Water-Stable, Nonsiliceous Hybrid Materials with Tunable Porosity and Functionality: Bridged Titania-Bisphosphonates

Abstract

Combining the properties of organic and inorganic moieties with high surface areas and pore volumes offers endless possibilities to design materials adapted to a wide range of advanced applications. The vast majority of mesoporous hybrid materials are siliceous materials, and developing low-cost synthetic methodologies leading to water stable nonsiliceous hybrid materials with controlled texture and functionality is essential. We report here an original strategy for the synthesis of mesoporous bridged titania-bisphosphonate hybrids based on a one-step, templateless nonhydrolytic sol–gel route. The reaction of Ti(OiPr)4 and a rigid bisphosphonate ester in the presence of Ac2O leads to the formation of TiO2 anatase nanorods cross-linked by fully condensed bisphosphonate groups. The porosity can be readily adjusted over a wide range by changing the reaction conditions, and very high specific surface areas (up to 720 m2 g–1) and pore volumes (up to 1.85 cm3 g–1) can be reached. The texture is stable in aqueous media between pH 1 and pH 12. Furthermore, accessible functional organic groups can be easily incorporated using either functional bisphosphonates or easily available monophosphonate compounds. The accessibility of bipyridyl organic groups was checked by Cu2+ adsorption from aqueous solutions. The unique combination of texture, functionality, and stability displayed by bridged titania-bisphosphonates makes these promising materials complementary of other hybrid materials such as organosilicas, MOFs, or mesoporous metal phosphonates.