Synthesis, characterization and mechanism of cetyltrimethylammonium bromide bilayer-encapsulated gold nanosheets and nanocrystals

Single-crystal Au nanosheets and fcc gold nanocrystals of uniform size were synthesized by a novel and simple route. The results of field-emission scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD) indicated the formation of the single-crystal structure of gold nanosheets and fcc nanocrystals. Energy-dispersive analysis of X-ray (EDAX) showed absorbance of cetyltrimethylammonium bromide (CTAB) molecules onto the surface of gold nanostructures. Moreover, zeta potential measurements showed that CTAB-coated nanostructures were positively charged and the zeta potential remained almost the same upon centrifugation and redispersion of the resulting nanostructures in methanol, confirming the high stability of the surfactant-protected nanocomposites. Evolution of the nanostructures during the reaction was monitored by TEM observations. The results indicated that the formation of the gold nanostructures followed a two-step mechanism with a bilayer CTAB structure on the surface of the gold nanostructures.