【摘要】：近年來,對諸如Graphene之類二維材料的研究方興未艾,吸引了人們廣泛的關注。此類材料由于其具有優(yōu)良豐富的物理、化學方面的性質(zhì),被認為會在下一代光電器件的發(fā)展中起到舉足輕重的作用。然而,由于本征Graphene結構沒有帶隙,極大地限制了其在相關領域內(nèi)的發(fā)展。因此,人們開始將注意力轉向?qū)ζ渌麩o機層狀二維材料的研究。最近,過渡金屬硫化物(TMDs)結構吸引了人們相當大的關注。這是由于此類材料為本征半導體特征,并且有著非常優(yōu)良的物理化學特性。例如,作為層狀材料的MoS_2,其單層或是多層結構的場效應管有良好的開關比和遷移率。此類過渡金屬硫化物結構也有著高響應率和光響應特性。單層過渡金屬硫化物包含三層原子結構:陽離子層被兩層陰離子層包裹在中間,這和單層原子結構的石墨結構有著明顯的區(qū)別。單層過渡金屬硫化物結構的三層原子相互之間是通過弱范德華力結合在一起。此外,過渡金屬硫化物的電子結構受到層數(shù)的明顯影響。例如,多層結構的MoS_2為1.2eV的間接帶隙,而單層結構則為1.9 eV的直接帶隙。納米結構MoS_2除了在潤滑和催化領域具有廣泛應用之外,其在機械化工等領域也有著十分廣闊的應用前景。從結構上而言,MoS_2體現(xiàn)各向異性特征,不同微觀結構形貌及相關構成明顯地影響著特定的性能。因而,為了顯著提升這類材料的實用性能并將之應用于更廣泛的領域,我們就需要對現(xiàn)有的制備技術進行微調(diào)和延拓,同時密切關注新工藝新技術的應用,豐富MoS_2納米結構的制備手段,以此實現(xiàn)對微結構的可控制備。本論文將主要介紹數(shù)種新穎MoS_2納米結構合成的實現(xiàn)技術,并著重圍繞所得產(chǎn)物的形貌結構研究其形成機理,進行有針對性的測試分析,拓展其潛在的應用范圍。首先,我們制備了 MoS_2@Graphene復合結構。Graphene是由C原子的sp2態(tài)雜化結合而成。由于其優(yōu)良的電導性、穩(wěn)定性和單層構型,吸引了大量的關注�；谏鲜鎏匦�,MoS_2與Graphene的復合結構將會在析氫應用中有相當明顯的優(yōu)勢。通過第一原理,分析了 MoS_2的吉布斯自由能在富電子狀態(tài)下的變化。計算結果表明,復合結構的吉布斯自由能在富電子狀態(tài)下更向0靠近,這解釋了為什么復合結構會有更好的析氫表現(xiàn)。實驗結果同樣證明了這個理論分析結果。此外,還通過靈活簡潔的水熱法制備了納米薄片狀WS_2@Graphene復合結構,實驗結果表明其電池性能與導電性有直接的聯(lián)系。其層狀結構由X射線衍射儀、場發(fā)射掃描電子顯微鏡和透射電鏡進行表征。純WS_2結構和WS_2@Graphene復合結構相比,后者顯示出更優(yōu)秀的充放電特性。復合結構在0.1 A/g放電電流的情況下,經(jīng)過100次循環(huán)后還有565 mAh/g的容量;而在2 A/g放電電流下,仍然保持著穩(wěn)定的337 mAh/g容量。電化學阻抗譜表明WS_2@Graphene復合結構有著明顯更低的接觸電阻,從而具備高響應的電化學特性。為了從機理上說明相應的實驗結果,同時進行了第一原理分析去揭示其內(nèi)在機理。我們首次制備出了球棍結構的α-MoO_3@MoS_2復合結構,其顯示出優(yōu)良的光催化活性。通過光電流測試和光致發(fā)光檢測,證實了其顯著的電荷分離特性。第一原理計算表明,α-MoO_3@MoS_2復合結構明顯利于光生載流子的分離。其光生電子載流子從MoS_2的導帶遷移到α-MoO_3的導帶,而空穴載流子則從α-MoO_3的價帶轉移到MoS_2的價帶。這種載流子轉移特性強烈抑制了載流子的復合,從而提高了光催化活性。此外,花狀MoS_2@BiVO_4復合結構可以通過簡單的兩步法制備。我們提出了這種異質(zhì)結結構的生長機制,光催化實驗表明復合結構的光催化活性顯著強于兩種純凈結構。通過計算發(fā)現(xiàn),MoS_2@BiVO_4復合結構的導帶帶階和價帶帶階分別為1.4和0.3 eV,表明其為標準的Ⅱ型異質(zhì)結結構。我們首次合成出了雙花瓣納米構型的WS_2@MoS_2異質(zhì)結結構。首先用球磨法制備出了 WS_2超薄納米片,然后將其置入水熱環(huán)境中繼續(xù)生長MoS_2次級花瓣。這種結構顯示出了顯著增強的光催化活性。基于實驗結果,我們提出了其可能存在的生長機理。WO_3和S粉的球磨過程對后續(xù)生成的WS_2納米片起著重要的作用。而生成的WS_2納米片又作為次級結構進一步將MoS_2納米花瓣生長在其初級結構上。總之,為了從更深入的內(nèi)在機理上分析和解釋相關的實驗現(xiàn)象,我們對所有的復合結構都做了嚴格的第一原理計算。這包括電荷分離轉移、吉布斯自由能變化、Li離子的遷移勢壘等。所有的計算結果都能夠很好地符合實驗結果,并且這種計算手段充當了和實驗現(xiàn)象之間的橋梁。我們相信這些有意義的工作將會對今后復合結構的研究起到重要的參考作用。
[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.
【學位授予單位】：華東師范大學
【學位級別】：博士
【學位授予年份】：2017
【分類號】：TB33;TB383.1
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本文編號：2357447