Cotton functionalized with nanostructured TiO2-Ag-AgBr layer for solar photocatalytic degradation of dyes and toxic organophosphates.

The functionalization of cotton fabric with photoactive TiO2-Ag-AgBr nanostructured layer has been successfully developed using a low temperature non-aqueous sol-gel route and aqueous suspension of AgBr. Evidence for the growth of TiO2 layer and the immobilization of AgBr nanoparticles have been confirmed by Raman, XRD and XPS. GSDR analysis revealed a strong absorption in the visible region brought by surface Plasmon resonance (SPR) of Ag nanocrystals generated at the surface of AgBr. The XPS evidenced the presence of Ag+, Ag0 and bromine, suggesting that Ag0 formed a shell around the deposited AgBr. The immobilized TiO2-Ag-AgBr heterostructured layer imparts a strong photocatalytic activity under visible light for the degradation of dyes in aqueous solution as well as of dimethyl methylphosphonate (DMMP), a chemical warfare agent simulant. These new catalytically active functionalized fabrics, with self-detoxification properties, have great potential for application in chemical protective clothes and might offer new opportunities for the design of functional materials for toxic chemical protection.

Chitosan-Ag-TiO2 films: An effective photocatalyst under visible light.

Aiming the degradation of harmful molecules under visible light, new photocatalytic systems were created. For this purpose, the surface of chitosan thin films was modified in heterogeneous phase via a simple and straightforward mild chemical process: chemisorption of silver ions followed by the synthesis in situ of TiO2 at low temperature (100 °C). A high photocatalytic activity under visible light was observed, leading to the degradation and/or mineralization of different organic products such as o-toluidine, salicylic acid and 4-aminomethyl benzoic acid. This efficiency is partly attributed to the formation of Ag NPs and also to the unexpected appearance of AgCl NPs, likely formed from the residual chlorine contained in the chitosan. The resulting TiO2/Ag/AgCl/Chitosan system is easy to prepare under mild conditions, avoiding calcination treatments and opens new perspectives for the production of visible light-driven photocatalysts. Samples were analysed by different techniques: XRD, Raman, FE-SEM, XPS, TGA, GSDR, LIF and LIP.

Functionalization of cotton fabrics with plasmonic photo-active nanostructured Au-TiO2 layer.

A simple approach to functionalize cotton fabrics with Au and TiO2 nanostructured layer is presented. Hybrid fabrics (Cot-Au-TiO2) are prepared through reduction of AuCl4- on cotton, followed by a non-aqueous sol-gel procedure using tetrabutyltitanate and a hydrothermal treatment at 110°C. The generation of crystalline TiO2 is confirmed by Raman spectroscopy. The fibres morphology and their roughness are characterized by AFM and FE-SEM. XPS shows how the concentration of the NPs precursors (Au and TiO2) affects the layer composition. GSDR (Ground State Diffuse Reflectance Absorption Spectroscopy) and LIL (Laser induced luminescence) reveal a strong quenching effect induced by Au NPs. Photocatalytic activity measured through the Remazol Blue (RB) degradation reveals an enhancement under visible light, which increases with Au loading. This strong enhancement is explained through the surface plasmon resonance brought by Au NPs.

Controlled growth of Cu2O nanoparticles bound to cotton fibres.

A green, safe and fast procedure is presented for in situ generation of nanoparticles (NPs) of cuprous oxide (Cu2O) onto cotton fibres at room temperature using water as a solvent. The method is based on a mild surface oxidation of cellulose fibres to generate in a controlled way carboxylic groups acting as a binding site for the adsorption of Cu(2+) via electrostatic coordination. Then, the adsorbed Cu(2+) ions were readly converted into Cu2O by dipping the treated cotton fibres into a aqueous solution of a reducing agent. Field-emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD), as well as UV-vis absorption and emission spectroscopic methods were used to analyse the size, morphology, chemical composition and the crystalline structure of the generated nanoparticles on the fabrics. The morphology of the ensuing Cu2O nanoparticles was shown to be dependent on the reduycing agent used. Antibacterial properties of the modified fibres were also investigated.

