Preparation Of Chemical Vapor Deposition Graphene And Its Application Towards Electrochemical Sensoring

Chemical vapor deposition(CVD)is an important method for the growth of large area and high quality graphene in the laboratory and industry.The CVD grown graphene has also been widely used in the fields of flexible electrodes,touch screens,smart glasses and wearable sensors because of its high electrical conductivity and crystalline quality.Scanning electron microscope(SEM),transmission electron microscopy(TEM),atomic force microscope(AFM),Raman spectrometer,thermo gravimetric analyzer(TG),UV-Vis spectrophotometer(UV-Vis)and contact angle tester were used to characterize and test the morphology,crystal quality and hydrophobicity of different substrate growth graphene.The noble metal nanoparticles were deposited on the surface of graphene grown on copper foil by magnetron sputtering technology.The free-standing graphene-supported noble metal particles film was obtained by polymer-free transfer method and used towards electrochemical detection field.This thesis focus on the sensitivity,linear range,detection limit,stability and feasibility of real sample testing of graphene-supported noble metal nanoparticles towards hydrogen peroxide(H2O2),nitrite and glucose detection.In addition,the graphene grown on quartz glass directly loaded noble metal nanoparticles were also applied to the electrochemical detection of H2O2.High-quality graphene prepared by CVD method was used as a platform for noble metal nanoparticles dispersed and maximize exposure of catalytic active sites.The polymer-free transfer method avoids stacking of graphene layers and agglomeration of noble metal nanoparticles.The process uninvolved polymer assist and residues has advantage for the electrochemical detection of ultra-low concentrations of the tested molecules.(1)Chemical vapor deposition graphene on metal substrateIn this thesis,the feasibility of high quality graphene grow on different shapes of substrates by low-pressure chemical vapor deposition method were studied.Different substrates was used to grow graphene,such as copper foil(25 ?m thick),copper wire(25 ?m diameter),copper-nickel alloy wire(75 ?m diameter)and nickel foam.Graphene was grown in a tube furnace with methane and hydrogen at 1030 ? by low-pressure chemical vapor deposition method.This part has explored the growth trend of graphene crystal domains and graphene islands.The difference in thermal expansion coefficient between graphene and substrate results in the formation of folds through the grain boundaries and steps of the metal substrate,illustrating the continuity growth of graphene.It was confirmed that single layer graphene could grow on copper,multilayer graphene on nickel and non-uniform layers of graphene on copper-nickel alloy.Graphene grown on copper foil(25 ?m thick)was transferred to SiO2/Si substrate by polymethyl methacrylate(PMMA)assist transfer method.The special coating thickness of SiO2 on Si substrate interference with single layer graphene could enhanced visible light reflection effect.The naked eye can initially distinguish the position and size of graphene because of the different contrast of graphene and surrounding.AFM was used to characterize the number of layers and morphology of graphene transferred to SiO2/Si substrate.The effect of the transfer process on the graphene structure such as wrinkles,damaged parts,and residual of PMMA was studied.In addition,the paper also explored the protective of graphene in preventing oxidation of the long-term placement copper foil.(2)Pt/graphene(Pt/G),Au/graphene(Au/G)applied in electrochemical fieldPlatinum and gold nanoparticles were deposited on the surface of CVD grown graphene by magnetron sputtering method applied to ultra-sensitive H2O2 non-enzymatic electrochemical detection.The dispersion,particle size distribution and morphology of noble metal nanoparticles were studied.After copper substrate etching,the self-supporting graphene-supported platinum and gold nanoparticle composites(Pt/G,Au/G)could be obtained.The sensitivity and detection limit of sensors toward H2O2 detection were investigated.The linear range of Pt/G/GCE sensors is 0.5 nM to 1.286 ?M,with low initial current(magnitude of 10-9 A),low detection limit(0.18 nM,S/N = 3)and fast response capability(2 s).The Au/G/GCE sensor has short response time(2 s),low detection limit(10 nmol/L,S/N = 3),and wide linear response range(25 nmol/L?1.5 mmol/L).Both them have the advantages of high stability,selectivity and are feasible in the field of actual samples detection.(3)Au/graphene microspheres applied in electrochemical sensorThe gold nanoparticles were in-situ loaded on the three-dimensional spherical graphene surface by spray drying and thermal reduction of graphene oxide solution.The formation conditions,morphology and structural stability of graphene microspheres and morphology,size and dispersion of gold nanoparticles were investigated.The composites were used for the electrochemical detection of nitrites with linear range of 5.0 ?mol/L to 2600 ?mol/L,detection limit of 0.5 ?mol/L(S/N =3)and response time of 5 s.The spray drying method can be widely used in industry.Three-dimensional graphene microsphere loaded gold nanoparticles have potentially valuable in practical applications of electrochemical detection field cause its special structure and properties.(4)Au/single layer graphene applied in glucose sensorThe composites of CVD grown graphene support sputtering gold nanoparticles was used for glucose electrochemical detection.Glucose oxidase(GOD)was immobilized on gold nanoparticles with glutaraldehyde as crosslinker by Schiff base reaction.The large specific surface area of monolayer graphene supported gold nanoparticles with maximized active sites provided was good for the attachment and immobilization of GOD on the electrode surface.The ferrocene derivatives were used as electron mediators to investigate the effect of electron mediators on glucose electrochemical detection performance.In the presence of ferrocene derivatives as electronic mediator,the sensor has detection limit of 0.2 nM(S/N = 3)and detection range of 1 nM to 5 mM.The sensor has good stability and anti-interference capability.The thesis explored the real sample detection in human sweat,and proposed the possibility applying of glucose wearable sensor in the future.(5)Chemical vapor deposition graphene on insulation substrate and its application towards electrochemical sensoringHeat-resisting quartz glass was used as substrate to grow graphene after reactive ion etching pretreatment,graphene can be directly grown on the surface of the substrate by atmospheric pressure CVD method.Different etching time and growth time were regulated,the morphology and crystal quality of graphene grown on quartz glass were characterized.The influence of reactive ion etching on the growth rate and morphology of graphene was also investigated.Optimum growth conditions of graphene on quartz glass substrates were explored.In this part,the relationship between etching/growth time with transparence and hydrophobicity of graphene grown on quartz glass substrate was obtained by UV-Vis spectrophotometer and contact angle teste,which will be used for future applications,such as smart glass and anti-fog glass and so on.The paper also studied non-enzymatic electrochemical detection of H2O2 by directly loaded platinum nanoparticles on the surface of graphene.The experiments focused on the electrochemical response towards different concentrations of H2O2,confirming the feasibility of electrochemical applications of graphene growth on the insulation substrate.