Nucleation and growth of iron sulfides: linking theory and experiment

铁硫化物广泛存在于环境中，调节和控制着全球地球化学铁硫循环。然而，尽管它们被用作海水缺氧的指示剂和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，硫化铁矿物仍然在很大程度上未被勘探。许多硫化铁相是已知的，但许多在环境中是高度不稳定的或仅在短时间内部分稳定。即使是最不活泼的硫化铁，黄铁矿，一旦暴露在地球表面的空气中就不再稳定。它的溶解导致酸性矿井排水问题，其中硫酸和任何捕获的有毒金属被释放，对矿井附近的环境造成破坏性影响。然而，铁硫化物也对环境有有益的影响，因为它们很容易将金属结合在其结构中，因此可能是有毒金属或放射性元素的汇。铁硫化物的一个有趣的方面是它们可能在生命起源中发挥了关键作用。铁镍硫化物的薄层被认为是在早期地球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的构建模块-被认为是由小的铁-镍-硫簇催化的，这些簇在结构上类似于当今高度反应性的硫化铁矿物硅铝石和硅镁矾，然而，我们对它们是如何形成的知之甚少。鉴于这种活性矿物质在早期地球上生物前二氧化碳转化中的可能作用，我们很有可能利用硫化铁作为当今的催化剂来进行同样的过程，从而通过将我们产生的二氧化碳转化为有用的化学品来帮助减缓气候变化。在当今世界，这种铁镍硫化物簇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有助于将挥发物如H2、CO和CO2转化为其他有用且危害较小的化学物质。重要的是要理解，导致形成所有这些矿物的反应是任何地质稳定矿物所必需的，存在（即，黄铁矿）都依赖于我们对不稳定前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，这些相的结构和反应性决定了其在环境中的作用和潜在应用。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研究，但是在成核过程的早期研究事件特别困难，即使它们为所有后续的转变奠定了基础。在这个项目中，我们建议采用一个强大的国家的最先进的计算和实验相结合，以解开硫化铁矿物相的成核。我们的目标是从溶液中第一个构件的出现，通过聚集成更大的簇，聚集成纳米颗粒，并最终转化为最终的晶体。我们预计，这个项目，调查短暂的过程，现在只能通过高时空分辨率的原位表征技术和高性能计算平台的发展来研究，将导致深入的一步一步的定量洞察硫化铁的形成途径，并提高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.