Prolonged Antimicrobial Effects of Eucalyptus Oil via C₈-Functionalized Silica Monolith

This study presents the synthesis and characterization of a mesoporous silica-based monolith functionalized with octyl (C₈) groups, developed as an absorbent for the controlled release of Eucalyptus oil (Eu-oil). The C₈-silica monolith was prepared via a two-step acid/base-catalyzed sol-gel process and characterized using various analytical techniques. Chemical profiling of the Eu-oil and Eu-oil-loaded monolith was conducted using gas chromatography-mass spectrometry (GC-MS). Evaporation tests revealed that Eu-oil exhibited rapid volatilization within 24 h, whereas Eu-oil-loaded on the C₈-monolith had a markedly slower release. The GC-MS analysis confirmed that the monolith effectively retained volatile constituents, particularly eucalyptol, β-myrcene, and γ-terpinene, thereby extending the release of bioactive compounds. Antimicrobial assays showed that Eu-oil delivered via the monolith maintained bacteriostatic activity against Escherichia coli and Staphylococcus aureus for up to 7 days, outperforming the rapid activity loss observed with Eu-oil applied on filter discs. Similarly, antifungal tests against Aspergillus sp. isolated from garlic demonstrated prolonged suppression of fungal growth. Kinetic modeling further confirmed that the Eu-oil release followed a concentration-dependent, diffusion-assisted mechanism, which was best described by the first-order and Weibull models. These findings underscored the potential of mesoporous C₈-silica monoliths as efficient carriers for volatile essential oils, offering a promising strategy for sustained antimicrobial delivery in healthcare and food preservation applications.