High surface area ordered mesoporous nano-titania by a rapid surfactant-free approach

Immersion of solid nanorods of the commercial metal–organic precursor [Ti(OCH3)4]4 into boilingwater results in their rapid topotactic transformation into rod-shaped colloid crystals built up ofuniform crystalline anatase nanoparticles with average particle diameter 5.0 +/- 1 nm forming ratherregular wormhole-type mesoporosity with average pore diameter 4.1 nm and a record-high surface areaand mesopore volume of 288 m2 g-1 and 0.42 cm3 g-1 respectively. This structure emerges throughreorganization of the intermediate ordered mesoporous lamellar structure. The distance betweenlamellae is about 3 nm. They are oriented parallel to the {1 0 0} crystallographic direction in theprecursor crystals and originate most probably through contraction and densification of the layers ofprecursor molecules in the course of the process. Similar mechanisms are observed even for hydrolytictransformation of nanocrystals of other alkoxide precursors, derivatives of volatile alcohols, permittingto achieve surface area up to 350 m2 g-1. The obtained material is completely free from organics, buthighly hygroscopic. Powders produced within 3 min show very broad X-ray diffraction peaks,indicating low volume coherence domains, but continued refluxing offers a strongly improved XPDpattern after 10 min and a fully crystalline material with coherence domain equivalent to the individualparticle size after only 30 min. The latter material exhibits well defined Ti–Ti distances in the structuretypical for a crystalline anatase phase according to EXAFS spectroscopy. It displays strongphotochemical activity in destruction of methylene blue dye. When an aqueous dispersion ofsuperparamagnetic Fe3O4 nanoparticles is applied for hydrolysis the product is a magneticnanocomposite, easily and rapidly removable from solution by a magnet. The produced fully crystallineporous TiO2 possesses attractive characteristics as an adsorbent for water remediation tested throughadsorption of dichromate anions.