Deposition and thermal transformation of metal oxides in mesoporous SBA-15 silica with hydrophobic mesopores

• Eight metal oxides were deposited in the SBA-15 with hydrophobic mesopores.
• Thermal transformation of the deposited oxides was studied.
• The oxides of Fe, Al and Cu were mainly located in the micropores of SBA-15.
• Ni, Zr and Ce tended to form crystalline oxide nanoparticles in the mesopores.
• The oxides of Zn and Cd transformed to metal silicates at 800 °C.

We have previously shown that mesoporous SBA-15 silica with hydrophobic mesopores can be applied to deposit nanosized metals or metal oxides selectively in the intra-wall micropores for catalysis and adsorption/separation of proteins. In this study, we extended the idea to deposit various metal salts in the SBA-15 support and study the influences of the nano-confinement of micropores on the structural and textural properties of the resulting nanocomposite materials after heat treatment at temperatures up to 800 °C. Nitrate salts of metals including iron, aluminum, copper, nickel, zirconium, cerium, zinc and cadmium were incorporated to the support with a nominal metal-to-silicon ratio of 0.2. We found that most of the metals transformed into highly dispersed oxide nanoparticles in host silica and, depending on the type of metal and the temperature of heat treatment, various degrees of pore clogging and/or decrease in mesostructural ordering were observed. Moreover, at 800 °C, the oxide species in the zinc- and cadmium-containing materials transformed to metal silicates that were rarely formed under similar conditions. The observations were discussed based on the surface free energy of metal oxides and the phase diagrams of zinc and cadmium oxides with silica. The results show that, from both the viewpoints of materials synthesis and applications, the SBA-15 with hydrophobic mesopores is a unique support to prepare oxide-containing nanocomposite materials.

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