Structure and Fabrication of MXene-Based Heterostructures

Structure and Fabrication of MXene-Based Heterostructures: Comparison

Please note this is a comparison between Version 1 by ruxue yang and Version 3 by Camila Xu.

MXene, as an emerging family of 2D nanomaterials, exhibits excellent electrochemical, electronic, optical, and mechanical properties. MXene-based heterostructures have already been demonstrated in applications such as supercapacitors, sensors, batteries, and photocatalysts. Nowadays, increasing research attention is attracted onto MXene-based heterostructures, while there is less effort spent to summarize the current research status.作为新兴的二维纳米材料家族，具有优异的电化学、电子、光学和机械性能。基于 MXene 的异质结构已经在超级电容器、传感器、电池和光催化剂等应用中得到证明。如今，越来越多的研究关注基于 MXene 的异质结构，而对当前研究状况的总结却很少。

two-dimensional materials
MXene
heterostructures

1. Introduction一、简介

Since自石墨烯发现以来，越来越多的二维材料家族因其在光学、电学、热学和机械方面的非凡性能以及广泛的应用潜力而受到研究人员的广泛研究 the[ discovery1 of graphene, a growing family of two-dimensional materials has been widely studied by2 researchers due to their extraordinary properties in optical, electrical,3 thermal, and4、5、6、7、8、9、10 ]。_ mechanical_ aspects,_ as_ well_ as_ the_ wide_ application_ potential_ ^{[1][2][3][4][5][6][7][8][9][10]}._ 2D二维层状材料主要包括类石墨烯族[ layered materials mainly include the graphene-like family ^[11][12][13], 11、12D、13 transition]、二维过渡金属硫族化物[ metal14、15、16 chalcogenides] ^[14][15][16],、二维氧化物族[17、18 the] 2D，以及具有其他结构的层状材料[ oxide family ^[17][18], and layered materials with other structures ^[19][20]. In 19、20 ]。2011, 年，Gogotsi et等人。[ al.21 ^[21]] discovered a type of发现了一种高导电性的二维氮化物和碳化物，称为 highly conductive 2D nitride and carbide, which were called MXenes. 。MXenes, as one of the major subfamilies of MAX phase materials, 作为 MAX 相材料的主要亚族之一，通过蚀刻和超声波处理剥离，生成二维过渡金属碳化物、碳氮化物或氮化物层 [ are22 stripped]。在 by etching and ultrasonic treatment to generate 2D transition metal carbides, carbonitrides, or nitride layers ^[22]. During the preparation of MXenes, the surface is often rich with functional groups (-O, -OH, and -F), which can bring different properties to 的制备过程中，表面通常富含官能团（-O、-OH 和 -F），它们可以为 MXenes. As a new family of 2D nanomaterials, 带来不同的性能。作为一个新的二维纳米材料家族，MXene shows excellent表现出优异的电化学、电子、光学和机械性能 [ electrochemical,23 electronic, optical,24] and mechanical properties ^[23][24] due to its graphene-like structure and mixed covalent由于其类似石墨烯的结构和混合的共价/metallic金属/ionic character, hydrophilicity, and unique metal conductivity. Therefore, 离子特性、亲水性和独特的金属导电性。因此，MXene materials have材料在世界范围内引起了广泛关注，并在过去十年中得到了迅速发展 [ attracted25 wide, attention26 in, the27 world and have developed rapidly in the past decade ^[25][26][27]. In general, ]。通常，MXene is prepared by是通过使用氢氟酸 selectively etching a layer in the MAX phase using hydrofluoric acid (HF). In order to improve the quality of MXene, simplify the experimental steps, and reduce the toxicity of the reagents, various preparation methods, such as thermal reduction, UV-induced etching, and(HF) 选择性蚀刻 MAX 相中的层来制备的。为了提高 MXene 的质量，简化实验步骤，降低试剂的毒性，出现了各种制备方法，如热还原、UV 诱导蚀刻和碱处理 [ alkali28 treatment, have29 emerged, ^{[28][29][30][31]}.30 Currently, the family of 31]。目前，MXene materials材料家族不断发展，在储能电池、传感器、催化剂等领域的应用不断扩大 continues[ to32 develop, and33 an increasing expansion of the applications in energy storage batteries, sensors,34 catalysts, and35 other fields has been witnessed ^{[32][33][34][35]}.]。

