超临界二氧化碳体系中二维层状材料制备及其异质结构筑的研究

Two-dimensional (2D) layered nanomaterials present the enormous potential in a wide range of fields including optoelectronics, sensors, catalysis, mechanics, biology, energy storage, and so on. The main methods for exfoliation include epitaxial growth, hydrothermal synthesis, chemical vapor deposition, micromechanical cleavage, liquid exfoliation, and ion intercalation. Apart from these methods mentioned above, supercritical CO2 (SC CO2)-assisted exfoliation is of particular interest, due to its high diffusion coefficients and negligible surface tension. Besides, it is well known that the emulsion environment is able to be built by introducing surfactants or nanoparticles into the SC CO2-water interface. Changing CO2 pressure, temperature or PH will produce the strong driving forces that can be used to manipulate the properties and phase behaviors of emulsions. In this application, we try to exfoliate a series of layered materials at the SC CO2-water interface of emulsion environment. Moreover, we will investigate the properties of exfoliated layered materials and their application in electrocatalysis and photoelectrocatalysis..(1) Exfoliation of a series of 2D materials in the Pickering emulsion built with the assistance of SC CO2..With the high-speed stirring, the great shearing forces produce at the SC CO2-water interface of emulsion environment, and then the bulk materials can be exfoliated into ultrathin 2D nanosheets efficiently at the SC CO2-water interface. Here ethanol will be used as the cosolvent for the SC CO2. In the exfoliation process, a series of experimental parameters such as experimental temperature, SC CO2 pressure, the solvent ratio and the concentration of bulk materials will be investigated to find the exfoliation optimum value.. (2) Exfoliation of layered materials in the emulsion environment built by SC CO2/surfactant/H2O system..A series of surfactants, including cationic surfactant, anionic surfactant and nonionic surfactant will be investigated to help to build microemulsion. It can be expected changing CO2 pressure will produce the strong driving forces to manipulate the interfacial tension and the curvature transition of surfactant lamella, eventually resulting in the dynamic inversion of emulsions. Herein we try to exfoliate a series of typical layered materials such as MoS2, WS2 , WO3, MoO3 and WSe2, etc. into ultrathin 2D nanosheets in the switchable emulsion environment of CO2/surfactant/H2O system, and investigated the effects of variable experimental parameters as CO2 pressure, ethanol/water ratio and initial concentration of bulk materials on the exfoliation efficiency. Based on this, we hope to supply the phase behavior of emulsion environment and the optimum data for the different 2D materials..(3) Solution-phase fabrication of two-dimensional multiple-heterostructures with assistance of SC CO2..Our previous study indicated that the adsorption of CO2 on 1T phase is much stronger than that on 2H surface, so the stronger interaction between CO2 and 1T-MoS2 may affect the morphology of nanosheets to form the protuberant 1T-phase, further the local lattice of 2H-MoS2 surrounding sulfur vacancies can transform into 1T resulting in the formation of lateral 2H-/1T- MoS2 nanosheets. In this program, a solution-based method to assemble and build complex heterostructure based on the obtained in-plane layered heterostructure will be investigated. We hope to present an efficient route for the successful building of multiple heterostructure composed of the various 2D building blocks via the peculiar solvent system. Further it is anticipated that the enhancement of photoelectrochemical performance of the complex heterostructure by the synergistic effect of the different components can be achieved.

溶液体系制备高质量、无缺陷的二维层状材料是目前物理化学领域具有挑战性的课题之一。本项目利用超临界CO2构筑的微乳液体系，包括Pickering乳液体系和反相微乳液体系，剥离制备系列典型二维层状纳米材料，如氧化钼、氧化钨、二硫化钼、二硫化钨和二硒化钨，同时借助超临界CO2的特殊溶剂化作用，进行二维材料新型异质结的构筑，基于此探索一条可控制备二维原子层纳米材料及其异质结的新策略和新方法。与此同时，申请项目还力求探索超临界流体体系中二氧化碳小分子对二维材料的相结构及表面电子密度的调整，并从异质结构筑及电子性质的调控入手，研究所构筑异质结的光电特性，有此拓宽超临界流体技术、二维材料制备及二维异质结构筑三个独立体系的交叉研究，促进相关学科的发展。此研究涉及材料合成化学、物理化学、超临界流体科学相互交叉渗透的课题，开展该课题研究不但促进相关学科的发展，还拓宽超临界流体在材料制备领域的应用范围。

利用绿色化学手段构建新型2D层状纳米材料，并研究其结构-性能相互关系，具有重要的科学理论意义和实际应用价值。但在2D纳米材料的实际应用过程中，如何可靠精确地剥离及制备、如何有效实现结构调控及复合组装，以及如何改进苛刻的制备条件、降低后处理难度等还有许多关键问题尚待解决。超临界CO2（SC CO2）作为有效“场”，其独特的低粘度、高扩散性以及高效传质能力，不但可以有效插层和剥离2D层状材料，而且可以诱导相转变和化学反应，并在2D异质结构的构筑以及2D材料的修饰方面均取得了令人惊喜的结果。基于此，本论文选取典型的2D层状纳米材料MoO3和WO3为研究对象，研究了SC CO2体系对其缺陷形成、异质结构构筑、原子结构调控和相变等方面的影响，此外也研究了过渡金属化合物基2D纳米材料在光电化学领域包括催化水分解、降解有机物、电催化氮气还原等方面的应用。主要研究内容如下：.（1）在超临界CO2的辅助下制备具有非晶结构和氧缺陷的介稳相h-MoO3-x，富含缺陷的非晶区域为金属原子提供了锚定位点。介稳相h-MoO3-x具有丰富的载流子，自身利用原位还原的方式可实现Pt的单原子负载，得到Pt1/MoO3-x单原子催化剂。.（2）在SC CO2体系中制备了具有独特2D富勒烯结构的WO3-x纳米片，并在此基础上合成了由等离子体金属Ag和WO3-x组成的新型等离子体光阳极异质结构Ag/WO3-x。.（3）使用超临界CO2技术通过诱导相变的方式制备了具有局域表面等离子共振（LSPR）效应的介稳相h-MoO3纳米棒，LSPR效应帮助h-MoO3对近红外光实现高效的光热转换。.（4）利用实验和理论计算相结合的手段探究了2D非晶介稳相MoO3-x纳米片的原子和电子结构信息，实验上证实了非晶MoO3-x可以表现出优异的电催化NRR性能。