二维复合纳米材料制备及其性能的第一原理研究
发布时间：2018-11-25 21:36
【摘要】：近年来,对诸如Graphene之类二维材料的研究方兴未艾,吸引了人们广泛的关注。此类材料由于其具有优良丰富的物理、化学方面的性质,被认为会在下一代光电器件的发展中起到举足轻重的作用。然而,由于本征Graphene结构没有带隙,极大地限制了其在相关领域内的发展。因此,人们开始将注意力转向对其他无机层状二维材料的研究。最近,过渡金属硫化物(TMDs)结构吸引了人们相当大的关注。这是由于此类材料为本征半导体特征,并且有着非常优良的物理化学特性。例如,作为层状材料的MoS_2,其单层或是多层结构的场效应管有良好的开关比和迁移率。此类过渡金属硫化物结构也有着高响应率和光响应特性。单层过渡金属硫化物包含三层原子结构:阳离子层被两层阴离子层包裹在中间,这和单层原子结构的石墨结构有着明显的区别。单层过渡金属硫化物结构的三层原子相互之间是通过弱范德华力结合在一起。此外,过渡金属硫化物的电子结构受到层数的明显影响。例如,多层结构的MoS_2为1.2eV的间接带隙,而单层结构则为1.9 eV的直接带隙。纳米结构MoS_2除了在润滑和催化领域具有广泛应用之外,其在机械化工等领域也有着十分广阔的应用前景。从结构上而言,MoS_2体现各向异性特征,不同微观结构形貌及相关构成明显地影响着特定的性能。因而,为了显著提升这类材料的实用性能并将之应用于更广泛的领域,我们就需要对现有的制备技术进行微调和延拓,同时密切关注新工艺新技术的应用,丰富MoS_2纳米结构的制备手段,以此实现对微结构的可控制备。本论文将主要介绍数种新颖MoS_2纳米结构合成的实现技术,并着重围绕所得产物的形貌结构研究其形成机理,进行有针对性的测试分析,拓展其潜在的应用范围。首先,我们制备了 MoS_2@Graphene复合结构。Graphene是由C原子的sp2态杂化结合而成。由于其优良的电导性、稳定性和单层构型,吸引了大量的关注。基于上述特性,MoS_2与Graphene的复合结构将会在析氢应用中有相当明显的优势。通过第一原理,分析了 MoS_2的吉布斯自由能在富电子状态下的变化。计算结果表明,复合结构的吉布斯自由能在富电子状态下更向0靠近,这解释了为什么复合结构会有更好的析氢表现。实验结果同样证明了这个理论分析结果。此外,还通过灵活简洁的水热法制备了纳米薄片状WS_2@Graphene复合结构,实验结果表明其电池性能与导电性有直接的联系。其层状结构由X射线衍射仪、场发射扫描电子显微镜和透射电镜进行表征。纯WS_2结构和WS_2@Graphene复合结构相比,后者显示出更优秀的充放电特性。复合结构在0.1 A/g放电电流的情况下,经过100次循环后还有565 mAh/g的容量;而在2 A/g放电电流下,仍然保持着稳定的337 mAh/g容量。电化学阻抗谱表明WS_2@Graphene复合结构有着明显更低的接触电阻,从而具备高响应的电化学特性。为了从机理上说明相应的实验结果,同时进行了第一原理分析去揭示其内在机理。我们首次制备出了球棍结构的α-MoO_3@MoS_2复合结构,其显示出优良的光催化活性。通过光电流测试和光致发光检测,证实了其显著的电荷分离特性。第一原理计算表明,α-MoO_3@MoS_2复合结构明显利于光生载流子的分离。其光生电子载流子从MoS_2的导带迁移到α-MoO_3的导带,而空穴载流子则从α-MoO_3的价带转移到MoS_2的价带。这种载流子转移特性强烈抑制了载流子的复合,从而提高了光催化活性。此外,花状MoS_2@BiVO_4复合结构可以通过简单的两步法制备。我们提出了这种异质结结构的生长机制,光催化实验表明复合结构的光催化活性显著强于两种纯净结构。通过计算发现,MoS_2@BiVO_4复合结构的导带带阶和价带带阶分别为1.4和0.3 eV,表明其为标准的Ⅱ型异质结结构。我们首次合成出了双花瓣纳米构型的WS_2@MoS_2异质结结构。首先用球磨法制备出了 WS_2超薄纳米片,然后将其置入水热环境中继续生长MoS_2次级花瓣。这种结构显示出了显著增强的光催化活性。基于实验结果,我们提出了其可能存在的生长机理。WO_3和S粉的球磨过程对后续生成的WS_2纳米片起着重要的作用。而生成的WS_2纳米片又作为次级结构进一步将MoS_2纳米花瓣生长在其初级结构上。总之,为了从更深入的内在机理上分析和解释相关的实验现象,我们对所有的复合结构都做了严格的第一原理计算。这包括电荷分离转移、吉布斯自由能变化、Li离子的迁移势垒等。所有的计算结果都能够很好地符合实验结果,并且这种计算手段充当了和实验现象之间的桥梁。我们相信这些有意义的工作将会对今后复合结构的研究起到重要的参考作用。
[Abstract]:In recent years, the study of two-dimensional materials, such as Graphene, has attracted a wide range of attention. This kind of material is considered to play a very important role in the development of the next generation of optoelectronic devices because of its excellent physical and chemical properties. However, the Graphene structure of the present invention has no gap, which greatly limits its development in the relevant field. Therefore, attention has been given to the study of other inorganic layered two-dimensional materials. Recently, the transition metal sulfide (TMDs) structure has attracted considerable attention. this is due to the fact that such materials are of the intrinsic semiconductor feature and have very good physical and chemical properties. For example, as the MoS _ 2 of the layered material, the field effect tube having a single layer or a multi-layer structure has good switching ratio and mobility. Such transition metal sulfide structures also have high response rates and light response characteristics. The single-layer transition metal sulfide comprises three-layer atomic structure: the cation layer is wrapped in the middle by two layers of anion layers, and the graphite structure of the single-layer transition metal sulfide has obvious difference. The three-layer atoms of the single-layer transition metal sulfide structure are bonded to each other by a weak Van der Waals force. In addition, the electronic structure of the transition metal sulfide is affected by the number of layers. For example, the MoS _ 2 of the multi-layer structure is an indirect band gap of 1. 2eV, while the single layer structure is a direct band gap of 1. 