Intriguing catalytic activity of a silver-functionalized COF in the reduction of nitroaromatics and synthesis of biologically relevant imidazoles

Abstract

The scalable and cost-effective synthesis of a silver-functionalized covalent organic framework (named Ag@TzTPT-COF; Tz: tetrazine, TPT: 2,4,6-tris-(4-formylphenoxy)-1,3,5-triazine) was achieved via a solution infiltration method. The heteroatoms, nitrogen and oxygen, within the framework provided abundant anchoring sites, enabling the uniform dispersion of silver nanoparticles (AgNPs) and effectively preventing agglomeration. Comprehensive spectroscopic and analytical characterizations confirmed the successful formation of Ag@TzTPT-COF with high catalytic activity, remarkable selectivity, and excellent chemical as well as thermal stability. The catalytic performance of Ag@TzTPT-COF was evaluated for the hydrogenation of toxic pollutants like nitroaromatics in aqueous media and for the synthesis of substituted imidazoles, demonstrating high activity and recyclability. Kinetic analysis of the hydrogenation reaction yielded a rate constant of 0.0177 s⁻¹ and a Gibbs free energy of 84.41 kJ mol⁻¹, indicating an endothermic, endergonic, and nonspontaneous process. A “catch–react–release” mechanism was predicted based on the experimental findings to describe the catalytic pathway. Moreover, the catalytic efficiency of Ag@TzTPT-COF in the synthesis of substituted imidazoles was found to be significantly high, further proving it as a promising catalyst. Thus, the study recognises Ag@TzTPT-COF as a robust, bifunctional catalyst for sustainable environmental remediation and biologically relevant organic synthesis.