To迄今为止，尽管基于 date, although MXene-based materials haveMXene 的材料已被证明可广泛应用于不同领域，但仍存在一些挑战 [ been36 demonstrated to be widely used in different areas, there are still some challenges ^[36]. For example, the application of ]。例如，由于难以在机械和电化学性能之间取得良好平衡，MXenes in在制造柔性储能装置中的应用受到限制 fabricating[ flexible37 energy storage devices is limited due to the difficulty in achieving a good balance between mechanical and electrochemical properties ^[37]. The serious stacking phenomenon of ]。MXenes impedes的严重堆叠现象阻碍了载流子在垂直方向上的扩散，降低了 the diffusion of carriers in the vertical direction, lowering the specific capacity of MXenes under a在高电流密度下的比容量 [ high38 current density ^[38]. The poor oxidation resistance of ]。MXenes in在水基柔性电池应用中的抗氧化性差，严重影响其导电性和循环稳定性[ the application of the water-based flexible battery seriously affects its conductivity and cycling stability ^[39]. To overcome these shortcomings, different 2D nanomaterial structures are suggested to be spliced or stacked on top of each other, and as a result, many novel physical properties have been discovered.39 ]]。为了克服这些缺点，建议将不同的二维纳米材料结构拼接或堆叠在一起，结果发现了许多新的物理性质。

In 2013, Geim and 年，Geim 和 Grigoreva proposed for the first time a multilayer heterostructure, namely, van der Waals (vdW) heterostructure, which is formulated by using only the vertical vdW force between different layers to connect each 2D material首次提出了多层异质结构，即范德华（vdW）异质结构，它是通过仅使用不同层之间的垂直 vdW 力来连接每个 2D 材料并让它们在一个稳定的方式[ and40 allow]。二维材料的发现为异质结构的构建注入了新的活力。传统的异质结构是通过掺杂同质材料（例如半导体硅的 them to coexist in a stable way ^[40]. The discovery of 2D materials has breathed new life into the construction of heterogeneous structures. Traditional heterostructures are constructed by either doping homogenous materials, such as PN junctions结）或在晶格匹配的衬底材料上外延生长来构建的 of[ semiconductor silicon, or by epitaxial growth on lattice-matched substrate materials ^[41]. In this way, the material is severely limited, and serious dislocations and defects are easily formed at the interface, thus affecting the quality of the heterostructures. However, the 41]。这样，材料受到严重限制，在界面处容易形成严重的位错和缺陷，从而影响异质结构的质量。然而，二维层状材料的表面没有悬空键，不同的二维原子层可以通过弱范德华力以选定的顺序堆叠在一起，形成具有原子级平面界面的人造异质结构。与传统的半导体异质结构相比，2D layered material has no dangling bonds on its surface, and different 2D atomic layers can be stacked together in selected order by means of weak van der Waals forcesvdW 异质结构不受晶格匹配和材料类型的限制，理论上可以像堆叠木头一样以任何形式（不同类型、角度、序列、层等）堆叠[ to form artificial heterostructures with atomically flat interfaces. Compared with traditional semiconductor heterostructures, 2D vdW heterostructures are not limited by lattice matching and material types, and can theoretically be stacked in any form (different types, angles, sequences, layers, etc.) like stacking wood ^[42][43][44]. The 42、43、44]。范德华异质结构的“arbitrary combination任意组合” of允许这些单独的材料组合在一起，同时仍保持超薄厚度 [ the45 ]。因此，van der Waals heterostructure allows these individual materials to be combined together while still maintaining the ultra-thin thickness ^[45]. Therefore, the emergence of vdW heterostructures offers a new structural platform for exploring new electronic and optoelectronic devices.dW异质结构的出现为探索新型电子和光电器件提供了新的结构平台。

