Hydrophilic swellable metal-organic framework encapsulated Pd nanoparticles as an efficient catalyst for Cr(VI) reduction

Controllable integration of metallic nanoparticles and metal-organic frameworks (MOFs) may create a new material with multifunctional applications. In this work, an emerging type of core-shell nanostructure, in which metallic Pd nanoparticle cores were encapsulated by MOF (ZIF-67) shells, was facilely synthesized through an impregnation-reduction process. The as-synthesized Pd@ZIF-67 material, with highly dispersed Pd nanoparticles encapsulated in the porous ZIF-67 structure, exhibited favorable catalytic performance towards the formic acid (HCOOH)-induced reduction of highly toxic hexavalent chromium (Cr(VI)). In this process Cr(VI) was converted to Cr(III) within 5 min, and the material could be reused 10 times without significant loss of its catalytic activity. The highly hydrophilic and swellable nature of the ZIF-67 was proposed to be responsible mainly for the favorable durability of the Pd@ZIF-67. The results provided in this work may pave a way for the concise preparation of nano-hybrid catalysts with high performance and durability for pollutant elimination.