Majumdar et al. Int. J. Res. Chem. Environ. Vol.2 Issue 4 Oct. 2012(338-344) (338) International Journal of Research in Chemistry and Environment Vol. 2 Issue 4 Oct. 2012(338-344) ISSN 2248-9649 Research Paper Terminalia Arjuna Bark Extract Mediated Size Controlled Synthesis of Polyshaped Gold Nanoparticles and Its Application in Catalysis Majumdar Rakhi, * Bag Braja Gopal Department of Chemistry and Chemical Technology, Vidyasagar University, Midnapore 721102, WB, INDIA Available online at: www.ijrce.org (Received 09 th September 2012, Accepted 28 th September 2012) Abstract: The bark extract of Terminalia arjuna, a well known cardiac tonic, is rich in different types of plant secondary metabolites such as triterpenoids, saponines, tannins, flavanoids, etc. We have demonstrated the use of the bark extract for the synthesis of gold nanoparticles at room temperature under very mild conditions. The synthesis of the gold nanoparticles was complete in several minutes and no extra stabilizing or capping agents were necessary. The gold nanoparticles were characterized by HRTEM, AFM, Surface Plasmon Resonance Spectroscopy and X-Ray Diffraction studies. The synthesized colloidal gold nanoparticles were used as a catalyst for the sodium borohydride reduction of 4-nitrophenol to 4- aminophenol. Keywords: catalytic reduction, gold nanoparticle, green synthesis, Terminalia arjuna, XRD Introduction Metal nanoparticles in the size range of 1-100 nm exhibit unique optical, physical, chemical and magnetic properties compared to the bulk solids [1] . Gold, the commonly used ornamental and coinage metal in the macroscale, has become an area of tremendous investigations in the nanoscale during the last two decades because of its applications in catalysis [2] , biotechnology [3] , drug delivery, biodiagnostics [4,5] , medicine and electronics [6] . Depending upon their size, shape and degree of aggregation, the gold nanoparticles (AuNPs) can exhibit different colors. Various methods for the synthesis of nanoparticles have been developed over the years focusing on control over their shape, size, solubility, stability, etc. [7,8] . The bio-based “bottom–up” protocol for the synthesis of AuNPs has recently been demonstrated to be a more environment friendly approach to obtain nanostructures with more homogeneous chemical composition with fewer defects. The extracts of Alfa-alfa [9] , Aloe vera [10] , Syzygium cumini [11] and Bayberry tannin [12] have recently been utilized for the synthesis of AuNPs. While investigating the utilization of triterpenoids, the C30 plant secondary metabolites, as renewable functional nano entities [13-16] , it occurred to us that the medicinally important bark extract of Terminalia arjuna, rich in polyphenolic compounds, can be utilized for the synthesis AuNPs from HAuCl 4 . Herein we report a very mild and environment friendly method for the synthesis of AuNPs from the bark extract of Terminalila arjuna without any additional capping or stabilizing agents. The AuNPs were characterized by High Resolution Transmission Electron Microscopy (HRTEM), Atomic Force Microscopy (AFM), Surface Plasmon Resonance spectroscopy and X- Ray diffraction studies. Catalytic activities of the synthesized colloidal gold nanoparticles were studied by the reduction of 4-nitrophenol to 4-aminophenol. Material and Methods Au(III) solution: HAuCl 4 (35.4 mg) was dissolved in deionized water (10 mL) to obtain a 10.42 mM Au(III) stock solution. Preparation of the Bark Extract of Terminalia arjuna: Finely powdered Terminalia arjuna bark (50 g) was suspended in methanol (200 mL) and stirred magnetically at room temperature for 2 h and then filtered. Volatiles of the reddish brown filtrate were removed under reduced pressure to afford a reddish brown solid (3.0 g). The finely powdered bark extract of Terminaia arjuna (0.005 g) was suspended deionised water (10 mL) and sonicated in an ultra sonicator bath for 10 minutes to get a semi transparent solution (500 mgL -1 ). Synthesis of Nanoparticles: Aliquots of Au (III) solution (0.16 mL, 10.42 mM each) were added drop-wise to the bark extract solution (containing polyhydroxy aromatic compounds) to prepare a series of stabilized AuNPs where concentration of the bark extract varied from