Porous zirconium and tin phosphonates incorporating 2,2 '-bipyridine as supports for palladium nanoparticles
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abstract
We have utilized a 2,2-bipyridinediyl-5,5-bis(phosphonate) crosslinker and methylphosphonate as a 'spacer' unit to prepare a series of porous ZrIV and SnIV phosphonates which possess covalently bound bipyridine moieties. The materials are agglomerates of 5-20 nm particles which show BET surface areas exceeding 500 m2/g. The surface area and size of the phosphonate nanoparticles have been shown to be strongly dependent on the amount of methylphosphonate spacer unit. These hybrid materials are stable to >450 C in TGA under air. The compounds have been used to coordinate PdII from solution, which was then reduced to form nanoparticles within the phosphonate matrix. After reduction, the bipyridyl sites are no longer occupied by PdII, and are available for further coordination. The Pd0 nanoparticles can be made in two different size regimes: 10-15 nm by reduction in ethanol and 2-4 nm when reduced at elevated temperature under hydrogen. The nanoparticles are stable to 450 C and are maintained without the use of surfactants or stabilizers. Increasing the reduction temperature has no evident effect on the final size of the nanoparticles, indicating that their growth is limited by the pore structure of the phosphonate matrix, which prevents aggregation, even at 450 C. These materials have been explored by PXRD, TGA, TEM, SAXS, and UV-Vis spectroscopy. 2011 Elsevier Inc. All rights reserved.
