The controlled synthesis of stable gold nanoparticles in quaternary ammonium ionic liquids by simple heating

Stable gold nanoparticle (AuNP) colloids were synthesized in a class of quaternary ammonium-based room-temperature ionic liquids (QAILs), [Me(3)NC(2)H(4)OH](+)[Zn(n)Cl(2n + 1)](-) (n = 1 or 2), by heating in air at 135-145 °C. The QAIL was employed as a solvent, a reducing agent, and as a stabilizer. The size of the QAIL-AuNPs can be varied between 20 and 40 nm by changing the reaction temperature. A symproportionation reaction was employed to further decrease the size of the AuNPs by the addition of Au(3+) ions. The surface covering of QAIL on the AuNPs had a significant impact on their surface plasmon resonance (SPR), which was red-shifted. The AuNPs synthesized by this simple and environmentally friendly reaction can be realized in several minutes and also exhibit high stability and good reproducibility, providing a new facile approach to metal nanoparticle preparation.