Water-based synthesis of gold and silver nanoparticles with cuboidal and spherical shapes using luteolin tetraphosphate at room temperature

The demand for eco-friendly synthetic methods of metal nanoparticles is on the rise. We hereby present a green approach for a one pot synthesis of nontoxic gold nanoparticles (AuNPs) and silver nanoparticles (AgNPs) using water soluble, naturally-derived luteolin tetraphosphate (LTP). LTP was used as the reducing and capping agent using water as the solvent excluding the use of other capping agents. The synthesis was achieved by varying the concentrations of the metal precursor and the reducing agent to form spherical and cuboidal AuNPs and spherical & quasi spherical AgNPs, respectively. The AgNPs and AuNPs were characterized by UV-vis spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive absorption spectroscopy (EDS) and high resolution transmission electron microscopy (HR-TEM). TEM images showed that the resulting AuNPs exhibited cuboidal characteristics with average particle sizes ranging from 16 to 23 nm, whereas those of the spherical nanoparticles of the synthesized AuNPs ranged from 8 nm to 11 nm. However, the average edge length of truncated AuNCs ranged from 372 nm to 509 nm. The average particle size for the spherical AgNPs ranged from 12 to 13 nm, whereas that of the larger quasi-spherical AgNPs ranged from 10 nm to 100 nm, respectively. Additional quantitative metrics assessing the properties of the nanomaterials made by our water-based, greener synthesis method and those made by other methods include lattice constant values of gold nanocubes (AuNCs) with TEM images, XRD data and 3-D models of the fcc structure using the Vesta software. The TEM images of AuNCs exhibited slightly truncated edges which are in agreement with AuNCs synthesized using organic solvents. Furthermore, the lattice constant of the SAED pattern of the AuNCs was calculated to be 4.052 Å which is in agreement with that for fcc gold of 4.078 Å (JCPDS 04-0784) and comparable to that for AuNCs in the literature of 4.068 Å. This confirms that the synthesized AuNCs were achieved at room temperature without using organic reducing solvents and toxic capping agents. The synthesized LTP derived AuNPs were found to maintain stability for a period of 8 months compared to those synthesized using luteolin alone which showed stability for only 336 hours.