Iron (hydr)oxides, which are ubiquitously distributed in the environment, often contain impurities such as Al. Aluminum-substituted goethite (AlG) is a typical assemblage of Al and Fe (hydr)oxides. In this study, the molecular-level mechanisms of PO₄ sorption in relation to structural changes in AlG with Al/(Al + Fe) molar ratios up to 17.4% and the PO₄ distribution between Al and Fe were determined. While the XRD results showed that Al preferred to substitute for Fe on relatively low-index planes of goethite, the Fe-XAS and XPS data indicated the particular Al substitution in edge-shared FeO₆ octahedral linkages and a tendency of Al segregation near the surface of AlG, respectively. The maximum PO₄ sorption capacity increased from 135 to 584 mmol kg⁻¹ as Al/(Al + Fe) mol% increased from 0 to 17.4%. Phosphorus-XANES data of PO₄ sorbed on AlG showed either preferential PO₄ bonding for Al or no preference for Al or Fe. Compared to goethite with adsorbed PO₄, the density functional theory (DFT) result of AlG containing 12.5 Al mol% showed more relaxed Al atoms relative to the topmost atomic layers of the supercell upon PO₄ adsorption, a smaller Al–O–P angle than the corresponding Fe–O–P angle, and a relatively stable PO₄ complex formed on the AlG surface. New insights into the PO₄ sorption mechanisms and related structural changes in Al/Fe assemblages could improve the assessment of the P dynamics and mass balance in agricultural and PO₄-induced eutrophication systems.

中文翻译：

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针铁矿上的优先磷酸盐吸附和铝置换

分布在环境中的氧化铁（氢）经常含有杂质，如铝。铝取代针铁矿（AlG）是Al和Fe（氢）氧化物的典型组合。在这项研究中，PO的分子水平的机制₄相对于在ALG用Al /（铝+ Fe）的结构变化的摩尔比高达17.4％和PO吸着₄ Al和Fe之间的分布进行了测定。X射线衍射结果表明，在相对较低指数的针铁矿平面上，铝更倾向于替代铁，但Fe-XAS和XPS数据表明，在边缘共享的FeO ₆八面体键中，特定的Al取代和表面附近Al偏析的趋势分别为AlG。最大PO ₄当Al /（Al + Fe）mol％从0增加到17.4％时，吸附容量从135增加到584 mmol kg ^-1。吸附在AlG上的PO _4的磷-XANES数据显示，Al优先选择PO ₄键，Al或Fe优先选择键。与吸附有PO _4的针铁矿相比，含有12.5 Al mol％的AlG的密度泛函理论（DFT）结果显示，相对于PO ₄吸附时超级电池的最顶层原子层，Al原子更弛豫，Al–O–P角更小比相应的Fe–O–P角大，并且在AlG表面形成了相对稳定的PO _4配合物。对PO _4的新见解Al / Fe组合物中的吸附机理和相关的结构变化可以改善对农业和PO ₄致富营养化系统中P动力学和质量平衡的评估。