9 eV. In addition to its wide application in the field of lubrication and catalysis, the nano-structure MoS _ 2 has a wide application prospect in the field of mechanical and chemical engineering. In terms of structure, MoS _ 2 has an anisotropic character, and the morphology and the relative composition of different micro-structures significantly affect the specific properties. Therefore, in order to improve the practicability of the class material and apply it to a wider field, we need to fine-tune and extend the existing preparation technology, and pay close attention to the application of the new technology and enrich the preparation method of the MoS _ 2 nano-structure. so as to realize the controllable preparation of the microstructure. In this paper, several novel MoS _ 2 nano-structure synthesis techniques are introduced, and the formation mechanism of several novel MoS _ 2 nano-structures is mainly introduced, and the formation mechanism of the novel MoS _ 2 nano-structure is studied, and a targeted test analysis is carried out to expand the potential application range. First, we prepared a MoS_2@Graphene composite structure. Graphene is formed by a sp2-state hybrid combination of C atoms. Due to its excellent conductivity, stability and single-layer configuration, a great deal of attention has been attracted. Based on the above-mentioned characteristics, the composite structure of MoS _ 2 and Graphene will have a significant advantage in the hydrogen evolution application. The variation of the Gibbs free energy of MoS _ 2 in the rich electronic state is analyzed by the first principle. The results show that the Gibbs free energy of the composite structure can be closer to 0 in the electron-rich state, which explains why the composite structure has better hydrogen evolution performance. The experimental results also demonstrate the results of this theoretical analysis. In addition, the nano-sheet-like WS_2@Graphene composite structure is prepared by a flexible and simple hydrothermal method, and the experimental results show that the battery performance is directly related to the conductivity. The layered structure is characterized by an X-ray diffractometer, a field emission scanning electron microscope and a transmission electron microscope. Compared with the pure WS _ 2 structure and the WS_2@Graphene composite structure, the latter shows excellent charge and discharge characteristics. The composite structure has a capacity of 565 mAh/ g after 100 cycles in the case of a discharge current of 0.1 A/ g, and a stable 337 mAh/ g capacity is still maintained at a discharge current of 2 A/ g. The electrochemical impedance spectra show that the WS_2@Graphene composite structure has a significantly lower contact resistance, thus having high response electrochemical characteristics. In order to explain the corresponding experimental results from the mechanism, the first principle analysis is carried out to reveal the mechanism. For the first time, the composite structure of the I-MoO _ 3@MoS _ 2 with a spherical stick structure is prepared, which shows excellent photocatalytic activity. The characteristics of charge separation were confirmed by photo-current and photoluminescence. The first principle calculation shows that the optical -MoO_3@MoS_2 composite structure is beneficial to the separation of the light-generating carriers. The light-generating electron carriers migrate from the conduction band of the MoS _ 2 to the conduction band of the MoS _ 3, while the hole carriers are transferred from the valence band of the MoS _ 3 to the valence band of the MoS _ 2. The carrier transfer characteristic strongly suppresses the recombination of the carriers, thereby improving the photocatalytic activity. In addition, the flower-like MoS_2@BiVO_4 composite structure can be prepared by a simple two-step process. We put forward the growth mechanism of the heterostructure, and the photocatalytic experiments show that the photocatalytic activity of the composite structure is obviously stronger than that of the two pure structures. It is found that the band-band and valence band of the MoS_2@BiVO_4 composite structure are respectively 1. 4 and 0. 