Preparation Of Graphene-based Composites And Their Application In Electrochemical Sensors

The level of some biomolecules in the human body is closely related to human health.Electrochemical sensor is widely used in environmental,medical and sanitary testing owing to its low cost,saving time and high sensitivity.In order to improve the detection effect of the sensor,a variety of different nano-materials are used to modify the electrode.Graphene and molybdenum disulfide have similar layered structures.As the typical representatives of two-dimensional materials,they have unique and excellent performance and are widely used in sensors,supercapacitors,batteries,and catalysis.There are many methods to prepare graphene.Graphene oxide(GO),prepared by chemical oxidation,exhibits water-solublity due to the oxygen-contaning functional groups on its surface.Pristine graphene(PG),prepared by liquid phase exfoliation,has the advantages of high quality,few defects,and high conductivity.In this thesis,GO/PG was prepared using two different methods.The GO/PG composite exhibits good performance with the combination of water solubility and high conductivity.At the same time,the Fe₃O₄ nanoparticles with catalytic properties were loaded on the surface of the GO/PG binary composite to prepare the Fe₃O₄/GO/PG composite.The Fe₃O₄/GO/PG ternary composite is modified on the surface of the glassy carbon electrode to construct an electrochemical sensor to detect dopamine(DA)and hydrogen peroxide(H₂O₂).On the other hand,the liquid phase exfoliation method could be used to prepare two-dimensional materials with high-quality and large-scale.This method is used to prepare graphene/molybdenum disulfide(Mo S₂)composite.The graphene/Mo S₂composite was prepared by co-exfoliate graphite powder and molybdenum disulfide powder in isopropanol with the assistance of potassium sodium tartrate.An electrochemical sensor based on graphene/Mo S₂ is used to detect DA.This thesis mainly includes the following three parts:(1)The graphite powder was as the raw material,graphene oxide(GO)and pure graphene(PG)were prepared by using the modified Hummer method and liquid-phase exfoliation method,respectively.The GO/PG composite was prepared by combination of GO and PG.The co-precipitation method was utilized to synthesize the Fe₃O₄ nanoparticles with catalytical performance on the GO/PG nanosheets to fabricate a Fe₃O₄/GO/PG ternary composite.Compared with the Fe₃O₄/GO and Fe₃O₄/PG composites,the Fe₃O₄/GO/PG ternary composite shows excellent electrochemical performance owing to the good water solubility of graphene oxide,the high conductivity of pristine graphene,and good catalytical performance of Fe₃O₄.An electrochemical sensor based on Fe₃O₄/GO/PG composite was prepared by dropping on the surface of the glassy carbon electrode.The electrochemical sensor is used to detect dopamine and hydrogen peroxide.The detection limits(signal-to-noise ratio of 3(S/N=3))are 0.18 and 0.09?M,respectively.(2)The GO/PG composites was prepared by one-step exfoliation of graphite powder in the GO solution with a certain concentration using an ultrasonic cell disruptor.Furthermore,the Fe₃O₄ was loaded on the GO/PG composite to prepare the Fe₃O₄/GO/PG ternary composites.This method greatly shortens the time on preparation of GO/PG composite.Besides,the concentration of GO/PG prepared in this method is higher.The prepared ternary composite was fabricated into an electrochemical sensor to detect DA.The detection range is 5-40?M with the detection limit(S/N=3)of 3.37?M.(3)As the start of graphite powder and molybdenum disulfide,isopropanol is used as a solvent to provide a liquid environment.With the assistance of potassium sodium tartrate,the graphite powder and molybdenum disulfide are exfoliated by ultra-sonication to prepare graphene/Mo S₂ composite.This method is simple and easy to operate.The relevant characterization technology indicates that the composite has been successfully prepared.Besides,an electrochemical sensor based on the graphene/Mo S₂ composite was fabricated to detect dopamine.It shows a good detection effect on DA.The detection range is 1-120?M with the detection limit(S/N=3)of 0.76?M.