Bio-inspired MIL-53(Fe)/Ball-Milled g -C3N4 Composites for Photocatalytic Nitrogen Fixation toward Solar-Driven Green Ammonia Fertilizer Production

Abstract Developing a highly efficient photocatalytic nitrogen fixation system for sustainable ammonia synthesis represents a crucial strategy for advancing green energy conversion and modern agriculture. Inspired by the structural and functional features of natural nitrogenase, a heterojunction photocatalyst composed of MIL-53(Fe) and ball-milled graphitic carbon nitride (g-C3N4) was rationally designed and constructed. The ball-milling process effectively introduced additional surface defects into g-C3N4, thereby enhancing N2 adsorption and facilitating charge carrier migration. Meanwhile, MIL-53(Fe) provided Fe-centered coordination sites that acted as biomimetic active centers. The intimate interfacial contact between MIL-53(Fe) and defect-engineered g-C3N4 established a bioinspired “metal-nonmetal” synergistic catalytic interface, closely resembling the cooperative mechanism of natural nitrogenase. Photocatalytic evaluations revealed that the optimal MIL-53(Fe)/g-C3N4 heterostructure (CNMIL-2) exhibited a markedly improved nitrogen reduction performance under visible-light irradiation, achieving an ammonia yield of 113.86 μmol·g–1·h–1, which was substantially higher than those of either component alone. The enhanced activity can be ascribed to the defect-mediated charge transfer, efficient spatial separation of photocarriers, and the synergistic interplay between Fe active centers and nitrogen adsorption sites. Moreover, the photo catalytically generated ammonia water fertilizer was directly applied to wheat seedling cultivation. The treated seedlings displayed significantly increased germination rates and accelerated early-stage growth, demonstrating the agricultural potential of the photo catalytically synthesized ammonia as a sustainable nitrogen source. This work provides new insights into solar-driven green ammonia synthesis, paving the way toward low-carbon and sustainable agricultural development.