Electrochemically assisted self-assembly of mesoporous silica thin films.

Supported mesostructured thin films are of major importance for applications in optical, electrochemical and sensing devices. However, good performance is restricted to mesostructured phases ensuring good accessibility from the film surface, which would be straightforward with cylindrical pores oriented normal to the underlying support, but this remains challenging. Here, we demonstrate that electrochemistry is likely to induce self-assembly of surfactant-templated (organo)silica thin films on various conducting supports, homogeneously over wide areas. The method involves the application of a suitable cathodic potential to an electrode immersed in a surfactant-containing hydrolysed sol solution to generate the hydroxyl ions that are necessary to catalyse polycondensation of the precursors and self-assembly of hexagonally packed one-dimensional channels that grow perpendicularly to the electrode surface. The method is compatible with controlled and localized deposition on heterogeneous supports, opening the way to electrochemically driven nanolithography for designing complex patterns of widely accessible mesostructured materials.

Interactions of selenate with copper(I) oxide particles.

The chemical mechanisms responsible for the immobilization of selenate (SeO4(2-) from aqueous solutions on cuprite (Cu2O) particles were determined from batch experiments. This was achieved by performing both solution-phase analyses and characterization of solid particles by X-ray photoelectron spectroscopy and transmission electron microscopy techniques, after equilibration of cuprite particles with selenate-containing solutions at various pH values, solid-to-solution ratios, and ionic strengths. Two distinct mechanisms have been pointed out. In the acidic medium, where the acid-catalyzed dissolution of cuprite into CuI species occurs, the immobilization of selenate implies a redox reaction with transient CuI leading to the precipitation of copper(II) selenite, CuSeO3. In the absence of protons added in the medium, Cu2O is chemically stable and immobilization of SeO4(2-) is essentially due to adsorption in the form of an outer-sphere surface complex. The uptake level of selenate by Cu2O is markedly lower than that observed for selenite species in the same conditions.

Efficient in vitro paraquat removal via irreversible immobilization into zeolite particles.

A new efficient mineral adsorbent, zeolite ZSM-5, has been evaluated for its ability to durably immobilize the herbicide paraquat in conditions simulating acute poisoning by oral ingestion of this toxic compound. The sorption properties have been studied in water, normal saline solution, as well as in artificial and simulated human gastric juices. Uptake kinetics and capacities have been determined and compared to the ion exchange resin Amberlite IR-120. Significant advantages of ZSM-5 over the resin have been demonstrated, especially with respect to long-term retention capability of the toxic herbicide. This solid is a promising primary treatment of acute paraquat poisoning.

In situ investigation of the ionisation of silica in aqueous ammonia by using a high frequency dielectric method.

The reaction of silica gel and Stöber beads of silica with ammonia was studied in aqueous medium using a high frequency dielectric method. Measurements of the complex impedance of silica pulps in both static and dynamic modes were found to be a new rapid, sensitive and non-destructive way for the in situ characterisation of the surface silica ionisation process in aqueous ammonia. The influence of various parameters (field frequency, ionic strength, ammonia concentration) was discussed. The apparent equilibrium constant for the following reaction (SiOH) + NH(3)<-->(SiO(-)NH(4)(+)) was found to be strongly affected by the degree of dissociation of both silica samples, so that the complete neutralisation was never observed. The porosity of the Stöber silica towards the NH(3) species was demonstrated experimentally through the formation of (SiO(-)NH(4)(+)) entities in the interior of the silica beads. The reversibility of the neutralisation reaction was applied to successive on-column analysis for which the hydrolysis of ammoniated silica was found to be catalysed by the presence of acids.