2. Structure of MXene-Based Heterostructures

The family of

2. 基于 MXene 的异质结构的结构

MXene materials has a great variety and excellent electrochemical, optical, and mechanical properties. However, the realization of the applications of 材料家族种类繁多，具有优异的电化学、光学和机械性能。然而，MXene materials is材料应用的实现往往受到一些固有缺陷的限制。为了克服这些问题，基于单个二维晶体的特殊光学和电学特性构建了许多新颖的异质结构，产生协同的光电特性，因此，该主题受到了研究人员的广泛关注 [ often53 limited by some inherent drawbacks. To overcome these issues, many novel heterostructures have been constructed based on the54 special optical and electrical properties of an individual 2D crystal, generating55 synergetic photoelectric properties, and56 therefore,]。一般来说，二维异质结构可以分为两种类型：垂直异质结构和横向异质结构。两种基于 wide attention has been received from researchers on this topic ^{[46][47][48][49]}. Generally, 2D heterostructures can be divided into two types: vertical heterostructures and lateral heterostructures. Two kinds of MXene-based heterostructures are described as following.

2.1. Vertical Heterostructures

的异质结构描述如下。

2.1。垂直异质结构

Vertical 垂直的基于MXene-based heterostructures are synthesized by stacking independent monolayer 2D materials layer-by-layer through direct的异质结构是通过直接生长或机械转移方法逐层堆叠独立的单层2D材料来合成的，这为异质结构提供了强大的层内共价键和相对较弱的层间vdW相互作用，产生了一个不受限制的系统材料的晶格匹配度[ growth57 or the mechanical transfer method, which58 provides]。由于层状结构之间不存在悬浮键和较弱的 the heterostructure with a strong intralayer covalent bond and relatively weak interlayer vdW interaction, generating avdW 力，因此可以通过堆叠不同的材料轻松构建垂直的 MXene 基异质结构。例如，易等人。[ system59] not制造用于光电探测器和 limited by the lattice matching degree of the materials ^[50][51]. LEDue to the absence of suspended bonds and the weak vdW forces between the layered structures, the vertical 的 MXene-based heterostructure can be easily constructed by stacking different materials. For instance, Yi et al. ^[52] fabricated GaN 范德华异质结构。基于 MXene-GaN van异质结构的器件表现出良好的光电探测性能。戴等人。[ der60 Waals] heterostructures for photodetectors and LEDs. Da通过冷冻干燥设计了垂直二维 Ti et₃ al.C ^[53]₂ designedT vertical 2D Ti₃C₂T_X MXene/V ₂ O ₅heterostructures异质结构用于膜电极的应用。在异质结构中形成垂直通道，以促进整个电极的电子和离子快速传输。此外，袁等人。[ by61 freeze-drying for the application of membrane electrodes. Vertical channels were formed in the heterostructures to promote rapid electron and ion transport throughout the electrode. Moreover, Yuan et al. ^[54] formed the ]形成了BN/Ti ₃ C ₂T_x van der Waals heterostructure for lithium-ion batteries by high-energy ball milling, which played a series of roles in increasing the layer spacing, reducing the size of nanosheets, and maintaining the structural integrity. The experimental results showed that the heterostructure had excellent rate performance and long-term cycle stability._x通过高能球磨制备锂离子电池的范德华异质结构，在增加层间距、减小纳米片尺寸、保持结构完整性等方面发挥了一系列作用。实验结果表明，异质结构具有优异的倍率性能和长期循环稳定性。 Although vertical heterostructures have become one of the hottest research fields in recent years, there are two major problems limiting the applications of vertical heterostructures in various devices: (虽然垂直异质结构已成为近年来最热门的研究领域之一，但有两大问题限制了垂直异质结构在各种器件中的应用：（1) foreign pollutants are easily introduced during the preparation process; (2) the stacking direction is not controllable. The construction of lateral heterostructures can overcome these limitations.）制备过程中容易引入外来污染物；(2)堆垛方向不可控。横向异质结构的构建可以克服这些限制。

2.2. Lateral Heterostructures

2.2. 横向异质结构

Lateral MXene-based heterostructures are generally prepared by seamlessly integrating 2D materials into one plane through direct growth, which can accurately control the direction and quality of the interface inside the 2D lateral heterostructures ^[55]. The 2D lateral heterostructure is connected by covalent bonds, which provide excellent intralaminar stability and improve the epitaxial quality.

