Ecofriendly ultrasound-assisted rapid synthesis of gold nanoparticles using Calothrix algae

In the present work we demonstrate the ultrasound assisted synthesis of gold nanoparticles (AuNPs) in an ecofriendly manner using Calothrix algae. The production of the AuNPs in the reaction mixture is significantly accelerated by inducing ultrasound irradiation. The optical property, size distribution, morphology and crystalline phase of the AuNPs were determined by visual, UV-vis spectroscopy, dynamic light scattering, transmission electron microscopy (TEM) and x-ray diffraction (XRD) technique. The appearance of a light pink color at lambda(max) = 550 nm indicated the synthesis of AuNPs. TEM images showed the formation of anisotropic AuNPs with predominant truncated shape and particles are in the range of 30-120 nm. The XRD spectrum of the AuNPs exhibited a Bragg reflections peak at 38.23 degrees, corresponding to elemental gold. Further, AuNPs showed significant catalytic efficiency (rate constant, k = 0.072 4752 min(-1)) in reducing 4-nitrophenol (2 mM) to 4-aminophenol. The advantage of using ultrasound relates to the ecofriendly and rapid synthesis of AuNPs and various biotechnological applications were suggested.