Photo upscaling of formic acid to H2 and C(sp2)–N cross-coupling via K+ intercalated carbon nitride: a new sustainable horizon towards fuel and high-end pharmaceutics

Abstract

Solar propelled liquid organic hydrogen (H₂) carrier - formic acid (FA) dehydrogenation is one of the promising pathways for green H₂ production. In this regard, we have used potassium intercalated (K⁺) carbon nitride (KPCN) as the photocatalyst to demonstrate a new route, photo-valorization of FA to H₂ in synergism with photo-redox cross-coupling of FA as the C1 source with o-phenylenediamine (PDA) to produce benzimidazole (BA). It was realized that Pt/1KPCN produces 94 μmol h⁻¹ g⁻¹ of H₂ (AQY of 0.93% at λ = 400 nm) which was 23-fold higher compared to bare Pt/CN along with 50% conversion of PDA to produce pharmaceutically important BA. Besides, charge transfer kinetics of Pt/1KPCN after K⁺ incorporation was ascertained by PL, photocurrent and solid-state EPR studies. Furthermore, the plausible mechanistic insights including basicity were thoroughly probed by scavenger-controlled experiments and CO₂ TPD analysis, respectively. Apparently, Pt/1KPCN has shown further potential to reduce in situ generated CO₂ molecules (via dehydrogenation) to CO molecules. Thus, the current work provides a new milder sustainable protocol to expedite FA as a renewable source not only to produce syngas, a solar fuel precursor for the Fischer–Tropsch synthesis (FTS) but also to nurture the carbon circular economy by producing high-end pharmaceutics.