PHYS01200704032 Debes Ray - Homi Bhabha National Institute

Chapter 6: High-Yield Synthesis of Gold Nanoparticles
purchased from Alfa Aesar. D 2 O (99.9 atom %D) was purchased from Sigma. All the
solutions were prepared in millipore H 2 O except in the case of neutron scattering experiments
for which H 2 O or D 2 O is used as solvent depending on the requirement of contrast condition.
All the products were used as received.
6.2.2. Synthesis of Gold Nanoparticles
The gold nanoparticles for obtaining high-yield in step-addition method were synthesized
from 1 wt% P85 block copolymer solution in presence of 0.02 wt% (0.508 mM) of
HAuCl 4 .3H 2 O added in steps of 0.004 wt% (5 times) in aqueous solution. This synthesis is
compared when the gold salt (0.02 wt%) is added directly. In the case of additional reductant
method, the amount of additional reductant (Na 3 Ct) is optimized by keeping the gold salt
concentration fixed and varying the Na 3 Ct concentration. The gold nanoparticles have been
synthesized using 1 wt% P85 up to gold salt concentration of 1 wt%. All the solutions were
kept at room temperature without any disturbances for about 3 hrs for the completion of the
reaction. The transparent solution becomes purple on the formation of nanoparticles.
6.2.3. Characterization of Gold Nanoparticles
The formation of gold nanoparticles is confirmed using UV-visible spectroscopy [19]. The
measurements were carried out using 6505 Jenway UV-visible spectrophotometer. The data
were collected in spectrum mode with a wavelength interval 1 nm from the samples held in
quartz cuvettes of path length 10 mm.
SANS has been used to examine the structures of block copolymers and gold
nanoparticles in the synthesis. The block copolymer structures were studied by preparing
samples in D 2 O where the block copolymer has a strong contrast. On the other hand, the
scattering from gold nanoparticles was measured by contrast matching block copolymer in a
mixed solvent of H 2 O and D 2 O (15% D 2 O). The measurements were performed on the SANS
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