Tuning the N-bonded cerium(iii) fraction/g-C3N4 interface in hollow structures using an in situ reduction treatment for superior photochemical hydrogen evolution

Abstract

The synthesis of inorganic/organic interfaces in spherical hollow structures (HS) is a promising but challenging task. Herein, we innovatively utilized porous CeO₂-HS as a scaffold to incorporate cyanamide molecules, which upon one-step in situ reducing treatment, yielded nitrogen-bonded CeO_2−x/g-C₃N₄-HS. The electron microscope and spectroscopic analysis validated two functions of cyanamide: i) it generates an in situ reducing atmosphere (CO, N₂, NO_x) to tune the cerium oxide vacancy population, and ii) it acts as a N and g-C₃N₄ precursor. Meanwhile, the unique HS geometry promotes cerium oxide reduction at low temperature due to the following: i) the high surface area of CeO₂-HS provides a larger area for CeO₂/CO interaction; ii) adequate pore volume enhances the cerium oxide reduction kinetics; and, iii) the CeO₂ nanoparticles increase the ceria surface defect population by obeying the ceria oxygen vacancy transport model. Remarkably, the N-CeO_2−x/g-C₃N₄-HS photocatalyst hydrogen evolution rate is 43.32 μmol g⁻¹ h⁻¹ under visible light (λ ≥ 420 nm), which is 3.8 times higher than pristine g-C₃N₄ (11.4 μmol g⁻¹ h⁻¹) due to: a) enhancement of the material's light-harvesting ability by HS, b) formation of controlled optically active Ce³⁺ sites, and c) intimate inorganic/organic interfaces, which boosted the minority carriers' separation efficiency.