Compared with vertical MXene-based heterostructures, the construction of 2D lateral heterostructures is more difficult in practice, and researchers cannot randomly choose the initial 2D materials to construct any heterostructure as researchers desire. Although the 2D lateral heterostructures are difficult to synthesize, the advantages of covalent bonding in the atomic plane and easy plane integration arouse people’s great interest. Zeng et al. ^[56] prepared 2D lateral WC-graphene (WC-G) heterostructures based on a versatile approach, which demonstrated excellent chemical stability and reactivity, as seen in Figure 3. Currently, there are limited studies on 2D lateral MXene heterostructures, but due to the special properties and significant application potential, more research efforts on this topic can be expected in the coming years.

3. Fabrication of MXene-Based Heterostructures

Two-dimensional heterostructures can be prepared by deterministic transfer methods, CVD epitaxial growth methods, and self-assembly ^[57]. The various synthesis approaches of 2D heterostructures directly affect their physical and chemical properties, thus affecting their application fields ^[58]. Generally, the deterministic transfer method and CVD epitaxial growth method are most often used to construct 2D heterostructures ^[59]. PDMS, PPC, and PMMA are commonly used in deterministic transfer methods. As for the CVD epitaxial growth method, it is suitable for both vertical heterostructures and lateral heterostructures ^[60]. By adjusting the temperature, composition, velocity, and direction of the flow, different types of heterostructures can be prepared. Currently, three major preparing methods have been proposed for constructing MXene-based heterostructures, namely, the hydrothermal method ^[61], electrostatic self-assembly method ^[62], and chemical vapor deposition ^[63].

3.1. Hydrothermal Method

The基于横向 hydrothMXermal method ^[64] refers to the method of preparing materials by 的异质结构通常通过直接生长将二维材料无缝集成到一个平面中来制备，这可以准确控制二维横向异质结构内部界面的方向和质量[ dissolving62 and]。二维横向异质结构通过共价键连接，提供出色的层内稳定性并提高外延质量。与垂直的基于 rMXecrystallizing powders with water as the solvent in a sealed pressurene 的异质结构相比，二维横向异质结构的构建在实践中更加困难，我们不能随意选择初始的二维材料来构建任何我们想要的异质结构。虽然二维横向异质结构难以合成，但在原子平面共价键合和易平面整合的优点引起了人们的极大兴趣。目前，关于二维横向 MXene 异质结构的研究有限，但由于其特殊的性质和巨大的应用潜力，预计未来几年将有更多的研究工作。

3. 基于 MXene 的异质结构的制造

二维异质结构可以通过确定性转移方法、CVD vessel.外延生长方法和自组装来制备 The[ hydrothermal64 method]。二维异质结构的各种合成方法直接影响其物理和化学性质，从而影响其应用领域[ has65 the]。通常，确定性转移方法和 advantages of relatively mild operatingCVD 外延生长方法最常用于构建 2D 异质结构 [ conditions,66 high]。PDMS、PPC crystallinity of products, environmental friendliness, and和 PMMA 常用于确定性传输方法。至于 CVD 外延生长方法，它适用于垂直异质结构和横向异质结构 [ good67]。通过调节流动的温度、成分、速度和方向，可以制备不同类型的异质结构。目前，已经提出了三种主要的制备方法来构建基于 dispMXersity. In addition, the cost ofne 的异质结构，即水热法 [ hydrothermal68 synthesis]、静电自组装法 is[ lower69 in] terms of和化学气相沉积法 [ instrumentation,70 energy,]。

