Photobiological synthesis of noble metal nanoparticles using Hydrocotyle asiatica and application as catalyst for the photodegradation of cationic dyes

The essential of nanotechnology is to synthesize dispersed nanoparticles for potential applications in optics, biomedical sciences, drug delivery, catalysis and electronics. In the past, number of methods such as chemical [ 1 – 4 ], photochemical [ 5 – 8 ] and thermal [ 9 , 10 ] have been developed to synthesize metallic nanoparticles. Recently an efficient method for fabrication of metallic nanoparticles from metallomicelles is reported [ 11 ]. Among these methods, photochemical method has gained considerable attention due to its convenience, but it employs toxic chemicals as reducing and stabilizing agent [ 12 ]. To avoid the utilization of highly toxic chemicals, the use of microorganisms and plant parts for nanoparticles synthesis has been explored [ 13 ]. Previous reports mention the use of microorganisms such as Alternaria alternate [ 14 ], and Amylomyces rouxii [ 15 ] for the synthesis of nanoparticles. Recently, several plants extracts such as Annona squamosa [ 16 ], Arbutus unedo [ 17 ], Cassia angustifolia [ 18 ] and many others [ 19 – 27 ] have been used to synthesize silver (Ag) and gold (Au) nanoparticles (NPs). However, these natural sources, which have active ingredients, produce nanoparticles at slower rate. To overcome this, photo-assisted biosynthesis of Ag and AuNPs using many plants has been qualitatively investigated [ 28 ]. The sunlight irradiation technique has been formerly reported for the synthesis of nanoparticles using few plant materials such as Allium sativum [ 29 ], Andrachnea chordifolia [ 30 ], Piper betle [ 31 ], Bacillus amyloliquefaciens [ 32 ] and Achyranthus aspera [ 33 ]. Apart from plant materials, dendrimers and starch are also used as reducing/stabilizing agents in the sunlight-induced synthesis of nanoparticles [ 34 , 35 ]. The nanoparticles produced by bio route have good stability due to the presence of capping agents like alkaloids, flavonoids and polyphenols, which are the major constituents present in the natural sources.