Collaborative Research: Thermochemistry and Chemical Kinetics of Halide-driven Crystal Structure Control of Manganese and Lanthanide Chalcogenide Nanocrystals

在化学系大分子、超分子和纳米化学计划的支持下，特拉华大学的Emil Hernández-Pagán博士、亚利桑那州立大学的Kristina Lilova博士和圣路易斯华盛顿大学的Robert Wexler将研究卤化物(氯化物、溴化物和碘化物)的存在如何影响某些类别纳米粒子的最终原子排列(晶体结构)。该团队将采用实验技术，包括在反应发生时提供信息的技术，以及深入了解这一过程的计算方法。特定的晶体多晶型通常决定了纳米晶体材料的关键性质，并因此决定了这些材料可用于例如光伏、催化和能量存储的应用。因此，拥有控制晶体结构的知识和能力是重要的。这项工作的更广泛影响集中在：(A)为参与该项目的学生提供实验和计算培训；(B)为来自波多黎各的本科生提供暑期研究体验，目的是补充他们在本国机构接受的培训，使他们更好地为工作和/或攻读研究生学位做好准备。合理地合成纳米颗粒的给定晶型或相的能力是可取的，因为这决定了它们的机械、光学和电学性质。这项拟议的工作协同结合了实验和计算方法，为模型系统提供了一个整体框架，在该模型系统中，卤化物驱动合成硫化物锰纳米晶的晶体结构/相控制。这个框架将包括识别预成核分子物种，执行反应和表面-配体相互作用的热化学测量，以及监测成核和生长的动力学。将采用一套原位技术来实现在反应条件下的这种测量。基于量子力学的计算将用于确定原子尺度的相互作用和导致观察到的晶体结构/相的机制。这些计算将为纳米晶体成核和生长的动力学和热力学模型提供输入，因此将为控制合成金属硫化物纳米晶体提供多尺度的计算指导。这些研究将扩展到稀土硫化物纳米晶体，尽管具有独特的光学和磁性，但这些纳米晶体在很大程度上仍未被探索。这项工作预计将进一步提高对合成硫化物纳米晶体的化学理解水平，这种洞察力有可能为科学界合成其他类别的材料提供指导。这一奖项反映了NSF的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

With the support of the Macromolecular, Supramolecular and Nanochemistry Program in the Division of Chemistry, Drs. Emil Hernández-Pagán of the University of Delaware, Kristina Lilova of Arizona State University, and Robert Wexler of Washington University in St. Louis will investigate how the presence of halides (chloride, bromide, and iodide) influences the final arrangements of atoms (crystal structure) in the synthesis of certain classes of nanoparticles. The team will employ experimental techniques, including ones that provide information as the reaction occurs, and computational methods to gain in depth insight into this process. The particular crystal polymorph often dictates key properties of nanocrystalline materials and, consequently, the applications for which these can be used, for example, in photovoltaics, catalysis, and energy storage. Therefore, having the knowledge and ability to control the crystal structure is important. The broader impacts of this work are centered around (a) providing experimental and computational training to the students working on this project and (b) summer research experiences for undergraduate students from Puerto Rico that aim to complement the training they receive at their home institutions to better prepare them for the workforce and/or pursuing a graduate degree. The ability to rationally synthesize a given polymorph or phase of a nanoparticles is desirable as these dictate their mechanical, optical, and electronic properties. The proposed work synergistically combines experimental and computational methods to provide a holistic framework for a model system where halides drive the control of crystal structure/phase in the synthesis of manganese chalcogenide nanocrystals. This framework will encompass identifying pre-nucleation molecular species, performing thermochemical measurement of reaction and surface-ligand interactions, and monitoring the kinetics of nucleation and growth. A suite of in situ techniques will be employed to enable such measurements under the reaction conditions. Quantum-mechanics-based calculations will be used to identify atomic-scale interactions and the mechanisms that lead to the observed crystal structures/phases. These calculations will provide input for kinetic and thermodynamic models of nanocrystal nucleation and growth and, therefore, will produce multi-scale-based computational guidance for the controlled synthesis of metal chalcogenide nanocrystals. The studies will be extended to lanthanide chalcogenide nanocrystals, which have remained largely unexplored despite unique optical and magnetic properties. This work is anticipated to further increase the level of chemical understanding of the synthesis of Mn and Ln chalcogenide nanocrystals, and such insights have the potential to provide guidance to the scientific community for the synthesis of other classes of materials.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.