Molecular insight into visible light driven photocatalytic hydrogen peroxide synthesis using a heptazine-imide structure

Abstract

The photocatalytic activity of melamine, melem, and melem-phthalimide condensed molecules for hydrogen peroxide generation under visible light in the presence of ethanol as a sacrificial material was investigated. The catalytic activity tests were performed under heterogeneous conditions. Upon irradiation with visible light, melem-phthalimide condensed molecules produced 939 µM hydrogen peroxide, while melem produced 509 µM hydrogen peroxide. The melem-phthalimide condensed molecules were stable in repeated tests, which was confirmed by solid-state nuclear magnetic resonance. Furthermore, the reaction taking place on the surface of the melem-phthalimide condensed catalyst was revealed by electron spin resonance, X-ray photoelectron spectroscopy, and Raman spectroscopy. The reaction mechanism was confirmed by photoluminescence decay spectroscopy and transient absorption spectroscopy. This study revealed that the extended donor–acceptor type heptazine structure significantly contributes to the improved activity through charge separation at the molecular level.