炭包覆纳米晶的"Oriented Attachment"生长及其多维结构构筑

The multidimensional carbon-based materials including 2D and 3D carbon structures, possessing unique properties, are very attractive candidates for various applications such as catalysts supports, adsorbents, biosensors, and energy storage. However, one of the great challenges for their practical applications is how to construct these multidimensional carbons. To address this challenge, a new strategy to construct the multidimensional carbon materials in this program is proposed, where multidimensional carbon-encapsulated nanocrystals (CENCs) will be constructed by oriented attachment (OA) growth of CENCs formed during the organometallic pyrolysis. One of the objectives of this program is to come true the controllable preparation of a variety of multidemensional CENCs with different morphologies and structures based on the OA mechanism via designing the synthesizing conditions. However, most of the crystal growth processes based on OA mechanism so far have been mainly carried out under the liquid conditions rather than organometallic pyrolysis environments and been used to prepare the products without core/shell structures. Therefore, the other objective of this program is to reveal the chief characteristics of OA growth of CENCs under the organometallic pyrolysis conditions by investigating the key information from the intermediates of multidimensional CENCs such morphologies, structures, crystal transformations, dislocations, etc. In addition, as-prepared multidimensional CENCs used as precursors will also be transformed into other structures, including: 1) multidimensional graphene-based nanostructures by annealing to improve the crystallinity of carbon shells and then removing the inner crystals; 2) multidimensional CENCs with porous carbon shells by the assist of air-oxidation or alkali’s activation. Then, lithium-ion storage properties of these nanosturctures including multidimensional CENCs and their transformation products will also be investigated, because their structures are very interesting and suitable for storage of lithium-ion, and they will be promising candidates for electrode materials for next generation lithium-ion batteries. Therefore, this program will expand the oriented attachment mechanism of crystal growth to the system of organometallic pyrolysis, which not only provides a suitable strategy for design of various multidimensional carbon-based nanostructures, but also is helpful to understand deeply the OA mechanism of crystal growth.

多维炭结构的制备对促进和丰富炭材料的实际应用具有重要意义，然而如何制备是关键。本课题提出一种制备多维炭结构的新理念，拟通过有机金属热解所形成炭包覆纳米晶的“Oriented Attachment”（简称OA）生长，实现一系列不同形貌结构的多维炭包覆纳米晶的构筑，考察不同阶段中间产物的形貌、结构、晶型、位错等关键信息以及纳米晶对炭包覆层催化生长的控制规律，阐明炭包覆纳米晶OA生长的微观机制和内在本质，建立多维炭包覆纳米晶的构筑模型。进而开展多维炭包覆纳米晶的转化研究，制备多维的石墨烯结构与多孔炭包覆纳米晶，并初步开展多维结构及转化产物的储能应用研究。OA机制是晶体生长的新理论，目前多限于对液相中晶体生长规律的研究。因此，本课题将OA机制应用到有机金属热解体系中，拓宽了OA生长的研究领域和应用范围，不仅为设计结构新颖的多维炭、炭包覆材料提供新思路，而且将加深对晶体OA生长行为的理解和认识。

本课题提出一种多维炭结构构筑的新理念，通过有机金属热解所形成炭包覆纳米晶的“Oriented Attachment”（简称OA）生长，实现一系列不同形貌结构的多维炭包覆纳米晶的构筑。首先，研究了二茂铁、二茂锰、乙酰丙酮铁、金属/有机网络等有机金属及配合物的热解规律。然后，通过调控纳米晶表面碳包覆层的催化生长，从而影响碳包覆纳米晶之间的相互作用实现其定向搭接(OA)生长，设计出系列形貌新颖、结构独特的多维碳包覆纳米晶：碳包覆氧化铁纳米片、碳包覆硫化锰(MnS@C)分枝状纳米链、碳包覆Fe7S8复合纳米片、石墨烯负载过渡金属硫属化合物纳米棒等。在此基础上，考察不同阶段中间产物的形貌、结构，揭示碳包覆纳米晶OA生长的微观机制，建立碳包覆纳米晶结构的生长模型。最后，以多维结构碳包纳米晶为研究对象，开展其结构转化研究以及在储能应用，探明结构与性能的构效关系，设计制备出高容量、高倍率形成、长周期循环稳定成的碳包覆金属晶的电极材料。