Despite long history and recent progress, the chemical behavior of graphene oxide (GO) is not fully understood. One of the remaining open questions is an extremely high cation exchange capacity, which cannot be explained in the frames of the commonly accepted Lerf-Klinowski structural model. The interaction of GO with metals, termed as sorption, is usually considered as physisorption, or as non-specific electrostatic attraction. Recently, we demonstrated that in fact this interaction has the coordinate-covalent bonding nature. In this work, by the means of the NMR relaxation, we investigated the interaction of Fe(III) and Gd(III) ions with several small molecule size chelators and with linear polymers in order to possibly mimic the GO structure. The experiments were conducted in the broad pH range, and at the different metal/chelator ratios. From the two tested metal ions, Fe(III) has the stronger affinity toward GO due to its higher charge density. GO binds Fe(III) with formation of strong high-relaxivity complexes, which do not undergo hydrolysis even in basic conditions. Numerous model small-size molecules, tested to mimic the GO structure, did not demonstrate the same effect on the relaxation of the Fe(III) and Gd(III) solutions, as does interaction with GO. From the tested linear polymers, only polyacrylic acid (PAA) can bind Fe(III), however, even PAA, consisting from carboxyl groups, cannot prevent Fe(III) from hydrolysis already in neutral solutions. Subsequently, carboxyl groups were excluded from the species in GO structure, responsible for the strong binding of meatal ions. We conclude that there are no preexisting sites or functional group fragments in GO structure, capable to strongly bind transition metal cations. The binding sites are formed from the existing structure upon the reaction with metal cations, to afford formation of the metal/GO coordination compounds. The most probable change in the GO structure is the formation of enolates from tertiary alcohols with rupture of the CC bonds. The newly reported data provide additional experimental evidence for the Dynamic Structural Model of GO and broadens the areas of its applicability.

尽管历史悠久且最近取得了进展，但对氧化石墨烯（GO）的化学行为尚未完全了解。尚待解决的问题之一是极高的阳离子交换能力，这在公认的Lerf-Klinowski结构模型的框架中无法解释。GO与金属的相互作用（称为吸附）通常被视为物理吸附或非特异性静电吸引。最近，我们证明了这种相互作用实际上具有配体-共价键的性质。在这项工作中，通过NMR弛豫的方法，我们研究了Fe（III）和Gd（III）离子与几种小分子螯合剂和线性聚合物的相互作用，以便可能模拟GO结构。实验是在较宽的pH范围内以及以不同的金属/螯合剂比率进行的。从两种测试的金属离子中，由于其较高的电荷密度，Fe（III）对GO具有更强的亲和力。GO结合Fe（III）形成强的高松弛络合物，即使在碱性条件下也不会水解。经测试可模仿GO结构的许多模型小分子，并未证明与Fe相互作用对Fe（III）和Gd（III）溶液的弛豫具有相同的作用。从测试的线性聚合物中，只有聚丙烯酸（PAA）可以结合Fe（III），但是即使是由羧基组成的PAA也无法防止Fe（III）在中性溶液中水解。随后，羧基从GO结构的物种中排除，这导致了肉类离子的强结合。我们得出结论，GO结构中没有预先存在的位点或官能团片段，能够牢固地结合过渡金属阳离子。结合位点在与金属阳离子反应时由现有结构形成，从而形成金属/ GO配位化合物。GO结构中最可能的变化是叔醇从C断裂形成烯醇化物C键。最新报告的数据为GO的动态结构模型提供了更多的实验证据，并拓宽了其适用范围。