3.1。水热法

水热法[ and71 material precursors compared to gas and solid-phase methods. ]是指在密闭的压力容器中，以水为溶剂，使粉末溶解并重结晶来制备材料的方法。水热法具有操作条件相对温和、产品结晶度高、环境友好、分散性好等优点。此外，与气相和固相方法相比，水热合成在仪器、能源和材料前体方面的成本更低。MXene is dispersed与另一种材料分散在液相中，以在水热条件下获得异质结构 [ in72 the liquid phase with another material to obtain a heterostructure under hydrothermal conditions ^[65]. Under the conditions of high temperature and high pressure, this method is able to improve the activity and manipulate the functional groups at the surface of ]。在高温高压条件下，该方法能够提高活性并操纵MXene.表面的官能团。 In在实际应用中，通常需要具有丰富功能的基于 practical applications, MXene-based heterostructures with rich functions are usually required. A hydrothermal environment can control the functional groups on the surface of MXene-based heterostructures,MXene 的异质结构。水热环境可以控制基于 MXene 的异质结构表面的官能团，从而提高其活性。乔等人。[ so73 as] to improve设计并制造了 Ti their₃ activity.C Qiao₂ et al. ^[66] designed and fabricated Ti₃C₂/CdS heterostructures for use as highly efficient co-catalysts by a hydrothermal strategy. 异质结构，通过水热策略用作高效助催化剂。表征结果表明，The characterizationi results₃ showedC that₂ the Ti₃C₂/CdS heterostructure was spontaneously decorated with a large number of hydrophilic functional groups (异质结构自发地被大量亲水性官能团（-OH and -O). In addition, the 和-O）修饰。此外，CdS/Ti ₃ C ₂具有花椰菜结构的异质结构显示出超高的可见光光催化活性，在光催化领域具有巨大的应用潜力。王等人。[ heterostructure74 with a cauliflower structure showed ultra-high visible light photocatalytic activity and has great application potential in the field of photocatalysis. Wang et al. ^[67] constructed a ]通过水热法构建了用于超级电容器的1T-MoS ₂ /Ti ₃ C ₂ MXene heterostructure for a supercapacitor via the hydrothermal method and studied the electrochemical storage mechanism of the heterostructure. The experimental results showed that the supercapacitor based on 异质结构，并研究了异质结构的电化学存储机理。实验结果表明，基于1T-MoS ₂ /Ti ₃ C ₂ MXene heterostructure had a high capacitance ratio and excellent rate performance, and maintained an excellent cycling stability after tens of thousands of cycles because of the synergistic effect between MoS_{MXene异质结构的超级电容器具有较高的电容比和优异的倍率性能，由于MoS 2}之间的协同作用，在数万次循环后仍保持优异的循环稳定性。和 and MXene.MXene。 Under the hydrothermal environment, the functional groups on the surface of 在水热环境下，MXenes are improved. Due to the electrostatic interaction and other effects, the second phase dispersed in the liquid phase can grow in situ on the surface of 表面的官能团得到改善。由于静电相互作用等作用，分散在液相中的第二相可以在MXene,表面原位生长，两种材料紧密接触形成异质结构，具有强界面相互作用，优异的电子传递能力，并能在界面处提供较大的界面接触面积。曹等人。[ and75 the] two kinds of materials are in close contact to form a heterostructure, which has strong interface interaction, excellent electron transfer ability, and can provide a large interface contact area at the interface. Cao et al. ^[68] successfully prepared a novel 通过水热策略成功制备了一种新型的 2D/2D Ti ₃ C ₂ /Bi ₂ WO ₆heterostructure through a hydrothermal strategy. 异质结构。合成的The synthesized Ti₃ C ₂ /Bi ₂ WO ₆ heterostructure showed an excellent ability forphotocatalytic reduction of 异质结构表现出优异的光催化还原CO ₂, which was mainly due to the improvement of the specific surface area and pore structure of the synthesized heterostructure, as well as the short charge-transfer distance and large interface contact area.的能力，这主要是由于合成的异质结构的比表面积和孔结构的改善，以及电荷转移距离短和界面接触面积大。

