Antibacterial activity of thymol/carvacrol and clinoptilolite composites prepared by supercritical solvent impregnation

Novel composites based on natural zeolite—clinoptilolite and monoterpene phenols—thymol and carvacrol were prepared by supercritical solvent impregnation (SSI) in supercritical carbon dioxide (scCO2) at 30 MPa and 35 °C during 18 h. The content of phenols in composites (thymol—23.0 and carvacrol—19.1 wt%) was determined using both C,H,N and thermal analysis (TGA); interactions of the phenols with the zeolite lattice studied by Fourier transform infrared spectroscopy (FTIR) and powder X-ray diffraction (PXRD) showed that the zeolite lattice was preserved in the composites. The composites exhibited antibacterial activity toward Gram-negative bacteria Escherichia coli DSM 498 and Gram-positive bacteria Staphylococcus aureus ATCC 25923 in different water media (phosphate buffer solution, spring water and lake water). After 1 h carvacrol-containing clinoptilolite showed better antibacterial activity than composite with thymol. Both composites expressed bactericidal effect after 24 h of contact. Leaching of the phenols from composite in water was more pronounced from thymol (22.7–32.1%) than for carvacrol (6.2–8.9%) suggesting influence of steric effect on the desorption process.