Preparation Of Two-Dimensional Layered Materials Of Molybdenum,Tungsten And Graphitic Carbon Nitrogen,and Their Application In Practical Detections

In this work, three two-dimensional layered materials, including molybdenum disulfide and tungsten disulfide by means of hydrothermal synthesis, and graphite carbon nitrogen nanosheets by pyrolysis under high temperature, were prepared. These layered materials were applied for quantitative analysis or detection, such as metal ions detection in the environment and harmful ingredients in veterinary medicine, as well as the detection of trace hydrogen peroxide. It indicated that the developed methods are simple, rapid and sensitive for detection, and can be applied to practical analysis. Therefore, the two-dimensional layered materials had better development prospects in the analysis detection area.Chapter one: It was illuminated that the development and synthesis method of the molybdenum disulfide and tungsten disulfide, as well as their physical properties, chemical properties and research application. Moreover, it was also explored that the development prospect of the two-dimensional layered materials in the analysis applications.Chapter two: Layered molybdenum disulfide was prepared by a hydrothermal process, and then its structure and morphology were investigated with the use of X-ray diffraction spectra, scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. Molybdenum disulfide possessed peroxidase-like catalytic properties. In the presence of hydrogen peroxide, molybdenum disulfide could catalyze the oxidation of 3,3′,5,5′-Tetramethylbenzidine, as a suitable enzymatic chromogenic substrate, to produce a blue product which had a strong absorption peak at 652 nm. According to this mechanism, we can quantitatively analyze the trace amounts of hydrogen peroxide by using the as-prepared layered molybdenum disulfide.Chapter three: The tungsten disulfide dots under hydrothermal conditions by using sodium tungstate and reduced L-glutathione, which had a strong emission fluorescence peak at about 405 nm and the associated excitation wavelength was 320 nm. It appeared that the absorption band of the nitrofurazone was effectively overlapped by the emission band of tungsten disulfide dots. So, after adding the nitrofurazone, the fluorescence intensity at 405 nm was significantly reduced, and no blue fluorescence peak was evident. These observation ssuggested that significant fluorescence quenching occurred after the addition of the nitrofurazone, and this indicated that a fluorescence resonance energy transfer had occurred between the tungsten disulfide dots and the nitrofurazone. According to this mechanism, we can construct a fluorescent sensor for rapid and sensitive quantitative analysis of nitrofurazone.Chapter four: Bulk graphitic carbon nitride was obtained by pyrolysis of urea at high temperature, which was then subjected to protonation and exfoliation to obtain strongly fluorescent graphitic carbon nitride nanosheets which had a strong emission fluorescence peak at about 434 nm and the associated excitation wavelength was 300 nm. When copper(II) was added to the graphitic carbon nitride nanosheets, the emitted fluorescence associated with these nanosheets was quenched. This was attributed to the strong binding affinity and rapid binding of copper with the N and O sites of the functional groups on the surface of the graphitic carbon nitride nanosheets. Additionally, the redox potential of the Cu2+/Cu+couple present between the conduction and valence bands of the graphitic carbon nitride nanosheets, promotes the photoinduced electron transfer from the conduction band to the complexed copper. According to this mechanism, we can quantitatively analyze the copper.The highlights in this work can be summarized as follows:(1) a series of two-dimensional layered materials sensors were constructed and used in the analysis and detection applications, and which exhibit well selectivity and high sensitivity;(2) It was revealed that two-dimensional layered materials had good practical application ability and which can provide a new development direction in preparation and application for researchers to further research.