Alumina interaction with AMPS-MPEG copolymers produced by RAFT polymerization: stability and rheological behavior.

Different copolymers of 2-acrylamido-2-methylpropanesulfonic acid sodium salt (AMPS), methoxypolyethyleneglycol methacrylate (MPEG), were prepared using two methods of radical polymerization: classical and RAFT-controlled radical polymerization. The effect of polymer structure and architecture on the adsorption behavior, electrokinetic and rheological properties of the alumina suspensions was investigated. Adsorption isotherms showed that copolymer interaction depended not only on the ratio of the monomers and their distribution within the macromolecular backbone, but also on the method of copolymerization. Electrokinetic analysis indicated that adsorption of the copolymer is accompanied by a shift in the isoelectric point (IEP) towards acid pH values. Above a certain concentration, of the order of 1 wt%, the absolute value of the zeta-potential reaches a saturation plateau. At this stage, the maximum zeta-potential value (in absolute value) depends on both the ratio of the monomers for statistical copolymer and the length of the two blocks in the case of block distribution. The rheological behavior is greatly affected in the presence of added polymer; the viscosity of the alumina suspension decreases and reaches an optimum, which depends on both the ratio of the monomers and their distribution within the macromolecular backbone. The viscoelastic properties of the suspensions were found to be functions of both the structure and the architecture of the copolymer. Adding AMPS-MPEG copolymer increases the stability of the suspension via electrostatic effects, but also via steric effects induced by the polyethylene glycol (PEG) segments. The steric contribution to the stabilization process is much important in the presence of block distribution, which is more efficient as dispersant for concentrated alumina suspensions.

Dispersion of alumina suspension using comb-like and diblock copolymers produced by RAFT polymerization of AMPS and MPEG.

Different copolymers of 2-acrylamido-2-methylpropanesulfonic acid sodium salt (AMPS) methoxypolyethyleneglycol methacrylate (MPEG) with statistical and diblock distributions were prepared using RAFT-controlled radical polymerization. The effect of polymer architecture and monomer ratio on the adsorption behavior, electrokinetic, and stability properties of the alumina suspensions was investigated. Adsorption isotherms showed that copolymer interaction depended on both the ratio of the monomers and their distribution within the macromolecular backbone. Changes in the electrokinetic properties of the alumina suspension after addition of the copolymers were investigated by monitoring the particle zeta-potential as a function of pH. A continuous shift in the isoelectric point IEP to a more acidic value was observed and particle charges were reversed when the amount of copolymer added exceeded a critical level.

Self-aggregation of cationic surfactants onto oxidized cellulose fibers and coadsorption of organic compounds.

In this work, the adsorption of cationic surfactant and organic solutes on oxidized cellulose fibers bearing different amounts of carboxylic moieties was investigated. The increase in the amount of -COOH groups on cellulose fibers by TEMPO oxidation induced a general rise in surfactant adsorption. For all tested conditions, that is, cellulose oxidation level and surfactant alkyl chain length (C12 and C16), adsorption isotherms displayed a typical three-region shape with inversion of the substrate zeta-potential which was interpreted as reflecting surfactant adsorption and aggregation (admicelles and hemimicelles) on cellulose fibers. The addition of organic solutes in surfactant/cellulose systems induced a decrease in surfactant cac on the cellulose surface thus favoring surfactant aggregation and the formation of mixed surfactant/solute assemblies. Adsorption isotherms of organic solutes on cellulose in surfactant/cellulose/solute systems showed that solute adsorption is strictly correlated to (i) the surfactant concentration, solute adsorption increases up to the surfactant cmc, where solute partitioning between the cellulose surface and free micelles causes a drop in adsorption, and to (ii) solute solubility and functional groups. The specific shape of solutes adsorption isotherms at a fixed surfactant concentration was interpreted using a Frumkin adsorption isotherm, thus suggesting that solute uptake on cellulose fibers is a coadsorption and not a partitioning process. Results presented in this study were compared with those obtained in a previous work investigating solute adsorption in anionic surfactant/cationized cellulose systems to better understand the role of surfactant/solute interactions in the coadsorption process.