3.2. Electrostatic Self-Assembly Method

3.2. 静电自组装法

Electrostatic self-assembly ^[69] uses the electrostatic interaction of two nanomaterials with opposite charges in an aqueous solution for self-assembly, so as to form nanoscale ultra-thin polymer materials. Among many self-assembly methods, electrostatic self-assembly has a wide range of applications, owing to its simplicity and controllable thickness ^[70]. As a common method for constructing two-dimensional heterostructures, a variety of MXene-based heterostructures have been constructed via electrostatic self-assembly and have been applied in many fields ^[64]. However, electrostatic self-assembly is less stable due to the electrostatic interaction and hydrogen bonding.

The静电自组装[ layer-by-layer77 stacking]利用两种带相反电荷的纳米材料在水溶液中的静电相互作用进行自组装，从而形成纳米级超薄聚合物材料。在众多的自组装方法中，静电自组装具有广泛的应用，因为它简单且厚度可控[ of78 the]。作为构建二维异质结构的常用方法，各种基于 layered structure can re-stack the nanosheetsMXene 的异质结构已通过静电自组装构建，并已应用于许多领域 [ with71 different functional properties into heterogeneous structures, which undoubtedly makes full use of the characteristics of each heterogeneous component and presents superior electrochemical performance coordinated with the mechanical structure. In ]。然而，由于静电相互作用和氢键，静电自组装不太稳定。层状结构的逐层堆叠可以将具有不同功能特性的纳米片重新堆叠成异质结构，这无疑充分利用了各异质组分的特性，并呈现出与机械结构相协调的优越电化学性能。2019,年，刘等人。[ Liu80] et报道了通过带负电的 al. ^[71] reported the heterostructure synthesis of MXenes@C for magnesium-ion storage via electrostatic interactions between negatively charged 2D MXene nanosheets纳米片和带正电的 and positively charged 3D carbon nanospheres, which could effectively prevent the re-stacking of MXene nanosheets, so as to promote the transmission of electrolytes and shorten the ion diffusion path. Tests revealed that the magnesium-ion storage battery exhibited high reversible specific capacity, outstanding rate capacity, and excellent cycle stability. Moreover, Wen et al.3D 碳纳米球之间的静电相互作用合成 MXenes@C 用于镁离子存储的异质结构，可以有效防止 MXene 纳米片的重新堆叠，从而促进电解质的传输并缩短离子扩散路径。测试表明，镁离子蓄电池具有高可逆比容量、优异的倍率容量和优异的循环稳定性。此外，温等人。[ ^[72]81 prepared]通过静电自组装制备了用于锂硫电池的三维分级 three-dimensional hierarchical nnMOF-867/Ti ₃ C ₂T_x heterostructures for lithium–sulfur batteries via electrostatic self-assembly. The lithium−sulfur battery based o_{x异质结构。}基于n the nMOF-867/Ti _{3的锂硫电池}C ₂T_x heterostructures had strong conductivity and could reduce the volume expansion during cycling. This work_x异质结构具有很强的导电性，可以减少循环过程中的体积膨胀。这项工作为制备基于 provided the inspiration for preparing high-performance lithium-sulfur batteries based on MXene-based heterostructures. Electrostatic self-assembly uses 异质结构的高性能锂硫电池提供了灵感。静电自组装使用表面具有官能团的 MXenes with functional groups on the surface and materials with opposite surface charges to construct heterostructures by electrostatic attraction. As a simple, easily operated method, it can effectively open the middle layer and prevent the re-stacking of MXene和具有相反表面电荷的材料通过静电引力构建异质结构。作为一种简单易操作的方法，它可以有效地打开中间层并防止MXene纳米片的重新堆叠，从而提供有效的电荷转移通道并缩短离子扩散路径。近年来，由于其简单性，静电自组装也被用于合成具有高光催化活性的光催化剂。胡等人。[ nanosheets,82 ] 综合gC ₃ thusN provid₄和Ting an₃ effectiveC charge-transfer₂的优点，通过简便的静电自组装方法合成了2D/2D channel and shortenTing the₃ ionC diffusion path.

