Heterogeneous iron-based catalysts for a sustainable photoinduced nitrogen fixation

Ammonia is nowadays one of the most important commodities chemicals intensively produced at about 175 million tons per year, contributing to 1.8 % of the global energy demand. The constantly increasing NH₃ demand is also paralleled to the high CO₂ emissions associated with its production. Therefore, decarbonizing NH₃ synthesis is one of the most urgent contemporary challenges. Taking inspiration from Nature, solar-driven nitrogen fixation under mild conditions is one of the most promising yet challenging alternatives to classic methods. In this review, we focused our attention on the photocatalytic methods for the synthesis of ammonia; in particular, we concentrated on stable and recyclable heterogeneous Fe-based photocatalysts for the production of NH₃. Indeed, recoverable and widely abundant and low-cost iron catalysts may represent a very promising tool for future sustainable access to this largely desired chemical target. After an overview of the pioneering works on Fe-driven nitrogen photofixation, the recent strategies on the use of Fe are herein reported. From the comparison with pristine photocatalysts, the addition of Fe as dopant or composite and heterojunction highly enhances the photocatalytic performances, opening the way to sustainable and low-cost nitrogen production.