(639b) Effect of Size and Charge of Metal IONS on Hydrogen Peroxide Stability in Silica Hydrogels

Currently, the most efficient method to increase the stability of hydrogen peroxide (H₂O₂) is microencapsulation in silica hydrogels and xerogels via environmentally-friendly sol-gel chemistry using sodium silicate as the starting precursor. The high stability of H₂O₂ in these systems arises from strong hydrogen bonding between silanol groups (Si-OH) and peroxide molecules. Our previous study showed that the amount of Na⁺ ions have a strong effect on the structure and morphology of hydrogels. Therefore in the present work, the effect of the size and charge of the ions other than Na⁺ on the properties of the hydrogel and stability of peroxide is studied. Monovalent (K⁺) and divalent (Mg⁺², Ca⁺²) ions were introduced into the sodium silicate precursor in the form of their respective salts. The pH of the sol was changed by using an ion exchange resin to replace a portion of the ions in the solution with H⁺ ions. Gelation time and structure, pH of the sol, stability and release rate of H₂O₂ in hydrogels are investigated for each ion. Results showed that the stability and release rate can be adjusted to the desired level by changing the ion content and pH of the sol. The increase in total ion concentration in the sol resulted in a decrease in gel time and the best H₂O₂ stability was obtained with the addition of the magnesium salt: seventy percent of the peroxide was retained in hydrogels containing Mg²⁺ ions, as compared to 61 % retention with hydrogels containing Na⁺ ions at the end of 70 days. Hydrogels are characterized by using scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET) analysis.