Didier Leonard

A novel biosorbent for dye removal: Extracellular polymeric substance (EPS) of Proteus mirabilis TJ-1

This paper deals with the extracellular polymeric substance (EPS) of Proteus mirabilis TJ-1 used as a novel biosorbent to remove dye from aqueous solution in batch systems. As a widely used and hazardous dye, basic blue 54 (BB54) was chosen as the model dye to examine the adsorption performance of the EPS. The effects of pH, initial dye concentration, contact time and temperature on the sorption of BB54 to the EPS were examined. At various initial dye concentrations (50-400 mg/L), the batch sorption equilibrium can be obtained in only 5 min. Kinetic studies suggested that the sorption followed the internal transport mechanism. According to the Langmuir model, the maximum BB54 uptake of 2.005 g/g was obtained. Chemical analysis of the EPS indicated the presence of protein (30.9%, w/w) and acid polysaccharide (63.1%, w/w). Scanning electron microscopy (SEM) images showed that the EPS with a crystal-linear structure was whole enwrapped by adsorbed dye molecules. FTIR spectrum result revealed the presence of adsorbing groups such as carboxyl, hydroxyl and amino groups in the EPS. High-molecular weight of the EPS with more binding-sites and stronger van der Waals forces together with its specific construct leads to the excellent performance of dye adsorption. The EPS shows potential board application as a biosorbent for both environmental protection and dye recovery.

A novel nitrite biosensor based on conductometric electrode modified with cytochrome c nitrite reductase composite membrane

A conductometric biosensor for nitrite detection was developed using cytochrome c nitrite reductase (ccNiR) extracted from Desulfovibrio desulfuricans ATCC 27774 cells immobilized on a planar interdigitated electrode by cross-linking with saturated glutaraldehyde (GA) vapour in the presence of bovine serum albumin, methyl viologen (MV), Nafion, and glycerol. The configuration parameters for this biosensor, including the enzyme concentration, ccNiR/BSA ratio, MV concentration, and Nafion concentration, were optimized. Various experimental parameters, such as sodium dithionite added, working buffer solution, and temperature, were investigated with regard to their effect on the conductance response of the biosensor to nitrite. Under the optimum conditions at room temperature (about 25 degrees C), the conductometric biosensor showed a fast response to nitrite (about 10s) with a linear range of 0.2-120 microM, a sensitivity of 0.194 microS/microM [NO(2)(-)], and a detection limit of 0.05 microM. The biosensor also showed satisfactory reproducibility (relative standard deviation of 6%, n=5). The apparent Michaelis-Menten constant (K(M,app)) was 338 microM. When stored in potassium phosphate buffer (100mM, pH 7.6) at 4 degrees C, the biosensor showed good stability over 1 month. No obvious interference from other ionic species familiar in natural waters was detected. The application experiments show that the biosensor is suitable for use in real water samples.

Development of a conductometric phosphate biosensor based on tri-layer maltose phosphorylase composite films.

A conductometric biosensor for phosphate detection was developed using maltose phosphorylase (MP) from recombinant Escherichia coli immobilized on a planar interdigitated electrode by cross-linking with saturated glutaraldehyde (GA) vapour in the presence of bovine serum albumin (BSA). The process parameters for the fabrication of the mono-enzymatic sensor and various experimental variables such as the enzyme loading, time of immobilization in saturated GA vapour, working buffer solution and temperature were investigated with regard to their influence on sensitivity, detection limit, dynamic range, operational and storage stability. The biosensor can work well at the temperature between 20 degrees C and 50 degrees C, and reach 90% of steady-state conductance in about 10s. The sensor has two linear ranges, one is from 1.0 microM to 20 microM phosphate with a detection limit of 1.0 microM, and the other is between 20 microM and 400 microM phosphate. When stored in citrate buffer (0.1M, pH 6.0) at 4 degrees C, the biosensor showed good stability over two months. No obvious interference from other anionic species like SO(4)(2-), Cl(-), NO(3)(-), NO(2)(-) and HCO(3)(-) was detected. The biosensor is suitable for use in real water samples.

Mechanically stable and photocatalytically active TiO2/SiO2 hybrid films on flexible organic substrates

Photocatalytic porous coatings (micro-, meso- and macroporous) are obtained by the dispersion of TiO2 nanoparticles in sol–gel hybrid matrices. The sol–gel silica matrix is used as a binder stabilizing the nanoparticle dispersion and as a protective layer for the organic substrates. Organic groups are introduced into the matrix to induce the film flexibility and a part of them is used to create the final microstructure allowing remarkable improvement of the photocatalytic properties. The film structure and UV stability are fully characterized. The photocatalytic activity is evaluated through a test with formic acid. Flexible efficient photoactive composites are obtained showing important capabilities for depollution (water and air) and self-cleaning applications.

ELECTROLESS PLATING OF GLASS AND SILICON SUBSTRATES THROUGH SURFACE PRETREATMENTS INVOLVING PLASMA-POLYMERIZATION AND GRAFTING PROCESSES

Electroless plating of nickel (or copper) was carried out on glass (or silicon) substrates that were previously surface modified by using plasma-polymerization and grafting processes, and then activated by immersion in a simple acidic PdCl2 solution. Three pretreatments based on the deposition of plasma-polymerized thin films (PACVD process) on O2 plasma-cleaned substrates were investigated. They include film deposition of (1) amorphous hydrogenated carbon (a-C:H) grown from CH4, whose surface is subsequently plasma-functionalized in NH3 or N2; (2) amorphous hydrogenated carbon nitride (a-CNx:H) grown from CH4/NH3 or CH4/N2 mixtures; and (3) amorphous hydrogenated carbon nitride grown from volatile organic precursors (allylamine, acetonitrile). In the three cases, X-ray photoelectron spectroscopy (XPS) results show that chemisorption of the catalyst occurs on the nitrogen-containing functionalities created by plasma polymerization and grafting and thus that the electroless deposition is possible. Differences were observed depending on the nature and thickness of the plasma-polymerized thin films, as well as on the nature and concentration of the nitrogen-containing functionalities present or grafted at the surface. Practical adhesion of Ni films was investigated using a Scotch® tape test. Ni films up to 3 or 4 μm in thickness were shown to pass this test successfully, i.e., without causing any metal detachment.

