Structural and optical investigations of biosynthesized bunsenite NiO nanoparticles (NPs) via an aqueous extract of Rosmarinus officinalis (rosemary) leaves

Abstract

Green synthesis of nanoparticles represents an important part of nanotechnology that offers outstanding eco-friendly and financial benefits when compared to conventional methods that use toxic substances and involve complex processes. In this paper, we report a completely green process in which aqueous extract of rosemary leaves containing bioactive molecular compounds (flavonoids, monoterpenoids, phenolic acids, and diterpenoids) acted as both chelating and stabilizing agents to facilitate the synthesis of NiO NPs. Apart from the nickel metal precursor, the synthesis was free of solvents and surfactants in this method to adhere to green chemistry principles and the impartation of environmental benignity. To achieve the aim of the study, structural and optical property analyses of Bunsenite annealed at 500 C were carried-out using complementary techniques namely high resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) and UV–Vis-NIR absorption spectroscopy. HRTEM micrographs revealed the self-assembled, highly agglomerated quasi-spherical shaped NPs with a cubic structure and the average size was found to peak at 8.09 ± 0.20 nm. SAED and XRD exhibited the polycrystallinity and the purity of NiO NPs and the average size was found in the range of 11.598–15.527 nm. Besides, EDS depicted the presence of Ni and O in the sample while ATR-FTIR illustrated the Ni-O chemical bonds. From UV–Vis-NIR, the optical band gap amounted to 3.39 eV confirmed the formation of NiO NPs.