In recent years, due to its simplicity, electrostatic self-assembly has also been adopted to synthesize photocatalysts with high photocatalytic activity. Hu et al. ^[73] synthesized 2D/2D Ti₃C₂/porous g-C₃N₄ (TC/PCN) photocatalysts through a facile electrostatic self-assembly method by integrating the merits of g-C₃N₄ and Ti₃C₂. The synthesized heterostructures exhibited exceptional performance compared with pure PCN and the observed activity had no significant decrease after four cyclic experiments. In another experiment, boron-doped graphite carbonitride (g-C₃N₄) and few-layer Ti₃C₂ MXene were combined to construct heterostructures by electrostatic self-assembly for enhanced photocatalytic reduction of CO₂ ^[74]. The optimized composite structure had excellent photocatalytic activity and stability. The yields of CO and CH₄ were 3.2 times and 8.9 times higher than that of a bare g-C₃N₄, respectively. Zhuang et al. ^[75] successfully prepared TiO₂/Ti₃C₂ heterostructures by the electrostatic self-assembly technique. The maximum hydrogen production rate was 2.8 times larger than that of pure TiO₂ nanofibers, and the nanocomposite maintained a good hydrogen production cycle capacity, owing to the heterogeneous interface between TiO₂ and Ti₃C₂ nanosheets.

3.3. Chemical Vapor Deposition (CVD)

Chemical vapor deposition mainly uses one or several /多孔gas-phaseC compounds₃ orN elements₄ containing(TC/PCN)光催化剂。与纯 film elements to generatePCN 相比，合成的异质结构表现出优异的性能，并且在四次循环实验后观察到的活性没有显着降低。在另一个实验中，硼掺杂的石墨碳氮化物（gC film₃ onN the₄) substrate和少层 surface by chemicalTi reaction.₃ In the CVD process,₂ parametMXers such as pressure, temperature, gas flow rate, and catalyst type can bene 相结合，通过静电自组装构建异质结构，以增强 CO adjusted₂的光催化还原[ to83 achieve]。优化后的复合结构具有优异的光催化活性和稳定性。CO和CH fine_{4的产率分别是纯gC 3} controlN of the size, layer number, morphology, and quality of ₄的3.2D lattices倍和8.9倍。庄等人。[ Chemical84 vapor depos]采用静电自组装技术成功制备了TitionO (CVD)₂ has been w/Tidely used₃ inC the preparation of heterostructures owing to its low cost, extensibility, and full controllability_{2异质结构。最大产氢率是纯TiO 2}的2.8倍由于 The synthesisiO of₂和 vertTical and₃ lateralC heterostructures₂纳米片之间的异质界面，纳米复合材料保持了良好的氢气生产循环能力。

3.3. 化学气相沉积 (CVD)

