Metal/triphenylamine Ethylene Dendrimer Nanocomposites: Preparation And Their Application In Catalysis

Triphenylamine ethylene derivative conjugated dendrimers (DPSDA) were synthesized and used as stabilizers for preparing a series of metal nanocomposites. Then the nanocomposites were applied as catalyst in hydrogenation of phenyl aldehydes and photodecomposition of water.(1) DPSDA were synthesized by Witting and Heck reactions in different generations, and their structures were both characterized by 'HNMR and mass spectrum. The Pt-diphenylamino styryl diacetic acid nanocomposites had been successfully prepared with the alcohol reduction method and characterized with UV-vis, TEM, FTIR, XRD, fluorescence spectroscopy and photo-electrochemical method, respectively. Platinum core/conjugated organic molecule shell nanocomposites formed as DPSDA molecules attached to the surface of Pt atoms through carboxyl groups. The sizes of the nanocomposites were both depended on the generation of DPSDA and the molar ratio of DPSDA/H2PtCl6. A higher generation dendrimer as the stabilizer or increasing the molar ratio of dendrimer/metal both could obtain metallic nanoparticles in smaller sizes.(2) The Pt nanoparticles stabilized by the conjugated dendrimers were found to be very effective for the catalytic hydrogenation of phenyl aldehydes to phenyl alcohols. Conversion of 3-phenoxybenzaldehyde reached to ca. 100% in a two-hour reaction with Pt@DPSDA-G2-150 as the catalyst, which were much higher than that of Pt nanoparticles stabilized by non-conjugated Fréchet-type dendrimers. The catalytic activity of Pt nanocomposites were both influenced by the composition of the catalyst and the molar ratio of the substrate to catalyst. The catalytic activity decreased with the increase of the molar ratio of substrate to catalyst.(3) The Pt nanocomposites showed good absorption in UV-vis region. DPSDA molecules in excited state could transfer photo-electron to the platinum nanoparticle. Under irradiation of UV-vis light, hydrogen was produced from photodecomposition of water using Pt@DPSDA nanocomposite as the catalyst in the presence of EDTA. The catalytic activity of Pt nanocomposites was both influenced by the composition and the amount of the catalyst. The Pt@DPSDA-G2 nanocomposite demonstrated nice activity and stability as the molar ratio of Pt/DPSDA-G2 equals to 100. The catalytic activity was much higher when use the mixtures of DPSDA-G1 and DPSDA-G2 as photosensitizers than use DPSDA-G2 only.(4) Au-core Pt-shell Bimetallic nanocomposites capped with dendrimer DPSDA-G1 were prepared by the sequential reduction method with Au nanoparticles as seeds, and were characterized by UV-vis, TEM, XRD, and photo-electrochemical methods. The catalytic activity in photodecomposition of water was significantly enhanced in the presence of bimetallic Pt-Au nanoparticles as compared to single metal or the mixtures of single-metal nanoparticles.