Synthesis and size regulation of gold nanoparticles by controlled thermolysis of ammonium gold(I) thiolate in the absence or presence of amines

Controlled thermolysis of gold(I) complex with no use of solvent was investigated as a novel synthetic method of gold nanoparticles. A series of precursors, ammonium gold(I) thiolate [RN(CH3)3][Au(SC12H25)2] (R = C8H17, C12H25, and C14H29) and [(C18H37)2N(CH3)2][Au(SC12H25)2], have been prepared and the thermolysis of those precursors was conducted at 180 °C for 5 h under an N2 atmosphere, providing spherical gold nanoparticles stabilized by alkyl groups derived from the precursor, gold(I) complex. In spite of thermolysis process, the average diameter of gold nanoparticles deriving from [C12H25N(CH3)3][Au(SC12H25)2] was 22 nm, but the size distribution ranges from 11 to 76 nm. For the purpose of the size regulation of the gold nanoparticles, equimolar primary, secondary, or tertiary alkylamines are added as stabilizer and mild reductant to the controlled thermolysis of gold(I) complex at lower temperature of 165 °C for 5 h. The gold nanoparticles obtained by the controlled thermolysis in the presence of stearylamine are well regulated and almost monodispersed nanoparticles with average diameter of 7.5 nm. Such size regulation resulted from the inhibition of the growth of gold nuclei by transforming reaction from ammonium and thiolate moieties to neutral tertiary amine, thiol and sulfide, which function as stabilizer for gold nanoparticles.