Hybrid Ag 0 /Ag 2 CO 3 –eggshell–plant nanocomposites for antimicrobial action prepared by bio-mechanochemical synthesis

Silver carbonate and elemental silver nanoparticles embedded in the matrix of biological materials were successfully prepared via a bio-mechanochemical synthesis, i.e., one-step solvent-free approach utilizing high-energy ball milling. Namely, the powders of silver nitrate as a precursor of silver and a mixture of natural materials (eggshell waste and Thymus serpyllum L. plant) powders as reducing and stabilizing agents, were milled together. The optimization of experimental conditions was performed using a Taguchi design. The presence of nanoparticles was confirmed by a bunch of experimental techniques including XRD and TEM, their size being up to 15 nm. By means of AAS, the level of Ag stabilization was determined, being better when eggshell content was higher. The products also exhibited the antibacterial activity, and although the agar well diffusion method did show better results for the nanoparticles prepared using the eggshell or the plant alone, the respiratory tests have shown a good response also for the product prepared using a combination of the two. The strongest respiratory inhibition against Escherichia coli was observed for the nanoparticles prepared using only eggshell, but the ones synthesized using both reducing agents caused a prolonged inhibition against Staphylococcus aureus . The proposed synthetic approach offers the use of environmentally harmless technique and natural materials to yield antibacterially active nanoparticles.