Catalytic activity of acid and base with different concentration on sol–gel kinetics of silica by ultrasonic method

• During the sol gel reaction of tri ethyl ortho silicate continuous decreases of the ultrasonic wave velocity was observed in the reaction medium as gelation proceeds.
• Ultrasonic wave velocity change is dependent on the change in bulk modulus due to hydrolysis and condensation.
• Faster gelation results by base catalysis.
• Acid catalysis produces more agglomeration.
• Nanosilica produced are amorphous in nature.

The effects of both acid (acetic acid) and base (ammonia) catalysts in varying on the sol–gel synthesis of SiO2 nanoparticles using tetra ethyl ortho silicate (TEOS) as a precursor was determined by ultrasonic method. The ultrasonic velocity was received by pulsar receiver. The ultrasonic velocity in the sol and the parameter ΔT (time difference between the original pulse and first back wall echo of the sol) was varied with time of gelation. The graphs of ln[ln 1/ΔT] vs ln(t), indicate two region – nonlinear region and a linear region. The time corresponds to the point at which the non-linear region change to linear region is considered as gel time for the respective solutions. Gelation time is found to be dependent on the concentration and types of catalyst and is found from the graphs based on Avrami equation. The rate of condensation is found to be faster for base catalyst. The gelation process was also characterized by viscosity measurement. Normal sol–gel process was also carried out along with the ultrasonic one to compare the effectiveness of ultrasonic. The silica gel was calcined and the powdered sample was characterized with scanning electron microscopy, energy dispersive spectra, X-ray diffractogram, and FTIR spectroscopy.