金属诱导下石墨烯的构象转变机制及包覆结构构筑

Graphene, which is a one atom thick and closely packed two-dimensional lattice, is viewed as a basic building block for the well-known carbonaceous materials including fullerences, carbon nanotubes and graphite. However, its confromational changes is crucial when using graphene as sources to assembly other nanocarbons such as nanotubes, nanoscrolls, even hollow carbon spheres, etc. Many theorectical work on the transformation from graphene to other nanocarbons and graphene-encapsulated nanostructures has been developed, but practical experimental investigation remains at its initial stage. How to control the confromational changes of graphene during the self-assembly process is a large grand challenge, because it is very difficult to find an effective driving force to overcome the resistance of confromational changes. To address this challenge, a new strategy to guid the conformational changes of graphene in this program is proposed, where metal are employed to induce the conformational changes of two-dimensional graphene sheets. In fact, metal not only acts as a catalyst to promote the growth of nanocarbons, but also guid the arrange of graphene layer due to the interaction between the graphene and metal. Once the metal nanoparticles are dposited on the planar graphene, they can melt and aggregate at high temperature that initiate conformational changes and help to overcome deformation battiers associated with them. The objectives of this program are to come true the controllable preparation of graphene-encapsulated metal crystals with various morphology and structure via designing the synthesizing conditions, investigate the driving force and key affecting factors (shapes and layer number of graphenes, kinds of metal, ratio of metal/graphene, temperature, substrates, etc.) for conformational changes of graphene, and reveal their assembly mechanism. Based on the controllable preparation, as-prepared graphene-encapsulated metal crystals used as precursors were transformed into other nanostructures: 1) graphene assemblies by removing the metal; 2)hollow graphene-encapsulated metal oxide nanostructures with the assist of the nanoscale Kirkendall effect. Lithium-ion storage properties of these nanosturctures including graphene assemblies and hollow graphene/metal oxide will also be investigated, because their structures are very interesting and suitable for diffusion of lithium-ion, and they will be promising candidates for anode materials for next generation lithium-ion batteries. This program will be of great significance for design of graphene-encapsulated metal crystals using a non-catalytic method and, also for fundamental science: interfacial interaction between metal and graphene and the role of metal during the confromational changes of graphene.

石墨烯构象转变（弯曲、折叠、卷曲等）是构筑各种新颖石墨烯基材料的基础，如何操纵构象转变是成功构筑的关键。相关报道多是理论模拟，实验研究仍处于探索阶段。本课题提出一种利用金属引发石墨烯构象转变的新理念，拟通过高温下金属熔并带动石墨烯卷曲，实现一系列不同形貌和结构的石墨烯包覆金属晶的大量制备，探讨金属类型、石墨烯结构（层数、形状、尺寸等）及合成工艺参数（温度、时间、配比、气氛等）对产物形态、结构的影响，考察石墨烯的构象转变机制和包覆结构的形成机理。在此基础上开展包覆结构转化研究：一方面通过去除金属制备石墨烯组装体；另一方面借助纳米Kirkendall效应实现石墨烯基金属氧化物空心结构的可控制备，并考察转化产物在储能方面的初步应用研究。这不仅提供了一种非催化法大量制备石墨烯包覆金属晶的通用新途径，拓宽石墨烯的研究领域和应用范围，而且将有助于加深对金属和石墨烯界面交互行为的认识。

石墨烯构象转变（弯曲、折叠、卷曲等）是构筑各种新颖石墨烯基材料的基础，如何操纵构象转变是成功构筑的关键。相关报道多是理论模拟，实验研究仍处于探索阶段。本课题提出一种利用金属引发石墨烯构象转变的新理念，通过高温下金属熔并带动石墨烯卷曲，利用此理念制备出石墨烯包覆金属微球，并初步考察了微球的形成机制，发现石墨烯与金属之间较强的界面交互作用是影响包覆结构形成的关键因素之一，并充分考察了金属/金属化合物与石墨烯之间存在的交互作用的类型。在此基础上开展包覆结构转化研究：一方面通过去除金属制备石墨烯组装体；另一方面借助纳米Kirkendall效应将预制备的石墨烯包覆金属微球转化为“海胆型”石墨烯/金属氧化物空心微球，考察了微球中金属原子在空气氧化诱导之下的向外扩散过程。初步研究了所制备的石墨烯/金属氧化物空心微球用于锂离子二次电池的电化学性能，容量可以达到800 mAh/g。该课题不仅提供了一种非催化法大量制备石墨烯包覆金属晶的通用新途径，拓宽石墨烯的研究领域和应用范围，而且加深了对金属和石墨烯界面交互行为的认识。