Green synthesis of silver nanoparticles using microalgal extract and its application in metal ion removal from aqueous solution

Abstract

Heavy metal pollution is of great concern and cannot be ignored as heavy metals are highly mobile in soil and are recalcitrant. Nanotechnology provides a novel sustainable approach for synthesizing materials of desired properties, composition, and structure, it is however expected to adsorb heavy metals and play a significant role in water treatment. Green chemistry is the cost-effective, non-toxic, and environment friendly approach that involves the use of biological components as reducing and stabilizing agents for the synthesis of nanoparticles. In the present study, heavy metals such as cadmium (Cd II) and lead (Pb II) were successfully removed from its aqueous solution by an adsorption process using the silver nanoparticles of size ~15nm biosynthesized using freshwater algal extract. The adsorption peak at 411 nm confirms the formation of silver nanoparticles. The maximum value of metal ion adsorption capacity (23.98 mg/g) was observed for Pb (II). The higher value of R2 showed that the experimental data were fitted best with Langmuir isotherm. The rate kinetics study showed that Pb (II) adsorption on Ag nanoparticles followed pseudo-second order kinetics (R2>0.9) indicating that Pb (II) was attached to the nanoparticles surface through electrostatic force of attraction, also referred to as chemisorption whereas Cd (II) adsorption on Ag nanoparticles followed pseudo-first order kinetics (R2>0.8) indicating physical adsorption between adsorbate and adsorbent.