Preparation Of Graphene Based 3D Nanocomposites And Their Application In Electrochemical Sensor

Graphene（Gr）,a two-dimensional,single-layer sheet of sp² hybridized carbon atoms,has unique advantages in the construction of electrochemical sensor owing to its large specific surface area,high electronic conductivity and excellent mechanical strength.graphene and its composites become a hot spot of material science nowadays.Three-dimensional graphene is a new kind of graphene derived material and it has been widely studied in recent years.It can not only keep unique properties of two-dimensional structure,but also obtain large surface area and controlled porous structure by integrating graphene into three-dimensional macroscopic structure.It is quite attractive to prepare multifunctional three-dimensional graphene composites.The small size effect,high surface area,excellent properties such as the effect of quantum dot nanomaterials in electrochemical sensors,capacitors,batteries,a plurality of electrochemical field electro catalysis are of concern.Especially the electrochemical sensing field,nano materials can improve the catalytic activity and electrochemical sensor sensitivity,stability and reproducibility。Metal oxide nanomaterials combine the qualities of metal oxide materials and nanomaterials,exhibiting excellent electrical conductivity and electrocatalytic property.Incorporating graphene with metal oxide nanomaterials can acquire a variety of graphene-metal oxide nanocomposites with preeminent electrocatalytic performance.Hereby,it can be expected to improve the sensitivity of sensors through the synergistic effect of graphene and metal oxide nanocomposites for the electrochemical sensors.According to the ideas,the aim of this thesis is to construct a three-dimensional porous structure with several catalytic active functional nanomaterials（metal oxide,molybdenum disulfide,gold nanoparticles,etc.）,thus reducing the degree of aggregation of graphene,improving the active surface area of the complex,and improving the function nanometer.The catalytic activity,stability and conductivity of materials are used to build electrochemical sensor with excellent properties by synergistic effect between materials.The following works were carried out:1.Nickel-cobalt oxide nanowrinkles with spinel-type crystal structure supported on reduced graphene oxide（NiCo₂O₄ NWs-rGO）was prepared to develop a sensitive and stable nonenzymatic glucose sensor.The NiCo₂O₄ NWs-rGO hybrid was prepared by a facile one-pot hydrothermal reaction,and sequential calcination in air.The morphology,composition and crystal structure of the NiCo₂O₄ NWs-rGO hybrid were characterized by scanning electron microscope,transmission electron microscope,selected area electron diffraction,and energy-dispersive spectroscopy.The electrochemical behavior of the hybrid and its catalytic activity towards glucose oxidation were investigated by several electrochemical methods.Compared with single component NiO or Co₃O₄,spinel type NiCo₂O₄ NWs displayed higher catalysis towards glucose oxidation.Further integration of NiCo₂O₄ with graphene could reduce the overpotential and enhance the catalytic current due to the improved conductivity and dispersity of NiCo₂O₄.The NiCo₂O₄ NWs-rGO based glucose sensor showed a wide linear range of 0.005-8.6 mM,a low detection limit of 2 mM（S/N=3）,and an improved stability.A satisfactory recovery was also obtained for glucose detection in human serum at physiological level.2.In this study,a polyoxometalate（POM）and graphene oxide（GO）were hydrothermally treated to form a novel three-dimensional（3D）macroporous hybrid3D-mp-rGO-POM for nitrite sensing.The 3D porous rGO not only obviously enhanced the conductivity and largely increased the active surface area,but also greatly facilitated the mass transport and efficiently decreased the leaching of the POM from the modified electrode.The synergistic interaction between the POM and3D porous rGO endowed 3D-mp-rGO-POM with a highly stable and efficient electrocatalytic