One-pot hydrothermal synthesis of silver nanowires via citrate reduction.

We report a novel and simple hydrothermal method to synthesize silver nanowires using only silver nitrate and sodium citrate without any external seeds or templates. The effects of the molar ratio of silver ions to citrate, pH, and the reaction temperature were investigated. Silver nanowires and particles were characterized using scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), powder X-ray diffraction (XRD), and UV/vis absorption spectroscopy. A high yield of nanowires (average diameter 53 ± 4 nm, length up to 6 μm) was obtained under optimized conditions with 1:1 M ratio of Ag(+) to citrate and pH 7.1 (no NaOH added) at 130 °C. Increasing the citrate ratio, increasing the pH with NaOH, or decreasing the reaction temperature all resulted in samples with shorter lengths and fewer nanowires compared to nanospheres. At pH 10.1, monodispersed nanospheres with diameter of 58 ± 9 nm were produced. The nanowire and nanosphere synthetic methods are attractive because of their simplicity, the lack of capping agents besides citrate, and the uniformity of the particles produced.