Synthesis, characterization and antibacterial properties of novel nano-silver loaded acid activated montmorillonite

This paper reports synthesis, characterization and antibacterial properties of a novel silver-exchanged montmorillonite (Ag-Mt) synthesized from acid activated sodium montmorillonite (Na-Mt). The silver-loaded nanostructures (Ag-Mt) were synthesized in a two-step approach in which Na-Mt was first converted into acid activated Na-Mt and further treated with two concentrations of silver nitrate solution to obtain two types of acid activated Ag-Mt for comparison, Ag-Mt without the acid activation step and isotropic silver nanoparticles were synthesized as control samples. EDX confirmed successful loading of elemental silver in all types of Ag-Mt and WXRD analysis showed undisturbed crystal structure with increased interlayer space compared to Na-Mt. TEM micrographs revealed formation of spherical silver nanocrystals on the supporting silicate layers although no external reducing agent was employed due to high reduction potential of silver ions. The results were further confirmed in UV spectroscopy where strong absorption bands related to the surface plasmon resonance (SPR) was observed. The bactericidal efficacy of the clay minerals were evaluated against Gram-negative bacteria Escherichia soli and Gram-positive bacteria Staphylococcus aureus using disk diffusion method which showed excellent inhibitory properties and large inhibition zones of all synthesized Ag-Mt. The minimum inhibitory concentration (MIC) of the clay minerals was also quantified and compared with synthesized isotropic silver nanoparticles. Acid activated Ag-Mt showed antimicrobial activity marginally lower than silver nanoparticles alone, although the silver content was 10 times lower than Ag-NP. This antibacterial agent is thus very effective and more attractive in terms of cost and environment friendly nature.