Room temperature surfactant-free syntheses of colloidal gold nanoparticles: Comparison of the precursors HAuCl4 and HAuBr4

The synthesis of nanomaterials is sensitive to various parameters, including the type of solvent, reducing agents, and the nature and concentrations of the chemicals selected, among others. Here, we study the effect(s) of using different precursors, namely HAuCl 4 and the far less common HAuBr 4 , for two room temperature surfactant-free colloidal syntheses of gold nanoparticles. The gold nanoparticles were obtained at room temperature by adding the precursor to a mixture of water and alcohol under alkaline conditions, or by mixing the precursor with only water and NaBH 4 . The use of HAuBr 4 leads to gold nanoparticles over a wide range of conditions including the use of different alcohols (methanol, ethanol, ethylene glycol, glycerol), for various amount of alcohols (10 to 95 v.%), leading to size control over the nanoparticles in the range 5-30 nm, and to some degree of shape control from spheres to triangles when high contents of ethylene glycol are used with HAuBr 4 . The reaction proceeds more slowly and tends to lead to larger nanoparticles when HAuBr 4 is used, while the overall formation pathway is the same as for HAuCl 4 , as exemplified with an ethanol-mediated synthesis. The use of HAuBr 4 also leads to nanoparticles in the size range 5-15 nm when NaBH 4 is used as reducing agent. The resulting nanoparticles are active catalysts, for instance for water treatment with the example of the 4-nitrophenol reduction. The results clarify the pros and cons in the selection of HAuCl 4 or HAuBr 4 for the synthesis of gold nanoparticles and catalysis. • HAuCl 4 and HAuBr 4 are compared as precursors for gold nanoparticles synthesis • x4 alcohol-mediated and a NaBH 4 -mediated surfactant-free syntheses are considered • HAuBr 4 leads to a slower formation and larger nanoparticles • Some degree of shape control can be achieved with HAuBr 4 • The nanoparticles are readily active catalysts, e.g. for 4-nitrophenol reduction