Covalent Organic Framework-Templated <i>N</i>-Heterocyclic Carbene-Functionalized Gold Nanoparticles for the Catalytic Reduction of Nitrophenol

Abstract

Herein, a hybrid material based on a covalent organic framework (COF) and N-heterocyclic carbene (NHC)-functionalized gold nanoparticles (AuNPs) was developed. The synthesis starts with the formation of an NHC@Au(I) complex, serving as the precursor for the AuNPs. This compound was either entrapped within the pores of the COF during its assembly (method 1) or infiltrated inside its pores after its formation (method 2). Our results demonstrate that method 1 yields AuNPs smaller than those produced by method 2. Electron microscopy analysis confirmed the successful embedding of AuNPs into the COF, with well-distributed NPs of smaller than 5 nm for method 1 and larger, agglomerated AuNPs (over 5 nm) for method 2. Additionally, nitrogen adsorption–desorption isotherms (BET analysis) indicated a significant reduction in surface area after gold integration, decreasing from an initial value of 1885 to 1106 m2/g and 910 m2/g for the two methods, respectively. The synthesized heterogeneous AuNP catalysts effectively facilitated the reduction of nitrophenol at ambient temperature, exhibiting rapid and efficient catalysis. Notably, the smaller AuNPs embedded within the COF showed enhanced catalytic performance compared to larger NPs.