Carvacrol incorporated on raw and acid-activated vermiculites and their antibacterial evaluation

The incorporation of bioactive species in clay minerals has been applied to produce materials with antimicrobial action. In this study, a clay mineral was acid activated with 1 and 2 mol L −1 nitric acid resulting in porous matrixes. Pristine and acid activated samples reacted with carvacrol, a natural phenolic monoterpene with antimicrobial properties, and the antimicrobial activity was evaluated against Staphylococcus aureus and Escherichia coli using the agar diffusion test. Oil release of the samples was also monitored until 72 h PBS buffer. Solids were characterized by X-ray diffractometry, infrared absorption spectroscopy, X-ray photoelectronic spectroscopy, thermogravimetry, Zeta potential, N 2 adsorption/desorption measurements, CHN elemental analysis and scanning electron microscopy. XRD patterns and the Zeta potential results suggested the presence of the oil on the surface of the matrixes and CHN indicated a higher amount of oil was obtained for activated clay minerals (0.51 and 0.67 mmol of carvacrol per gram of solid activated at 1 and 2 mol L −1 nitric acid, respectively). The higher inhibition diameter values for were 13, 27 and 32 mm against S. aureus by pristine and acid activated samples prepared with higher amount of carvacrol. All oil loaded samples released in PBS buffer solution at pH 7.4 until 72 h and higher values were 5.2 and 8.1% for samples prepared at 1 and 2 mol L −1 nitric acid, respectively. After 72 h, a slow release of the essential oil was observed. Results indicated good incorporation of the carvacrol in the surface of the acid activated clay samples and improvement of the antibacterial activity of the solids resulted of the carvacrol. • Activated acid clay minerals were obtained by reaction in HNO 3 . • Raw and activated solids were applied to incorporate carvacrol. • A higher amount of oil was observer for activated samples. • The oil-loaded solids showed antimicrobial activity.