Roles of interfacial water in carbon mineralisation Shurui Miao and Susan Perkin University of Oxford, UK
The latest Intergovernmental Panel on Climate Change report highlights that less than 5 % of simulated scenarios may suppress global warming below 1.5 °C by the end of this century. 1 It is clear that reducing greenhouse gas emissions alone will not be enough to prevent climate disasters. Carbon mineralisation emerged as a promising candidate for long-term carbon sequestration. Once mineralised, CO 2 is removed from the natural carbon cycle without the need for costly storage and monitoring. The natural process of carbon mineralisation involves dissolved CO 2 reacting with various naturally abundant ions such as Mg 2+ and Ca 2+ . However, its molecular mechanism remains largely unknown due to the complexity of natural systems and the lack of direct experimental data probing structures and forces near the solid-liquid interface. Recent work has suggested that many minerals including calcite (a form of carbonate mineral) display nonclassical crystal growth. 2,3 Different to the traditional Ostwald ripening model, aligned aggregation of particles ranging from multi-ion complexes to nanocrystals is now recognised as a pathway of crystallisation. As a result, concepts from colloidal science (e.g., the DLVO theory) have been applied to describe crystal growth with some success. 4 However, many mysteries remained, such as the sensing and alignment of particles over very long distances and the draining of solution during aligned attachments. It is postulated that these phenomena and the nonclassical crystallisation mechanism are closely related to the ordering of the water near the particle surface. 2 Our work uses dynamic light scattering and surface force balance (SFB) to monitor the bulk behaviour of mineral nanoparticles and the structure of solutions near the solid-liquid interface. The SFB can directly measure free energy of interaction with a resolution of ~ 10 -6 J/m 2 , and with a spatial resolution of 0.1 nm (a water molecule is roughly 0.3 nm in diameter), both required to resolve the role of interfacial water. We have studied the solution structure and how it modulates particle-particle interactions as a function of ionic strength and salt composition. This work provides key experimental results and molecular insights for the rational design and optimisation of carbon capture processes based on mineralisation. References 1. IPCC Sixth Assessment Report 2. J. J. De Yoreo, et al., Science 349 , aaa6760 (2015) 3. N. Gehrke, et al., Crystal Growth & Design 5 , 1317-1319 (2005) 4. G. Mirabello, et al., Nat. Mater. 19 , 391-396 (2020)
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