activity towards the oxidation of nitrite.A nonenzymatic sensor for nitrite based on this hybrid showed two linear response ranges of 0.5μM to 221μM and 0.221 mM to 15.221 mM,with a detection limit of 0.2 mM（S/N=3）,which displayed higher sensitivity,higher stability,a wider linear range and a lower detection limit than sensors based on POMs or 2D-rGO supported POM hybrids.Interference from H₂O₂ was effectively avoided by monitoring the oxidation current of nitrite instead of its reduction current.The 3D-mp-rGO-POM hybrid with facile preparation,high stability and good catalytic activity may have promising applications in catalysis,sensors,and so on.3.A facile one pot hydrothermally induced self-assembly approach was proposed to prepare a novel three-dimensional（3D）macroporous graphene wrapped cuprous oxide composite（3D-p-rGO-Cu₂O）for the stable and sensitive electrochemical detection of hydrogen peroxide（H₂O₂）.3D-rGO could reduce the aggregation of two-dimensional graphene（2D-rGO）nanosheets and increase the surface area,while the connected macroporous structure enhances the electron and mass transport.The synergistic interaction between Cu₂O and 3D porous rGO makes 3D-p-rGO-Cu₂O had a good electrocatalyst towards the reduction of H₂O₂.A nonenzymatic sensor for H₂O₂ based on 3D-p-rGO-Cu₂O showed a linear response range from 0.5 mM to10.17 mM,with a detection limit of 0.2 mM（S/N=3）,which showed the advantages of higher sensitivity,higher stability and wider linear range than those sensors based on Cu₂O or 2D-rGO supported Cu₂O particles（2D-rGO-Cu₂O）.Our results indicate that hydrothermally induced selfassembly is a good alternative approach to prepare a3D graphene-nanomaterial composite/hybrid,which may have great potential in fabricating advanced electrochemical sensors.4.A three dimensional hybrid named as 3D-f-Mo S₂-rGO composed of worm-like and flower-like molybdenum disulfide（MoS₂）grown on reduced graphene oxide（rGO）was prepared for sensitive electrochemical detection of dopamine（DA）.The hybrid 3D-f-MoS₂-rGO was prepared by a facile hydrothermal reaction.The electrochemical behavior and electrocatalytic property of the 3D-f-MoS₂-rGO hybrid were explored by electrochemical impedance spectroscopy（EIS）,cyclic voltammetry（CV）and differential pulse voltammetry（DPV）.The results revealed that the3D-f-MoS₂-rGO hybrid displayed much higher catalysis towards dopamine oxidation than that of single component rGO or MoS₂ due to the synergistic interaction between rGO and MoS₂.The hybrid modified electrode was used for nonenzymatic detection of dopamine,which showed a linear response range of 0.2μM to 150μM,a detection limit of 0.05μM,a good selectivity and reproducibility.Furthermore,the sensor also displayed satisfactory results in real samples analysis,which demonstrates its great potential in practical applications.5.A simple and efficient eletrochemical sensing platform for simultaneous and sensitive detection of hydroquinone（HQ）,catechol（CC）and resorcinol（RC）based on the 3D molybdenum disulfide/reduced graphene oxide and Au nanoparticleis（AuNPs@3D-f-MoS₂-rGO）were prepared.Electrochemical oxidation of the three dihydroxybenzene isomers were investigated using cyclic voltammetry（CV）and differential pulse voltammety（DPV）,and the results showed that they can be catalyticallyoxidizedanddiscriminatedsimultaneouslyonthe AuNPs@3D-f-MoS₂-rGO/GCE.The presence of AuNPs made the performance of the sensor superior to that of in the absence of it.Owing to the integrated superior conductivity and excellent catalytic property of AuNPs@3D-f-MoS₂-rGO/GCE,the sensitive and simultaneous detection of HQ,CC and RC was realized in the individual or triple-components solution based on the as proposed sensor,which showed wide linear range and low detection limit.The sensor also displayed satisfactory results in real samples analysis for three dihydroxybenzene isomers.Therefore,the remarkable electrochemical advantage of AuNPs@3D-f-Mo S₂-rGO/GCE makes it a promising material in electrochemical biosensing field.