Biogenic Synthesis of Metal Based Functional Nanostructures
Metal nanoparticles receive immense attention due to their unique size and shape dependence physicochemical properties. When they combined with other materials such as metals, metal oxides, and carbon structures their unique interfacial effects brings extensive functional properties with lot of potentials for many applications. Various physical and chemical process have been widely explored for the synthesis of those metal nanoparticles, however, they faces many challenges including sophisticated equipments, complicated protocols, toxic chemicals and solvents. Thus, the plat extract mediated bioreduction process has been investigated for the synthesis of silver (Ag) and palladium (Pd) nanoparticles with controlled structural and morphological features. In this aspect, our research work mainly focus on the functionalization of various materials with metal nanoparticles effectively using bioreduction process for antimicrobial and photocatalytic applications.
Ag and Pd Nanoparticles through Biological Process
Plant leaf extract mediated biological process has been explored for the synthesis of silver and palladium nanoparticles. Leaf extracts from different plants such as soybean (Glycine max), curry (murraya koenigii), maple (Acer sp.) and switch grass (Panicum virgatum) have been explored for the synthesis of silver nanoparticles. It is also proved that the plant extract based bioreduction process can be used for the synthesis of palladium nanoparticles. The figure shows the TEM images of the synthesized silver nanoparticles (AgNPs) by soy leaf extract. It has also been effectively used for the synthesis of palladium nanoparticles Portions in the leaf extract play vital role in the reduction of metal ions in to zero valent metal and stabilize them as nanoparticles.
Bioreduction process has been first explored for the functionalization of various materials (metal, metal oxides and carbonaceous materials) surfaces, which has been schematically shown in the above figure.
Functional Carbon Nanotubes with Ag Nanoparticles
Novel plant extract mediated biological process has been developed for the functionalization of various nanostructures with silver nanoparticle. In our preliminary studies, Glycine max (soybean) leaf extract has been successfully employed for the functionalization of the multiwall carbon nanotube (MWCNT) with silver nanoparticles. Functionalization process through this biological route is rapid and the transmission electron microscope analysis clearly shows the formation of silver nanoparticles with ~10 nm size on carbon nanotubes as shown in the figure.
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Cellulose Fibres Impregnated with Ag Nanoparticles
Curry leaf (Murraya koenigii) extract mediated greener method has been successfully employed to impregnate the silver nanoparticles into microcrystalline cellulose (MCC). The active reduction of silver ions by curry leaf extract was explored for the in situ impregnation AgNPs into MCC. Transmission electron microscopy (TEM) analysis of MCC coated with AgNPs showed the formation of silver particle sizes in the range of 10 - 25 nm and have a spherical shape. Further the, EDS analysis of MCC/Ag nanocomposite confirms the formation of Ag structure on microcrystalline cellulose. Solvent casting of poly(lactic-acid) was used to produce composite films containing silver impregnated MCC aiming for antimicrobial applications.
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AgNP: Metal Oxide Nanoparticles
Metal nanostructures have been investigated for many applications and their performance can be further improved by coupling them with various metal nanoparticles such as silver, gold, platinum, or palladium. First time in the literature, functionalization of ZnO powders with silver nanoparticles (AgNPs) through the maple leaf extract mediated biological process was demonstrated. Maple leaf extract was found to be a very effective bioreduction agent for the reduction of silver ions. The reduction rate of Ag+ into Ag0 was found to be much faster than other previously reported bioreduction rates and was comparable to the reduction rates obtained through chemical means. It was found that the ZnO particles did get coated with silver nanoparticles 5-20nm in diameter. The photocatalytic ability of the ZnO particles functionalized with silver nanoparticles was found to be significantly improved compared to the photocatalytic ability of the neat ZnO particles.
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Decoration of Graphene with Ag Nanoparticles
Integrating metal nanoparticles of silver, gold, platinum and palladium with graphene structures receives immense potential due to their unique electron distribution between the carbon and metal. Particularly, silver nanoparticles have excellent electrical, antimicrobial, and catalytic properties, which is also relatively cost effective compared to gold and platinum. Soy leaf extract mediated bioreduction process has been successfully employed for the decoration of graphene sheets with silver nanoparticles. Silver content on the graphene sheets has been varied by manipulating the silver nitrate concentration in the reaction mixture. Using transmission electron microscopy, it has been found that the silver nanoparticles deposited on the graphene sheets were exist in spherical shape with the diameter range of 2-25 nm.
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