PHYS01200704032 Debes Ray - Homi Bhabha National Institute

Absorbance
Chapter 6: High-Yield Synthesis of Gold Nanoparticles
function of time. The value of t s (~ 3 hrs) corresponds to when at which the absorbance curve
shows saturation. Figure 6.1 shows the UV-visible spectroscopy of 1 wt% P85 with 0.004
wt% salt and after the gold salt added in next 4 steps of 0.004 wt% up to resultant salt
concentration of 0.02 wt%. There is an increase in absorbance as the gold nanoparticles
concentration increases with increasing salt by step addition. A linear gain in the nanoparticle
yield is observed in step-addition method as expected if all the gold concentration is utilized
in the formation of nanoparticles (inset of Figure 6.1).
2.5
2.0
1 wt% P85 + 0.02 wt% HAuCl4.3H2O
Step addition
Direct addition
1.5
1.0
0.5
0.0
200 400 600 800
Wavelength (nm)
Figure 6.2. UV-Visible spectra of 1 wt% P85 with 0.02 wt% HAuCl 4 .3H 2 O compared with
and without step-addition.
Figure 6.2 shows comparison of the data if the salt concentration of 0.02 wt% (5
0.004 wt%) is added directly instead of steps, which suggests a very low yield of gold
nanoparticles. Thus step-addition method can be used to greatly enhance the yield of gold
nanoparticles using block copolymers if the step addition concentration is sufficiently small
in each step to maintain the reduction of gold ions. However, the application of this method is
135