Core-Shell nanoparticle models for in-situ SERS measurements of carbonate dissolution under environmentally realistic conditions

我们的目标是开发一种溶解过程的原位分析探针，可以在分子水平上解决由生物碳酸盐溶解速率不确定性引起的机制问题。表面增强拉曼光谱（SERS）将用于监测在定制金纳米颗粒（“核-壳”结构）上生长的碳酸盐壳的行为。通过控制这些体系中碳酸盐的结构和习性，我们将利用原位分子特异性探针探索化学成分、矿物结构和晶格缺陷对碳酸盐溶解度的个别影响。我们正在处理的具体问题是海洋碳酸盐的溶解问题，这是全球碳循环的一个基本组成部分。海洋表层生物碳酸盐的产生远远超过了河流提供的成分，如果这些碳酸盐在沉入海底之前没有溶解，这个系统就无法维持自身。然而，人为排放二氧化碳导致海洋酸化（OA），有效地降低了海洋中碳酸盐的饱和状态，并引起了对未来海洋碳平衡的相当大的关注。尽管经过几十年的研究，碳酸盐溶解的一些最基本的方面仍然存在很大的不确定性：甚至碳酸盐溶解的速率顺序也有4的不确定性因子。此外，根据经验，碳酸盐岩壳的部分溶解会影响它们的化学成分，而化学成分本身经常被用来代表古代海洋的条件。目前关于溶解如何精确影响成分的不确定性对这些工具的适用性提出了严重的限制。这些不确定性中有许多是由于“典型的”生物成因碳酸盐（例如有孔虫和球粒岩，它们构成了全球大部分海洋碳酸盐的生产）的复杂性（矿物学和形式）引起的。该项目旨在开发核壳纳米粒子SERS作为一种分析技术，能够在现实条件下提供机械表面信息。将开发碳酸盐的纳米颗粒核壳合成技术，测定溶解速率，并与TEM （FENAC）和XPS测量的体积速率和壳厚度进行比较。拉曼可以区分碳酸钙的所有不同结构的多晶型，因此将使项目进展到不同的碳酸盐结构的调查。特定的金核形状（球体、棒状、立方体等）将被合成，以研究结构应力对碳酸盐壳结构、生长习惯和随后的溶解的作用。该项目将为开发高压系统奠定基础，该系统将成为未来应用的主题。该项目为博士生提供了一个独特的机会，可以在纳米科学技术和纳米尺度合成方面获得广泛的培训，并结合分析化学领域应用于环境问题的经验。

Our aim is to develop an in-situ analytical probe of dissolution processes that can address, at a molecular level, the mechanistic questions raised by uncertainties in the rates of biogenic carbonate dissolution. Surface enhanced Raman spectroscopy (SERS) will be used to monitor the behaviour of carbonate shells grown on custom made gold nanoparticles ('Core-Shell' structures). By manipulating the structure and habit of the carbonate in these systems we will explore the individual effects of chemical composition, mineral structure and lattice imperfection on carbonate solubility with an in-situ, molecularly specific probe. The particular issue we are addressing is that of the dissolution of marine carbonates, which represents a fundamental component of the global carbon cycle. The production of biogenic carbonate in the surface ocean greatly outweighs the supply of its ingredients from rivers and without dissolution of much of this carbonate prior to its burial at the seafloor, the system could not sustain itself. However, anthropogenic emission of CO2 leading to ocean acidification (OA), is effectively lowering the saturation state of the oceans with respect to carbonate and raising considerable concerns regarding the future carbon balance in the oceans. Despite decades of study there remains great uncertainty concerning some of the most fundamental aspects of carbonate dissolution: even the rate order for carbonate dissolution has an uncertainty factor of 4. Furthermore, the partial dissolution of carbonate shells is empirically known to affect their chemical composition, which itself is often used to proxy ancient oceanic conditions. The current uncertainty as to how dissolution precisely affects composition presents critical limitations on the applicability of these tools. Many of these uncertainties have arisen from the complexity (in mineralogy and form) of 'typical' biogenic carbonates (e.g. foraminifera and coccoliths, that comprise most of the global production of marine carbonates). The proposed studentship aims to develop core-shell nanoparticle SERS as an analytical technique capable of providing mechanistic surface information under realistic conditions. Nanoparticle core-shell synthesis techniques for carbonates will be developed and rates of dissolution determined and compared against bulk rates and shell thickness measurements from TEM (FENAC) and XPS. Raman can distinguish between all the different structural polymorphs of calcium carbonates and thus will enable the project to progress to an investigation of the different carbonate structures. Specific gold core shapes (spheres, rods, cubes etc) will be synthesised to investigate the role of structural stress on the carbonate shell structure, growth habit and subsequent dissolution. The project will lay the ground work for the development of a high pressure system which will be the subject of a future application. The project offers a unique opportunity for a PhD student to gain extensive training in nanoscience techniques and nanoscale synthesis combined with experience in the field of analytical chemistry applied to environmental problems.