Continuous flow synthesis of citrate capped gold nanoparticles using UV induced nucleation

A new approach for synthesising gold nanoparticles of controlled size in the presence of trisodium citrate is presented. UV light is employed as a photoinitiator for the reduction of Au(III) by citrate. The UV induced nucleation takes place in a glass capillary tube (0.8 mm internal diameter) illuminated by a series of germicidal UVC lamps. This has been coupled sequentially with a heated coil to accelerate growth. In this way the processes of nucleation and growth are effectively separated. Slug flow is utilised in order to avoid tube fouling using heptane as segmenting fluid. Increasing UV intensity and temperature of the growth section lead to decrease of nanoparticle size, whilst varying UV exposure time results in a nonmonotonic effect on particle size. By varying UV intensity from 0 to 1461 mW cm 2 at a contant exposure time of 10 s, and a constant growth time of 20 min, the nanoparticles obtained range in size from 9.5 1.3 nm to 36.1 6.9 nm at a low growth temperature of 60 C, and 6.6 0.8 nm to 14.2 6.4 nm at a high growth temperature of 100 C.