Synthesis,Characterization And Application Of Molybdenum Disulfide Quantum Dots And Tungsten Disulfide Quantum Dots

Transition metal chalcogenides,especially molybdenum disulfide（MoS₂）,have recently attracted wide attention from researchers as graphene-analogous materials.When the size of MoS₂is controlled to be less than 10 nm,zero-dimensional MoS₂quantum dots（QDs）can be synthesized.Because of quantum confinement and edge effects,MoS₂QDs possess unique optical and electronic properties and are potentially applicable in fluorescence sensing,bioimaging,etc.In this thesis,MoS₂QDs and WS₂QDs were synthesized using a facile one-step hydrothermal method.We explored the effects of the reaction conditions on the fluorescence properties and morphologies of the obtained QDs.The applications of the MoS₂QDs and WS₂QDs were also investigated.This dissertation includes the following aspects:1.Synthesis and characterization of MoS₂QDsMoS₂QDs were synthesized using sodium molybdate as a molybdenum source and L-cysteine as a sulphur source by hydrothermal method at different conditions.The MoS₂QDs were characterized by scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,atomic force microscopy（AFM）,fluorescence spectroscopy,FT-IR spectroscopy,UV-vis spectroscopy and energy duspersive spectrometer（EDS）.The results showed that the reaction time affected the luminescence property,morphology and size of MoS₂.MoS₂-36h were monodispersed QDs,with small size of 2.19 nm,good water solubility and excellent luminescence properties;MoS₂-4h were a unique hybrid morphology presented as MoS₂QDs attached to few-MoS₂nanosheets.2.Study on the interaction and applications of MoS₂-4h and MoS₂-36hMoS₂-4h has remarkable quenching effect on the fluorescence of MoS₂-36h,and the prescence of H₂O₂could recover the quenched fluorescence.Under the optimal conditions,a linear relationship between the relative fluorescence intensity（F-F₀）/F₀and H₂O₂concentration was obtained in a range of 0.2-40μM with a detection limit of 0.09μM and RSD of 2.8%.When exploring the effects of metal ions on MoS₂-36h,we found that the fluorescence intensity of MoS₂-36h decreased apparently with the addition of Fe³⁺and showed high selectivity and sensitivity,so as to realize the quantitative detection of Fe³⁺.3.Synthesis and characterization of WS₂QDs and the preliminary inquiry of applicationsBy replacing sodium molybdate with sodium tungstate,the same hydrothermal method was employed to synthesize a series of WS₂QDs by controlling the reaction time and the ratio of tungsten to sulfur.We found that the quantum yields of WS₂QDs gradually increased with the increase of reaction time from 4 h to 36 h.However,the difference is that WS₂-4h did not have a quenching effect on WS₂-36h.The SEM and TEM results showed that the morphologies of the obtained WS₂from 4 h to 36 h were spherical structure,and the size of WS₂-24h and WS₂-36h were 2.33 nm and 2.25 nm respectively.The influence of metal ions on the fluorescence intensity of WS₂QDs was also investigated,and the quantitative detection of Fe³⁺was accomplished.Meanwhile,the effects of BSA,HIg G and Hb on the fluorescence intensity of WS₂-36h were preliminary studied,and the results revealed that Hb possessed the similar quenching effect on WS₂-36h with Fe³⁺.