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Since the discovery of graphene, a growing family of two-dimensional materials has been widely studied by researchers due to their extraordinary [properties 1in optical, 2electrical, thermal, 3and mechanical aspects, 4、5、6、7、8、9、10 ]。_as well as the wide application _potential _[ _1、2、3、4、5、6、7、8、9、10 ]. _2D _layered _materials _mainly _include _the _graphene-like 二维层状材料主要包括类石墨烯族family[ 11、111、12、13 ], 2、13D transition metal ]、二维过渡金属硫族化物chalcogenides[ 14、15、16 ], 、二维氧化物族the 2D oxide family[17、18 ], ，以及具有其他结构的层状材料and layered materials with other structures [ 19、20 ]。]. In 2011, 年，Gogotsi 等人。et al.[ 21 ] 发现了一种高导电性的二维氮化物和碳化物，称为 discovered a type of highly conductive 2D nitride and carbide, which were called MXenes。. MXenes 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, as one of the major subfamilies of MAX phase materials, are stripped by etching and ultrasonic treatment to generate 2D transition metal carbides, carbonitrides, or nitride layers [ 22 ]。在. During the preparation of MXenes 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 带来不同的性能。作为一个新的二维纳米材料家族，MXene 表现出优异的电化学、电子、光学和机械性能 [, the surface is often rich with functional groups (-O, -OH, and -F), which can bring different properties to MXenes. As a new family of 232D nanomaterials, 24] 由于其类似石墨烯的结构和混合的共价/金属/离子特性、亲水性和独特的金属导电性。因此，MXene 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shows [excellent 25electrochemical, electronic, 26 optical, 27and ]。通常，MXmene 是通过使用氢氟酸chanical properties [ (HF)23、24] 选择性蚀刻due 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 [to its graphene-like structure and mixed covalent/metallic/ionic 28character, hydrophilicity, 29and unique ,metal 30conductivity. Therefore, 31]。目前，MXene 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materials [have 32attracted ,wide 33attention ,in 34the ,world 35and ]。

迄今为止，尽管基于have MXdevelopene 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 d rapidly in the past decade[ 3625 、26 、27 ]。例如，由于难以在机械和电化学性能之间取得良好平衡，. In general, MXenes 在制造柔性储能装置中的应用受到限制 [ is prepared by selectively etching a layer in 37the ]。MXenes 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AX phase using hydrofluoric acid (HF). In order to improve the quality of MXenes 在高电流密度下的比容量 [, simplify the experimental steps, and reduce the toxicity of the reagents, various preparation methods, 38suchas thermal reduction, UV-induced etching, and alkali treatment, have emerged [28、29、30、31]. Currently, the family of MXene materials continues to develop and an increasing expansion of the applications in energy storage batteries, sensors, catalysts, and other fields has been witnessed [32、33、34、35].

To date, although MXene-based materials have been demonstrated to be widely used in different areas, there are still some challenges [36]. For example, the application of MXenes in fabricating flexible 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 the diffusion of carriers in the vertical direction, lowering the specific capacity of MXenes under a high current density [38]. The poor oxidation resistance of MXenes in 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.

In 2013, Geim and 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 and allow 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 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 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 forces 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 “arbitrary combination” of the 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.

2. Structure of MXene-Based Heterostructures

The family of MXene materials has a great variety and excellent electrochemical, optical, and mechanical properties. However, the realization of the applications of MXene materials is often limited by some inherent drawbacks. To overcome these issues, many novel heterostructures have been constructed based on the special optical and electrical properties of an individual 2D crystal, generating synergetic photoelectric properties, and therefore, wide attention has been received from researchers on this topic [53、54、55、56]. 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

Vertical ]。MXenes 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[-based heterostructures are synthesized by stacking independent monolayer 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。

2013D 年，Geim 和 Grigoreva 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[materials layer-by-layer through direct growth or the mechanical transfer method, which provides the heterostructure with a strong intralayer covalent bond and relatively weak interlayer vdW interaction, generating a system 40not ]。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limited PN 结）或在晶格匹配的衬底材料上外延生长来构建的 [by the lattice 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，2Dmatching vdW 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egree of the materials [57、58]. 42、43、44]。范德华异质结构的“任意组合”允许这些单独的材料组合在一起，同时仍保持超薄厚度Due [to 45the ]。因此，vdW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. 基于 MXene 的异质结构的结构

MXabsence 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 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 [of suspended bonds and the weak 53vdW ,forces 54between ,the 55layered structures, 56the ]。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vertical MXene 的异质结构描述如下。

