Kinetics study on the sol-gel reactions in supercritical CO2 by using in situ ATR-FTIR spectrometry

Direct sol-gel processing in supercritical CO2 (ScCO2) has been of significant interest for synthesizing oxide nanomaterials, and the reactions of metal alkoxides with organic acids have been extensively used for preparing metal complex crystals; however, a kinetics analysis of these reactions has not been reported. In this research, in situ ATR-FTIR spectra were collected during the sol-gel synthesis of Si, Ti, and Zr oxides in scCO(2). Because of overlapping of the IR peaks, it was difficult to directly correlate the optical absorbance with the analyte concentrations. To solve this problem, we used a chemometrics method, simple-to-use interactive self-modeling mixture analysis (SIMPLISMA), to calculate the concentration profiles. The precursor conversions and the intermediate concentration profiles under different synthesis conditions were obtained. The different kinetics profiles of Ti and Zr complexes in the sol-gel reactions were related to the activity of the metal complexes, and the competition of the various condensation reactions.