One-Pot Silver Nanoring Synthesis
© The Author(s) 2009
Received: 13 October 2009
Accepted: 1 December 2009
Published: 16 December 2009
Silver colloidal nanorings have been synthesized by reducing silver ions with NaBH4 in trisodium citrate buffers. pH increase, by addition of NaOH, was used to speed up reduction reaction. The UV–vis absorption spectra of resulting silver nanorings showed two peaks accounting for transverse and longitudinal surface plasmon resonance, at ≈400 nm, and between 600 and 700 nm, respectively. The shapes of these silver nanoparticles (nanorings) depended on AgNO3/NaBH4 ratio, pH and reaction temperature. Particles were analysed by transmission electron microscopy, scanning electron microscopy and X-ray diffraction. A reaction pathway is proposed to explain silver nanoring formation.
Nanoscale materials and structures for high value applications is an emerging area of nanoscience and nanotechnology. Nanomaterials, usually ranging from 1 to 100 nanometers (nm), may provide solutions to technological and environmental challenges in the areas of solar energy conversion, catalysis, medicine and water treatment . Among such materials, silver nanoparticles have been intensively studied because of their intriguing optical, electronic, mechanical and bactericidal properties . Several techniques have been employed for the synthesis of noble metal nanoparticles, such as gas evaporation, arc plasma, sputtering, electrochemical methods, laser ablation , etc. This communication describes the synthesis of silver nanoparticles by chemical reduction of silver ions by NaBH4. We report herein the formation of ring-shaped silver nanoparticles synthesized in a one-pot experiment. Extraordinary optical properties from noble metal such as gold and silver are termed surface plasmon resonance induced by the collective oscillation of electron density . It is known that the optical response of silver nanospheres exhibits a single absorption peak corresponding to surface plasmon resonance at about 400 nm. However, aggregated silver nanospheres give rise to two surface plasmon bands corresponding to transverse and longitudinal resonance . Several techniques are already known for the elaboration of silver nanoparticles of different shapes like rods, triangular or hexagonal plates by varying the conditions of reduction and capping agent [7–10]. In contrast, little work has been done on the influence of pH conditions on the production of silver nanoparticles .
Trisodium citrate was obtained from Alfa Aesar; sodium hydroxide, silver nitrate and sodium borohydride were purchased from VWR and used as received. Photomicrographs of nanoparticles were obtained with a JEOL 7400 FEGSEM and a JEOL 2010 TEM operated at 400 KV accelerating voltage. XRD pattern was obtained with JEOL 2010 TEM. UV–Vis spectra of nanoparticle suspensions were recorded with a Perkin Elmer λ 25 UV–Vis spectrophotometer.
Seven pill boxes containing 4 mL of 10−3M trisodium citrate and variable amounts of sodium hydroxide were maintained at 21 ± 0.5 °C under stirring. Identical volumes of 5.10−3M silver nitrate (0.35 mL) and 10−2M NaBH4 (0.15 mL) were quickly added simultaneously to each pill box under vigorous stirring. Pill boxes were then stored in the dark. The same experiment was repeated at 25± 0.5 °C.
Results and Discussion
pH values of the different mixtures
We have realized for the first time a one-pot synthesis and structure characterization of silver nanorings. Uniformly sized silver nanorings are characterized by well-defined crystalline structure along the whole ring as shown by XRD patterns. These crystalline structures have unique plasmonic properties that would find applications in nanoscaled photonics, plasmonic devices and optical manipulation.
We acknowledge Dr. M. Guilloton for help in editing this manuscript and the ‘Conseil Régional du Limousin’ for financial support.
This article is distributed under the terms of the Creative Commons Attribution Noncommercial License which permits any noncommercial use, distribution, and reproduction in any medium, provided the original author(s) and source are credited.
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