Defect Engineering in NiAl Mixed-Metal Oxides Derived from Layered Double Hydroxide for Enhanced Photocatalytic Nitrogen Fixation

The development of efficient photocatalysts for overall photocatalytic nitrogen fixation to ammonia (NH3) and nitrates (NO3-) has garnered immense attention, addressing various environmental and agricultural needs. Conventionally, NH3 and NO3- are synthesized by high energy-intensive Haber-Bosch and Ostwald's processes, respectively. Therefore, the production of NH3 and NO3- using photocatalysis is a potential alternative for the conventional approaches. However, contemporary research in this field predominantly overlooks the simultaneous production of NH3 and NO3-. In this context, this work presents the synthesis of defect-rich NiAl mixed-metal oxides (MMO) derived from NiAl layered double hydroxide (LDH) via a facile coprecipitation technique followed by hydrothermal and calcination treatment. The photocatalytic activity was tested to produce NH3 and NO3- in visible light using water as a hydrogen source. It was observed that the MMO catalysts showed higher photocatalytic activity as compared to the LDH catalysts, exhibiting eight times higher NH3 production (C-NAO catalyst) without any sacrificial agent. Based on detailed catalytic investigations, it was inferred that the photocatalytic reaction followed the associative distal mechanism. The current work broadens the scope of using LDH-derived MMO catalysts to establish effective photocatalytic reaction protocols for facile NH3 production, offering a straightforward method for a more sustainable nitrogen economy.