近临界区CO2中超声诱导的异相成核空化特性和石墨烯片层的剥离机制

Graphene has broad application prospects, near-critical CO2 coupled with ultrasonic technique is expected to realize industrial production of graphene with a non-polluting manufacturing process. Aiming at analysis of ultrasonic cavitation process in CO2 near-critical region with suspended graphite particles, a visual high-pressure ultrasound reactor system will be established. By using advanced testing and theoretical analysis methods, the cavitation phenomenon of ultrasound-induced heterogeneous nucleation can be online observed and analyzed. The agglomeration, merge, shrink and collapse feature of bubbles generated from ultrasonic cavitation in near-critical CO2 will be studied, and the association between the state parameters for near -critical CO2 and the characteristics and strength of cavitation are to be clarified. The interaction between polar or non-polar molecules and graphite particles with different surface properties will be investigated, and the wetting, adsorption and aggregation at the micro interface will also be analyzed. The dynamic behaviors of nucleation, growth and collapse of ultrasonic cavitation bubbles on hydrophobic/hydrophilic surface are to be revealed, and the influence of hydrophobic/hydrophilic interfacial interaction on cavitation of ultrasonic-induced heterogeneous nucleation in near-critical CO2 will be uncovered. The impact of particle wettability on its adsorption of dissolved gas, and the influence of gas adsorption behavior on the cavitation of ultrasound-induced heterogeneous nucleation are to be investigated. How the ultrasonic cavitation accelerate the intercalation and exfoliation of graphite into graphene at near-critical point will be examined, and the thermalphysics mechanism of ultrasound cavitation on the intercalation and exfoliation will also be explored. This Project will provide a reliable theoretical basis and experimental data for the development and application of graphene technology.

石墨烯具有广泛的应用前景，近临界区CO2中耦合超声波作用可望突破石墨烯的量产化，工艺绿色环保无污染。本项目针对悬浮着石墨颗粒的近临界区CO2中的超声空化过程，采用现代先进的测试手段和理论分析方法，对超声诱导的异相成核空化现象进行在线观察；研究近临界区CO2中超声空化产生的气泡聚团、合并、收缩和崩溃特性，揭示近临界区状态参数变化导致的超声空化特征的瞬态演化规律。考查极性分子和非极性分子与不同表面特性的石墨颗粒的相互作用，分析微界面上发生的润湿、吸附、聚集等现象，探索疏水/亲水表面上超声空化气泡成核、生长和崩溃的动力学行为特征，寻找相界面上疏水/亲水作用对近临界区CO2中超声诱导的异相成核空化特性的影响规律。澄清超声空化现象是如何强化近临界CO2对石墨烯片层的剥离，阐明超声空化效应对石墨烯片层剥离的热物理作用机制。研究结果将为石墨烯大规模制备工艺的开发应用提供可靠的实验数据和理论基础。

针对悬浮着石墨颗粒的近临界区CO2中超声空化过程，建立了可视化超声耦合高压釜系统装置，对超声诱导的异相成核空化特性及其对石墨烯片层剥离效率的影响机制进行了在线观察、实验测试和理论分析。通过改变CO2和H2O的组成比例，探索了极性分子H2O和非极性分子CO2的影响；通过比较天然石墨、氧化石墨和膨胀石墨等多种不同表面特性的石墨颗粒的产物产率，探索了疏水/亲水作用的影响；通过添加表面活性剂，探索了流体界面相互作用的影响。研究结果表明，单纯使用超/近临界二氧化碳，并不能有效地将石墨剥离；而离开了二氧化碳分子的插层作用，超声诱导的异相成核空化效能也十分有限。超声诱导的异相成核空化作用和近临界流体分子的优异扩散能力是成功插层和剥离的关键因素，两者的耦合作用极大地提升了剥离程度和效率。数值模拟结果证实了超/近临界二氧化碳在分子插层和石墨烯片层剥离的作用机制。存在着“插层剥离”和“表面洗脱”两种不同的剥离机制：插层剥离是从整体上发生层层分离，超声诱导的异相成核空化作用是插层剥离的关键驱动力。表面洗脱是利用相间界面作用力将石墨烯片层从石墨颗粒表面洗脱。超声诱导的声流效应即流体剪切作用主要强化了表面剥离，是石墨烯片层表面洗脱的主要作用驱动力；对于已经插层和溶胀了的石墨颗粒，石墨烯片层更易于从表面洗脱，说明超声空化作用也间接促进了石墨烯片层的表面洗脱。反胶束界面相互作用也是石墨烯片层表面剥离的另一种机制，在近临界CO2微乳液中反胶束是否存在对石墨烯产率的影响很小，说明反胶束界面相互作用对石墨烯产率的贡献很小。界面疏水亲水相互作用和溶剂极性是影响超声空化强化分子插层剥离石墨烯片层的主要因素，提高近临界CO2/H2O介质中的水量，氧化石墨烯片层的产率增大，而天然石墨片层的剥离效率减少。通过探索超声辅助超/近临界CO2制备石墨烯工艺，突破了本征石墨烯量产化关键技术，使得石墨烯一次剥离产率达到50%以上，制备时间少于2小时，石墨烯单层率大于95%。