Structural Evolution upon Thermal Heating of Nanostructured Inorganic−Organic Hybrid Materials to Binary Oxides MO2−SiO2 (M = Hf, Zr) as Evaluated by Solid-State NMR and FTIR Spectroscopy

Abstract

The structural and compositional evolution of inorganic−organic silica-based hybrid materials and their conversion to mixed oxides, consisting of host silica with variable amounts of zirconia or hafnia (1:1 Si:M, 40:1 Si:M, M = Zr, Hf), was studied by multinuclear solid-state NMR spectroscopy, FTIR spectroscopy, and thermogravimetry. It is shown that the as-prepared materials, composed of M4O2(OMc)12 oxoclusters (M = Zr, Hf; OMc = methacrylate) and methacryloxymethyltriethoxysilane (MAPTMS), are not completely polymerized. Rather, a finite number of double bonds remain independent of the actual sample composition. Thermolysis between 300 and 500 °C is accompanied by drastic changes in the structural composition, as reflected by the complete loss of all organic components. The incorporation of oxoclusters is found to catalyze the cleavage of Si−C bonds. At the same time, continuous alterations in the inorganic/oxide part are registered. The degree of condensation, as derived from the 29Si NMR data, increas...