Essential oil in bentonite: Effect of organofunctionalization on antibacterial activities

Essential oils are natural molecules with intense bioactivity, mainly antimicrobial activity, and are used in several industries such as health and food. However, the high volatility of the essential oils limits their application. Therefore, the incorporation of essential oils into solid materials is a strategy to maintain their properties. In this study, the incorporation of nerolidol at 5-50% v/v concentrations in raw and organophilic bentonites was investigated. The antibacterial activities of the oil/clay hybrids against Staphylococcus aureus and Escherichia coli were evaluated using the direct contact test. Transmission electron microscopy and X-ray diffractometry patterns confirmed the intercalation of the oil in sodium bentonite, resulting in a 1.26-1.50 nm increase in basal spacing (d), and in cetyltrimethylammonium clay (CTAB-Bent), which showed a d value of 3 nm. Thermogravimetry indicated that the maximum amount of nerolidol incorporated was 41% by mass (1.84 mmol g-1) in the NE50/ CTAB-Bent sample, suggesting a good affinity between the species. The Fourier transform infrared spectra were in concordance with the interactions between the oil and OH groups and the organic groups in the raw and organophilic samples, respectively. Transmission electron microscopy suggested that the layered structure of the samples was maintained without the formation of exfoliated phases. The antibacterial of the hybrids revealed 100% inhibition of both bacteria. The promising results associated with the slow release and effective anti-bacterial action of the oil-clay hybrids indicate that the obtained materials can be used in the manufacture of pharmaceutical, cosmetic, and healthcare products.