Infrared spectroscopic study of sol–gel derived mixed-metal oxides

Binary, mixed-metal oxides of silicon–aluminum, silicon–cobalt, silicon–copper, silicon–iron, and silicon–nickel were produced via a sol–gel method and characterized with in situ Fourier transform infrared (FTIR) spectroscopy over the temperature range from 30°C to 350°C. Characteristic Si–O–Si IR stretches, observed at 1086 and 798 cm−1, shifted to lower frequencies as the second metal oxide was introduced to the system, suggesting a weakening of the Si–O–Si network. In addition, new peaks observed in the 600–700 cm−1 range were assigned to silicon–oxygen–metal vibrations providing further evidence that the second metal was chemically incorporated into the gel network. Heating these mixed-metal oxides to 350°C only dehydroxylated the surface, with no other structural changes observed. This result indicated that the mixed-metal oxide structure, including silicon–oxygen–metal bonds, was formed during the synthesis and drying stages at relatively low temperatures (i.e., 90–110°C).