Synthesis of phosphine stabilized gold nanoparticles based on 9-BBN as a novel reducing agent and application in catalysis.

摘要

A simple, versatile single step method to synthesize phosphine-stabilized gold nanoparticles (TPP-AuNPs) of narrow size distribution using the mild reducing agent 9-borabicyclo [3.3.1]nonane (9-BBN) was developed. This single step procedure produces particles of less than 2 nm in diameter. The use of 9-BBN offers many advantages over other commonly used reducing agents. The particle growth process can be controlled and the particle size can be tuned by carefully controlling the conditions under which the reduction takes place. In addition, the approach is inexpensive and greener because the use of phase transfer reagents and the attendant rigorous purification steps are eliminated. Since 9-BBN is a mild reducing agent, the synthesis is compatible with a wide variety of o-functionalized capping ligands.;TPP-AuNPs can be used as precursors to AuNPs functionalized with various ligands by way of ligand exchange reactions to obtain AuNPs stabilized with different &ohgr;-functionalized alkythiols, other phosphines and bipyridines. The in-situ addition of capping ligands other than TPP to the reaction was demonstrated to reduce the need for ligand exchange reactions.;TPP-AuNPs also are soluble in water, thereby expanding their potential applications. The stability of TPP-AuNPs in water as a function of salt and sodium borohydride concentration, solvents with different dielectric constants, pH and temperature was investigated. The NPs were found to be stable in water as evidenced by UV-vis spectroscopy, TEM imaging and zeta potential measurements over time. Addition of salt and NaBH4 induced aggregation of the NPs.;The catalytic activity of TPP-AuNPs in aqueous solution was investigated using two model reactions: reduction of 4-nitrophenol by NaBH4 and the electron transfer reduction of hexacyanoferrate (III) by NaBH 4. The rate constants for the reduction reactions were found to depend on the surface area of the TPP-AuNPs. The TPP-AuNPs were recycled, however aggregation of the NPs was observed at the end of the reduction. The kinetic data for both reactions for the unsupported TPP-AuNPs was better compared with that for supported AuNP catalytic systems, indicating the good catalytic activity of TPP-AuNPs for these reactions.