New Insight of Fe Valence State Change Using Leaves: A Combined Experimental and Theoretical Study

Fe 2+ is of considerable importance in plant growth and crop production. However, most Fe elements in nature favor existing in the trivalent state, which often causes the deficiency of Fe 2+ in plants. Here, we report the Fe valence state change from Fe 3+ to Fe 2+ by using leaves. This valence state change was confirmed by x-ray photoelectron spectroscopy in Fe-Cl@leaves. Fourier transform infrared and ultraviolet-visible spectroscopy demonstrated that aromatic ring groups were included in leaves, and cation- π interactions between Fe cations and the components containing aromatic rings in leaves were measured. Further, density functional theory calculations revealed that the most stable adsorption site for hydrated Fe 3+ cation was the region where hydroxyl groups and aromatic rings coexist. Moreover, molecular orbital and charge decomposition analysis revealed that the aromatic rings took the major part (59%) of the whole net charge transfer between leaves and Fe cations. This work provides a high-efficiency and eco-friendly way to transform the Fe valence state from Fe 3+ to Fe 2+ , and affords a new insight into the valance change between plant organisms with cations.