Surface modification of transition metal oxide mesoporous thin films and xerogels

PAULA C. ANGELOMÉ; SARA A. BILMES; MIGUEL BLESA; GALO J. A. A. SOLER-ILLIA

Conferencia; 11th International Conference on Surface and Colloid Science; 2003

Mesostructured and mesoporous networks are one of the most striking examples of nanostructured advanced materials. The construction of these networks can be tailored by the adequate combination of sol-gel and self-assembly techniques, tuning the hydrolysis-condensation of the metallic cations with the organization behavior of the organic counterparts. A great deal of work has been accomplished on silica and transition-metal (TM) based oxides, which can be processed as powders, films or fibers, displaying high surface areas (200-1000 m2/g), and controlled pore arrays with great variety of mesostructures (2D- or 3D- Hexagonal, micellar or bicontinuous cubic,…). A further step in the development of these materials is the ability to modify the pore surface, to develop mesoporous structures with well-defined functionalities, which can provide a particular property to the material. This is particularly important in view of advanced applications (i.e., sensors, actuators, controlled delivery devices…). The simplest approach is to post-functionalize a mesoporous oxide phase, by grafting organic, or organometallic groups. TM oxides present a double interest: a) nanocrystalline walls with remarkable electronic properties, b) the possibility to be functionalized by using complexing agents such as phosphate, phosphonate, acetylacetonate or carboxylate. In this work, titania and zirconia mesoporous films or xerogels with 2D-Hex (p6m) or Im3m cubic mesostructure and nanocrystalline walls were prepared by evaporation-induced self-assembly (EISA), using poly(ethylene oxide)-based block copolymers as structure directing agents. Organic molecules presenting complexing grafting groups and diverse functions (phenyl, alkyl, thiol, amine, hydroxy…) were explored as surface modifiers. The incorporation of these functions to the mesoporous network was monitored by FT-IR, EDS, XRF. Phosphate or acetylacetonate grafting groups lead to higher incorporation and less ‘bleeding’ than carboxylate grafting groups. A dramatic difference between the incorporation of functions in mesoporous materials compared to non-mesoporous films or gels is observed. Furthermore, the polarity of the pore surface was explored by means of incorporating fluorescent probes (cresyl violet, erythrosine B) inside the pore network, and analyzing the optical behavior.