请用专业的学术英语润色这段话X-ray absorption fine structure spectroscopy XAFS was performed to verify the chemical states and the atomic dispersion of Fe species with precise coordination structure As can be seen i

X-ray absorption fine structure spectroscopy (XAFS) was employed to verify the chemical states and atomic dispersion of Fe species with precise coordination structures. As seen in Figure 2d, the K-edge X-ray absorption near-edge structure (XANES) spectrum of 2.5%Fe@KJ exhibits a profile that closely resembles that of Fe2O3 reference, thereby verifying the trivalent oxidation state of Fe atoms in 2.5%Fe@KJ. Fourier transforms (FTs) of XANES further reveal a dominant peak at ~1.5 Å, which is attributed to the Fe-O bond (Figure 2e), while the absence of a peak at approximately 2.2 Å signifies the non-existence of Fe-Fe bonds in 2.5%Fe@KJ. This finding is in agreement with STEM results and confirms the single-atom dispersion of Fe with oxygen atom coordination. To distinguish the coordination information of Fe, an extended XAFS (EXAFS) wavelet transform analysis was performed (Figures 2g-i). The results show that 2.5%Fe@KJ has a maximum intensity at ~5.0 Å-1, and Fe atom is the single nucleation center. Subsequently, EXAFS curve-fitting analysis was conducted to extract quantitative coordination structures for the Fe moiety in 2.5%Fe@KJ (Figures 2f and S3, supplementary table 1). These analyses revealed that the coordination number of Fe in 2.5%Fe@KJ was estimated to be 5 in the first shell, with the Fe-O distance of 2.1 Å. In the fore-edge region, a weak peak at ∼7113 eV was observed in the 2.5%Fe@KJ spectrum, which is mainly due to the charge transfer from the 1s orbit of O ligand to 3d orbit of Fe metal. These results suggest that the ligand geometry around Fe is a square structure, as this fore-edge peak is usually considered as a fingerprint of a square planar with a porphyrin-like configuration.