Article pubs.acs.org/Langmuir
Syntheses and Characterization of Nearly Monodispersed, SizeTunable Silver Nanoparticles over a Wide Size Range of 7−200 nm by Tannic Acid Reduction Yanzhen Cao, Rongfeng Zheng, Xiaohui Ji, Hong Liu, Renguo Xie, and Wensheng Yang* State Key Laboratory for Supramolecular Structure and Materials, College of Chemistry, Jilin University, Changchun 130012, P. R. China S Supporting Information *
ABSTRACT: Nearly monodispersed spherical silver nanoparticles (Ag NPs) were synthesized by using tannic acid (TA) as both reductant and stabilizer in a 30 °C water bath. The size of the as-prepared Ag NPs could be tuned in a range of 7−66 nm by changing the molar ratio of TA to silver nitrate and pH of the reaction solutions. UV−vis spectra, TEM observations, and temporal evolution of the monomer concentrations for the reactions carried out at different experimental conditions showed that the improved size distribution and size tunability of the Ag NPs were mainly attributed to the use of TA, which could promote the balance of nucleation and growth processes of the NPs effectively. The size of the Ag NPs was extendable up to 200 nm in onepot fashion by the multi-injection approach. The size-dependent surfaceenhanced Raman scattering (SERS) activity of the as-prepared Ag NPs was evaluated, and the NPs with size around 100 nm were identified to show a maximum enhanced factor of 3.6 × 105. Moreover, the as-prepared TA-coated Ag NPs presented excellent colloidal stability compared to the conventional citrate-coated ones.
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INTRODUCTION Gold nanoparticles (Au NPs) and silver nanoparticles (Ag NPs) have attracted extensive research interests due to their size/shape-dependent optical/electric properties and potential applications in catalysis,1−3 chemical and biological sensing,4,5 electronics,6 nonlinear optics,7 and surface-enhanced Raman spectroscopy (SERS).8 During the past decades, great efforts had been devoted to control the size and shape of Au and Ag NPs.9−23 In the classic Frens method, activity of the gold salt (tetrachloroauric acid) could be readily tuned by changing both the molar ratio of the gold salt/citrate and pH of the reaction solutions. As a result, nearly monodispsersed Au NPs with different sizes could be acquired by tuning the activity of the gold precursor.24,25 However, tuning the activity of silver salt (AgNO3) was less effective to control over the size of Ag NPs since the activity of the silver precursor is almost insensitive to molar ratio of the precursors/reductant and/or pH of the reaction solutions.17−19 Usually, strong reductant such as borohydride was used to prepare small Ag NPs (
