Encapsulation and controlled release of isothiazolinones in zeolite NaY (FAU)

Abstract

NaY zeolite, an ordered, large pore molecular sieve pertaining to the FAU zeolite structural group, was studied as a novel matrix for the efficient preparation of a supported isothiazolinone-based biocide, and the results were compared to those corresponding to mesoporous silicas. To analyze the possibility of reducing the biocide ecotoxicity by encapsulation, a commercial biocide used for latex preservation (CMIT/MIT) was incorporated in the NaY zeolite structure by using two different methodologies: equilibrium adsorption (Zeo/Bio sample) and impregnation by total wetting (Zeo/Impreg sample). In the corresponding release tests, despite the large difference in the initial biocide amount released, the shape of the curve is nearly the same for both methods. Microbiological tests against fungi and bacteria were performed. The obtained results were compared to those previously obtained using mesoporous ordered silica SBA-15 and mesoporous foam MCF matrices (mesoporous/ biocide samples named SBA-15/Bio, SBA-15/Impreg and MCF/Bio and MCF/Impreg respectively). For the Staphylococcus aureus the results from agar well diffusion assay shows that the inhibition zone is about 64 mm for Zeo/Impreg and about 55 mm for Zeo/Bio. As regards all the other materials, the inhibition zone does not exceed 46 mm. In the case of Escherichia coli, Zeo/Bio and Zeo/Impreg have an inhibition zone of about 43 and 37 mm, respectively. No one of the other materials shows an inhibition zone larger than 30 mm. Zeo/Impreg showed a greater inhibition zone against fungi (47 mm versus Chaetomium globosum and 53 mm versus Alternaria alternata, respectively) than SBA-15 and MCF impregnated with biocide.