Self-limiting synthesis of Au–Pd core–shell nanocrystals with a near surface alloy and monolayer Pd shell structure and their superior catalytic activity on the conversion of hexavalent chromium

Abstract In eliminating environmental chromium pollution, hexavalent chromium (Cr(VI)) reduction by HCOOH on Pd-based bimetallic/multimetallic nanocatalysts is attracting an increasing attention. However, it is still a challenge by precisely controlling the surface interface structure of the nanocrystals (NCs) to obtain highly efficient nanocatalysts on Cr(VI)) conversion. Here, a simple and robust synthesis method for Au-Pd core-shell NCs with a special interface structure has been developed by a novel self-limiting strategy. This interesting structure has a near surface alloy (NSA) of AuPd layer on Au core with outer surface of monolayer (ML) of Pd shell (denoted as NSA/ML), which is achieved only by one-pot synthesis. The self-limiting strategy is developed based on the unique catalysis reduction reaction of Au core, with which the growth of Pd shell is internally regulated by the surface Au atoms until the Au–Pd NCs with NSA/ML structure i.e. Au@AuPd@Pd ML NCs are formed. Furthermore, the Au–Pd core–shell NCs with the shell from NSA to NSA/ML structure can be simply obtained by adjusting the added amount of Pd precursor. More importantly, the catalytic activities of Au–Pd NCs for the conversion of Cr(VI) to Cr(III) present a notable difference for the Pd in Au@AuPd and Au@AuPd@Pd ML structures, and the Au@AuPd@Pd ML NCs exhibited the superior catalytic activity for the conversion of Cr(VI). The present study demonstrates the core@NSA@shell ML is an efficient nanostructure to promote the catalytic performance of core–shell NCs for practical applications.