Green synthesis of water-dispersible silver nanoparticles at room temperature using green carambola (star fruit) extract

Silver nanoparticles (AgNPs) dispersible in water were synthesized at room temperature in the presence of carambola fruit extract at different pH. The UV–Vis absorption revealed that with increase in pH of the solution, the intensity of the peaks became higher and narrower along with blue shift signifying decrease in particle size. Crystallinity of Ag in the synthesized product was determined by X-ray diffraction. Fourier transform infrared spectroscopy confirmed the presence of polyols, aldehydes, amines and organic acids in the fruit extract which became useful as capping and reducing agent for the synthesis of AgNPs. Transmission electron microscopy showed the average particle size of Ag as 16, 13 and 12 nm for pH 4, pH 7 and pH 10, respectively, while the corresponding sizes determined by DLS method were found to be 169, 134 and 80 nm. The high negative zeta potential values indicated dispersion stability of AgNPs. The present method is important in terms of green, energy-efficient and environmentally friendly process.