The Design And Detection Application Of Enzyme Free Electrochemical Sensors Based On Graphene And Molybdenum Disulfide

Graphene and graphene-like molybdenum disulfide nanomaterials have a good application prospect in the field of chemical sensors.They have many unique physical and chemical properties,such as:graphene has good conductivity,a large specific surface area,rapid electron transfer ability,good electrocatalytic activity,easy functionalization and large-scale production,etc.,and graphene-like molybdenum disulfide has large specific surface area,high reactivity,large band width,easy modification and strong adsorption ability.Introducing these materials into electrochemical sensors could improve the sensing performance due to these unique properties.Nevertheless,with the continuous research on the above materials,researchers find that they have some shortcomings limiting their application in electrochemical sensing.In order to improve the performance of electrochemical sensors,we need to prepare new nanomaterials with better conductivity,larger specific surface area,excellent catalytic performance and higher stability.The work of this thesis focused on the combination of graphene and molybdenum disulfide with other nanomaterials to prepare novel nanocomposites and investigated their applications in enzyme-free electrochemical sensors.The aim was to overcome some drawbacks of graphene or MoS₂ including aggregation,low catalysis,large mass transfer resistance etc.,to improve the sensing performance,and explore new approach to fabricate advanced electrochemical sensors.The main research content includes the following four parts:In the first work,copper nanoparticles?CuNPs?were grown in situ on polydopamine-modified graphene oxide GO to obtain CuNPs@GO complexes.Cu-3D-N-rGO complexes were obtained after calcination.An enzyme-free sensor for detecting hydrazine hydrate was constructed based on this complex.The formation of polydopamine can increase the loading of CuNPs on the surface of GO,while N can be doped into rGO using polydopamine as N source.These characteristics could improve the conductivity,electron transfer ability and electrocatalytic activity of nanocomposites.The catalytic activity of Cu-3D-N-r GO composites for hydrazine hydrate increases,such as lower catalytic potential and higher catalytic current.The composite was used for the electrochemical detection of hydrazine hydrate,showing a wider linear range of 0.05 m?to 6.8 mM,the sensitivity was 64.12?A·mM^-1·cm^-2,and a detection limit was 0.02?M.In the second work,three-dimensional hierarchical porous?multi-level?graphene nanomaterial?3DHPG?was prepared by a hydrothermal self-assembly method combined with an in-situ carbothermal reduction reaction.The 3DHPG was used to modify glassy carbon electrode to construct an enzyme-free dopamine sensor.Compared to two-dimensional graphene nanosheets?GNS?,multi-hole graphene has a large specific surface area and a large number of site defects,thereby improving electrochemical sensing performance.The detection of dopamine by three-dimensional multi-level pore graphene?3DHPG?displayed a larger catalytic current compared to macroporous graphene?3DPG?.The linear range of dopamine detected by the 3DHPG sensor was 0.01?M to 0.3 mM,the sensitivity was 1.37?A·mM^-1·cm^-2,and the detection limit was 0.003?M.In the third work,a new three-dimensional POM-MoS₂/rGO composite was formed by one step hydrothermal treatment of mixture of polyoxometallate?POM?,thiourea and graphene oxide?GO?.The obtained composite nanomaterial was used to construct a nitrite sensor.Graphene not only significantly improves the conductivity of the material,but also greatly enhances the active surface area,and it is greatly beneficial to the mass transfer.At the same time,MoS₂ isolates the graphene layer and further reduces the aggregation of graphene.The combination of POM and Mo S₂-rGO reduces the leaching loss of POM,improves the stability of the electrode response,and improves the catalytic activity of the complex to sodium nitrite.The synergy between POM,MoS₂ and GO results in highly efficient and stable electrocatalytic activity for nitrite oxidation.The nitrite sensor shows a linear range of 0.5?M to 8mM,a sensitivity of 379.39?A·mM^-1·cm^-2,and a detection limit of 0.2?M.Applied to the detection of nitrite in water samples,the recovery was between 99.5 to 102.9%.In the fourth work,a new type of Cu-MoS₂/GO nanocomposite was prepared by hydrothermal one-step synthesis,which was used to construct an enzyme-free glucose sensor.The electrochemical behaviors of Cu-MoS₂/GO modified electrode and its catalysis towards the oxidation of glucose catalysis were investigated.The results revealed that the main catalysis to glucose was from doped Cu specie,while graphene can greatly improvet the conductivity of the composite and MoS₂ could reduce the aggregation of graphene.These factors work togenther leads to an enhanced catalysis and improved sensing performance of the Cu-MoS₂@GO based sensor.The linear range of glucose detection for this sensor was 5?M to 6.33 mM,the sensitivity was308.17?A·mM^-1·cm^-2,and the detection limit was 2?M.