Preparation of monometallic and bimetallic alloy nanoparticles stabilized with sulfobetaine-based block copolymer and their catalytic activities

Abstract

Zwitterionic sulfobetaine-containing diblock copolymer, poly(ethylene glycol)methyl ether-block-poly[3-dimethyl(methacryloyloxy ethyl)ammonium propane sulfonate] (MPEG-b-PSBMA), was successfully synthesized and utilized as a stabilizer to prepare mono- and bimetallic nanoparticles. Precursor poly(ethylene glycol)methyl ether-block-poly[2-(N-dimethylamino)ethyl methacrylate] (MPEG-b-PDMA) diblock copolymer was first synthesized via atom transfer radical polymerization. PDMA blocks were reacted with 1,3-propanesultone to obtain MPEG-b-PSBMA diblock copolymer. Spherical monometallic gold (Au), platinum (Pt) and bimetallic alloy gold/platinum (Au/Pt), gold/silver (Au/Ag), and silver/platinum (Ag/Pt) nanoparticles (with a diameter below 8.0nm) were synthesized in aqueous media via sonochemical method using diblock copolymer as stabilizer. The zwitterionic sulfobetaine block copolymer provided thermodynamic (5days at 65 degrees C) and kinetic (1year at 25 degrees C) stability to the synthesized NPs without aggregation. Zwitterionic PSBMA blocks of MPEG-b-PSBMA diblock copolymer showed an upper critical solution temperature (UCST) in aqueous media. This thermo-responsive block copolymer provided better stabilization to metal NPs as compared with MPEG and PSBMA homopolymers. The structures of bi- and monometallic NP dispersions were characterized by measuring surface plasmon resonance and transmission electron microscopy. The prepared metal NP/polymer dispersions showed good catalytic activities (Ag/Pt>Au/Ag>Au>Au/Pt>Pt) in the reduction of p-nitrophenol to p-aminophenol.