Preparation Of NiFe-LDH For Adsorption,Absorbing And Electrochemical Performance

With the aggravating of environmental pollution and energy crisis,the world has an urgent need to seek friendly,efficient new materials to satisfy both environmental governance and the development of new energy.Layered double hydroxides（LDHs）is a class of two-dimensional clay material with dirrerent types of layered metal hydroxides.Because of its unique layer structure,the special performance of controllable metal ions in layer plate and exchangeable interlayer anion,LDHs have been widely applied as catalysts,pollution absorbents,photoactive materials,drug delivery,electrochemistry,and so on.NiFe-LDH,which is a typical layered double hydroxide material,not only has the unique characteristics of LDH,such as large surface area and porous structure,but also has low cost in materials,environment-friendly in preparation and special magnetic properties.Thus,the N iFe-LDH has attracted the attention of researchers all around the world in recent years.The performance of N iFe-LDH in oxygen evolution reaction has been studied and reported extensively.However,the research on adsorption,absorbing,electrochemistry and its application in environmental pollution,energy storage devices,and biosensors are few.In this paper,two simple and efficient methods,coprecipitation and hydrothermal method were used to prepare N iFe-LDH nanometer powder and nanosheets array.The morphology,structure and composition of the N iFe-LDH were characterized and their adsorption,electrochemical and electromagnetic wave absorption properties were studied systematically and deeply.In addition,its application in organic dye and heavy metal ion adsorption,electromagnetic wave absorption,supercapacitor and glucose sensor were explored.The main conclusions of this thesis are summarized as follows:（1）The N iFe-NO₃-LDHs with different mole ratio of N i/Fe（1:1,7:3,3:1 and 4:1）were successfully prepared by a simple coprecipitation method with ammonia as precipitant.The nanosheets is agglomerated together and form a porous structure with a pore size of 16-23 nm and a specific surface area of 17.85 m² g^-1.The N iFe-NO₃-LDH has a good adsorption effect on anionic contaminants.The adsorption performance of NiFe-NO₃-LDH with N i/Fe=4:1 is the best than the other N iFe-CO₃-LDHs.The saturated adsorption capacity of N i4Fe1-LDH is found to be as large as 205.76 mg g^-1for MO and 26.78 mg g^-1 for Cr（VI）.The adsorption behavior of this new adsorbent is a monolayer and mainly controlled by chemical adsorption.The adsorption synergistically originates from exchangeable anions mechanism and layer charge density.（2）The N iFe mixed metal oxide（N iFe-MMO）was prepared by calcinated with NiFe-NO₃-LDH powder as precursors.The N iFe-MMO nanoparticals are cluster together after calcinated with a composite oxide phase of N iO and N iFe₂O₄ structure.The analysis of the electromagnetic parameters of the samples shows that the real parts of the permittivity for NiFe-LDH and NiFe-MMO are lower than those of other materials,The microwave magnetic loss in the frequency around 6.1 GHz are mainly from natural resonance.In addition,the reflection losses of NiFe-LDH and N iFe-MMO can reach-58.79 dB and-64.43 d B in C-band,respectively,which are attributed to the good impedance matching and a large amount of interface scattering as well as the interfacial electric polarization.However,the absorption bandwidths（<-10 dB）for NiFe-LDH and MMO are narrow compared with other absorbers.Thus,it is necessary to broaden its absorption bands in the future research.（3）N iFe-CO₃-LDH nanosheets were prepared on a N i foam by an one-step hydrothermal method with urea as precipitant.The feeding content of N i,Fe and the total content of metal cations in the initial solution have great influence on the morphology and electrochemical properties of N iFe-CO₃-LDH nanosheets.The results show that the nanosheets are thinner,vertically aligned on the surface of N i foam and the electrochemical performance is the best when the molar ratio of N i/Fe is 1:1.Raman spectroscopy and SEM test show that after numbers of charge/discharge process,the irreversible conversion of N i²⁺to Ni³⁺leads the gradual decrease of Ni²⁺in the active materials and the top parts of some nanosheets collapsed leads to a reduced specific surface area,which can deduce the decrease of specific capacitance.（4）The pseudocapacitors assembled using N iFe-CO₃-LDH nanosheets exhibit a superior specific capacitance of 2708 F g^-1 at 5 A g^-1,higher than the previously reported LDHs.Asymmetric supercapacitors with the N iFe-CO₃-LDH nanosheets film as the positive electrode（N iFe-CO₃-LDH/N i foam）and active carbon as the negative electrode（AC/Ni foam）display a high energy density(52 Wh kg^-1 at 800 W kg^-1)and excel ent cycle stability.（5）It is proved that the N iFe-CO₃-LDH/N i foam electrode can be used in nonenzymatic glucose sensors without further treatment.As an integrated binder-free electrode for glucose sensor,the N iFe-CO₃-LDH/N i foam electrode exhibits a superior sensitivity of 3680.2μA mM^-1 cm^-2 with a low limit of detection（0.59μM,S/N=3）as well as fast response time（<1 s）.An excellent selectivity from potential interference species and acceptable stability were also achieved.In conclusion,N iFe-NO₃-LDH and N iFe-CO₃-LDH was synthesized by different methods,and its application in pollutant adsorption,electromagnetic wave absorption,supercapacitor and glucose sensor was studied,and the reaction mechanism was discussed.The research provides theoretical guidance and valuable reference for its practical application in related fields.