Kristof Cassiers

Controlled formation of amine-templated mesostructured zirconia with remarkably high thermal stability

In order to control the reactivity of the inorganic precursor and the hybrid formation, the evaporation induced self-assembly procedure (EISA) has been applied to direct alkyl amines into zirconia hybrid composites. It is demonstrated that, with controlled water amounts, a mesostructured wormhole-like high-surface-area zirconia can be formed but the mesostructure collapses due to massive crystallisation of the zirconia walls into tetragonal zirconia as the calcination temperature rises to 400 °C. To overcome the lack in thermal stability, zirconia hybrids are treated in aqueous ammonia to protect the primary particles in the zirconia walls against uncontrolled particle growth and crystallisation. The growth of the initially amorphous zirconia particles in the walls is limited by increasing the condensation degree upon ammonia treatment resulting in mesostructured zirconia consisting of nanosized ‘tetragonal’ particles at higher temperatures. It is shown that the alkaline-treated zirconias have a remarkable thermal stability with retention of most physical characteristics such as high surface area, pore volume and mesoporosity up to a temperature of 800 °C.

Synthesis of stable and directly usable hexagonal mesoporous silica by efficient amine extraction in acidified water

The amine template of hexagonal mesoporous silica (HMS) can be efficiently recovered and re-used by a new extraction procedure in acidified water rendering a directly usable high quality mesoporous support.

A new strategy towards ultra stable mesoporous titania with nanosized anatase walls

A new and generally applicable synthesis procedure is developed in order to synthesise micelle-templated mesoporous titania built up of nanosized anatase walls with thermal stability up to 600 degrees C.

Novel strategies towards mesoporous titania and titania-silicate composites

Abstract Two new pathways are developed to synthesize thermally stable and highly porous structures of nanosized anatase (titanium dioxide). The first is a new synthesis route towards mesoporous titania, based on an amine or CTABr-templating procedure. By a post-treatment of the titania hybrids in aqueous ammonia, a method has been developed to increase the thermal stability of the mesostructured titania up to 600°C. Parts of the amorphous titania walls of the NH 3 -treated titania hybrids are first transferred into rutile nano building blocks before the template is thermally removed. After a subsequent increase in temperature, the remaining amorphous particles are transformed into anatase with retention of the pore structure. This leads to ordered high surface area (up to 600 m 2 /g) mesostructured titania having a pore volume up to 0.28 cm 3 /g and an outstanding thermal stability. In a second pathway, thermally stable composite nanostructures of titanium dioxide (anatase) and silicate nanoparticles are prepared from laponite clay and a sol of titanium hydrate in the presence of PEO surfactants. The acidic sol solution reacts with the clay platelets and leaches out most of the magnesium in the clay, while the sol particles hydrolyze further due to the high pH of the clay dispersion. Large precursors of TiO 2 nanoparticles are formed and condense on the fragmentized pieces of the leached silicate, leading to surface areas and pore volumes up to 627 m 2 /g and 0.741 cm 3 /g.

The synthesis and hydrothermal stability of directly usable hexagonal mesoporous silica by efficient primary amine template extraction in acidified water

Publisher Summary This chapter discusses the synthesis and hydrothermal stability of directly usable hexagonal mesoporous silica (HMS) by efficient primary amine template extraction in acidified water. This very efficient extraction (100%) does not affect the physical properties of the resulting mesostructure. Compared to the ethanol-extracted HMS, no subsequent calcination step is required to remove the surface ethoxy groups produced during the ethanol extraction. The recovered surfactant can be easily re-used in a fresh synthesis. An improved hydrothermal stability is also observed after using the acidified water-extraction procedure.