to 20%). Electrochemical and transient spectroscopy studies demonstrate that these Zn-poor nanoparticles exhibit a p-type conductivity that is stable over more than 2 years under ambient conditions.

Long-Lived Charge Separated State in NiO-Based p-Type Dye-Sensitized Solar Cells with Simple Cyclometalated Iridium Complexes

Three new cyclometalated iridium complexes were prepared and investigated on nanocrystalline NiO cathodes. Nanosecond transient absorption spectroscopy experiments show they present a surprisingly slow geminate charge recombination upon excitation on NiO, representing thus the first examples of simple sensitizers with such feature. These complexes were used in dye-sensitized solar cells using nanocrystalline NiO film as semiconductor. The long-lived charge separated state of these Ir complexes make them compatible with other redox mediators than I3(-)/I(-), such as a cobalt electrolyte and enable to reach significantly high open circuit voltage.

Heteroleptic copper(I)–polypyridine complexes as efficient sensitizers for dye sensitized solar cells

The synthesis and the physico-chemical characterization of HETPHEN based heteroleptic copper(I)–bis(diimine) complexes are reported. For TiO2 based dye sensitized solar cells (DSCs), the latter display impressive photoconversion efficiencies (PCEs), unprecedented for first row transition metal coordination complexes.

Biosensors for analysis of ethanol in food: effect of the pasting liquid

An amperometric biosensor for ethanol was constructed by using an alcohol dehydrogenase and NAD+ modified carbon paste electrode. The sensor response to ethanol was studied using various pasting liquids. The electrode made with hexadecane as the pasting liquid showed an increase in sensitivity and linearity, compared to the one prepared with paraffin oil. This sensor was tested by assaying ethanol in beer and wine and the results compared favourably with spectrophotometric determinations.

A carbon paste electrode modified by entrapped toluidine blue-O for amperometric determination of l-lactate

Abstract In this study a new approach to enhance the analytical performance of modified carbon paste electrode with l -LDH ( l -lactate dehydrogenase), NAD+ (nicotinamide adenine dinucleotide) and TBO (toluidine blue-O) is described. This approach consists of entrapping the mediator on carbon powder using two properties of the proteins: adsorption on the graphite powder and cross-linking with glutaraldehyde. The immobilisation of TBO in the carbon paste matrix showed that TBO responds rapidly to the variation of NADH concentration in the vicinity of the electrode surface with good repeatability.

Carbon nanowalls as material for electrochemical transducers

The electrochemical reactivity of a carbon nanowalls electrode was highlighted. The carbon nanowalls were synthesized at 520 °C in an acetylene/ammonia electron cyclotronic resonance plasma without any metal catalyst. The electrode surface was characterized by scanning and transmission electron microscopy. Its electrochemical reactivity was studied by both cyclic voltammetry and electrochemical impedance spectroscopy. After the carbon nanowalls deposition, the electronic transfer rate constant and the electroactive surface area were found to be increased by a factor of 7 and 3, respectively.

Molecular Structure – Optical Property Relationships for a Series of Non-Centrosymmetric Two-photon Absorbing Push-Pull Triarylamine Molecules

This article reports on a comprehensive study of the two-photon absorption (2PA) properties of six novel push-pull octupolar triarylamine compounds as a function of the nature of the electron-withdrawing groups. These compounds present an octupolar structure consisting of a triarylamine core bearing two 3,3′-bis(trifluoromethyl)phenyl arms and a third group with varying electron-withdrawing strength (H < CN < CHO < NO2 < Cyet < Vin). The 2PA cross-sections, measured by using the femtosecond open-aperture Z-scan technique, showed significant enhancement from 45 up to 125 GM for the lowest energy band and from 95 up to 270 GM for the highest energy band. The results were elucidated based on the large changes in the transition and permanent dipole moments and in terms of (i) EWG strength, (ii) degree of donor-acceptor charge transfer and (iii) electronic coupling between the arms. The 2PA results were eventually supported and confronted with theoretical DFT calculations of the two-photon transition oscillator strengths.

In situ ultrafast 2D NMR spectroelectrochemistry for real-time monitoring of redox reactions.

The in situ implementation of an electrochemical cell (EC) inside a nuclear magnetic resonance (NMR) spectrometer is extremely powerful to study redox reactions in real time and identify unstable reaction intermediates. Unfortunately, the implementation of an electrochemical device near the sensitive volume of an NMR probe significantly affects the quality of the NMR signal, inducing significant line broadening resulting in peak overlap and partial loss of the multiplet structures. Two-dimensional (2D) NMR spectroscopy allows one to bypass signal overlapping by spreading the peaks along two orthogonal dimensions, while providing precious information in terms of structural elucidation. Nevertheless, the acquisition of 2D NMR data suffers from long acquisition durations which are incompatible with fast redox processes taking place in solution. Here, we present a new approach to deal with this issue, consisting of coupling EC-NMR with ultrafast 2D spectroscopy, capable of recording 2D spectra much faster than conventional 2D NMR. This approach is applied to the real-time monitoring of a model reaction. Fast correlation spectroscopy (COSY) spectra are recorded every 3 min in the course of the 80 min reaction, leading to the unambiguous identification of one reaction intermediate and two reaction products. The evolution of 2D NMR peak volumes in the course of time provides further insight into the mechanism of this reaction involving an unstable intermediate. This study demonstrates the feasibility and the relevance of coupling in situ spectroelectrochemistry with ultrafast 2D spectroscopy to monitor real-time electrochemical reactions in the NMR tube.