Effect of citrate on poly(vinyl pyrrolidone)-stabilized gold nanoparticles formed by PVP reduction in microwave (MW) synthesis

Colloidal PVP (poly(vinyl pyrrolidone))–stabilized gold nanoparticles (PVP–AuNPs) are synthesized in aqueous solution with PVP as a reducing and stabilizing agent using a short microwave (MW) heating duration of 1 min. The size and uniformity of the synthesized PVP–AuNPs can be varied by modifying the concentration of sodium citrate (Na3Ct), which acts predominantly as mediator of the stability of PVP–AuNP formation during the rapid synthesis. Due to the increase in the Na3Ct concentration, the number of citrate ions adsorbed on the growing surface of AuNPs increase, and less reactive gold solute complexes are formed, leading to slow stable reactions that produce small, uniform colloidal PVP–AuNPs. We therefore demonstrate that by adjusting the Na3Ct concentration used in the PVP reduction, the diameter of PVP–AuNPs was varied from 19.47 ± 3.97 nm to 7.94 ± 0.14 nm when using constant concentrations of chloroauric acid (HAuCl4) and PVP.

► We report the citrate effect on PVP–AuNPs formed by PVP reduction in MW synthesis.
► An increase in citrate concentration leads to slow stable reactions in synthesis.
► It contributes to the size decrease and the uniformity improvement of PVP–AuNPs.
► Therefore, we produced uniform PVP–AuNPs with diameter of 7.94 ± 0.14 nm in 1 min.