The gold urchin and snowflake nanoparticles were prepared in the presence of hexadecyltrimethylammonium bromide (HTABr) by reduction of NaAuCl4 using gallic acid (GA) in water. Effects for HTABr and GA were examined. The mixed solution of 0.5 mM (1 M = 1 dm3) with 1.1 ~ 4.4 mM HATBr and 1.0 ~ 20 mM GA were heated from 30 °C to 70 °C for 13 minutes. The obtained nanoparticles were characterized by UV-vis spectroscopy and transmittance electron microscopy (TEM). At [HTABr] = 4.4 mM or [GA] =20 mM, HTABr and GA promote the formation of snowflake gold nanoparticles. In the concentration range of [HTABr] ≤ 2.2 mM and [GA] =10 mM, particles of various shapes and sizes were obtained. The effects of pH were also examined. At low pH ranges, asymmetric triangular particles with protrusions were obtained. Fern-like particles were prepared in the neutral pH range. At high pH ranges, small urchin-loke particles were obtained. High pH and Cl—ions accelerate the formation of urchin-like gold nanoparticles.
