Natural sugar surfactant capped gold nano-disks: Aggregation, green synthesis and morphology

Abstract

In the present study, sugar based bola bio-surfactant, crocin, was used as a reducing and capping agent to the one pot controlled green synthesis of gold nanoparticles (AuNPs) for the first time. Self-aggregation, and critical micellar concentration (CMC) of crocin were determined using visible spectrophotometric technique. Crocin was also used as probe to the determination of CMC of cetyltrimethylammonium bromide (CTAB). UV–visible absorption spectra showed one surface plasmon resonance peak (SPR) at 570 nm attesting the spherical crocin-capped AuNPs formation. Very tiny (quantum dots) spherical mono-dispersed and/or aggregated AuNPs were revealed by the transmission electron microscopic (TEM) and selected area electron diffraction (SAED) ring patterns data. Upon addition of CTAB the morphology changes drastically to triangular, truncated triangular and hexagonal gold nano-disks. Scanning electron microscopy (SEM), X-ray diffraction pattern (XRD), and energy dispersion X-ray spectroscopy (EDX) ascertain the surface morphology and structure of AuNPs as face centered cubic (fcc). The complex formation between aqueous solution of gold salt and CTAB was also characterized by the conventional techniques. Polar head groups of crocin, gentiobiose disaccharide, are responsible to the reduction of HAuCl4 into the metallic gold.