Mesoporous Au-loaded Fe 2 O 3 Nanoparticle Assemblies for Chemoselective Reduction of Nitroarenes
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Mesoporous Au-loaded Fe2O3 Nanoparticle Assemblies for Chemoselective Reduction of Nitroarenes Ioannis Papadas1, Stella Fountoulaki2, Ioannis N. Lykakis2 and Gerasimos S. Armatas1,* 1
Department of Materials Science and Technology, University of Crete, Heraklion 71003, Greece. 2 Department of Chemistry, Aristotle University of Thessaloniki, Thessaloniki 54124, Greece
ABSTRACT In this article, we report the synthesis of unique mesoporous Au-loaded Fe2O3nanoparticle assemblies (Au/Fe2O3-NPAs) through a surfactant-assisted aggregating assembly method. The resulting network structure, which composed of small Au nanocrystals (ca. 5 nm) finely dispersed on surface of Fe2O3 NPs (ca. 6–7 nm), possesses a 3D open-pore structure with a BET surface area of 123 m2g-1 and uniform mesopores (~4.5 nm). Au/Fe2O3NPAs showed high catalytic activity and chemical stability for the selective transformation of nitroaromatic compounds into the corresponding amines, using 1,1,3,3-tetramethyl disiloxane as reducing agent at ambient conditions.
INTRODUCTION Porous assembly architectures from inorganic nanoparticles (NPs) are of great interest for applications in catalysis, solar energy conversion, optoelectronics and size-selective adsorption and separation [1]. Beyond individual NPs, three-dimensional (3D) porous networks of assembled NPs hold great promise for the development of novel materials with advantageous characteristics. For instance, the unique catalytic activity of metal-oxide NPs will be best exploited when they are integrated into extended mesoscopic structures. This is because a 3D open pore structure may enable fast diffusion of the target molecules within the assembled NPs, yet could prevent interparticle agglomeration during catalytic reactions. In addition, the assembly of catalytic NPs into aligned nanostructures could induce new collective properties between adjacent particles not present in the original constituents [2]. Recently, we have reported a surfactant-assisted aggregating method for obtaining mesoporous Au-loaded TiO2 NP assemblies with accessible pore channels and large surface area. The pore walls of these materials are made of interconnected gold (particle size from ~3 to ~9 nm) and TiO2 (ca. 8 nm) NPs and exhibited high catalytic activity for the reduction of nitroaromatics into the corresponding amines, using sodium borohydride (NaBH4) as reducing agent [3]. Indeed, in these materials the chemoselective propensity of gold for the transformation of nitro into amine groups was attributed to the activation of –NO2 group on the gold atoms located at the metal–support interface. However, apart from gold NPs, the nature of support has also a strong influence on such hydrogenation reactions [4]. Considering the possibility that suitable preparation of supported gold NPs might offer new opportunities to develop new efficient catalytic materials, we examined the surface of Fe2O3 NP assemblies (NPAs) as an effective host matrix for stabilizing gold NPs, and we studied the hydrogenation of nitroaromatic compounds
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