3eV, indicating that it is a standard type II heterojunction structure. For the first time, we synthesized the WS_2@MoS_2 heterostructure of the double-petal nano-structure. The thin film of WS _ 2 was first prepared by ball milling, and then it was placed in the water thermal environment to continue to grow the secondary Petals of MoS _ 2. this structure shows a significantly enhanced photocatalytic activity. Based on the experimental results, we put forward the possible mechanism of growth. The process of ball milling of WO _ 3 and S powder plays an important role in the subsequent generation of the WS _ 2 nanosheet. and the generated WS _ 2 nano-sheet further acts as a secondary structure to further grow the MoS _ 2 nano-petals on the primary structure. In summary, in order to analyze and explain the relevant experimental phenomena from the more in-depth internal mechanism, we have made a strict first principle calculation for all the composite structures. This includes charge separation transfer, Gibbs free energy change, Li ion mobility barrier, and the like. All the results of the calculation can be well in line with the experimental results, and this means of calculation serves as a bridge between the experimental phenomena. We believe that these meaningful work will play an important role in the research of the composite structure in the future.
【学位授予单位】：华东师范大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TB33;TB383.1
，
本文编号：2357447
[Abstract]:In recent years, the study of two-dimensional materials, such as Graphene, has attracted a wide range of attention. This kind of material is considered to play a very important role in the development of the next generation of optoelectronic devices because of its excellent physical and chemical properties. However, the Graphene structure of the present invention has no gap, which greatly limits its development in the relevant field. Therefore, attention has been given to the study of other inorganic layered two-dimensional materials. Recently, the transition metal sulfide (TMDs) structure has attracted considerable attention. this is due to the fact that such materials are of the intrinsic semiconductor feature and have very good physical and chemical properties. For example, as the MoS _ 2 of the layered material, the field effect tube having a single layer or a multi-layer structure has good switching ratio and mobility. Such transition metal sulfide structures also have high response rates and light response characteristics. The single-layer transition metal sulfide comprises three-layer atomic structure: the cation layer is wrapped in the middle by two layers of anion layers, and the graphite structure of the single-layer transition metal sulfide has obvious difference. The three-layer atoms of the single-layer transition metal sulfide structure are bonded to each other by a weak Van der Waals force. In addition, the electronic structure of the transition metal sulfide is affected by the number of layers. For example, the MoS _ 2 of the multi-layer structure is an indirect band gap of 1. 2eV, while the single layer structure is a direct band gap of 1. 9 eV. In addition to its wide application in the field of lubrication and catalysis, the nano-structure MoS _ 2 has a wide application prospect in the field of mechanical and chemical engineering. In terms of structure, MoS _ 2 has an anisotropic character, and the morphology and the relative composition of different micro-structures significantly affect the specific properties. Therefore, in order to improve the practicability of the class material and apply it to a wider field, we need to fine-tune and extend the existing preparation technology, and pay close attention to the application of the new technology and enrich the preparation method of the MoS _ 2 nano-structure. so as to realize the controllable preparation of the microstructure. In this paper, several novel MoS _ 2 nano-structure synthesis techniques are introduced, and the formation mechanism of several novel MoS _ 2 nano-structures is mainly introduced, and the formation mechanism of the novel MoS _ 2 nano-structure is studied, and a targeted test analysis is carried out to expand the potential application range. First, we prepared a MoS_2@Graphene composite structure. Graphene is formed by a sp2-state hybrid combination of C atoms. Due to its excellent conductivity, stability and single-layer configuration, a great deal of attention has been attracted. Based on the above-mentioned characteristics, the composite structure of MoS _ 2 and Graphene will have a significant advantage in the hydrogen evolution application. The variation of the Gibbs free