Utility of a Rh(III) embedded covalent organic polymer as an efficient photocatalyst for visible-light driven N-formylation of amines and CO2 reduction under green and sustainable condition

Abstract

An imidazole-linked covalent organic polymer (COP) was synthesized with the combination of 2,4,6-triformylphluroglucinol and 3,3`-diaminobenzidine, TPDB. To enhance the photocatalytic activity of the synthesized COF, Rhodium was grafted as Rh(III) for post-synthetic modification (PSM). The structural and photophysical properties of the synthesized Rh(III) embedded Covalent Organic Polymer (Rh(III)@TPDB) and TPDB COP were explored using different characterization techniques (PXRD, BET, XPS, EIS, etc.). With a band gap of 1.69 eV, Rh(III)@TPDB shows exceptional photo activity. The efficiency of Rh(III)@TPDB was established in both photocatalytic CO2 fixation and CO2 reduction. The N-formylation of amines via photocatalytic CO2 fixation under mild conditions was performed, and a maximum isolated yield of 89% was achieved in a reaction span of 12 hrs. In the course of photoreduction of CO2 using water as a solvent and Rh(III)@TPDB as the photocatalyst for 4 h under visible light, HCOOH (1625 Mmol gcat-1 h-1) and CH3OH (267 Mmol gcat-1h-1) were formed with a significant production rate. The catalyst was heterogeneous in nature. The heterogenicity of Rh(III)@TPDB catalyst was checked via a leaching test. The Rh(III)@TPDB catalyst was recycled up to five cycles without appreciable loss of its activity. The structural integrity and stability of the recycled catalyst were checked via different characterization techniques (FT-IR, SEM, TEM etc).