2.1。垂直异质结构

垂直的基于MX-based heterostructure cane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[ be 57easily ,constructed 58by ]。由于层状结构之间不存在悬浮键和较弱的stacking vdW 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。[different materials. For instance, Yi 59]et 制造用于光电探测器和al. LED[59] 的fabricated MXene-GaN 范德华异质结构。基于 MXene-GaN 异质结构的器件表现出良好的光电探测性能。戴等人。van der Waals heterostructures for photodetectors and LEDs. Dai et al. [60] 60designed ]vertical 通过冷冻干燥设计了垂直二维2D Ti ₃ C ₂ T _X MXene/V₂O₅ heterostructures ₂by Ofreeze-drying ₅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。[for 61the ]形成了BN/Tapplication ₃of membrane Celectrodes. ₂Vertical Tchannels _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。 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）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. 横向异质结构

基于横向were MXformene 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[d in the heterostructures to 62promote ]。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rapid MXelene 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。ctron and ion transport throughout the electrode. Moreover, Yuan et al. [61] formed the BN/Ti₃C₂T_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.

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、CVDAlthough vertical heterostructures have 外延生长方法和自组装来制备become [one 64of ]。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[the 65hottest ]。通常，确定性转移方法和research CVD 外延生长方法最常用于构建 2D 异质结构 [fields in recent years, there 66are ]。PDMS、PPCtwo 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 [major problems limiting the applications of 67]。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vertical MXheterostructurene 的异质结构，即水热法 [s in various devices: (1) foreign pollutants 68are ]、静电自组装法easily [introduced 69during ]the 和化学气相沉积法 [preparation process; 70(2) ]。

3.1。水热法

水热法[the 71stacking ]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。MXdirene 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 [ction is not controllable. The construction of 72lateral ]。在高温高压条件下，该方法能够提高活性并操纵MXheterostructurene表面的官能团。s can overcome these limitations.

2.2. Lateral Heterostructures

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 [62]. 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 we cannot randomly choose the initial 2D materials to construct any heterostructure as we 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. [63] 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 [64]. The various synthesis approaches of 2D heterostructures directly affect their physical and chemical properties, thus affecting their application fields [65]. Generally, the deterministic transfer method and CVD epitaxial growth method are most often used to construct 2D heterostructures [66]. 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 [67]. 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 [68], electrostatic self-assembly method [69], and chemical vapor deposition [70].

3.1. Hydrothermal Method

The hydrothermal method [71] refers to the method of preparing materials by dissolving and recrystallizing powders with water as the solvent in a sealed pressure vessel. The hydrothermal method has the advantages of relatively mild operating conditions, high crystallinity of products, environmental friendliness, and good dispersity. In addition, the cost of hydrothermal synthesis is lower in terms of instrumentation, energy, and material precursors compared to gas and solid-phase methods. MXene is dispersed in the liquid phase with another material to obtain a heterostructure under hydrothermal conditions [72]. 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 MXene.

In 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, so as to improve their activity. Qiao et al. [73] designed and fabricated Ti₃C₂/CdS heterostructures for use as highly efficient co-catalysts by a hydrothermal strategy. The characterization results showed that the Ti₃C₂/CdS heterostructure was spontaneously decorated with a large number of hydrophilic functional groups (-OH and -O). In addition, the CdS/Ti₃C₂ heterostructure with a cauliflower structure showed ultra-high visible light photocatalytic activity and had great application potential in the field of photocatalysis. Wang et al. [74] constructed a 1T-MoS₂/Ti₃C₂ 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 1T-MoS₂/Ti₃C₂ 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 MoS₂ and MXene.

在实际应用中，通常需要具有丰富功能的基于Under the hydrothermal 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。[environment, the functional groups on the surface of MXenes are improved. Due 73to ]the 设计并制造了 Tielectrostatic interaction ₃and other effects, the second phase dispersed Cin ₂the /CliquidS 异质结构，通过水热策略用作高效助催化剂。表征结果表明，Ti phase can grow in situ ₃on the surface Cof ₂MXene, /CandS异质结构自发地被大量亲水性官能团（-OH和-O）修饰。此外，CdS/Ti the two kinds of materials ₃are in Cclose 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。[contact 74to ]通过水热法构建了用于超级电容器的1T-MfoSrm a ₂heterostructure, /Twhich ₃has strong Cinterface ₂interaction, MXexcellene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-MoSt electron ₂transfer /Tability, ₃and can Cprovide _{2 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a MXlargene。 在水热环境下，MX interface cones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。tact area at the interface. Cao et al. [75] 75successfully prepared ]a 通过水热策略成功制备了一种新型的novel 2D/2D Ti ₃ C ₂ /Bi ₂ WO₆ heterostructure ₆异质结构。合成的through a hydrothermal strategy. The synthesized Ti₃ C ₂ /Bi ₂ WO_{6 6}异质结构表现出优异的光催化还原heterostructure showed an excellent ability forphotocatalytic reduction of CO₂, ₂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。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.

