Precise tuning of porosity and surface functionality in Au@SiO2 nanoreactors for high catalytic efficiency.

Abstract

Nanoreactor frameworks have many advantages over bulk catalyst structures in terms of providing a regular reaction environment and conformational stability. In this work, Au@SiO2 nanoreactor frameworks were chemically modified to improve the catalytic efficiency of o-nitroaniline reduction. The porosity of silica shells was readily controlled by introducing C18TMS as a porogen with heat treatment. The diffusion rate of the silica layers was tuned from 5.9 x 10(-19) to 2.1 x 10(-18) m(2) s(-1), which directly altered the turnover frequency and rate constant of the reaction. Carboxylate functionality was introduced on the gold cores of Au@SiO2 nanoreactors by 3-MPA addition. The reaction rate was enhanced by a maximum of 2.4 times compared to unfunctionalized catalysts through a strong interaction between carboxylate anions and o-nitroaniline. Totally, the rate constant of Au@SiO2 yolk-shell nanoreactors exhibits a 13-fold enhancement by diffusion and surface functionality control. These results indicate that the rational design of a nanoreactor framework with appropriate chemical functionalization can maximize the catalytic efficiency of various solution-phase reactions.