Sunlight‐Driven Gram‐Scale Nitrate Reduction to Ammonia by an In Situ Formed Fe 3 + 1‐x Fe 2+ x OOH/CdSeS Photocatalyst

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Sunlight‐driven conversion of NO 3 − ‐to‐NH 3 holds immense significance for fostering a green and sustainable society. However, most of the existing photocatalysts have weak light absorption and a wide band gap, making the synthesis of NH 3 challenging on a large scale under sunlight. Herein, a photocatalyst Fe 3+ 1‐x Fe 2+ x OOH/CdSeS that was in situ formed from MPA‐CdSe QDs and transition metal ions (i.e., Fe 3 + used here) under visible light irradiation at room temperature, accomplished a gram‐scale synthesis of NH 3 in a 625 cm 2 plate‐type reactor. Under sunlight, 177.18 mmol NH 3 was synthesized, and 7.83 g of NH 4 Cl solid was collected after five cycles totaling 115 h, and the solar‐to‐ammonia (STA) was 0.664%. Experimental characterization and density functional theory (DFT) calculations reveal that the formation of Fe 3+ 1‐x Fe 2+ x OOH/CdSeS nanostructures is the key to the exceptional activity. The reversible Fe 3+ /Fe 2+ redox cycling within the clusters facilitates charge separation and interfacial transfer from CdSeS QDs to Fe 3+ 1‐x Fe 2+ x OOH under irradiation, while oxygen vacancies in Fe 3+ 1‐x Fe 2+ x OOH clusters bind NO 3 − for subsequent NH 3 formation. The apparent quantum yield is 15.89% ± 1.75% at 436 nm, and the yield of NH 3 is 522.47 mmol g cat −1 h −1 based on Fe 3+ 1‐x Fe 2+ x OOH/CdSeS photocatalyst, a 5.82‐fold enhancement over the reported record of 89.79 mmol g cat −1 h −1 , demonstrating remarkable application potential for sunlight‐driven NO 3 − reduction to NH 3 .