Selective Metal Pattern Fabrication Through Micro-Contact or Ink-Jet Printing and Electroless Plating onto Polymer Surfaces Chemically Modified by Plasma Treatments

Simple versatile processes combining plasma treatments, micro-contact printing (µCP) or ink-jet printing (IJP), and electroless deposition (ELD) have been developed to produce micrometer and sub-micrometer scale metal (Ni, Ag) patterns at the surface of polymer substrates. Plasma treatments were mainly used to graft the substrate surfaces with either nitrogen-containing functionalities on which a palladium-based catalyst can be subsequently chemisorbed (case of Ni deposition through a tin-free process in solution) or oxygen-containing functionalities on which a tin-based sensitization agent can be subsequently chemisorbed (case of Ag deposition through a redox reaction). µCP of the catalyst or of self-assembled monolayers (SAMs) as well as ink printing were used to obtain locally active or non-active areas at the polymer surfaces. The metal micro-patterns were characterized using optical microscopy, scanning electron microscopy (SEM), and atomic force microscopy (AFM). Surface chemical characterization was carried out by X-ray photoelectron spectroscopy (XPS).

Toward tunable amphiphilic copolymers via CuAAC click chemistry of oligocaprolactones onto starch backbone

Starch-based tunable amphiphilic copolymers are easily obtained by grafting polycaprolactone chains via 1,3 dipolar Copper-Catalyzed Azide-Alkyne Cycloaddition (click chemistry CuAAC), starting from propargylated starch and azido oligocaprolactones with different chain lengths as the precursors. The copolymers are characterized by (1)H and (13)C NMR, from which a degree of substitution of starch can tentatively be deduced. Besides these bulk characterizations, the surface of the functionalized starch is also characterized by XPS which confirms the triazole formation, particularly through the deconvolution of the N 1s peak, and by ToF-SIMS which, not only confirms the surface modification, but also highlights the disappearance of the Cu(+) cations. The solubility and swelling behaviours of these copolymers have been investigated, which clearly show the dependence both on the solvent and the PCL chain length. These investigations highlight the swelling dependence on the δd component of the Hansen solubility parameter of solvents. Finally, at low concentration, they present the capacity to organize themselves in aggregates in aqueous solutions, as seen from TEM and DLS investigations.

Aqueous Photocurrent Measurements Correlated to Ultrafast Electron Transfer Dynamics at Ruthenium Tris Diimine Sensitized NiO Photocathodes

Understanding the structural and electronic factors governing the efficiency of dye-sensitized NiO photocathodes is essential to optimize solar fuel production in photoelectrochemical cells (PECs). For these purpose, three different ruthenium dyes, bearing either two or four methylphosphonate anchoring groups and either a bipyridine or a dipyridophenazine ancillary ligand, were synthesized and grafted onto NiO films. These photoelectrodes were fully characterized by XPS, ToF-SIMS, UV-vis absorption, time-resolved emission and femtosecond transient absorption spectroscopies. Increasing the number of anchoring groups from two to four proved beneficial for the grafting efficiency. No significant modification of the electronic properties compared to the parent photosensitizer was observed, in accordance with the non-conjugated nature of the grafted linker. The photoelectrochemical activity of the dye-sensitized NiO electrodes was assessed in fully aqueous medium in the presence of an irreversible electron acceptor and photocurrents reaching 190 μA.cm-2 were recorded. The transient absorption study revealed the presence of two charge recombination pathways for each of the sensitizers and evidenced a stabilized charge separated state in the dppz derivative, supporting its superior photoelectrochemical activity.

A novel conductometric sensor based on a PVC membrane containing nonactin for ammonium determination.

This work presents a new sensor for ammonium determination based on interdigitated conductometric thin-film planar electrodes. It was fabricated by including nonactin in a plasticised poly(vinyl chloride) membrane deposited on the sensitive area of the transducer. The effects of pH, buffer concentration, the interferences of Na+, K+ and Ca2+ ions, the effect of ionic strength and of temperature were investigated. The linear working range and sensitivity of the biosensor were also determined. The sensitivity of the ammonium detection was around 6.2 µS µM−1 and the detection limit was 2 × 10−5 M. The biosensor exhibits the advantages of a simple fabrication procedure, good sensor-to-sensor reproducibility, wide dynamic range and good storage stability (12 weeks).

Microwaves-assisted synthesis of La1−xAgxMnO3+δ (0 ≤ x ≤ 0.2) perovskites with high surface area: Application to catalytic combustion of methane

ABSTRACT Lanthanum-manganese based perovskites were prepared, both at atmospheric pressure (MW) and at higher pressure (MWHyd), under microwaves irradiation. Structural and physico-chemical properties of the catalysts were investigated using X ray diffraction, X-ray photoelectron spectroscopy (XPS), BET-sorption, and temperature programmed reduction-, or desorption coupled with mass spectrometry, (TPR-MS or TPD-MS). While MW and MWHyd catalysts exhibited the same XRD patterns indexed as pure perovskite structure, their surface physico-chemical properties were found to be strongly influenced by the preparation procedure. The influence of the nature of oxygen species, their amount and their mobility, evidenced by temperature programmed experiments, on the catalytic properties in catalytic combustion of methane in the presence and in the absence H 2 S has been studied.