Study On Composites Of Mangnesium Dioxide And Two-Dimensional Nanomaterials And Their Applications In Electrochemistry

Electroanalysis has become a hot topic and received considerable attention due to its great advantages,such as low cost,simple operation,wide detection range,high sensitivity,fast response etc.Meanwhile,mankinds are faced with serious energy problems nowadays.Supercapacitor as a new type of energy storage system provides a possible route to solve the energy crisis.Supercapacitor has many advantages such as high theoretical capacitance,high safety,fast charge and discharge and large power density,long cycle life,environmental friendliness etc.Transition metal manganese dioxide has attracted more research attentions,because of its abundance,low cost,friendly environmental nature and high electrochemical activity.However,MnO₂ as a semiconductor,suffers from intrinsically low electrical conductivity,which greatly limits its charging and discharing ability under high current,also leads to poor power density.Two-dimensional materials with layered structure,such as graphene and graphitic-like carbon nitride have drew much attention due to their excellent physical and chemical properties.Nanocomposites based on metal oxides and graphene or g-C₃N₄ possess the properties of individual components or even with a synergistic effect.Therefore,in this thesis,metal oxides/GO and metal oxides/ g-C₃N₄ nanocomposites were developed,and their applications for electrochemical sensors and supercapacitors were studied.Based on that,some valuable results have been obtained.The main points of this thesis are summarized as follows:?1?MnO₂ nanowires were prepared by using manganese sulfate and potassium permanganate as raw materials.Composites of GO and MnO₂ nanowires were prepared by grinding and sonication.Then,the GO/MnO₂ nanocomposite as an electrode material for non-enzymatic determination of hydrogen peroxide was dropped onto a GCE.The proposed sensor exhibits excellent electrocatalytic performance for the determination of hydrogen peroxide at an applied potential of 0.75 V.The non-enzymatic biosensor for determination of hydrogen peroxide displayed a high sensitivity of 191.22 ?A(mmol L^-1)^-1 cm^-2?signal/noise,S/N = 3?,a low detection limit of 0.48 ?mol L^-1,and a wide linear range of 4.90 ?mol L^-1-4.50 ?mol L^-1.Moreover,the non-enzymatic biosensor shows an excellent selectivity.With these advantages,the study may provide a feasible approach to develop new electrochemical sensors and detection of other biochemical reagent.?2?Composites of g-C₃N₄ and MnO₂ nanowires were prepared by an in situ chemical redox reaction.In such a process,MnO₂ grown to self-assembled long nanowires in the present of g-C₃N₄,which was prepared by thermal polycondensation of urea.The g-C₃N₄ was used to induce the growth of the manganese dioxide in the mixture solution of manganese sulfate and potassium permanganate.The final morphology of the manganese dioxide changed from nanorods into nanowires.The XRD,BET,FTIR,FESEM and TEM images reveal that the MnO₂ nanowires grew on the surface of g-C₃N₄.With current density of 0.5 A g^-1,the supercapacitance of the prepared sample reaches 365.65 F/g,which is almost five times of that of the pure manganese dioxide.Meanwhile,the manganese dioxide with superstructures displays excellent cycle stability.The capacitiance retention remains 95.64 % after 1000 cycles.The nanocomposite not only shows excellent electrochemical performance,but also low cost.The nanocomposite is expected to be potential applications as high performance supercapacitor materials.