Electrochemical Detection And Hydrogen Evolution Of Graphene And Molybdenum Disulfide Modified Electrode

Graphene and molybdenum disulfide（MoS₂）have similar layered structure with numerous excellent properties.This thesis studied the combination of graphene and MoS₂,and investigated their synthesis mechanism,morphology and chemical composition.The applications on electrochemical sensor and electrocatalytic hydrogen evolution were also developed based on graphene and MoS₂.The main contents include as following:（1）Graphene was prepared by the oxidation-reduction method,and MoS₂ was synthesized using the hydrothermal method with molybdate and L-cysteine as precursors of molybdenum and sulfur,respectively.The preparation mechanism of graphene and molybdenum disulfide was analyzed.The crystal structure,chemical composition and morphology of the products were characterized by X-ray powder diffraction（XRD）,X-ray photoelectron spectroscopy（XPS）,scanning electronic microscope（SEM）and energy dispersive X-ray（EDX）.The results show that:①the graphene oxide reduction process can be better promoted to obtain well-water dispersed graphene by controlling pH.XRD show that the produced material is graphene with multi-layers;XPS indicate that graphene oxide was completely reduced;TEM images reveal there are continuous and crumpled nanosheets of graphene with a large surface area.② MoS₂ with 3D flower structure was prepared was characterized by XRD.The characterization results of XPS and EDX presents the element valence and atomic ratio of MoS₂.SEM images clearly reveal the diameter of MoS₂ flower structure is about 200 nm,and TEM indicate the lattice stripe spacing along the growth axis is 0.62 nm.（2）The graphene-MoS₂ modified electrode was fabricated via stepwise modification method and used as electrochemical sensor to detect dopamine.The experimental conditions and electrochemical behavior were carried out by cyclic voltammetry and differential pulse voltammetry.The optimum experimental conditions are found:the pH value is 7.5,the modification amounts of graphene and MoS₂ are 10 μL and the accumulation time is 3 min.The linear relationship between the peak current and scan rate indicates the electrochemical surface action is an adsorption-controlled process.The detection range of dopamine was from 5.0×10-8 to 1.0×10-5 mol/L,and the linear relationship between the concentration and the peak current was described as the regression equation:Ipa = 12.63c + 0.4950（R = 0.999）.The detection limit is 7.13×10-9 mol/L（S/N = 3）.Furthermore,the reproducibility,stability and interference of the electrochemical sensor were also evaluated.The results of the spiked test of serum samples show that the electrochemical method has the advantages of good reproducibility and anti-interference ability with practical application.The recovery of the spiked dopamine in bovine serum was in the range of 96.0-101.4%,revealing the sensor can be successfully applied for the evaluating dopamine in real samples.（3）The graphene/MoS₂ composites were prepared by one step.The effects of different kind of MoS₂ and graphene/MoS₂ composites were studied on the electrocatalytic hydrogen evolution.SEM image show that the composites retain the three-dimensional structure of MoS₂,and the addition of graphene reduces the size of molybdenum disulfide flower structure.The electrochemical impedance spectroscopy indicates that the composites have excellent electrical conductivity.Linear sweep voltammetry results show that the graphene/MoS₂ composites have the best catalytic hydrogen evolution with good stability,and the hydrogen evolution potential is 125mV,Tafel slope is 54 mV/dec.