Harnessing mpg-C3N4 Photocatalyst for Selective Oxidative Coupling of Amines to Azoaromatics Compounds

Abstract

The advancement of sustainable and efficient methods for the oxidative coupling of arylamines into aromatic azo compounds, under mild conditions, remains a significant challenge within the realm of sustainable chemistry. In this study, a metal-free mesoporous graphitic carbon nitride (mpg-C3N4) photocatalyst was synthesized using a straightforward one-step thermal polymerization of urea, resulting in a material with high surface area (109.40 m2/g) and enhanced charge separation. The mpg-C3N4 photocatalyst was thoroughly characterized through XRD, XPS, HR-TEM, and BET analysis, confirming its mesoporous structure, crystallinity, and thermal stability. Under light irradiation in ambient air, mpg-C3N4 efficiently activated atmospheric O2 to generate reactive superoxide radicals, enabling selective azo formation with up to 99% conversion and selectivity across a range of aromatic amines. DFT calculations and adsorption studies revealed the role of π–π stacking and favorable adsorption Gibbs energies, underpinning effective substrate activation and surface interaction. Mechanistic investigations, aided by EPR and DFT elucidated that photoexcited electrons reduce O2 to superoxide radicals, which mediate the oxidative coupling process. Reusability tests confirmed the catalyst's stability across five cycles, exhibiting no significant loss of activity or structural integrity. This sustainable, metal-free photocatalytic strategy harnessing renewable light energy, not only demonstrates the scalable synthesis of azo compounds but also paves the way for new approaches in the green synthesis of functional azoaromatics.