Alumina interaction with AMPS-MPEG random copolymers III. Effect of PEG segment length on adsorption, electrokinetic and rheological behavior.

The effect of different 2-acrylamido-2-methylpropanesulfonic acid sodium salt (AMPS)-methoxypolyethyleneglycol methacrylate (MPEG) comb-like copolymers on the adsorption behavior, electrokinetic and rheological properties of alumina suspensions has been investigated. The change in adsorption isotherms with the content of the two monomers, the medium pH and the ionic strength indicated that the interaction of these copolymers was found to be controlled by both the fraction of ionic groups on the polymer and by the length of the polyethyleneglycol (PEG) segments. Adsorption of the copolymers on alumina particles is accompanied by a shift in the IEP toward acid pH values and may lead to a charge reversal above a certain level. The presence of the PEG segment equally affects the magnitude of the zeta potential by moving the shear plane forward. Addition of the copolymers greatly affects the rheological behavior of the suspension; the viscosity at a defined shear rate decreases and reaches an optimum, which is all the lower as the fraction of the ionic groups is higher. The dispersing effect of the copolymer was controlled by both the ionization level of the copolymer and by the length of the PEG segments.

Adsorption of organic compounds onto polyelectrolyte immobilized-surfactant aggregates on cellulosic fibers.

The adsorption of anionic surfactants with different hydrophobic chain lengths onto cellulose fibers pretreated with a cationic polyelectrolyte has been investigated. Five steps are involved in the adsorption process, which was ascribed to the formation of monolayer and bilayer surfactant aggregates. Electrostatic interaction between the residual surface charges followed by hydrophobic interaction among the alkyl chains are considered the main factors in the adsorption process. The adsorption of the anionic surfactant was found to greatly enhance the retention of organic compounds onto the polyelectrolyte-treated cellulose. The coadsorption phenomenon, which was dependent on the saturation level of the adsorbed surfactant, has been explained in terms of the accumulation of the organic solute on the hydrophobic core generated by the adsorbed layer.

[Coagulation-flocculation performances for cuttlefish effluents treatment]. / Performances de la coagulation-floculation dans le traitement des effluents de seiche.

Coagulation-flocculation of the colloids particles present in the cuttlefish effluents was investigated using a coagulation step with aluminium sulphate (SA), followed by a flocculation step with starch, SiO2 or MgO and then poly dimethyl ammonium chloride (PDMAC), in order to reduce the turbidity and chemical oxygen demand (COD). Kinetic aspects, adsorption equilibrium, pH and conductivity were studied in order to determine the optimum coagulation conditions and SA quantities. The addition of organic polymer as a flocculant agent gave a better performance than the use of salt alone with a reduction of 50% of the SA consumption. Polymer molecular weight of PDMAC and charge density of starch have been also investigated. The best result, which is 90% of removal rate in chemical oxygen demand (COD) and a turbidity value of 7 NTU was obtained with the combination using 165.5 mg l(-1) of aluminium sulphate, 750 mg l(-1) of MgO and 35 mg l(-1) of PDMAC 400000.

Alumina interaction with AMPS-MPEG random copolymers I. Adsorption and electrokinetic behavior.

Adsorption of brush copolymers, bearing sulfonate groups and polyethylene glycol segments, on to alumina particles in suspension in water has been investigated. Study of the adsorption isotherms revealed that the copolymers displayed a strong affinity for the surface of the alumina regardless of the fraction of ionic groups on the polymer. For poly(ethylene glycol) content greater than 50%, the adsorption isotherms revealed an initial adsorption plateau followed by a second one. The shape of the adsorption isotherms was interpreted in terms of the polymer configuration at the solid-to-liquid interface. The effects of the pH and the ionic force on adsorption were studied and connected to the effects of interaction between chain segments at the surface of the alumina particles. Changes in the electrokinetic properties of the alumina particles after addition of the copolymers were investigated by following the zeta potential of particles as a function of pH. In the presence of the copolymer continuous shift of the isoelectric point IEP to a more acidic values was observed. Beyond a certain concentration the zeta potential remained negative regardless of the pH.