(217r) Microencapsulation of Hydrogen Peroxide

Hydrogen peroxide is an environmentally friendly oxidant whose disproportionation products are oxygen and water, with applications ranging from sterilization to catalysis. The shelf-life of hydrogen peroxide is very limited due to its propensity to disproportionate exothermally (activation energy of the reaction is ~75 kJ/mol) in the presence of certain catalytic impurities such as metal ions. Aqueous solutions of H₂O₂ can be stabilized in the presence of acid, which can promote peroxide encapsulation into stable matrices of certain size. Lipid gels and biodegradable polymer matrices containing hydrogen peroxide are known, but organic matrices tend to degrade upon storage and/or allow for rapid H₂O₂ release in the presence of moisture. In the present work, a two-step strategy toward microencapsulation of hydrogen peroxide into silica (SiO₂) core-shell structures is developed. The first step involves stabilization of acidic H₂O₂ solutions by ortho-silicic acid, which forms xerogels upon polymerization and drying. Under certain conditions, the resulting xerogels contain variable, but significant (up to  60 wt%) fractions of hydrogen peroxide, which can be readily released into the environment by shearing xerogel matrices.  The xerogel particles are further encapsulated by tetraethoxysilane and other, functional silanes using Stöber method. The morphology, hydrogen peroxide loading, and release rates of hydrogen peroxide at different temperatures are discussed.