Mesostrucutres obtained by Self Assembly Processes. From Multifunctional porous materials to ordered nanocomposites

PAULA C. ANGELOMÉ; EUGENIO OTAL; DIEGO N. PASSARELLA; M. CECILIA FUERTES; SARA A. BILMES; GALO J. A. A. SOLER-ILLIA

Workshop; Frontiers in Materials Research (a CIAM-CIMAT-CONICYT Workshop); 2004

Mesostructured materials can be synthesised by the combination of sol-gel chemistry and self-assembly. A striking example is the synthesis of supramolecularly templated mesoporous oxides (MPO), which can be produced and processed as powders or films, displaying a great variety of mesostructures with controlled pore size, wall thickness, wall composition, pore system symmetry. Once these structures have been designed and constructed, their surface can be further modified with organic functions, obtained either by one-pot or post-grafting methods, which lead to multifunctional materials. The regular pore size and surface control also makes the pore systems ideal candidates for nanoparticle (NP) templates, leading to NP@MPO composites, which can be tailored to combine the properties of two kinds of nanometric size elements, which are in intimate contact through an extended interface, all combined in a robust matrix. In this work, we present examples of multifunctional mesoporous films, created by adding organic functions to MP silica or transition metal oxides (TMO, such as TiO2 or ZrO2). Organic molecules bearing grafting (phosphate, phosphonate, diolate, carboxylate...) and functional (hydrophobic, ionic, metallophilic) groups are used to perform functionalisation. Grafting kinetics have been followed in order to assess pore accessibility and to optimise function incorporation. Diffusion is relatively quick for thin films or small particles; however, mass transport seems to be limiting function uptake in particles larger than 1-2 micrometers. Leaching experiments show that phosphate are better anchoring groups than diolate or carboxylate. Multilayered films with compositional or pore size differences are also presented. Cation adsorption into the pore systems of these films has been monitored, and metal uptake has been found dependent on the pH and surface chemistry of the host oxide. Reducing conditions (chemical or electrochemical) have been employed to generate Au, Ag, Fe or Cu metallic particles within the pores, generating robust nanocomposites with interesting properties.