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 8.0 nm) were synthesized in aqueous media via sonochemical method using diblock copolymer as stabilizer. The zwitterionic sulfobetaine block copolymer provided thermodynamic (5 days at 65 °C) and kinetic (1 year at 25 °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.