Characterization of Silver Ions-Doped Organomodified Nanoclays

Abstract

In this study, montmorillonite (MMT) and halloysite nanoclays were organomodified with cationic surfactants N-cetyl-N, N, N-trimethylammonium bromide (CTAB) and poly diallyl dimethylammonium chloride (PDAC) to enhance intercalation characteristics. The organomodified nanoclay samples were doped with Ag+ ions in order to enhance antimicrobial properties, and their XRD, ATR-FTIR, ICP-MS, SEM, TEM, zeta potential, mean particle size, and in vitro Ag+ release properties were further investigated. The antibacterial activity of the Ag-doped organoclays was analyzed by broth dilution method as well as the determination of minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) against gram-positive (Staphylococcus aureus ATCC 25,923 and Listeria monocytogenes ATCC 13,932) and gram-negative (Escherichia coli O157:H7 ATCC 25,922 and Salmonella enterica subsp. enterica serovar Typhimurium ATCC 14,028) bacterial strains. The surface load of the organomodified nanoclays changed to positive due to the cationic surfactants, and as a result of the XRD examinations, the interlayer space of the nanoclays increased. ATR-FTIR and ICP-MS analysis indicated that Ag+ ions successfully doped into the nanoclay structure. Also, MMT-type nanoclay samples released the Ag+ ions into the water medium more than halloysite-type nanoclay samples. Nanoclays organomodified by CTAB had an effective bactericidal effect on each bacterial strain than PDAC-modified nanoclays. Ag-doped nanoclays had MIC and MBC values varying from 0.6 to 5 mg/ml in the nutrient broth medium for all the bacterial strains. In conclusion, intercalated and Ag+-doped MMT and halloysite nanoclays were successfully prepared and effectively used for bacterial growth inhibition.