energy of MoS _ 2 in the rich electronic state is analyzed by the first principle. The results show that the Gibbs free energy of the composite structure can be closer to 0 in the electron-rich state, which explains why the composite structure has better hydrogen evolution performance. The experimental results also demonstrate the results of this theoretical analysis. In addition, the nano-sheet-like WS_2@Graphene composite structure is prepared by a flexible and simple hydrothermal method, and the experimental results show that the battery performance is directly related to the conductivity. The layered structure is characterized by an X-ray diffractometer, a field emission scanning electron microscope and a transmission electron microscope. Compared with the pure WS _ 2 structure and the WS_2@Graphene composite structure, the latter shows excellent charge and discharge characteristics. The composite structure has a capacity of 565 mAh/ g after 100 cycles in the case of a discharge current of 0.1 A/ g, and a stable 337 mAh/ g capacity is still maintained at a discharge current of 2 A/ g. The electrochemical impedance spectra show that the WS_2@Graphene composite structure has a significantly lower contact resistance, thus having high response electrochemical characteristics. In order to explain the corresponding experimental results from the mechanism, the first principle analysis is carried out to reveal the mechanism. For the first time, the composite structure of the I-MoO _ 3@MoS _ 2 with a spherical stick structure is prepared, which shows excellent photocatalytic activity. The characteristics of charge separation were confirmed by photo-current and photoluminescence. The first principle calculation shows that the optical -MoO_3@MoS_2 composite structure is beneficial to the separation of the light-generating carriers. The light-generating electron carriers migrate from the conduction band of the MoS _ 2 to the conduction band of the MoS _ 3, while the hole carriers are transferred from the valence band of the MoS _ 3 to the valence band of the MoS _ 2. The carrier transfer characteristic strongly suppresses the recombination of the carriers, thereby improving the photocatalytic activity. In addition, the flower-like MoS_2@BiVO_4 composite structure can be prepared by a simple two-step process. We put forward the growth mechanism of the heterostructure, and the photocatalytic experiments show that the photocatalytic activity of the composite structure is obviously stronger than that of the two pure structures. It is found that the band-band and valence band of the MoS_2@BiVO_4 composite structure are respectively 1. 4 and 0. 3eV, indicating that it is a standard type II heterojunction structure. For the first time, we synthesized the WS_2@MoS_2 heterostructure of the double-petal nano-structure. The thin film of WS _ 2 was first prepared by ball milling, and then it was placed in the water thermal environment to continue to grow the secondary Petals of MoS _ 2. this structure shows a significantly enhanced photocatalytic activity. Based on the experimental results, we put forward the possible mechanism of growth. The process of ball milling of WO _ 3 and S powder plays an important role in the subsequent generation of the WS _ 2 nanosheet. and the generated WS _ 2 nano-sheet further acts as a secondary structure to further grow the MoS _ 2 nano-petals on the primary structure. In summary, in order to analyze and explain the relevant experimental phenomena from the more in-depth internal mechanism, we have made a strict first principle calculation for all the composite structures. This includes charge separation transfer, Gibbs free energy change, Li ion mobility barrier, and the like. All the results of the calculation can be well in line with the experimental results, and this means of calculation serves as a bridge between the experimental phenomena. We believe that these meaningful work will play an important role in the research of the composite structure in the future.
【学位授予单位】：华东师范大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TB33;TB383.1
，
本文编号：2357447
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