Nanoparticle spectra as a function of K
concentration and aging. UV-visible spectra of AuNPs produced from a mixture of 0.38 mM HAuCl4 aqueous solution with 2.71 mM or 3.62 mM K2CO3. A and B are 2.71 mM K2CO3 aged at 30 and 40 min, respectively, at an aeration volume of 40 mL. C, D, and E are 3.62 mM K2CO3 aged for 30 min each at aeration volumes of 20, 40, and 50 mL, respectively. All samples were aerated at a gas flow rate of 25.5 mL/min.