超临界二氧化碳诱导的二硫化钼的相转变及其应用

发布时间：2018-06-06 05:12

本文选题：二硫化钼 + 超临界二氧化碳　；参考：《郑州大学》2017年硕士论文

【摘要】：超薄二维材料领域的兴起和快速发展使其在催化、生物、电子和光电领域拥有广阔的应用前景,其中二硫化钼(MoS_2)作为一种典型的层状过渡金属硫属化合物具有卓越的理化性质,在许多领域拥有极大的应用潜力。层状MoS_2主要分为两相:2H相和1T相。其中2H相为半导体相,1T相为金属相。相对于2H相,1T相具有更高密度的活性位点和催化活性,但是由于其制备方法主要依赖于碱金属离子插层,电子辐射等,而这些制备方法在材料的制备和应用时都会存在一些不足,所以寻求一种高效、简便、绿色的相转化方法仍然是现存的一个巨大挑战。超临界流体做为一种传统有机溶剂的替代溶剂,已经被广泛应用于纳米材料的制备当中。超临界CO_2由于其临界点容易达到,具有低粘度、低表面张力和高扩散性等优点,并且通过调节温度和压力等条件可以大幅度地改变溶剂本身的性质,而单层MoS_2对CO_2分子又具有很强的吸附能力,本文研究了MoS_2和CO_2间的相互作用,使层状MoS_2与CO_2分子之间发生反应,并对发生相转化的MoS_2进行了光电催化和电催化领域的应用。主要内容如下:1)超临界CO_2诱导的MoS_2的1T相转变及其光电催化领域的应用通过对已剥离的单层或少层MoS_2纳米片进行刺激,由于不同相对CO_2分子吸附能的不同,成功诱导部分稳定的2H相转化成1T相从而合成1T@2H-MoS_2平面异质结。理论计算和实验结果阐明了超临界二氧化碳促进二硫化钼进行相转化并使其稳定的机理。由于金属1T相的引入增加了载流子在电极间的传输效率,使载流子更快地转移到具有催化活性的位点上,减少了光生电子空穴的复合几率,延长了光生载流子的寿命,最终大大提高了其在光电催化方面的表现。该方法通过卸压后可以得到纯净的MoS_2平面异质结分散液,避免了传统锂离子插层时间长效率低的流程,和复杂的后期处理过程。2)超临界CO_2诱导的MoS_2非晶化转变及其电催化制氢应用的研究。我们通过高温超临界CO_2的辅助,将晶体二硫化钼非晶化,使用超临界CO_2与水反应形成具有腐蚀性的碳酸,破坏MoS_2原有的晶格结构从而形成表面无序的非晶二硫化钼。我们的研究表明由于非晶二硫化钼表面暴露了更多的活性位点,其在HER反应上显示了良好的催化活性。另一方面超临界CO_2通过使原子在结构上发生重排,使二硫化钼表面发生钝化从而抑制了光电子的非辐射复合,提高了其光致发光性能,这种共存的电学催化性能和光致发光性能为二维材料未来的发展提供了一个更广阔的想象空间。
[Abstract]:The rise and rapid development of ultra-thin two-dimensional materials make them have a broad application prospect in the fields of catalysis, biology, electronics and photoelectricity, among which molybdenum disulfide (MoS _ 2) has excellent physicochemical properties as a typical layered transition metal sulfur compound. It has great application potential in many fields. The layered MoS_2 is mainly divided into two phases: 2H phase and 1T phase. Among them, 2H phase is semiconductor phase and 1 T phase is metal phase. The activity sites and catalytic activity of 2H phase ~ 1T phase are higher than that of 2H phase, but their preparation methods mainly depend on alkali metal ion intercalation, electron radiation and so on. However, these methods have some shortcomings in the preparation and application of materials, so it is still a great challenge to seek a kind of efficient, simple and green phase transformation method. Supercritical fluid has been widely used in the preparation of nanomaterials as a substitute for traditional organic solvents. Supercritical CO_2 has the advantages of low viscosity, low surface tension and high diffusivity due to its easy reaching critical point, and the properties of the solvent can be greatly changed by adjusting the temperature and pressure. However, monolayer MoS_2 has strong adsorption ability to CO_2 molecules. In this paper, the interaction between MoS_2 and CO_2 has been studied to make the reaction between layered MoS_2 and CO_2 molecules take place, and the application of MoS_2 in the field of photocatalysis and electrocatalysis has been carried out. The main contents are as follows: (1) the 1T phase transition of MoS_2 induced by supercritical CO_2 and its application in photocatalytic field stimulate the MoS_2 nanoparticles which have been peeled off, because of the different adsorption energies of different relative CO_2 molecules. The partially stable 2H phase was successfully induced to be transformed into 1T phase to synthesize the 1T@2H-MoS_2 plane heterojunction. The theoretical calculation and experimental results illustrate the mechanism of supercritical carbon dioxide (SCCO _ 2) promoting the phase transformation and stabilization of molybdenum disulfide. As the introduction of metal 1T phase increases the transport efficiency of carriers between electrodes, the carriers are transferred to the sites with catalytic activity more quickly, which reduces the recombination probability of photogenerated electron holes and prolongs the lifetime of photogenerated carriers. In the end, the performance of photocatalysis is greatly improved. In this method, the pure MoS_2 plane heterojunction dispersion can be obtained after decompression, and the traditional process of lithium ion intercalation with long time and low efficiency can be avoided. And complex post-treatment process. 2) MoS_2 amorphous transition induced by supercritical CO_2 and its application in hydrogen production by electrocatalysis. With the aid of supercritical CO_2 at high temperature, molybdenum disulfide (MoS) _ 2 was amorphous and reacted with water by supercritical CO_2 to form corrosive carbonic acid. The original lattice structure of MoS_2 was destroyed and the surface disordered molybdenum disordered (MoS) _ 2 was formed. Our results show that the amorphous molybdenum disulfide exhibits good catalytic activity in HER reaction due to the exposure of more active sites on the surface of amorphous molybdenum disulfide. On the other hand, supercritical CO_2 inhibits the non-radiative recombination of photoelectrons by rearranging the atoms and passivation on the surface of molybdenum disulfide, which improves the photoluminescence properties of molybdenum disulfide. This coexistence of electrocatalytic and photoluminescence properties provides a broader imagination for the future development of two-dimensional materials.
【学位授予单位】：郑州大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TQ136.12;O643.36

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