Size matters: incorporation of poly(acrylic acid) and small molecules into hierarchically porous metal oxides prepared with and without templates

Abstract

Template synthesis of metal oxides can create materials with highly controlled and reproducible pore structures that can be optimized for particular applications. Zirconium titanium oxides (25:75 mol %) with three different pore structures were synthesized in order to relate polymer loading capacity to macropore architecture. Sol−gel chemistry was used to prepare the materials in conjunction with (i) agarose gel templating, (ii) no template, and (iii) stearic acid templating. The three materials possessed high surface areas (212−316 m2 g−1). Surface modification was performed postsynthetically using propionic acid (a monomer), glutaric acid (a dimer), and three molecular weights of poly(acrylic acid) (2000, 100000, and 250000 g mol−1). Higher loading (mg g−1) was observed for the polymers than for the small molecules. Following surface modification, a perceptible decrease in surface area and mesopore volume was noted, but both mesoporosity and macroporosity were retained. The pore architecture had a strong bearing on the quantity and rate of polymer incorporation into metal oxides. The templated pellet with hierarchical porosity outperformed the nontemplated powder and the mesoporous monolith (in both loading capacity and surface coverage). The materials were subjected to irradiation with 60Co γ-rays to determine the radiolytic stability of the inorganic support and the hybrid material containing the monomer, dimer, and polymer. The polymer and the metal oxide substrate demonstrated notable radiolytic stability. © 2010, American Chemical Society