Thymol-Functionalized Silica Nanomaterials Prepared by Post-Grafting Method: Preparation, Characterization, Bactericidal Activity and Mechanism Research

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In this study, thymol was covalently connected to mesoporous silica nanomaterial by a post-grafting method to obtain a stable antibacterial system, thus overcoming the volatilization of thymol, prolonging the effective time of antibacterial action, and enhancing the antibacterial efficiency of thymol. It was proposed for the first time that such a synthetic route be adopted to synthesize silica-based mesoporous/essential oil antibacterial materials. The post-grafting method could be capable of retaining the mesoporous original structure, which could effectively avoid the porosity reduction and disordered products caused by condensation. Among them, the minimum bactericidal concentration (MBC) of functionalized MCM-41 (silica support) for E. coli and S. aureus were 0.3 mg mL−1 and 0.4 mg mL−1, which were equivalent to 3/4 and 4/5 of free thymol (0.4 mg mL−1 and 0.5 mg mL−1), respectively. Meanwhile, the MBC of functionalized SBA-15 (silica support) for E. coli and S. aureus were both 0.2 mg mL−1, which also reduced the MBC of free thymol. These results revealed thymol-functionalized mesoporous silica nanomaterial could efficiently improve the bactericidal activities of the organic component. Finally, the inhibition mechanism of the post-grafting strategy was also discussed, which referred to how the antibacterial material directly acts on the cell membrane, resulting in cell inactivation.