Mechanochemistry as an Alternative Method of Green Synthesis of Silver Nanoparticles with Antibacterial Activity: A Comparative Study.

Matej Baláž,Aneta Salayová,Radovan Bureš,Zdenka Bedlovičová,Zdenka Lukáčová Bujňáková,Mária Kováčová,Nina Daneu,Ľudmila Tkáčiková,Róbert Džunda,Patrik Siksa,Libor Sokoli

doi:10.3390/nano11051139

Abstract

This study shows mechanochemical synthesis as an alternative method to the traditional green synthesis of silver nanoparticles in a comparative manner by comparing the products obtained using both methodologies and different characterization methods. As a silver precursor, the most commonly used silver nitrate was applied and the easily accessible lavender (Lavandula angustofolia L.) plant was used as a reducing agent. Both syntheses were performed using 7 different lavender:AgNO3 mass ratios. The synthesis time was limited to 8 and 15 min in the case of green and mechanochemical synthesis, respectively, although a significant amount of unreacted silver nitrate was detected in both crude reaction mixtures at low lavender:AgNO3 ratios. This finding is of particular interest mainly for green synthesis, as the potential presence of silver nitrate in the produced nanosuspension is often overlooked. Unreacted AgNO3 has been removed from the mechanochemically synthesized samples by washing. The nanocrystalline character of the products has been confirmed by both X-ray diffraction (Rietveld refinement) and transmission electron microscopy. The latter has shown bimodal size distribution with larger particles in tens of nanometers and the smaller ones below 10 nm in size. In the case of green synthesis, the used lavender:AgNO3 ratio was found to have a decisive role on the crystallite size. Silver chloride has been detected as a side-product, mainly at high lavender:AgNO3 ratios. Both products have shown a strong antibacterial activity, being higher in the case of green synthesis, but this can be ascribed to the presence of unreacted AgNO3. Thus, one-step mechanochemical synthesis (without the need to prepare extract and performing the synthesis as separate steps) can be applied as a sustainable alternative to the traditional green synthesis of Ag nanoparticles using plants.

Highlights

In the case of mechanochemical synthesis, we proved a significant content of AgNO3 after the milling and washed it out, we can definitely say that the observed antibacterial activity is due to the silver nanoparticles produced
Green synthesis of silver nanoparticles has been tackled from almost any perspective possible in the last years
We have successfully prepared Ag nanoparticles using both approaches by applying the common Lavandula angustofolia L. plant as a reducing agent

Summary

Introduction

Green synthesis of silver nanoparticles (Ag NPs) with antibacterial activity is a wellestablished environmentally friendly approach [1,2]. In contrast with traditional synthetic creativecommons.org/licenses/by/ 4.0/). Nanomaterials 2021, 11, 1139 approaches, it does not require the use of toxic chemicals or solvents, as the synthesis is performed using various biological organisms, plants being the most commonly used [3,4,5]. In the vast majority of the papers on green synthesis, the authors do not investigate the actual content of residual silver nitrate (most common Ag precursor) in the produced nanosuspension, so they do not have the information about the actual reaction progress

Objectives

Methods

Results

Conclusion