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A new solvent-exchange method for preparation of undoped anatase TiO2 nanoparticles with unprecedented thermal stability has been presented.

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a b s t r a c tWe propose in this manuscript a new peroxo-mediated procedure for preparing magnesia-zirconia mixed oxides, with Mg/Zr molar ratio between 1 and 3, with enhanced distribution of basic sites. The mixed magnesia-zirconia oxides have been prepared from the gelled complex by Pechini-type method. The MgO-ZrO 2 materials have been characterized and used as catalysts for acetone aldol condensation. The proposed preparation method provides a high degree of molecular homogeneity and favours the formation of magnesia-stabilized zirconia phase. Acetone gas-phase self-condensation was carried out over these catalysts as model reaction requiring the presence of basic sites. The condensation yields diacetone alcohol and mesityl oxide as mean C6 products, and phorones, isophorones and mesitylene as C9 products. In comparison to Mg-Zr oxide prepared by co-precipitation, these new materials present better conversions and higher selectivity to linear dimers and trimers (as mesitylene), whereas the selectivity for isophorones is significantly lower.

Composite microporous SiO2-TiO2 spheres and micro/mesoporous TiO2 spheres were prepared via the template-free two-step synthetic route using aqueous peroxotitanate solution and tetraethyl orthtosilicate (TEOS) as precursors. Both the composite SiO2-TiO2 and pure TiO2 spheres prepared by the solventexchange method were initially non-porous, but the applied reflux treatment in water-ethanol suspension successfully transformed them into microporous materials with high apparent surface areas approaching 500 m 2 •g-1 and the micropore volume of 0.17 cm 3 •g-1 , while maintaining the same morphology. The prepared composites retained high values of pore volume and specific surface area up to 400 ºC of thermal treatment temperature. The crystallization of TiO2 into the anatase phase in the mixed oxide occurred only at 700 ºC, that process was also accompanied by the significant reduction of pore volume, as well as apparent surface area values. Both synthesized composite oxides and pure titania were tested, in aqueous media, on the lead(II) removal; they demonstrated high adsorption capacities, reaching 340 mg(Pb 2+)•g-1. Moreover, the mixed silica-titania oxide was found to be more efficient adsorbent at low pH values.