Selective Entching And Thermal Stablebility Of Gold Nanorods

The tiny change in shape and size could directly affect the optical properties of the gold nanorods, so the chemical stability and thermal stability of the gold nanorods in an aqueous solution are important for a variety of practical applications. Herein, UV-Visible absorption spectra and TEM images were used to investigate the stability of the gold nanorods at different enviroments.Firstly, we report a chemical etching reaction of the gold nanorods induced by ferric chloride at room temperature. In the etching reaction, halide ions act as a ligand to reduce the electron potential of the gold species, which enables ferric ions to oxidize the gold nanorods and results in the etching of the gold nanorods. The redox etching leads to a significant decrease of the gold nanorods in length but little change in diameter, which could be attributed to less surface passivation or higher chemical reactivity of the tips of the gold nanorods. It is believed that the selective shortening not only provides an alternative way to obtain the gold nanorods with desirable aspect ratios and specific optical properties, but also offers a safe way to remove gold nanostructures, which is important for the preparation of hollow nanostructures with gold as a template.Secondly, we investigated the thermal stability of the gold nanorods in different environments. It was found that the LSPR absorption of the gold nanorods gradually moved to lower wavelengths at high temperature, suggesting the decreasing of the aspect ratio. The decrease of the aspect ratio originated from the increase of the diameter and the reduction of the length, which might be caused by Ostwald ripening and/or surface melting. This shape deformation could be inhibited by reducing the concentration of Cetyltrimethyl Ammonium Bromide (CTAB), coating the surface with poly(sodium styrenesulfonate)(PSS) or treating with NaBr in alkaline environment. The results are very important to the future applications of the gold nanorods where they have to be heated at high temperature without change of their optical properties.