乳液水热碳化法制备空心碳球的工艺及机理研究

Hollow carbon spheres have many advantages of large inner space, low density, and high chemical stability etc., so they have great application potential in the fields of catalyst, batteries, gas separator, and so on. Because the common used preparation method is complex, environmentally harmful, and difficult to control the structure of product, in this project a new strategy for the synthesis of hollow carbon spheres is proposed by the combination of emulsion soft-template and hydrothermal carbonization. Using biomass as the raw material, emulsion droplet as the soft template, the carbon material is in-situ polymerized on the interface of oil and water by hydrothermal carbonization. By optimizing process and studying mechanism, the characteristics of hollow sphere can be precisely controlled. The research will be focused on the surface tension of droplet, the stabilizing thermodynamically conditions, the uniformity of droplet and the interface structure. The species of chemical bonds between carbon source and surfactant molecule and the formation mechanism of composite emulsion will be identified. According to colloid stability theory, the parameters like emulsifier, size distribution of droplet, density difference of two phases, charge, interfacial film, viscosity, and temperature will be studied. The emulsion interface instability law, and molecule transfer and deemulsification model will be established. The carbonization mechanism and the relation of emulsion, temperature and structure, composition will be identified. The aim of project is to facilely and reliably prepare hollow carbon spheres by biomass. This study will develop the understanding of hydrothermal carbonization mechanism, enrich the theory of emulsion, and finally promote the large-scale utilization of hollow carbon spheres.

空心碳球具有大内部空间、低密度、高化学稳定性等优点，广泛应用于催化剂、储能、气体分离等领域。本项目针对传统制备方法工艺流程复杂、碳源不可再生、结构控制困难的问题，提出将乳液软模板与水热碳化相结合构筑空心碳球的新思路，以生物质原料为碳源，乳液为软模板剂，在液滴的油/水两相界面处原位水热碳化聚合碳材料，经工艺优化和机理研究达到空心球特征的精确调控。重点研究液滴表面张力和热力学稳定条件，液滴均匀性和界面结构控制，明确乳液与碳源分子化学键类型和复合乳液形成机理；拟依据胶体稳定理论，分析乳化剂、液滴大小分布、两相密度差、电荷、界面膜、黏度和温度等参数，揭示乳液失稳化学界面过程规律，建立乳液分子转移和破乳模型；拟分析乳液水热碳化反应机制，确定乳液、温度等参数与产物结构、形态、成分的关系。本研究旨在实现生物质原料高效可控制备空心碳球，将加深对水热碳化的理解，丰富乳液稳定性理论，促进空心碳球的工业化推广。

空心碳球具有大内部空间、低密度、高化学稳定性等优点，广泛应用于催化剂、储能、气体分离等领域。本项目以三辛胺（TOA）为油相，水为溶剂，二茂铁为辅助剂，抗坏血酸（VC）为碳源，制备出空心碳球和碗形碳。与硬模板法相比，极大地缩短了反应时间，避免了去除模板时造成结构破坏。产物为水热碳质，表面富含含氧官能团，直径分布在1~2微米之间，内壁厚度仅为几十纳米，外壁厚约为100纳米。水热环境下，VC在TOA/水乳液液滴表面发生聚合反应，水热碳化生成一层富碳壳；由于乳液在高温下的不稳定性，碳壳内油相发生逃逸，产生指向球心内部的毛细力，一侧碳壳向内凹陷，形成空心碗形。TOA作为软模板剂，是形成空心结构的必要条件，TOA添加量直接影响乳液液滴的分布和产物的尺寸分布。反应温度同时对碳化反应和乳液的稳定性产生影响，温度过低，水热碳化反应无法触发，而温度过高时，乳液容易发生破乳，模板失效，碳源发生自形核，生成实心球产物。空心碗形碳电极的超级电容器具有较高的比电容、高的大电流电容保持率和循环稳定性。在1 A·g-1的电流密度下，比电容为103 F·g-1；在2 A·g-1电流密度下，循环5000次后，仍能维持96%的初始电容。本研究旨在实现生物质原料高效可控制备空心碳球，将加深对水热碳化的理解，丰富乳液稳定性理论，促进空心碳球的工业化推广。