Application of X-ray Absorption Spectroscopy in Environmental Science: A Review and Future Perspectives

X-ray absorption fine structure (XAFS) spectroscopy enables precise characterization of elemental speciation, coordination environment, and electronic structure at the atomic and molecular scales, serving as a key technique to overcome the limitations of conventional analytical methods and to reveal the behavior of environmental pollutants at the molecular level. Over the past three decades, XAFS has progressively established a full-chain application framework—encompassing source identification, transformation tracking, remediation assessment, and risk evaluation—within the field of environmental science, with notable advances in detection limit reduction, spatial resolution enhancement, and multi-technique integration. This review provides an overview of the fundamental principles, measurement modes, and spectral analysis methods of XAFS, and then focuses on three core research areas: pollutant speciation analysis, environmental interfacial adsorption mechanisms, and characterization of remediation materials, presenting a comprehensive account of the current state of XAFS-based research. In the area of speciation analysis, linear combination fitting (LCF) of X-ray absorption near-edge structure (XANES) spectra has enabled quantitative identification of heavy metals and non-metallic elements, as demonstrated by the predominance of PbSO₄ as the primary Pb species in industrially contaminated soils and the dominance of sulfate as the main sulfur form in atmospheric PM₂.₅, providing direct evidence for pollution source apportionment and transformation pathway studies. Regarding interfacial adsorption mechanisms, EXAFS has quantitatively resolved various complexation modes of heavy metals at mineral/organic matter interfaces, covering coordination configurations ranging from inner-sphere to outer-sphere adsorption and from monodentate to multidentate binding. In the field of remediation material characterization, EXAFS has revealed the core-shell structure of nanoscale zero-valent iron 45.5% Fe(OH)₃ + 54.5% FeOOH and its coprecipitation immobilization mechanism for Pb(Ⅱ), as well as the Fenton-like active center characteristics of Fe-N₄ single-atom catalysts, providing atomic-scale structural evidence for the rational design of high-performance remediation materials. Furthermore, breakthroughs in advanced XAFS techniques—including high-energy-resolution fluorescence detection XAFS (HERFD-XAFS), operando/quick-scanning XAFS (Operando/QXAFS), and micro/nano-XAFS—have significantly enhanced the detection sensitivity and spatial resolving power for trace elements. The integration of XAFS with complementary techniques such as X-ray fluorescence spectrometry (XRF), X-ray diffraction (XRD), and density functional theory (DFT) calculations has further expanded the analytical capabilities for complex environmental samples. Current development priorities in this field are centered on continuously improving sensitivity for trace and light-element detection, deeply empowering spectral interpretation through artificial intelligence-assisted analysis, advancing the general applicability of in situ/operando measurement techniques, and systematically constructing an integrated multi-technique and cross-scale research framework.