基于分子外延组装构筑纳米晶/二维材料叠层超晶格及其应用研究

The self-assembly of colloidal nanocrystals into ordered superlattices provides an efficient bottom-up pathway for constructing new functional materials. However, owing to the presence of the native organic ligands, nanocrystal assemblies usually suffer from low electrical conductivity and poor mechanical strength and can hardly exist as large-area freestanding architectures. These drawbacks will inevitably hamper the widespread applications of nanocrystal superlattices, especially in the energy-related field. To address these issues, we propose to introduce 2D materials such as graphene oxide and MXene, which have intrinsic excellent electronic and mechanical properties, into the realm of colloidal assembly as 2D building blocks. Given the large difference in size, dimensionality, and self-assembly behaviors between nanocrystal and 2D sheets, we propose to induce the cooperative co-assembly of these two types of building blocks to access 0D/2D multilaminate superlattices based on a molecular approach. Specifically, we plan to modify 2D sheets with ligands such as oleic acid and/or oleylamine, making them dispersible in nonpolar organic solvents. Importantly, the alkyl chain of the tethered ligands ideally matches that of the ligands originally attached to the nanocrystal surface, enabling the epitaxial assembly of nanocrystals on the nanosheet surface during the stacking assembly of 2D materials. The resulting 0D/2D multilaminates can be converted to carbon-coated composites without degrading the structural ordering by in situ ligand carbonization. Taking one step further, ordered mesoporous carbon/nanosheet multilaminates will be produced after the removal of nanocrystals by acid etching. We aim to implement these 0D/2D multilaminates as well as their carbon-based derivatives as freestanding electrode materials in electrochemical energy storage and conversion. This proposal will not only address the poor electrical conductivity and mechanical stability issues of nanocrystal assemblies, but also provide a new strategy for co-assembling multicomponent building blocks for rationally designing sophisticated superlattice architectures.

通过纳米晶自组装获得有序的超晶格结构是自下而上构筑新型功能材料的有效途径。然而，纳米晶组装体因为配体分子的影响普遍存在导电性能差与机械强度低的缺陷，难以实现大尺寸的自支撑结构，限制了其在能源领域的应用潜力。本项目拟将具有优异电学与力学性能的二维材料（氧化石墨烯和MXene等）作为构建单元引入到胶体纳米晶组装范畴。围绕配体分子表面改性及其所诱导的外延组装策略，从分子水平指导纳米片与纳米晶这两种维度、尺度及组装行为迥异的构建单元协同有序组装，构筑大尺寸纳米晶/二维材料叠层超晶格，并结合配体原位碳化制备介孔碳/二维材料叠层衍生物。从叠层超晶格及其衍生物两个方面分别考察它们在电化学能源存储与转换中的应用。本项目研究不仅能够解决传统纳米晶超晶格机械强度低、导电性能差的问题，拓展其应用领域，而且为集成多尺度、多维度构建单元，理性设计与构建复杂体系超晶格材料奠定了研究基础。

针对0D纳米晶/2D纳米片组装容易相分离的问题，我们利用小分子配体修饰本征亲水性的二维材料，使其表面疏水化，并且能稳定分散到非极性溶剂中，实现了和传统纳米晶胶体相容；然后，通过溶剂挥发诱导组装，驱动纳米颗粒和二维纳米片有序组装，通过实验和理论证实配体密度差异化对抑制相分离具有重要的作用，进而发展了普适性的跨维度有序组装方法学。所获叠层超晶体在储能、催化等领域具有潜在的应用价值。此外，针对传统纳米晶超晶体三维密堆积不利于传质的问题，我们立足于颗粒表面固有的有机配体，引入新的分子间相互作用，并结合合适的限域环境与后续化学转化，驱动纳米颗粒多级次有序组装，获得了系列开放型超晶体，其在电催化析氢、析氧等反应中显示出非常高的催化活性与稳定性。我们还基于纳米晶超晶体衍生制备的介孔石墨烯平台，探究了复合材料的可控制备及其在能源领域中的应用，进一步拓展了纳米组装体材料的应用领域。通过本项目的研究，以（共）通讯作者在包括Sci. Adv.、JACS、Angew. Chem. Int. Ed.、 Adv. Mater.等在内的期刊发表本项目资助的论文24篇；申请国家发明专利15项，其中5项已授权。培养博士后两名，博士研究生10名，其中5名毕业，硕士研究生4名，其中2名已毕业。项目承担者获2020年度上海市自然科学二等奖（第一完成人），2020年获国家杰出青年基金支持。