Biosynthesis optimization and characterization of silver nanoparticles from imperata cylindrica / Afiza Ahmad Fairuzi

Biosynthesis of nanoparticle has gained great attention towards the economic and environmentally friendly process. However, there is a limited number of studies that describe the parameters for tuning the dimension and geometry of nanoparticle in the biosynthesis process. In this study, the aqueous extract of Imperata cylindrica (I. cylindrica) was used as a green reducing agent to produce silver nanoparticles from silver nitrate solution. The biosynthesis parameters were optimized by varying the synthesis condition to produce monodisperse silver nanoparticles. The particles were characterized by visual observation; colour changes, UV-visible spectroscopy, dynamic light scattering (DLS), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD). Changing the parameters such as plant extract concentration, silver salt concentration, the temperature of biosynthesis and pH of reaction mixture influence the size and dispersion of the nanoparticles. Characterization using FESEM revealed the presence of excessive biogenic material from plant extract encourage agglomeration. The formation of silver nanoparticles began as early as 10 minutes at 60°C, compared to the synthesis carried out at 30°C. However, at higher temperatures (100°C) nanoparticles started to grow larger. Modification of pH disturbed the reducing and stabilizing ability of I. cylindrica extract which lead to the formation of large and highly polydisperse particles. The optimum parameters for synthesizing silver nanoparticles are 10% of aqueous extract, 10 mM of silver nitrate, pH 5.7 with a reaction temperature of 60ºC. The optimized silver nanoparticles (sample AG05) are in spherical with an average diameter of 29.34nm. The X-ray diffraction result shows that the silver nanoparticles formed through the reduction of Ag+ ions by I. cylindrica extract are crystalline in nature. Energy dispersive X-ray spectroscopy analysis exhibited a strong signal in the silver region confirmed the presence of elemental silver. The phytochemical compound presence in I. cylindrica was determined by using the phytochemical test and Fourier transform infrared spectroscopy (FTIR). The reduction reaction by I. cylindrica might be caused by the phytochemical compounds which are alkaloids, tannins, and flavonoids. The degradation of aqueous methylene blue was used as the model system to monitor the catalytic activity of the biosynthesized silver nanoparticles. The degradation recorded was up to 82.49% in 2 minutes. The outcome of this study suggests that silver nanoparticles synthesized using the aqueous extract of I. cylindrica have the potential to be used as a catalyst. The biosynthesis parameter optimization enables the production of silver nanoparticles with uniform shape and narrow size distribution.