Biobased synthesis of silver and titanium dioxide nanoparticles and their applications

Abstract

Silver nanoparticles (AgNPs) and titanium dioxide nanoparticles (TiO2-NPs) have found wide range of applicability in engineering, healthcare, consumer goods, pollution abatement and electronics. Biobased routes for their synthesis is gaining prominence, as they are safer and environmental friendly routes with low chemical footprint compared to physical and chemical routes. In the present research work, the plant sources such as leaves of Terminalia catappa and Tectona grandis Linn F leaves were selected based on their ability to synthesize AgNPs. The bacterial sources were isolated from the silver rich environment based on their ability to reduce the silver ions extracellularly and were identified as Brevundimonas vancanneytii, Leucobacter aridicollis, Enterobacter cloacae and Alcaligenes aquatilis. AgNPs could be synthesized effectively using aqueous extracts of the leaves and the cell free culture supernatants of these bacterial strains. Extracellular TiO2-NPs were also synthesized using the bacterial cell free culture supernatants. The synthesis parameters influencing the conversion of precursor ions and the morphological characteristics such as size, shape, isotropy and monodispersity of the nanoparticles being synthesized were studied and optimized. In plant based synthesis, plant bioactive components acted as reducing and capping agents, while the bacterial based synthesis was brought about by the extracellular enzymes. AgNPs and TiO2- NPs synthesized in the present research work were found to be capped with biobased moieties which imparted stability to the particles. The AgNPs exhibited antibacterial efficacy and colorimetric mercury sensing property, while the TiO2-NPs exhibited photocatalytic activity. Crystalline AgNPs synthesized with a conversion of 98.98% using the bacterial strain Alcaligenes aquatilis were of average particle size of 23±0.9 nm, isotropic, quasispherical shaped along with narrow size range and exhibited the best antibacterial property and colorimetric mercury sensing ability as compared to other AgNPs synthesized. TiO2-NPs synthesized using the cell free culture supernatant of the same bacterial strain were isotropic, monodispersed, quasi spherical shaped, and with an average size of 4.0±0.5 nm containing brookite phase of titania. They exhibited higher photocatalytic activity as compared to Degussa P-25 in terms of degradation of Acid blue and Remazol brilliant blue R dyes, with complete degradation of 50 mg/L of dyes in 120 min. Thus the process developed in the current study could harness the biobased components from the selected plant and bacterial sources for the synthesis of AgNPs and TiO2-NPs under ambient conditions with promising large scale applicability.