9.2
Seed-Mediated Growth Approach to the Synthesis of Inorganic Nanorods and
Nanowires
We have developed a seed-mediated growth approach to make silver and gold
nanorods and nanowires of controllable aspect ratio in aqueous solution, at room
temperature [20, 26–28]. Our method (Figure 9.2) starts with the reduction of a
metal salt in aqueous solution, by a strong reducing agent, to make 3–4 nm metallic ‘‘seeds’’ which are generally spherical. The seed reaction is done in the presence of sodium citrate to prevent the seeds from aggregating and precipitating.
The seeds are then added to a ‘‘growth’’ solution that consists of fresh metal salt,
and a surfactant, cetyltrimethylammonium bromide, CTAB, that directs the growth
of nanoparticles into nanorods and nanowires. Growth is initiated by the addition
Ag(I) or Au(III) salt + NaBH 4
seeds
more seeds
+ metal salt + ascorbic acid + CTAB
less seeds
+ metal salt + ascorbic acid + CTAB
Fig. 9.2. Cartoon showing the seed-mediated
growth approach to the synthesis of metallic
nanorods of controllable aspect ratio. In the
first step, metal salts are reduced with sodium
borohydride, a strong reducing agent, to metal
nanospheres (‘‘seeds’’) that are 3–4 nm in
diameter. In the subsequent growth steps,
seeds are added to fresh solutions of metal
salt in the presence of CTAB, and are reduced
with the weak reducing agent ascorbic acid.
The ratio of metal seed to salt controls the
aspect ratio, fewer seeds leading to longer rod
growth.
9.2 Seed-Mediated Growth Approach to the Synthesis of Inorganic Nanorods and Nanowires 287
Seed-Mediated Growth Approach to the Synthesis of Inorganic Nanorods and
Nanowires
We have developed a seed-mediated growth approach to make silver and gold
nanorods and nanowires of controllable aspect ratio in aqueous solution, at room
temperature [20, 26–28]. Our method (Figure 9.2) starts with the reduction of a
metal salt in aqueous solution, by a strong reducing agent, to make 3–4 nm metallic ‘‘seeds’’ which are generally spherical. The seed reaction is done in the presence of sodium citrate to prevent the seeds from aggregating and precipitating.
The seeds are then added to a ‘‘growth’’ solution that consists of fresh metal salt,
and a surfactant, cetyltrimethylammonium bromide, CTAB, that directs the growth
of nanoparticles into nanorods and nanowires. Growth is initiated by the addition
Ag(I) or Au(III) salt + NaBH 4
seeds
more seeds
+ metal salt + ascorbic acid + CTAB
less seeds
+ metal salt + ascorbic acid + CTAB
Fig. 9.2. Cartoon showing the seed-mediated
growth approach to the synthesis of metallic
nanorods of controllable aspect ratio. In the
first step, metal salts are reduced with sodium
borohydride, a strong reducing agent, to metal
nanospheres (‘‘seeds’’) that are 3–4 nm in
diameter. In the subsequent growth steps,
seeds are added to fresh solutions of metal
salt in the presence of CTAB, and are reduced
with the weak reducing agent ascorbic acid.
The ratio of metal seed to salt controls the
aspect ratio, fewer seeds leading to longer rod
growth.
9.2 Seed-Mediated Growth Approach to the Synthesis of Inorganic Nanorods and Nanowires 287