The formation of iron oxide mineral–organic associations can regulate long-term preservation of soil organic matter (SOM) by providing shelter for SOM from degradation through adsorption on different crystalline/amorphous phase surfaces. However, little is known about the energetic basis for the phase- and facet-dependent SOM–iron oxide interactions at the molecular scale. Here, we use a representative organic molecule, alginate, which is present ubiquitously in soils, and investigate its adsorption on the surfaces of amorphous iron oxides (Fe_xO_y) or hematite (α-Fe₂O₃) by calculating the Kelvin potential difference and measuring the binding energy (ΔG_B) between an alginate molecule and a specific surface of the hematite or amorphous Fe_xO_y phase by atomic force microscopy (AFM). Single-molecule determination of alginate–amorphous Fe_xO_y/hematite interactions provides mechanisms of the origin of the phase- or facet-dependent adsorption by systematically changing the pH and ionic strength/compositions of environmentally relevant reaction solutions. We show that the adsorption capacities of alginate follow the order amorphous Fe_xO_y > the (100) > (110) > (0001) faces of hematite. These molecular-scale investigations may improve our understanding of the phase-dependent or face-specific adsorption of SOM on other soil minerals in aqueous environments and potentially predict the preservation mechanisms and the fate of SOM.

中文翻译：

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单分子测定藻酸盐在氧化铁上的相和面依赖性吸附

氧化铁矿物-有机缔合的形成可以为土壤有机质提供长期庇护，从而为土壤有机质提供庇护，使其免受吸附在不同晶体/非晶态表面上的降解。然而，关于分子尺度上依赖于相和刻面的SOM-氧化铁相互作用的能量基础知之甚少。这里，我们用一个代表性的有机分子，藻酸盐，这是目前普遍在土壤中，并调查其无定形铁氧化物的表面上吸附（FE _X Ò _Ý）或赤铁矿（α-的Fe ₂ ö ₃通过计算开尔文电势）差并测量结合能（ΔG _B通过原子力显微镜（AFM）在藻酸盐分子和赤铁矿或非晶Fe _x O _y相的特定表面之间形成一个）。通过单分子测定藻酸盐与非晶态Fe _x O _y /赤铁矿的相互作用，可以通过系统地改变环境相关反应溶液的pH值和离子强度/组成来提供依赖于相或面的吸附的机理。我们表明藻酸盐的吸附能力遵循无定形Fe _x O _y >（10 0）>（110）>（0001）赤铁矿面。这些分子规模的研究可能会增进我们对SOM在水性环境中其他土壤矿物上的相依性或特定于面的吸附的了解，并可能预测SOM的保存机理和命运。