Size control over spherical silver nanoparticles by ascorbic acid reduction

Quasi-spherical silver nanoparticles were synthesized by using ascorbic acid as reductant and citrate as stabilizer in a 30 °C water bath. Average size of the silver nanoparticles decreased from 73 nm to 31 nm as pH of the reaction system increased from 6.0 to 10.5. Quantitative analyses indicated that reduction of the silver precursor was promoted at elevated pH attributed to increased activity of ascorbic acid. As a result, number of the nucleus and thus the size of the silver nanoparticles were tunable by simply changing pH of the reaction system. Moreover, the shape of the nanoparticles became more spherical-like after being heated at 100 °C for 2 h to facilitate the intraparticle ripening.