Biosynthesis of Ag@Au bimetallic nanoparticles from Hymenaea courbaril extract (Jatobá) and nonlinear optics properties

Abstract

Green synthesis of metal nanoparticles (NPMs) has been considered an innovative and sustainable alternative to produce metallic nanoparticles, due to the use of biological structures or parts thereof as reducing and stabilizing agents. This study reports, for the first time, the use of leaf extract from Hymenaea courbaril (Jatobá) as a reducing and stabilizing agent in the synthesis of bimetallic nanoparticles (Ag@AuNPs) in different proportions. Also, the nonlinear optical properties were investigated with continuous laser excitation at 532 nm by Thermal lens spectroscopy and Z-scan technique. The leaf extract is composed of chemical groups such as tannins, flavonoids, and others, confirmed by infrared spectroscopy, responsible for the process of chemical reduction. The UV–VIS spectra confirmed the formation of nanoparticles, through the presence of typical Surface Plasmon Resonance (SPR) bands characteristic of these nanostructures, ranging from 433 nm to 508 nm, depending on the proportion of silver and gold precursors. The nanostructures have an average hydrodynamic radius value of 48 nm and all exhibit a negative surface charge. TEM analysis shows that the Ag@AuNPs were spherical-like shape. The thermo-optical properties were investigated using thermal lens spectroscopy and showed thermal diffusivity values in the range of (8–10) × 10−4 cm2/s, depending on the SPR position. The Z-scan technique shows that the nonlinear refractive index is negative, and we observe the reverse saturable absorption. The results obtained indicate that these nanostructures have potential for nonlinear optics and photothermal applications.