Simultaneous photocatalytic production of H2 and acetal from ethanol with quantum efficiency over 73% by protonated poly(heptazine imide) under visible light

In the work, protonated poly(heptazine imide) (H-PHI) was obtained by adding acid to the suspension of potassium poly(heptazine imide) (K-PHI) in ethanol. It was established that the obtained H-PHI demonstrates very high photocatalytic activity in the reaction of hydrogen formation from ethanol in the presence of Pt nanoparticles under visible light irradiation in comparison with K-PHI. This enhancement can be attributed to improved efficiency of photogenerated charges transfer to the photocatalyst's surface where redox processes occur. Various factors influencing the system's activity were evaluated. Notably, it was discovered that the conditions of acid introduction into the system can significantly affect the size of Pt (co-catalyst metal) deposition on the H-PHI surface, thereby enhancing the photocatalytic system stability in producing molecular hydrogen. It was established that the system can operate efficiently in the presence of air without additional components on the photocatalyst surface to block air access. Under optimal conditions, the Apparent Quantum Yield (AQY) of molecular hydrogen production at 410 nm is around 73%, the highest reported value for carbon nitride materials to date. The addition of acid not only increases activity of the reduction part of system but also leads to formation of a value-added product from ethanol - 1,1-diethoxyethane (acetal) with high selectivity.