Phosphine-based porous aromatic frameworks for gold nanoparticle immobilization with superior catalytic activities

Triphenylphosphine (PPh3) and dipheny-2-pyridylphosphine (PPh2Py), which are usually used as ligands to protect gold nanoparticles (AuNPs), were selected as monomers to build up porous aromatic frameworks (PAFs) with high surface areas for AuNPs immobilization. Using the cost-effective Friedel-Crafts alkylation reaction, phosphine-based PAFs (PAF-93 and PAF-94) were successfully synthesized, and they possessed high stabilities as well as high surface areas. AuNPs with sizes of smaller than 2 nm in Au@PAF-94 were obtained owing to the stronger interactions with P and N donors in PAF skeletons, thus leading to high catalytic activities. According to the pseudo-first-order kinetics, the k(app) (apparent rate constant) value for Au@PAF-94 in the reduction reaction of 4-nitrophenol is 2.2 x 10(-2) s(-1), which is superior to most of the presently reported AuNP catalysts with solid supports under similar conditions. Additionally, Au@PAFs exhibited excellent recyclability and retained their high catalytic activities after five successful cycles.