Solution Synthesis And Photo/Electro Catalytic Properties Of Stable Metallic 1T-MS₂（M=Mo/W）

The unique structure of the layered material can regulate their intrinsic physical properties by intercalation, exfoliation, hybrid and other ways. Especially when the thickness is at the near-atomic scale, its modified surface states will bring a wealth of scientific connotation, excellent physical and chemical property and broad application prospects. The transition metal chalcogenide metal compound (transition metal chalcogenides, TMDs) as a typical representative of the layered material attracted widespread attention. In this paper, from the phase regulation of TMDs structure start exploring the design, controllable synthesis and related properties research of stable 1T-MS2 (M=Mo/W) structure. In this dissertation, the author developed bottom-up hydro thermal/so lvo thermal method to synthesize stable 1T-MS2 (M=Mo/W) and corresponding 1T heterostructure. Besides, we studied reaction mechanism, atomic structure and photo/electro catalytic properties. The optimization strategy by function-oriented design of IT-MS2 (M=Mo/W) and 1T heterostructure will shed new light on the design and fabrication of high-performance energy conversion materials.The details of this dissertation are summarized briefly as follows:1. We have developed a new bottom-up hydrothermal synthetic strategy to successfully synthesize highly stable 1T-WS2 nanoribbons and investigate the correlation between structure and electrical/optical properties. The excessive ammonium ions hydrolyzed from starting materials play a key role in the formation of the intercalated structure. The atomic microscope and synchrotron radiation-based XAFS analysis clearly revealed W-W reconstruction and W-S distorted octahedral coordination, resulting in zigzag chain superlattice with W-W bond length of 2.77 A. The nanoribbons exhibited very distinctive features in el ectrical transport and Raman scattering properties, which significantly differ from semiconducting 2H-WS2. Our density functional theory calculations have been further used to provide better understanding on the correlation between structure and electrical/optical properties. In a nutshell, we conclude that this presented work will provide a new route to selectively synthesize stable metallic TMD-based nanostructures such as 1T-MoS2, 1T-MoSe2 and1T-WSe2 so on. Thus it can provide a wealth of materials for exploring both fundamental researches and potential applications for electronics, optics and catalyst.2. We have developed improved hydrothermal synthesis of gram-scale few-layered 1T-MoS2 highly stabilized by intercalated ammonium ions. The HAADF-STEM and EXAFS characterizations directly revealed a distorted octahedral structure with a 2aoxao basal plane zigzag chain superlattice in N-MoS2, in which a shorten Mo-Mo bond length of 2.72 A was observed as compared with 2H-MoS2. Our density functional calculations further confirmed these experimental observations. Moreover, in a proof-of-concept demonstration, the metallic N-MoS2 structure was proved to be a dramatically more efficient hydrogen evolution earth-abundant cocatalyst than the corresponding semiconducting one due to its marvelous electron-hole separation efficiency and more active sites. It can be expected that this bottom-up preparation of stable 1T-MoS2 can realize in situ growth of various heterojunction photocatalyst or electrocatalyst with more effective electron transfer between interfaces. We envision that this study offers a possibility to synthesize other stable 1T phase LTMD (such as MoSe2 andWSe2) and provide a chance to explore potential applications in electronics, optics, catalysts, and other related fields.3. Herein, we firstly reported the fabrication of stable 1T-MoS2 slabs in-situ grown on the CdS nanorods (namely, 1T-MoS2@CdS) using a facile solvothermal synthesis. Notably, the heterostructure cocatalyst with the optimum loading of 0.2 wt% 1T-MoS2 can exhibit almost 39-fold enhancement than bare CdS. As demonstrated by ultrafast transient absorption spectroscopy, combined with steady-state and time-resolved photoluminescence, the photoexcited electrons are quickly transferred due to the presence of 1T-MoS2, resulting in significantly surpressing electron-hole recombination. Meanwhile, we extend this method to other semiconductor, successfully synthesizing TiO2@ 1T-MoS2 heterostructure for enhanced photocatalytic hydrogen evolution. This work represents a step towards the in-situ realization of 1T phase MoS2-based heterostructure as promising cocatalysis with high performance and low cost, providing a opportunity to design high-efficient photocatalytic systems.4. We have firstly in-situ synthesized highly dispersed metallic 1T-MoS2 nanopatches grown around SWNT film via a facile one-step solvothermal approach and realized the multiple synergistic effects of nanostructuring, phase engineering and integration with highly conductive substrates. Our theoretical calculations well authenticate that for electron doped 1T-MoS2, the adsorption capacity of H atom on its surface is weakened, indicating that the following H recombination and release process in 1T-MoS2/SWNT hybrids becomes relatively easier than the pristine ones. This hybrid material exhibited outstanding HER activity with onset overpotential as small as approximate 40 mV, low Tafel slope of 36 mV/dec and excellent chemical stability. These merits of densely catalytic sites, metallic conductivity and fast charge transport enable the 1T-MoS2/SWNT architecture to serve as an excellent molybdenum sulfide-based electrocatalyst. Such combined modulations may pave a new pathway for improving the activity of various electrocatalysts.