Nucleation and growth of iron sulfides: linking theory and experiment

硫化铁广泛存在于环境中，它们调节和控制着全球的铁和硫的地球化学循环。然而，尽管将其用作海水缺氧的指示器以及早期生命同位素和古地磁数据的记录器，但与氧化铁矿物或硅酸盐或碳酸盐相比，硫化铁矿物在很大程度上仍未被勘探。已知有许多硫化铁相，但许多在环境中高度不稳定或只在很短时间内部分稳定。即使是活性最低的硫化铁黄铁矿，一旦暴露在地球表面的空气中，也不再稳定。它的溶解导致了酸性矿山排水的问题，硫酸和任何被困的有毒金属被释放出来，对矿山附近的环境造成毁灭性的影响。然而，硫化铁对环境也有好处，因为它们很容易将金属融入其结构中，因此可能是有毒金属或放射性元素的汇。硫化铁的一个耐人寻味的方面是，它们可能在生命起源中扮演了关键角色。铁镍硫化物薄层被认为是在地球早期海洋底部温暖的碱性泉水中形成的。它们越来越被认为是导致生命出现的一系列化学反应的早期催化剂。各种有机化合物的无氧生产，包括氨基酸和核酸碱基--DNA的组成单元--被认为是由小的铁-镍-硫簇催化的，这些小的铁-镍-硫簇在结构上类似于当今高度活跃的硫化铁矿物--灰岩和麦基纳威石，但我们对它们的形成知之甚少。鉴于这些活性矿物在早期地球上生物前二氧化碳转化中可能起到的作用，我们很可能能够利用硫化铁作为当今同样过程的催化剂，从而通过将我们产生的二氧化碳转化为有用的化学物质来潜在地帮助减缓气候变化。在当今世界，这种铁-镍-硫化物簇合物作为催化剂的重要性已经得到证实，因为几种生命必需的铁-硫蛋白质有助于将挥发物如H2、CO和CO2转化为其他有用的、危害较小的化学物质。在所有上述例子中，重要的是要了解导致所有这些矿物的形成的反应，这些矿物是任何地质稳定的矿物(即黄铁矿)存在所必需的，都依赖于我们对不稳定前驱体的成核和生长或将一种相转化为另一种相的反应的理解。此外，每个阶段的结构和反应性决定了它在环境中的作用和潜在的应用。英国和国外的一些研究小组已经对一些硫化铁矿物的性质进行了高质量的调查，但特别困难的是调查成核过程早期的事件，即使它们为随后的所有转变奠定了基础。在这个项目中，我们建议使用最先进的计算和实验的强大组合来揭示硫化铁矿物相的成核。我们的目标是跟踪从第一个构建块在溶液中出现的反应，到凝聚成更大的团簇，它们聚集成纳米粒子，最后转变为最终晶体。我们预计，该项目将通过开发高时间和空间分辨率的原位表征技术和高性能计算平台来调查目前才能研究的短暂过程，从而逐步深入定量地洞察硫化铁的形成途径，并加强我们对矿物如何在溶液中成核的基本理解。

Iron sulfides are widespread in the environment, where they regulate and control the global geochemical iron and sulfur cycles. However, despite their application as indicators for seawater anoxia and recorders of early-life isotopic and paleomagnetic data, iron sulfide minerals are still largely unexplored compared to, for example, iron oxide minerals or the silicates or carbonates. Numerous iron sulfide phases are known, but many are highly unstable or only partially stable for a short time in the environment. Even the least reactive iron sulfide, pyrite, is no longer stable once exposed to air at the Earth's surface. Its dissolution leads to the problem of acid mine drainage, where sulfuric acid and any trapped toxic metals are released with devastating effects on the environment near the mine. However, iron sulfides also have beneficial effects on the environment, as they easily incorporate metals within their structure, and thus could be sinks for toxic metals or radioactive elements. An intriguing aspect of iron sulfides is the crucial role they may have played in the Origin of Life. Thin layers of iron-nickel sulfide are believed to have formed in the warm, alkaline springs on the bottom of the oceans on Early Earth. They are increasingly considered to have been the early catalysts for a series of chemical reactions leading to the emergence of life. The oxygen-free production of various organic compounds, including amino acids and nucleic acid bases - the building blocks of DNA - is thought to have been catalyzed by small iron-nickel-sulfur clusters, which are structurally similar to the highly reactive present day iron sulfide minerals greigite and mackinawite, yet we know little about how they form.In view of the likely role of such reactive minerals in the conversion of pre-biotic CO2 on Early Earth, we may well be able to harness iron sulfides as present-day catalysts for the same process, thereby potentially aiding the slowing down of climate change by converting the CO2 we produce into useful chemicals. In today's world, the importance of such iron-nickel-sulfide clusters as catalysts has been confirmed, as several life-essential iron-sulfur proteins help transform volatiles such as H2, CO and CO2 into other useful and less harmful chemicals.In all of the above examples, it is important to understand that the reactions that lead to the formation of all these minerals which are necessary for any of the geologically stable minerals to exist (i.e., pyrite) all rely on our understanding of the nucleation and growth of unstable precursors or of the reaction transforming one phase to another. Furthermore, the structure and reactivity of each of these phase determines its role and potential application in the environment. A few research groups in the UK and abroad have carried out high quality investigations of the properties of a number of iron sulfide minerals, but it is particularly difficult to investigate events early on in the nucleation process, even though they set the scene for all subsequent transformations. In this project we propose to employ a robust combination of state-of-the-art computation and experiment to unravel the nucleation of iron sulfide mineral phases. We aim to follow the reactions from the emergence of the first building block in solution, through agglomeration into larger clusters, their aggregation into nano-particles and the eventual transformation into the final crystal. We anticipate that this project, investigating short-lived processes which are only now accessible to study through the development of high temporal and spatial resolution in-situ characterization techniques and High Performance Computing platforms, will lead to in-depth step-by-step quantitative insight into the iron sulfide formation pathways and enhance our fundamental understanding of how a mineral nucleates in solution.