Figure 8.

The evolution of the optical absorption spectrum of three samples. With different volume ratios of HAuCl₄ and Na₂S₂O₃ during the reactions: (a) 5 ml HAuCl₄ + 2.2 ml Na₂S₂O₃, (b) 5 ml HAuCl₄ + 1.4 ml Na₂S₂O₃, and (c) 5 ml HAuCl₄ + 0.8 ml Na₂S₂O₃. Samples were taken during the reaction and diluted five times with DI water then immediately measured by UV–vis-NIR spectrophotometer.