Insight into multivalent iron complex-bound oxygen vacancy-rich BiOBr nanodiscs for photocatalytic ammonia synthesis

Abstract

Photocatalytic conversion of N₂ to green NH₃ has become extremely promising as an alternative to the traditional Haber–Bosch process for a resilient future. In this context, developing noble metal-free nanomaterials with highly efficient photocatalytic activity is highly demanding. Herein, oxygen vacancy-rich disc-shaped BiOBr (BOB_OV) has been synthesized, and a multivalent Fe–phytic acid complex has been further coupled with it to form the final composite – BOB_OV@Fe_x. It is utilized for photocatalytic NH₃ production from N₂, and further compared with other controlled samples. Detailed structural and elemental properties have been correlated with the intrinsic optoelectronic properties. The results suggest that the coupling of the Fe complex acts synergistically with the oxygen vacancies (OVs), which improve the visible light absorption, charge separation, and N₂ adsorption. It eventually elevates the photocatalytic efficiency. The photocatalytic efficiency for the optimized samples reaches up to 385.5 µM g_cat.⁻¹ h⁻¹ with an AQE of 5.24%. It has been thoroughly supported by a series of computational studies. Quantum mechanical calculations employing the PBE-D method are utilized to provide the crucial role of polyvalent Fe atoms and OVs on the surface of BOB for N₂ activation. Thermodynamic analysis further confirms that the N₂ reduction proceeds most favorably through the associative distal pathway.