单斜相二氧化钒纳米晶水热可控制备机理的原位同步辐射和第一性原理计算研究

Hydrothermal method has been widely used in the nanomaterials synthesis. However, the physical and chemical characteristics of the nucleation and crystallization, thermodynamics and kinetics and their influencing factors have not been fully understood due to the limitations of ex situ characterization. It has become an obstacle for precisely controlled synthesis of nanocrystals. In situ time-resolved synchrotron radiation characterization is an effective method to make up the shortage of ex situ detection. In this proposal, we will study the hydrothermal synthesis of VO2(M) nanocrystals using capillary microreactor combined with in situ synchrotron radiation characterization. The crystal phase evolution and the reaction pathways will be explained by analysis of phase compositions and calculation of the formation energies of the intermediate phases and VO6 octahedral arrangements by first principles. Besides, the key influencing factors will be screened. The qualitative and quantitative relationship between key experimental parameters and phase, morphology and size will be summarized as well. Then the thermodynamic model will be built. The present project is expected to elucidate the formation and growth mechanism of VO2(M) nanocrystals and provide theory foundation for precise design and tailored synthesis, thus improving the wide application of VO2(M) nanocrystals in smart windows. At the same time, the results of this project will provide guidance for the hydrothermal preparation of other nanomaterials.

“水热法”是纳米粉体制备最常用的技术之一。局限于“离线式”检测方法，科学家对水热条件下纳米晶形核结晶过程的物理化学，特别是热力学和动力学及其影响因素的理解只能是碎片式非连续的。这已成为纳米材料精确可控制备的制约因素。高时间分辨率的同步辐射原位表征技术是弥补离线检测手段不足的有效方法。利用自行设计研发的毛细管微反应装置结合同步辐射原位表征技术，本研究拟开展单斜相二氧化钒（VO2(M)）纳米晶水热制备过程的在线监测。通过分析不同阶段晶相组成并结合理论计算的过渡相生成能及VO6八面体堆垛方式，预测水热反应路径和物相演变规律；筛选关键影响因素，总结实验参量与纳米晶晶相结构、形貌和尺寸的定性定量关系；建立水热结晶热/动力学模型。本研究将为深入理解VO2(M)纳米晶的形成与生长机理、实现VO2(M)纳米晶的设计与定制合成提供理论依据，促进其在智能窗等领域的应用；同时为其他纳米晶材料的水热制备提供借鉴。

水热制备在密闭环境中进行，类似于“暗箱操作”，通常采用的“离线式”的观察方法只能粗略地反映成核生长过程的部分信息。本项目建立并完善了观测水热反应的毛细管微反应装置，借助同步辐射原位表征技术完成了若干反应体系水热制备VO2(M)纳米晶的水热合成过程的观测，揭示了VO2(M)水热结晶形成与生长机理，实现了VO2(M)纳米晶的定制合成。研究发现：反应物的浓度、摩尔比、压力、温度等决定了最终产物和中间亚稳态产物的晶相。该方法可应用于VO2(A)和V2O2(OH)3纳米晶材料的水热合成条件优化。同时，VO2(M)纳米晶薄膜及二氧化钒复合透明木基材料具有较好的可见光透过率和太阳能调控效率，在智能窗领域具有广阔的应用前景。