Investigating antimicrobial behavior of thymol/Zn encapsulated hierarchically structured zeolite and thymol release kinetics

Abstract

A new bioactive material was proposed by encapsulating thymol molecules and Zn2+ cations within the post-modified intracrystalline voids of hierarchical zeolite X crystals. To enhance the accessibility of thymol molecules within zeolite X crystals, commercial zeolite samples underwent post-synthesis treatment involving consecutive aqueous KCl, NH4Cl, and Na2H2EDTA solutions. The gas adsorption method utilized the encapsulation of both Zn2+ cation and thymol molecules into the resulting hierarchical zeolite X framework, which demonstrated improved antimicrobial activity. While sole thymol-encapsulated zeolite X exhibited no antimicrobial activity against S. aureus, Zn2+ encapsulated zeolite X (ZnX), thymol encapsulated post-treated zeolite X (HX-thy), and both Zn2+ and thymol encapsulated post-treated zeolite X (ZnHX-thy) displayed zone of inhibition values of 18.7 mm, 25.0 mm, and 37.5 mm, respectively. Adding Zn2+ and creating a hierarchical pore system in the zeolite X framework altered the release profiles. The Higuchi kinetic release model has the highest R2 value to describe the process of thymol release from X-thy, whereas the Elovich release model has the best fitting profile of thymol release kinetics from ZnX-thy, HX-thy, and ZnHX-thy. Results indicate that thymol and Zn2+ containing hierarchical porous materials could be beneficial tools for obtaining enhanced antibacterial activity and stability with reduced degradation and volatility of thymol with extended protection against microbial attack due to the controlled release. These findings highlight an innovative approach to designing sustainable and green materials, utilizing modified porous networks that encapsulate natural antibacterial compounds with environmentally benign metal ions.