Properties of Hydrogen Peroxide Encapsulated in Silica Hydrogels and Xerogels

Hydrogen peroxide (H2O2) was entrapped in silica hydrogels using the sol gel approach, and its transition to xerogel was studied by monitoring H2O2 retention as a function of weight loss at ambient temperature. The transition took place in different drying regimes, and the maximum H(2)O(2)concentration was obtained at 80% weight loss of the initial hydrogel. The stability of H2O2 at a higher initial concentration of 33.2 wt % was studied and found to be comparable to the values obtained with hydrogels having lower initial concentrations (10-20 wt %). The release rate of entrapped H2O2 from silica gel was studied as a function of the initial H2O2 concentration, the sodium content of the gel, the pH of the aqueous medium, and the form of the gel (hydrogel/xerogel). The release occurred via a hiphasic process, with an initial fast liberation during the first 10 min where 60-70% of the H2O2 was released, followed by a much slower release rate from 10 to 60 min. The release rate was independent of the initial H2O2 concentration but was affected significantly by the other parameters. Thermal stability of the silica gels was studied using thermogravimetric analysis, and was found to depend strongly on the sodium content. The form of the gel (hydrogel/xerogel) did not have an appreciable effect on the thermal stability. Substituting sodium partially with magnesium decreased the gelation time and increased the stability of entrapped H2O2.