PHOTOCHEMICALLY GENERATED Au NANOPARTICLES ON SOLID SUPPORTS AND THEIR USE AS CATALYSTS

MARÍA GONZÁLEZ BÉJAR; GENIECE HALLETT-TAPLEY; JAZMÍN SILVERO; DANIELA MÁRQUEZ-SOTO; CHARLES-ONEIL CRITES; KATHERINE L. MCGILVRAY; J. C. NETTO-FERREIRA; J. C. SCAIANO

Valencia

Simposio; VII SIMPOSIO INVESTIGADORES JÓVENES REAL SOCIEDAD ESPAÑOLA DE QUÍMICA (RSEQ) Y SIGMA-ALDRICH; 2010

RSEQ

PHOTOCHEMICALLY GENERATED Au NANOPARTICLES ON SOLID SUPPORTS AND THEIR USE AS CATALYSTS María González Béjar, Geniece Hallett-Tapley, Jazmín Silvero, Daniela Márquez-Soto, Charles-Oneil Crites, Katherine L. McGilvray, J. C. Netto-Ferreira and J. C. Scaiano Department of Chemistry and Centre for Catalysis Research and Innovation, University of Ottawa. 10, Marie Curie. Ottawa, Ontario, K1N 5N6. Fax: (+)1 613 562 5633, maria@photo.chem.uottawa.ca Nanoparticles have attracted a lot of attention as heterogeneous catalysts for organic reactions in the 21ST century. The development of metal nanoparticles, in particular gold nanoparticles (AuNP), utilizing the basic fundamentals of photochemistry and physical organic chemistry has been successfully applied in the Scaiano group. Specifically, Scaiano et al. have been able to produce unprotected, ?naked? AuNP in aqueous solutions. Au nanoparticles can be efficiently generated from HAuCl4 and Irgacure 2959 (I-2959) in aqueous and CH3CN solutions. Following UVA irradiation of I-2959, 2-hydroxy-2-propyl (ketyl) radicals are generated via Norrish Type I  cleavage and rapidly reduce Au3+ to Au0 (Scheme 1). The exceptional stability of these AuNP and narrow size distribution (8-40 nm) make these nanomaterials ideal candidates for catalytic testing. The use of Au nanoparticle composites in catalysis presents two important advantages. The first advantage focuses on the ability of the solid support to reduce nanoparticle mobility, thus decreasing the probability of Au nanoparticle agglomeration. Minimizing aggregation of the nanoparticles is crucial for conserving small particle size and the catalytic properties of the nanomaterial composites. The second advantage is that a simple centrifugation allows for catalyst removal from the reaction mixture. Therefore, we have focused on the formation of AuNP on various solid supports (hydrotalcite, γ-Al2O3 and TiO2-P25) using photochemical methods and the potential applications of these composites as green catalysts. The use of photochemistry eliminates the need for harsh reaction conditions, such as high temperature and pressure, preventing the loss or destruction of the NPs. The nanoparticles were successfully characterized using diffuse reflectance UV-visible spectroscopy, SEM, TEM, X-ray diffraction spectroscopy (XRD) and X-ray photoelectron spectroscopy (XPS). The supported AuNPs were found to be predominantly spherical and ranged in size from 20 ? 140 nm depending on the support and the % Au loading. Three model reactions have been used to test our new systems as heterogeneous catalysts in different media: 1) Reduction of 4-nitrophenol to 4-aminophenol; 2) Alcohol oxidation and 3) Diels-Alder reaction between 2-hydroxychalcone and 1,3-cyclohexadiene. In all three cases, supported AuNP have proven to be efficient as catalysts. Reaction conditions and product yields will be discussed in further details in this contribution. Figure 1. Photochemical synthesis of supported AuNP and catalytic reactions tested.