Nanotechnology deals with the particles of diameter size less than 100 nm. Nanoparticles are different from their bulk counterparts due to their distinctive shapes and sizes. They provide larger surface area, essential to carry out different chemical reactions. Other than the physical and chemical methods of nanoparticle synthesis, biological method is getting more popularity, as the process is less toxic, cost effective and eco-friendly. Various biological sources such as algae, plants, bacteria, fungi etc. have been explored for their potential to synthesize nanoparticles. In the literature, algae was found to be more reliable source for the green synthesis of metal nanoparticles as they are readily available in nature and are easy to grow in normal conditions. Metal nanoparticles like gold, silver and iron synthesized from algal source have widespread application in treating environmental pollutants like heavy metal removal, degradation of organic dyes, antimicrobial agents etc.
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.
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