Synthesis and characterization of microscale gold nanoplates using Langmuir monolayers of long-chain ionic liquid

Triangular, hexagonal, and truncated triangular single-crystal gold nanoplates are successfully synthesized under Langmuir monolayers of long-chain ionic liquid molecules 1-hexadecyl-3-methylimidazolium bromide (C(16)mimBr) through interfacial reduction of AuCl4- by formaldehyde gas. The Au nanoparticles are characterized using transmission electron microscopy (TEM), selected-area electron diffraction (SAED), high-resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), and UV-vis spectroscopy. It is found that the size of the Au plates varies from several hundred nanometers to several micrometers, up to 20 mu m, and the thickness is ca. 35 nanometers. The atomically flat planar surfaces of the Au nanoplates correspond to {111} planes and the lateral surfaces are {110} planes. The concentration of HAuCl4 aqueous solution strongly influences the formation of the Au nanoplates. The formation of the nanoplates should be attributed to the preferential adsorption of 1-hexadecyl-3-methylimidazolium cations onto the {111} planes of Au nuclei and the connection of small, triangular nanoplates.