Sonochemical preparation of high surface area MgAl2O4 spinel.

High surface area MgAl(2)O(4) has been synthesised by a sonochemical method. Two kinds of precursors were used, alkoxides and nitrates/acetates and in both cases nanostructured MgAl(2)O(4) was obtained. The effect of the addition of a surfactant during the sonication, cetyl trimethyl ammonium bromide, was also investigated. In the case of alkoxides precursors the as-made product is a mixture of hydroxides of aluminium and magnesium, while with nitrates/acetates a gel is obtained after sonication, containing the metal hydroxides and ammonium nitrate. Heating at 500 degrees C transforms the as-made products into MgAl(2)O(4) spinel phase. The surface area is up to 267 m(2)/g after treatment at 500 degrees C and 138 m(2)/g at 800 degrees C.

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.