Adsorption of bentazone herbicide onto mesoporous silica: application to environmental water purification.

Within the last few years, the presence of bentazone herbicide has been observed in many water resources. For the first time, removal of bentazone using mesoporous silica was investigated revealing reversible adsorption. The adsorption isotherm was well described using the Freundlich model. The affinity towards bentazone is strongly affected by pH in the range of 2-7, decreasing with the increase of the pH, becoming negligible at the neutrality. Regeneration of the adsorbent was possible, and a recovery as high as 70 % was obtained using CH3OH-NaOH solution. Furthermore, appreciable recovery (47 %) was also obtained using water. Applications on the purification of lake water and wastewaters, both characterized by a significant organic carbon load, spiked with 2 mg L(-1) bentazone were tested, observing removal yields in the range of 61-73 %. Taking advantage of the fast adsorption kinetics observed, an in-flow purification treatment was set-up, with quantitative removal of bentazone from polluted water.

Gold-assisted E' centres formation on the silica surface of Au/SBA-15 catalysts for low temperature CO oxidation.

SH-functionalized SBA-15 was synthesized and gold nanoclusters were grafted inside its channels. Different portions of such gold-containing material were subjected to a variety of thermal treatments, including calcination in the 300-560 °C temperature range and further treatments under a hydrogen atmosphere at diverse temperatures (up to 600 °C). The resulting materials were thoroughly characterized by CHS elemental analysis, X-ray diffraction, transmission electron microscopy, N2 physisorption and H2 chemisorption, as well as by Raman, NMR, FTIR and EPR spectroscopies, in order to investigate the influence of the temperature and atmosphere of the pretreatment on the gold particle size and oxidation state, the formation of defective E' centres on the silica support and their ability to induce the formation of reactive O2(-) surface species. Catalytic testing for the CO oxidation reaction was carried out in the 40-150 °C temperature range. Significant differences in catalytic behaviour were observed among the catalysts, which are discussed in the light of the characterization results. A mechanism for the "activation" of the non-reducible ("inert") SBA-15 support involving Au(0)→ Au(+) transformation is proposed, where gold metal plays an essential twofold role: it induces the formation of atomic hydrogen by dissociatively adsorbing H2 and triggers the formation of E' centres by transferring an electron to positively charged silicon species.

SBA-15 ordered mesoporous silica inside a bioactive glass-ceramic scaffold for local drug delivery.

The paper reports the synthesis of an ordered silica mesostructure of the SBA-15 type inside a macroporous bioactive glass-ceramic scaffold of the type SiO(2)-CaO-K(2)O, to combine the bioactivity of the latter with the release properties of the former, in view of local drug delivery from implants designed for tissue engineering. The standard procedure for SBA-15 synthesis has been modified to minimize the damage to the scaffold caused by the acidic synthesis medium. The composite system has been characterized by means of Scanning Electron Microscopy (coupled with EDS analysis), Small Angle X-Ray Diffraction, Thermogravimetry analysis and Infrared Spectroscopy: the formation of a well ordered hexagonal mesostructure was confirmed. Ibuprofen has been chosen as model drug. The uploading properties have been investigated of the scaffold-mesoporous silica composite as compared with the scaffold as such, and a five-fold increase in the adsorbing properties toward ibuprofen was found, due to the presence of the ordered mesoporous silica. The ibuprofen release to a SBF solution in vitro is complete in 1 day. Retention of bioactivity from the glass-ceramic scaffold after the silica mesostructure incorporation has been observed.

Vapor-phase self-assembled monolayers of aminosilane on plasma-activated silicon substrates.

Aminosilane self-assembled monolayers on silicon substrates have been prepared via a gas-phase procedure based on the consecutive reactions of the aminosilane precursor and water vapor. X-ray photoelectron spectroscopy, atomic force microscopy, and contact angle measurements have been used to characterize the aminosilane layers. For comparison, substrates modified with aminosilane through a liquid-phase procedure have been prepared and characterized by means of the same techniques. The vapor-based procedure was found to yield more uniform layers characterized by fewer and smaller aggregates as compared with liquid-treated substrates. Grazing angles reflection Fourier transform infrared measurements were carried out on the vapor-treated substrates before and after water exposure to investigate the hydrolysis of the alkoxy groups and further reaction to form siloxane bonds. The surface density of amino groups, as estimated through a colorimetric method, is very similar for vapor- and liquid-treated substrates, suggesting a similar reactivity and accessibility of the functional groups on the surface.

Hydroxyl species in large-pore phenylene-bridged periodic mesoporous organosilica.

Silanol species in phenylene-bridged periodic mesoporous organosilica (PMO), templated via tri-block copolymer Pluronic P123 and thus characterized by large pores and amorphous wall structure, have been characterized by means of FT-IR spectroscopy. Investigation has been carried out on both the naked sample outgassed at different temperatures and the sample when interacting with molecular probes able to form H-bonding (ammonia and carbon monoxide). After outgassing at 773 K, the material shows both isolated silanols and silanols engaged in "intraframework" H-bonding with the pi-cloud of structural aromatic rings. Interaction with ammonia showed that a fraction of these species is inaccessible, being probably located inside the pore walls. Thermal treatment above 673 K causes the appearance of SiO3(OH) species formed as a consequence of the cleavage of some Si-C bonds. The presence of hydroxyls slightly more acidic than isolated silanols has been evidenced: these are interpreted as perturbed geminal species.

IR detection of NO2 using p+ porous silicon as a high sensitivity sensor.

Mesoporous silicon doped with 3.0 x 10(19) B atoms cm-3 (p(+)-type) is an insulating material which dramatically increases its electrical conductivity when exposed to traces of gaseous NO2; nitrogen dioxide chemisorption at the surface generates carriers, the population of which is readily evaluated through the intensity of IR absorption.

Permeability of micelles in surfactant-containing MCM-41 silica as monitored by embedded dye molecules.

Mesoporosu (MCM-41 type) silica containing surfactant-embedded Congo Red has been prepared and tested against gas phase HCl and ammonia, as well as solutions of ionic species; it is shown that the hybrid (organic-inorganic) material is permeable to both gases and ionic species, and can act as a pH indicator and as a selective chelating agent.