Gamma radiation induced synthesis of 2,3-Epoxy propyl methacrylatestabilized Gold Nanoparticles for catalytic application

i.Introduction

�The high surface area provided by metal nanoparticles make them extremelyefficient as catalytic materials to carry out reactions that are otherwise difficult toinitiate [1].�In recent years, radiolytic reduction route for generation of metal nanoparticleshas emerged as a clean, environment friendly, room temperature technique fordesigning nanoparticles of desired morphology [2].�The choice of a suitable capping agent/ stabilizer for providing optimum stabilityto the metal nanoparticles is essential to ensure efficient catalytic activity.

ii. Experimental

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Nilanjal Misra*, Virendra Kumar, N.K. Goel, Lalit VarshneyRadiation Technology Development Division

Bhabha Atomic Research Centre, Mumbai-400085

Noble metal nanoparticles are widely employed as catalysts for carrying out a vast array of organic reactions. The primarychallenge involved in the synthesis of noble metal nanoparticles is the stabilization of these particles using a suitable capping/stabilizing agent. The use of ionizing radiation for the synthesis of metal nanoparticles is a clean, room temperature process devoidof use of any external chemical reducing agents. In this work, we report the 60Co-Gamma radiation induced synthesis of 2,3-Epoxypropyl methacrylate stabilized gold nanoparticles (EPMA-Au-NPs) and their application as a catalyst for reduction of p-nitrophenolto p-aminophenol in presence of NaBH4. The system was tested for catalytic application by spectrophotometrically monitoring thereduction of p-nitrophenol (PNP) to p-aminophenol (PAP) in presence of NaBH4. The intensity of p-nitrophenol, which absorbs at400 nm, was observed to decrease with time in presence of NaBH4 and EPMA-Au NPs catalytic system, whereas no change wasobserved in absence of the catalyst. The reaction was found to proceed rapidly to completion in presence of EPMA-Au-NPscatalytic system within 25 minutes.

Schematic diagram of catalytic reduction of p-nitrophenol by Au NP catalyst

ii. Experimental

�For fabrication of EPMA-Au NPs, An aqueous solution containing 1 ×10-4 moldm-3 Au3+, 0.1% EPMA (w/v), 0.5 mol dm-3 2-propanol was purged with N2 andirradiated for an absorbed dose of 1.0 kGy. The formation of Au NPs wasindicated by development of pink color�To determine the catalytic efficiency of EPMA-Au NPs, Aqueous solutions of p-nitrophenol and NaBH4 were mixed and the solution diluted with nanopure waterto maintain a final molar ratio of 1:100. To the solution was added an optimizedconcentration of radiolytically synthesized EPMA-Au NPs. The reaction mixturewas monitored using a spectrophotometer within the wavelength range of 290-450nm.

iii. Result & discussion

�The EPMA-Au NPs were characterized by TEM analysis. It was observed thatthe nanoparticles formed were uniformly dispersed and spherical in shape withaverage particle size in the range of 8-10 nm .�PNP solution exhibits a strong absorption peak at 317 nm which isinstantaneously red-shifted to 400 nm when treated with an aqueous solution ofNaBH4. The intense yellow colour of p-nitrophenolate ions (400 nm) remainsunchanged in the absence of any catalysts. However, addition of EPMA-Au NPscatalytic solution to the p-nitrophenolate solution results in a gradual decrease inthe peak intensity with time. Simultaneously, a second, broad peak appears at~295nm which confirmsn the formation of the product i.e. p-aminophenol. Theentire reaction was found to proceed to completion within a period of 25 minutes.

iv. Conclusion

The present work highlights the first reported use of EPMA as a stabilizer forgamma radiation induced fabrication of Au nanoparticles in the absence of anyexternal reducing agent. These EPMA-Au NPs were effectively employed ascatalysts for carrying out the catalytic reduction of p-nitrophenol to p-aminophenolin presence of NaBH4. The reaction was observed to show maximum activitywhen catalyst concentration was optimized at 10µM

Figure 1: TEM image of EPMA-Au NPs

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Figure 2: UV-Visible spectra of 100µM PNP in presence of NaBH4 and 10µM EPMA-Au NPs after (a) 0 min (b) 5 min (c) 10 min (d) 15 min (e) 20 min and (f) 25 min

v. References1. Britt H., Janssens T. V. W., Clausen B. S., Falsig H., Christensen C. H., Nørskov J. K., Nano Today. 2007, 2, 14-18.2. Misra N., Kumar V., Borde L., Varshney L., Sens. Actuat. B. 2013, 178, 371– 378.