Green Synthesized Silver-Soda Lime Glass Nanocomposite, Made by Neolitsea Cassia Leaf Extracts Inhibits Microcystis sp. Under Aquarium Conditions

Abstract

Microcystis sp., one of the most common cyanobacteria releases cyanotoxins which cause severe ecological consequences to both aquatic organisms and human. There is a high demand for developing an eco-friendly safer methods to control harmful algal blooms. Medicinal and antibacterial properties of silver nanoparticles (Ag NPs) has gained a prominent role in developing such methods. Green synthesis of Ag NPs is eco-friendly and cost effective than that synthesized by conventional chemical methods. Therefore, the objectives of the study were to; (1) produce green synthesized AgNPs using 80% methanol extract of Neolitsea cassia leaves and produce a nanocomposite by overlaying Ag NPs on soda lime glass beads, and (2) incooperate nanocomposite into an aquarium tank trickling filter to evaluate its performance as an anti-algal agent against Microcystis sp. Three concentrations of AgNO3, 0.1, 0.2 and 0.3 mol dm-3 were chemically reduced to elemental Ag by the plant extract and the synthesized NPs were coated on soda lime glass beads (4 mm diameter). Ultraviolet-visible spectroscopy, Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Analysis (EDXA) and Fourier Transform Infrared (FTIR) analysis techniques were used in characterizing green synthesized Ag NPs. An experiment was conducted for a period of three weeks and at the end of the experiment, Ag NPs synthesized using 0.3 moldm-3 AgNO3 were found to be more efficient in inhibiting Microcystis sp. with a percentage of 62.27. There was a significant difference in the mean chlorophyll content of controls and the three treatments (p<0.05). Morphological variations of Microcystis colonies depend on Ag NP concentration while showing the most significant variations in treatments with 0.3 moldm-3 Ag NPs. Disk diffusion test indicates the highest zone of inhibition (approximately 18 mm) with respect to 0.3 moldm-3 Ag NPs, affirming the anti-algal activity of green synthesized Ag NPs. Study conclude that the anti-algal activity remarkably increased with the increasing concentration of AgNO3 used to synthesize Ag NPs.