In situ construction of Mn3O4 cocatalyst on sodium poly(heptazine imides) for enhanced photocatalytic reduction of water and synergetic oxidation of amines

Abstract

Photocatalytic hydrogen production utilizing solar energy provides a pivotal strategy for realizing a carbon–neutral society. Cocatalyst-modified semiconductor materials have emerged as promising candidates for photocatalytic applications due to their ability to facilitate the spatial separation and directional migration of photogenerated electron-hole pairs. Nevertheless, those systems often face challenges such as intricate preparation procedures and issues with non-compact recombination. Herein, we report a one-pot thermal treatment approach for synthesizing a composite of Mn₃O₄ nanoparticles and sodium poly(heptazine imides) (Na-PHI). Mn₃O₄ nanoparticles were in situ generated and embedded within the Na-PHI matrix during the sintering process. The resulted photocatalyst demonstrated significantly enhanced photoinduced charge separation efficiency, exhibiting approximately 6-fold and 3-fold improvements compared to pristine Mn₃O₄ and Na-PHI, respectively. The photocatalytic hydrogen evolution rate reached 14 μmol h⁻¹, nearly 9 times that of Na-PHI (1.6 μmol h⁻¹) in the aqueous solution of benzylamine (BA) under visible light illumination (780 nm ≥ λ ≥ 420 nm). Furthermore, the optimized Mn₃O₄-Na-PHI sample (Mn-Na-PHI) displayed a remarkably high photocatalytic hydrogen generation rate alongside the synchronous photo-oxidative coupling of aliphatic and aromatic amine under visible light. This work underscores the potential for rational design and synthesis of novel Na-PHI-based functional composites for sustainable energy applications.