Arsenic pollution poses a serious threat to human health, and is one of the most concerning environmental problems worldwide. The adsorption, fixation, and dissolution behaviors of arsenic on the surface of iron-(hydr-) oxides influence the environmental routes of arsenic cycle geochemistry. Both inner-sphere and outer-sphere adsorption configurations of arsenic on iron oxides have been proposed based on X-ray adsorption spectra. However, there is no systematic study on the in situ speciation analysis and adsorption kinetics of these species at such interfaces, because of the lack of an efficient monitoring strategy. The correlation of surface speciation and environmental stability is still unknown. Here, a shell-isolated SiO₂@Ag@Au-based surface-enhanced Raman spectroscopy (SERS) platform was developed for speciation analysis of the adsorbed arsenic species by eliminating the chemical interaction between arsenic and silver. Using ferrihydrite as a typical iron oxide, the intrinsic Raman spectra of the inner-sphere (∼ 830 cm⁻¹) and outer-sphere (∼ 660 cm⁻¹) complexes at the adsorption interface were identified. For the first time, the in situ kinetic monitoring of the formation and transformation of these species was realized. By correlating the speciation to the sequential extraction results, the environmental stability of arsenic on ferrihydrite was shown to be closely related to the adsorption configuration. It was shown that stability can be significantly promoted by transforming loosely bonded species (outer-sphere complexes) into inner-sphere structures. Our work demonstrated the applicability of SERS with shell-isolated plasmonic particles for arsenic geochemical cycle monitoring and mechanism studies. It also provided a convenient tool for developing effective strategies for arsenic pollutant control and abatement.

砷污染对人类健康构成严重威胁，是全球最受关注的环境问题之一。砷在铁（氢）氧化物表面的吸附、固定和溶解行为影响着砷循环地球化学的环境路径。已经基于 X 射线吸附光谱提出了砷在氧化铁上的内球面和外球面吸附构型。然而，由于缺乏有效的监测策略，没有对这些物质在这些界面的原位形态分析和吸附动力学进行系统研究。表面形态和环境稳定性的相关性仍然未知。这里，壳层隔离的 SiO ₂开发了基于@Ag@Au 的表面增强拉曼光谱 (SERS) 平台，通过消除砷和银之间的化学相互作用，对吸附的砷物种进行形态分析。使用水铁矿作为典型的氧化铁，确定了吸附界面处内球（～ 830 cm ^-1）和外球（～ 660 cm ^{-1 ）配合物的本征拉曼光谱。}首次在现场实现了对这些物种形成和转化的动力学监测。通过将形态与连续提取结果相关联，水铁矿上砷的环境稳定性与吸附构型密切相关。结果表明，通过将松散结合的物质（外层复合物）转化为内层结构可以显着提高稳定性。我们的工作证明了 SERS 与壳隔离等离子体粒子在砷地球化学循环监测和机制研究中的适用性。它还为制定有效的砷污染物控制和减排战略提供了便利的工具。