title: Monodisperse sub-10 nm gold nanoparticles by reversing the order of addition in Turkevich method--the role of chloroauric acid.
abstract: The Turkevich method for synthesizing gold nanoparticles, using sodium citrate as the reducing agent, is renowned for its ability to produce biocompatible colloids with mean size >10 nm. Here we show that monodisperse gold nanoparticles in the 5-10 nm size range can be synthesized by simply reversing the order of addition of reactants, i.e. adding chloroauric acid to citrate solution. Kinetic studies and electron microscopic characterization revealed that the reactivity of chloroauric acid, initial molar ratio of citrate to chloroauric acid (MR), and reaction mixture pH play an important role in producing monodisperse gold nanoparticles. Reversing the order of addition also enhanced the stabilization of nanoparticles at high MR values. Remarkably, the system exhibits a 'memory' of the order of addition, even when the timescale of mixing is much shorter than the timescale of synthesis.
authors: Department of Chemical Engineering, Indian Institute of Science, Bangalore 560 012, India. kalidas@chemeng.iisc.ernet.in
authors: Sankar Kalidas
authors: SK
authors: Sivaraman
authors: Sanjeev
authors: S
authors: Kumar
authors: Venugopal
authors: V
authors: Santhanam
mesh_terms: D001672:Biocompatible Materials / Q000032:analysis / Q000138:chemical synthesis*; D002712:Chlorides / Q000737:chemistry; D019343:Citric Acid / Q000737:chemistry; D003102:Colloids / Q000737:chemistry; D006046:Gold / Q000737:chemistry*; D017612:Gold Compounds / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D053768:Metal Nanoparticles / Q000737:chemistry* / Q000648:ultrastructure; D046529:Microscopy, Electron, Transmission; D036103:Nanotechnology / Q000379:methods*; D010084:Oxidation-Reduction; D010316:Particle Size; D019163:Reducing Agents / Q000737:chemistry; D012996:Solutions; D013499:Surface Properties
chemical_list: D001672:Biocompatible Materials; D002712:Chlorides; D003102:Colloids; D017612:Gold Compounds; D019163:Reducing Agents; D012996:Solutions; D019343:Citric Acid; D006046:Gold; C024568:gold tetrachloride, acid