Two-line ferrihydrite (Fh) is an omnipresent iron oxyhydroxide nanomineral with high surface reactivity and weak crystallinity, and its phase transformation in nature has drawn significant concerns. A number of studies have investigated the effects of coexisting natural substances (e.g., ions, organic molecules, and clay minerals) on the phase transformation processes of Fh. This work, for the first time, studied the effects of coexisting carbon nanomaterials (CNM) on the phase transformation of Fh, and CNM with different morphologies, that is, graphene oxide (GO) and fullerol (PHF), were applied. Characterization results from X-ray diffraction, transmission electron microscopy, and Mössbauer spectroscopy showed that the transformed products of Fh are mainly hematite (Hem) with a small amount of goethite (Gth) in the absence/presence of CNM; however, the transformation kinetics, morphologies, and Hem/Gth ratio of the transformed products are distinctly different in each system. In particular, GO decreased the transformation rate of Fh (compared with the Fh system), whereas PHF not only accelerated the transformation rate but also favored the formation of larger Hem particles and higher Hem/Gth ratios in the transformed products. We hypothesized that these results could be attributed to the different behaviors of CNM in affecting the aggregation of Fh as the transformation of Fh into Hem is a solid phase transformation process (via dehydration), which strongly relies on the aggregation of Fh particles. In this term, the samples of CNM–Fh mixtures before transformation were characterized. The results obtained from atomic force microscopy and sedimentation experiments showed that the large lamellar GO could act as a dispersing agent and inhibit the aggregation and contact of Fh particles while the nanogranular PHF functioned as a “bridge” and enhanced the aggregation of Fh particles. This study revealed that the coexisting nanoparticles (e.g., PHF and GO) could exert different influences on the transformation of Fh by influencing its aggregation and dispersion.

中文翻译：

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富勒醇和氧化石墨烯对两线水铁矿相变的影响

两线水铁矿（Fh）是一种无处不在的羟基氧化铁纳米矿物，具有高表面反应性和弱结晶性，其自然界中的相变已引起人们的极大关注。许多研究调查了共存的天然物质（例如离子，有机分子和粘土矿物）对Fh的相变过程的影响。这项工作首次研究了共存的碳纳米材料（CNM）对Fh的相变的影响，并应用了具有不同形态的石墨烯，即氧化石墨烯（GO）和富勒醇（PHF）。X射线衍射，透射电子显微镜和Mössbauer光谱的表征结果表明，在无CNM存在下，Fh的转化产物主要是赤铁矿（Hem）和少量针铁矿（Gth）。然而，在每个系统中，转化产物的转化动力学，形态和Hem / Gth比值明显不同。特别是，GO降低了Fh的转化率（与Fh系统相比），而PHF不仅加快了转化率，而且还有利于在转化产物中形成更大的Hem颗粒和更高的Hem / Gth比。我们假设这些结果可能归因于CNM在影响Fh聚集方面的不同行为，因为Fh到Hem的转化是一个固相转化过程（通过脱水），该过程强烈依赖于Fh颗粒的聚集。在此术语中，对转化前的CNM–Fh混合物样品进行了表征。原子力显微镜和沉降实验的结果表明，大的层状GO可以作为分散剂，抑制Fh颗粒的聚集和接触，而纳米颗粒PHF起到“桥”的作用，并增强Fh颗粒的聚集。这项研究表明，共存的纳米颗粒（例如PHF和GO）可以通过影响Fh的聚集和分散而对Fh的转化产生不同的影响。