3.4 and 3.6), the process of phase transfer is seen as a transfer of color from the
organic phase to the aqueous phase. That the movement of the gold particles between phases was almost 100% can be observed from the UV–vis spectra recorded
from toluene before phase transfer (full line, Figure 3.11) and water after phase
transfer (dashed line, Figure 3.11). The UV–vis spectra recorded from the two
phases are almost identical. There is little broadening of the surface plasmon resonance after phase transfer, indicating no aggregation of the nanoparticles consequent to their movement [76]. The authors have shown that the aqueous gold and
palladium solutions were extremely stable with no sign of degradation even after
storage for several months [76]. This is graphically illustrated in the TEM micrographs recorded from the gold nanoparticles in the toluene phase (Figure 3.12A)
and the aqueous phase one month after phase transfer of the gold nanoparticles
Fig. 3.10. TEM micrographs of o-thiol carboxylic acid
functionalized gold colloid at (a) pH 10, (b) pH 7, and (c) pH
4. Scale bars represent 10 nm, 25 nm and 50 nm, respectively.
(Reprinted with permission from [74], 8 2000, Royal Society of
Chemistry).
3.4 Moving Gold Nanoparticles Around 45