Seeded and Non-Seeded Methods to Make Metallic Nanorods and Nanowires in Aqueous Solution
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Seeded and Non-Seeded Methods to Make Metallic Nanorods and Nanowires in Aqueous Solution Ta pan K . Sau a nd Ca therine J . Murp hy Depar tment of Chemistr y an d Biochemistr y, Univer sity of South Car olina, Columbia, SC 29208.
ABSTRACT Gold and silver nanorods/wires of different dimensions were obtained by wet-chemical seeded and non-seeded growth methods. INTRODUCTION Considerable attention has been attracted to prepare nanomterials confined in various dimensions to harvest their unique size- and shape-dependent physicochemical properties such as optical, electronic, electrical, magnetic, catalytic, etc. for their potential applications in nanodevices.1 We have reported2 the synthetic methods for the production various aspect ratio Au and Ag nanorods and nanowires. Here we describe in addition to so-called ‘seed-mediated’ process, ‘non-seeded’ processes to synthesize Au and Ag nanorods and nanowires. We explore the effects of variation of [Au3+]/[seed] ratio and surfactant on the seeded Au nanorod preparation, and two new one-pot synthetic methods for the preparation of Au nanorod and Ag nanorod/wires.
EXPERIMENTAL HAuCl4.3H2O, l-Ascorbic acid (AA), cetyltrimethylammonium bromide (CTAB), trisodium citrate, and silver nitrate were used as purchased (Aldrich). A 10mL solution of Au seed particles was prepared by the reduction of 2.5 x 10-4 M HAuCl4.3H2O by 4.0 x 10-4 M ascorbic acid containing 2.5 x 10-4 M tri-sodium citrate. The seed solution was used between one and two hour after its preparation. Typically appropriate amount of such as 0.125 mL 0.01 M HAuCl4.3H2O, 0.020 mL 0.1 M ascorbic acid (AA), and finally seed particles were added one by one to a given quantity of 0.1 M CTAB solution. The reaction mixture was gently mixed (by inversion of test tube) after addition of each reactant. The reversal in the order of addition of ascorbic acid and seed particles did not give rise to any noticeable change. Addition of the yellow solution of HAuCl4.3H2O to the CTAB solution led to a brown-yellow color. The brown-yellow color disappeared on the addition of ascorbic acid.
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In the one-pot synthesis of Au nanorods, appropriate quantity of silver nitrate was added to a solution containing desired amount of CTAB, HAuCl4.3H2O, and AA.
In a typical
experiment, 0.030 mL silver nitrate (0.01 M) was added to a solution containing 4.8 mL CTAB (0.1 M), 0.200 mL HAuCl4.3H2O (0.01 M), and 0.032 mL AA (0.1 M). The reaction mixture was gently mixed after the addition of silver nitrate. A good yield of short aspect ratio rods were obtained in the range roughly between 3.0 x 10-4 M and 6.0 x10-4 M HAuCl4.3H2O, and 6.0 x 104
M and 8.0 x10-4 M AgNO3 for 0.1 M CTAB. One-pot synthesis of silver nanorods/wires
involves boiling of aqueous AgNO3 with trisodium citrate in the presence of small quantity of NaOH.3 Au nanorods were obtained as usual by centrifuging the sample solution twice and redispersing the desired solid residue in DI water. No separation by centrifugation is required for silver nanowires/rods. TEM
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