Template-free sol-gel synthesis of hierarchically macro- and mesoporous monolithic TiO2

Monolithic titania exhibiting a hierarchical, bimodal meso-macroporosity has been prepared through a template free sol-gel synthesis route. The macropore diameter can be controllably varied in the range 0.4-4 mu m still maintaining a narrow pore size distribution. The macropores form as a consequence of parallel gelation and microscopic phase separation, where their relative kinetics determine the macropore diameter. We utilize the chelating property of acetic acid to control the kinetics of the reaction, which allows the synthesis to be carried out without the addition of otherwise commonly used hydrogen-bonding polymers or surfactants. The synthesis is thus both interesting from an economical and an environmental point of view. In addition to macropores, the monoliths also contain textural mesopores, which makes the monoliths interesting for chromatographic and catalytic applications.