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 degreesC to 350 degreesC. 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-l 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 degreesC 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 degreesC). (C) 2001 Elsevier Science B.V. All rights reserved.