Aqueous dispersions of monodisperse Pt, Pd, and Au nanoparticles stabilized by thermosensitive polymer for the efficient reduction of nitroarenes

Abstract

The reduction of nitroarenes is usually catalyzed by heterogeneous catalysts. In this work, highly stable aqueous dispersions of monodisperse Pt, Pd, and Au nanoparticles stabilized by thermosensitive polymer, poly(N-isopropylacrylamide) (PNIPAM), are conveniently synthesized with the average sizes of 2.3, 3.1, and 2.3 nm, respectively. The modulation of the hydrophilic-hydrophobic nano-environments of the catalysts can be selectively provided by utilizing the temperature-responsive characteristics of PNIPAM. They are effective and thermosensitive pseudohomogeneous catalysts for nitroarenes reduction. The decreasing trend of catalytic activity is as follows: PNIPAM-Au > PNIPAM-Pd > PNIPAM-Pt. The catalytic reduction of nitrobenzene (NB), 4-nitrophenol (4-NP), and o-nitroaniline (o-NA) follow the pseudo-first-order kinetics, and the catalytic rates can be tuned by utilizing their temperature-responsive behavior. PNIPAM-Au nanocatalysts exhibit high turnover frequencies (TOF) up to 84, 12.9, and 40 min−1 for catalytic reduction of NB, 4-NP, and o-NA at 20 °C, respectively, which are one of the highest values ever reported.