Echinophora platyloba extract-mediated green synthesis of silver nanoparticles: Fine-tuning the size towards enhanced catalytic and antibacterial properties

Abstract

Green synthesis of nanomaterials for environmental application is a double win approach for environment and humanity. In this work, we present how silver nanoparticles (AgNPs) could be synthesized using Echinophora platyloba (E.P) plant extract as an environmentally friendly source, which acts as both reducing agent and capping agent for synthesis of small-sized AgNPs with maximum antibacterial and catalytic efficacy. The as-synthesized AgNPs were characterized by UV–Visible spectroscopy, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, and X-ray diffractometry. The size of AgNPs were fine-tuned by adjusting the synthesis parameters such as pH of plant extract, temperature, and amount of AgNO3. It was found that pH is a determining factor, where the size of AgNPs could be tuned from 15 nm to 53 nm by decreasing the pH from 10 to 7. In addition, the kinetic of growth was found pH-dependent, where small-sized AgNPs grow faster than large ones, culminating in shortening reaction time at alkaline pH. Green synthesized AgNPs (15 nm) showed remarkable catalytic performance in degradation of different individual azo dyes (i.e., Congo red (CR), Rhodamine B (Rh), methyl red (MR), bromocresol blue (BCB), Imido Black (IB)) as well as their mixture. It was found that the 90.11 % of mixture of dyes were decomposed in 8 min, following a pseudo-first order kinetic model. In addition, the antibacterial activity of the as-synthesized AgNPs (15 nm) was obtained against both gram-positive and gram-negative bacteria. The minimum inhibitory concentration (MIC) was found to be 119.06 µg/mL of silver nanoparticles for Escherichia coli (G-) and 59.53 µg/mL for Staphylococcus aureus (G + ). The results of this work emphasize on how a cost-effective and green approach could be used for environmental application and affect circular economy by its potential future applications in medical and environmental fields.