化学气相沉积主要是利用一种或几种含有薄膜元素的气相化合物或元素，通过化学反应在基材表面生成薄膜。在 from different 2CVD materials can result in many excellent physical properties and has been applied in the fields of batteries, catalysts, and sensors, which largely depends on the arrangement, quality, and interface of the combined 2D layered crystals工艺中，可以通过调整压力、温度、气体流速和催化剂类型等参数来实现对二维晶格的尺寸、层数、形貌和质量的精细控制。化学气相沉积（CVD）由于其低成本、可扩展性和完全可控性而被广泛用于异质结构的制备。由不同的二维材料合成垂直和横向异质结构可以产生许多优异的物理性能，并已应用于电池、催化剂和传感器领域，这在很大程度上取决于组合的二维层状晶体的排列、质量和界面. BasZed on a one-step CVD method,ng 等人基于一步法 CVD 方法。[ Zeng63 et] al. ^[56]报道了将 reported the embedding of a 2D WC crystal into graphene to fabricate 2D WC-graphene lateral heterostructures on metal gallium (Ga) by integrating a liquid metal-based co-segregation strategy. The as-synthesized heterostructure exhibited excellent catalytic potential, which provided a good reference for fabricating other high-quality in-plane 2D transition metal carbide-based晶体嵌入石墨烯中，通过整合基于液态金属的共偏析策略，在金属镓 (Ga) 上制造 2D WC-石墨烯横向异质结构。合成后的异质结构表现出优异的催化潜力，为制造其他高质量的平面内二维过渡金属碳化物结构提供了很好的参考。一般来说，石墨烯和其他二维材料的异质结构是通过堆叠制造的，这导致在制备过程中随机排列、弱界面相互作用和不可避免的界面污染物。徐等人。[ structures.85 In] general, the heterostructures of graphene and other 2D materials are fabricated by stacking, which leads to random arrangement, weak interface interactions, and inevitable interface pollutants during the preparation process. Xu et al. ^[76] constructed high-quality graphene构建优质石墨烯/α-Mo ₂通过两步 C crystal vertical heterostructures with uniformly well-aligned lattice orientation and strong interface coupling by a two-step CVD method. VD 方法获得具有均匀排列的晶格取向和强界面耦合的 C 晶体垂直异质结构。在两步 CVD 过程中，作者保持恒定的气氛以避免缺陷，从而形成高质量的异质结构。目前，化学气相沉积（CVDuring the two-step ）已广泛用于制备垂直和横向异质结构。与堆叠方法相比，CVD, the researchers maintained a constant atmosphere to avoid defects, thus forming high-quality heterostructures.制备的MXene基异质结构可以获得非常干净的界面。此外，通过仔细控制制备参数，可以合成高质量的基于 MXene 的异质结构。更重要的是，合成后的异质结构具有很强的界面相互作用。

At present, chemical vapor deposition (CVD) has been widely used to prepare vertical and lateral heterostructures. Compared with the stacking method, the MXene-based heterostructures prepared by CVD can obtain a very clean interface. In addition, high-quality MXene-based heterostructures can be synthesized by carefully controlling the preparation parameters. What’s more, the synthesized heterostructures have a strong interface interaction.

Among the three common synthesis approaches of 在MXene-based heterostructures, the hydrothermal method has the advantages of relatively mild operating conditions, environmental friendliness, good dispersion, and low cost. At the same time,基异质结构的三种常见合成方法中，水热法具有操作条件相对温和、环境友好、分散性好、成本低等优点。同时，可以提高异质结构的活性，并且可以在水热环境中操纵 the activity of heterostructures can be improved and the functional groups on the surface of MXenes can be manipulated in the hydrothermal environment. Electrostatic self-assembly is widely used because of its simple preparing procedures and controllable thickness. However, the surface of the constituent materials needs to be pretreated. In the CVD process, the parameters such as pressure, temperature, gas flow rate, and catalyst type can be adjusted to realize the fine control of the size, layer number, morphology, and quality of MXene-based heterostructures, and CVD is applicable to synthesize both vertical and lateral heterostructures. The high-quality heterostructures synthesized by the aforementioned three methods are able to provide a large interface contact area and a short charge-transfer distance at the interface, as well as prevent the stacking of 表面的官能团。静电自组装因其制备程序简单、厚度可控而得到广泛应用。但是，需要对构成材料的表面进行预处理。在CVD工艺中，可以调节压力、温度、气体流速、催化剂类型等参数，实现对MXene基异质结构尺寸、层数、形貌和质量的精细控制，CVD适用于合成垂直和横向异质结构。通过上述三种方法合成的高质量异质结构能够提供较大的界面接触面积和较短的界面电荷转移距离，并防止 MXene layers, generating an improved interfacial carrier transport.层的堆叠，从而产生改进的界面载流子传输。