Nanoarchitectonics in the Ionothermal Synthesis for Nucleation of Crystalline Potassium Poly (heptazine imide) Towards an Enhanced Solar-Driven H 2 O 2 Production.

Solar-driven selective oxygen reduction reaction on polymeric carbon nitride framework is one of the most promising approaches toward sustainable H 2 O 2 production. Potassium poly(heptazine imide) (PHI), with regular metal sites in the framework and favorable crystalline structure, is highly active for photocatalytic selective 2e oxygen reduction to produce H 2 O 2 . By introducing NH 4 Cl into the eutectic KCl-LiCl salt mixture, the PHI framework exhibits a remarkable performance for photocatalytic production of H 2 O 2 , for example, a record high H 2 O 2 photo-production rate of 29.5 μmol h -1  mg -1 . The efficient photocatalytic performance is attributed to the favorable properties of the new PHI framework, such as improved porosity, negatively shifted LUMO position, enhanced exciton dissociation and charges migration properties. A mechanistic investigation by quenching and electron spin resonance technique reveals the critical role of superoxide radicals for the formation singlet oxygen, and the singlet oxygen is one of the critical intermediates towards the formation of the H 2 O 2 by proton extraction from the ethanol.