Hierarchically Porous Rutile Titania: Harnessing Spontaneous Compositional Change in Mixed-Metal Oxides

In numerous applications involving fluid flow through a porous structure, performance improvements, such as better flow characteristics and increased fluid−solid contact, are obtained when multiple length scales of porosity are present in the porous medium. To this end, we have developed a route to hierarchically porous rutile titania that obviates the need for preformed or preassembled structure-directing agents. The preparation involves the successive leaching of phases and components from a dense composite of wurtzite ZnO and inverse spinel Zn 2 TiO 4 . The resulting monoliths are composed of grains of highly crystalline rutile titania and possess a hierarchy of interconnected pores with length scales of 5 μm and 100 nm. Ex situ solid-state 67 Zn and 47,49 Ti NMR has helped probe local environments around these elements in both the mixed and pure crystalline materials that are formed during the leaching processes.