Nonionic Fluorinated Surfactant Removal from Mesoporous Film Using sc-CO2.

Surfactant templated silica thin films were self-assembled on solid substrates by dip-coating using a partially fluorinated surfactant R8F(EO)9 as the liquid crystal template. The aim was 2-fold: first we checked which composition in the phase diagram was corresponding to a 2D rectangular highly ordered crystalline phase and second we exposed the films to sc-CO2 to foster the removal of the surfactant. The films were characterized by in situ X-ray reflectivity (XRR) and grazing incidence small angle X-ray scattering (GISAXS) under CO2 pressure from 0 to 100 bar at 34 °C. GISAXS patterns reveal the formation of a 2-D rectangular structure at a molar ratio R8F(EO)9/Si equal to 0.1. R8F(EO)9 micelles have a cylindrical shape, which have a core/shell structure ordered in a hexagonal system. The core contains the R8F part and the shell is a mixture of (EO)9 embedded in the silica matrix. We further evidence that the extraction of the template using supercritical carbon dioxide can be successfully achieved. This can be attributed to both the low solubility parameter of the surfactants and the fluorine and ethylene oxide CO2-philic groups. The initial 2D rectangular structure was well preserved after depressurization of the cell and removal of the surfactant. We attribute the very high stability of the rinsed film to the large value of the wall thickness relatively to the small pore size.

Investigation of mixed fluorinated and triblock copolymer liquid crystals: imprint for mesostructured bimodal silica.

Due to the difference in «mutual phobicity¼ between fluorocarbon and hydrocarbon chains, mixtures of fluorinated and hydrogenated surfactants are excellent candidates to design bimodal systems having two types of mesopores. In literature, only a few papers deal with these bimodal systems. Here hexagonal liquid crystal mixtures of the polyoxyethylene fluoroalkyl ether [R(F)8(EO)9] and the Pluronic [P123] have been used to template this kind of mesostructure through the liquid crystal mechanism, which is barely considered. After the detailed investigation of the R(F)8(EO)9/P123/water liquid crystal domain, materials have been synthesized and characterized by small angle X-ray scattering, transmission electron microscopy and nitrogen adsorption-desorption analysis. Our results show that this system provides two separate pore sizes in the materials over the mesoporous range. The ratio between the small mesopores and the large ones depends on the proportion between the porogens in the mixture. Nonetheless, we also outline that a minimum quantity of silica is required to recover the two hexagonal networks.

A sensitive spectrofluorimetric method for the quantification of melamine residue in milk powder using the Mannich reaction in aqueous solutions.

The objective of this study was to develop a spectrofluorimetric method for the quantitative determination of melamine. The method was based on the complexation of melamine with a mixture of formaldehyde and chemicals including a ketone group, as described by the Mannich reaction. The complex was determined by spectrofluorimetric measurement as it is characterized by specific spectroscopic properties that are related to the chromophore of the ketone compounds. 1,3-Diphenylpropane-1,3-dione (DPPD) was tested as a ketone compound. The fluorescence spectrum of the complex presented a maximum of absorption at 325 nm.A quenching of the fluorescence occurred when melamine was added into the solution. The kinetic of fluorescence quenching was followed to determine quantitatively the melamine concentration. An internal standard was added to quantify melamine. The method was tested to determine the level of melamine in contaminated milk powder. The recovery value was 97% and the limit of detection was 0.007 µg mL(-1.)

Remediation of 4-nonylphenol in aqueous solution by using free radicals generated by the oxidative reactions.

INTRODUCTION: This study relates to use of zerovalent iron to generate hydroxyl free radicals and undergo subsequent oxidation to destroy 4-nonylphenol (NP) by mild process in aqueous solution and activation of oxygen gas (O2) at room temperature. This technology is based on a novel oxidative mechanism mediated by zerovalent iron rather than commonly used reduction mechanism. MATERIALS AND METHODS: A laboratory scale device consisting of a 250 ml pyrex serum vials fixed to a Vortex agitator was used. Different amounts of zerovalent iron powder (ZVI; 1, 10, and 30 g/l) at pH 4 and room temperature with bubbling of oxygen gas were investigated. RESULTS AND CONCLUSION: Experiments showed an observed degradation rate k (obs) directly proportional to the amount of iron. 4-Nonylphenol degradation reactions demonstrated first-order kinetics with a half-life of about 10.5 ± 0.5 and 3.5 ± 0.2 min when experiments were conducted at [ZVI] = 1 and 30 g/l respectively. Three analytical techniques were employed to monitor 4-nonylphenol degradation and mineralization: (1) spectrofluorimetry; (2) high-performance liquid chromatography; (3) total organic carbon meter (TOC meter). Results showed a complete disappearance of 4-nonylphenol after 20 min of contact with ZVI. The intermediate by-products of the reaction were not identified but the disappearance of NP was monitored by the three above-mentioned techniques.