3.2. Electrostatic Self-Assembly Method

Electrostatic self-assembly [77] uses the electrostatic interaction of two kinds of 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 [78]. 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 [71]. However, electrostatic self-assembly is less stable due to the electrostatic interaction and hydrogen bonding.

3.2. 静电自组装法

静电自组装[The layer-by-layer stacking of the layered structure can re-stack the nanosheets with different functional properties into heterogeneous structures, which undoubtedly makes full use of the characteristics of each heterogeneous component 77and ]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[presents 78superior ]。作为构建二维异质结构的常用方法，各种基于electrochemical MXene 的异质结构已通过静电自组装构建，并已应用于许多领域 [performance coordinated with the mechanical structure. 71In ]。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。, Liu et al. [80] 80]reported the heterostructure synthesis of MXenes@C for magnesium-ion storage via electrostatic interactions between negatively 报道了通过带负电的charged 2D MXene 纳米片和带正电的 3D 碳纳米球之间的静电相互作用合成nanosheets and positively charged 3D carbon nanospheres, which could effectively prevent the re-stacking of 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。 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. [81] 81prepared three-dimensional ]通过静电自组装制备了用于锂硫电池的三维分级hierarchical nMOF-867/Ti₃C₂T_{x 3}heterostructures for lithium–sulfur batteries via Celectrostatic ₂self-assembly. The _{x异质结构。}基于lithium−sulfur battery based on the nMOF-867/Ti _{3的锂硫电池}C₂T_{x 2}heterostructures had strong conductivity and could reduce the volume expansion during cycling. This _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work provided the inspiration for preparing high-performance lithium-sulfur batteries based on MXene-based 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heterostructures. Electrostatic self-assembly uses MXenes 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。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 nanosheets, thus providing an effective charge-transfer channel and shortening the ion 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. [82] 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 [83]. 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. [84] 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)

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。[Chemical 82 ] 综合gC ₃vapor Ndeposition ₄和Tmainly ₃uses one or several gas-phase compounds Cor ₂的优点，通过简便的静电自组装方法合成了2D/2Delements Tcontaining ₃film Celements ₂to /多孔gCenerate film on the substrate surface by chemical reaction. In the CVD ₃process, parameters Nsuch ₄as (TC/PCN)光催化剂。与纯pressure, PCN 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（gCtemperature, gas flow rate, and catalyst type can ₃be Nadjusted ₄)to 和少层achieve Tifine ₃control of Cthe ₂size, MXlayene 相结合，通过静电自组装构建异质结构，以增强 COr number, morphology, and quality of 2D lattices. Chemical ₂的光催化还原[vapor 83deposition ]。优化后的复合结构具有优异的光催化活性和稳定性。(CO和CHVD) has been widely used in the preparation _{4的产率分别是纯gC 3}of Nheterostructures ₄的3.2倍和8.9倍。庄等人。[owing 84to ]采用静电自组装技术成功制备了TiOts low ₂cost, /Textensibility, ₃and Cfull _{2异质结构。最大产氢率是纯TiO 2}的2controllability.8倍由于 TiOhe synthesis ₂和of Tvertical ₃and lateral heterostructures Cfrom ₂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different CV2D 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 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. ZBaseng 等人基于一步法 CVD 方法。d on a one-step CVD method, Zeng et al. [63] 63reported the embedding ]of 报道了将a 2D WC 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。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 structures. 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. [85] 85constructed ]high-quality 构建优质石墨烯graphene/α-Mo₂C ₂通过两步crystal vertical heterostructures with uniformly well-aligned lattice orientation and strong interface coupling by a two-step CVD 方法获得具有均匀排列的晶格取向和强界面耦合的method. During 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。the two-step CVD, the authors maintained a constant atmosphere to avoid defects, thus forming high-quality heterostructures.

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.

目前，化学气相沉积（CVD）已广泛用于制备垂直和横向异质结构。与堆叠方法相比，CVD制备的Among the three common synthesis approaches of 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-based heterostructures, the hydrothermal method has the advantages of relatively mild operating conditions, environmental friendliness, good dispersion, and low cost. At the same time, the activity of heterostructures can be improved and the functional groups on the surface of 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。 在MXs 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 cone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 MXenes 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stituent 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 MXene 层的堆叠，从而产生改进的界面载流子传输。layers, generating an improved interfacial carrier transport.