超临界流体中石墨烯高效制备方法及其聚合物导电纳米复合材料研究

It remains a great challenge how to ecnomically and efficiently convert cheap graphite into graphene sheets with controlled structure and properties. Considering the large defects and low electrical conductivity of graphene derived from the oxidation and reduction of graphite, in this project, a non-covalent intercalation technique with metal chloride will be adopted to enlarge the interlayer spacing of graphite and reduce the constraint of Van Der Waals forces on sheets, which will provide convenience for the rapid exfoliation of graphite intercalation compounds (GICs). Subsequently, GICs with larger interlayer space wille be filled with a large amount of carbon dioxide molecules when subjecting to supercritical carbon dioxide which has low surface tension and high diffusion coefficients, and transient pressure adequate for graphite exfoliation will be established upon the release of pressure, which would force GICs to expand and be exfoliated into individual graphene sheet. What is novel about this project is that the use of metal chlorides instead of strong acid/oxidizer as intercalation agent significantly increases the interlayer spacing, but not disrupt to the sp2 conjugate structure of graphite, combined with the high efficiency of supercritical carbon dioxide in exfoliating graphite, the efficient production of graphene with high structural integrity and low thickness can be realized. With the effective reduction in the viscosity of the polymer melt, high-quality graphene sheets obtained can be homogeneously dispersed in matrix, and polymer/graphene nanocomposites with excellent electrically/thermally coductivity and high electrical and magnetic shielding efficiency can be fabricated at low filler loadings.

如何从廉价的石墨经济高效地制备结构性能可控的石墨烯仍然面临巨大挑战。针对石墨氧化-还原法制备的石墨烯结构缺陷多和电导率低问题，本项目拟采取金属氯化物非共价键插层策略，扩大石墨层间距，减小范德华力束缚，为其快速剥离制备石墨烯提供条件；然后，利用超临界CO2低表面张力和高渗透性的特点，高压下在增大的石墨层间充入大量超CO2分子，而后快速卸压在层间建立起足够高的瞬时压力，迫使石墨片层迅速膨胀剥离制得石墨烯。本项目的创新点在于以金属氯化物替代强酸/强氧化剂作插层剂，既避免了对石墨sp2共轭结构的破坏，又增大了其层间距，同时结合超临界流体对石墨的高效剥离作用，从而实现高结构规整度、低厚度石墨烯的非氧化高效宏量制备。以所制备优质石墨烯为填料，利用超临界流体降低熔体粘度、促进纳米粒子分散的特性，在低填料含量下获得具有优秀导电、导热和电磁屏蔽性能的聚合物/石墨烯纳米复合材料。

本项目开展了以非氧化插层为基础的高品质、低缺陷石墨烯制备新方法、超临界流体法石墨烯杂化材料制备和聚合物多功能复合材料等研究，取得了系列重要研究成果。具体总结如下：（1）为应对针对氧化法制备石墨烯结构缺陷多和环境污染问题，我们以安全稳定、环保的金属氯化物插层剂替代强酸、强氧化剂，制备层间作用力极弱、易于剥离的石墨插层前驱体，通过超声处理或高温热处理可实现缺陷少、少数层石墨烯的制备(<2 nm)；为提高石墨烯制备效率，我们也开发出高压均质机液相剥离规模化制备石墨烯新方法，可连续、批量制备高品质石墨烯。通过控制反应条件，保留部分插层剂可高效制备出高性能夹层结构石墨烯杂化材料，有望在导电、电磁屏蔽、吸波及能源领域取得广泛的应用。(2)发展了利用超临界流体制备多级结构石墨烯纳米杂材料的策略，实现了系列金属/金属化合物纳米颗粒在惰性石墨烯表面的均匀、稳定负载，如高比表面积AlOOH@石墨烯杂化材料和石墨烯/Fe2O3杂化材料，并首次实验证实石墨烯与Fe2O3间碳热反应，发现调节纳米Fe2O3晶型新方法，为高性能多级结构纳米材料构筑提供新思路。(3) 在聚合物导热复合材料方面，利用石墨烯和其他导热填料杂化制备了UL-94 V-0等级阻燃、绝缘导热环氧纳米复合材料和高导热石墨烯包覆T-ZnO复合材料，同时在石墨烯表面构筑致密Al2O3绝缘导热层，制备绝缘导热环氧纳米复合材料，相关技术成果正在积极向企业转化。同时，我们在聚合物电磁屏蔽复合材料研究方面，取得了系列重要研究成果。通过构筑三维连续碳纳米管海绵结构材料，解决了纳米材料在基体中易团聚难题，制得兼具优异导电/电磁屏蔽和力学性能聚合物纳米复合材料。在石墨烯研究基础上，我们又开展了新型二维过渡金属碳/氮化物的研究工作，首次成功制备轻质、柔性、疏水的MXene多孔高性能电磁屏蔽薄膜，实现了MXene材料从亲水性向疏水性的转变，解决了制约其应用的稳定性差的关键问题。通过静电组装策略制备了高强、高导电/电磁屏蔽PS/MXene纳米复合材料，导电阈值仅为0.26 vol%，导电率高达1081 S/m，屏蔽效能达62 dB。总之，在本项目资助下，我们在包括Adv. Mater和Adv. Funct. Mater.等权威学术期刊发表高水平SCI期刊论文17篇和会议论文8篇，申请中国发明专利2项(1项授权)，培养博士研究生4名，硕士研究生6名。