Study On Preparation,Adsorption And Supercapacitive Performance Of NiCo-LDH And Its Nanocomposite

With the ever-increasing environmental pollution and energy crisis,the environmentally friendly,efficient new materials to satisfy both environmental improvement and the development of new energy have been urgent demanded.Layered double hydroxides?LDHs?are a class of inorganic multi-metal clay materials composed of positively charged brucite-like layers with charge-balancing anions and water molecule.Owing to its unique layer structure,the special performance of controllable metal ions in layer plate and exchangeable interlayer anion,LDH has been widely applied in catalysis,drug delivery,pollutant adsorption,electrochemistry and so on.In view of its easy preparation,large specific surface area,high redox activity and stability,NiCo-LDH is selected as the research object.Three-dimensional flower-like NiCo-LDH microspheres,NiCo-LDH/Ag nanowires and NiCo-LDH/graphene?Gr?nanocomposites were prepared using hydrothermal method.The structure,morphology,composition and specific surface area of these samples were characterized via micro-analysis detection techniques.The adsorption and electrochemical properties of NiCo-LDH composites were studied systemativally.The main research content is as follows:?1?Uniform flower-like NiCo-LDHs microspheres with different Ni/Co ratios were synthesized by a facile hydrothermal method via the hydrolysis of hexamethylenetetramine.The SEM shows 25 nm thick of NiCo-LDH nanosheets was accumulated into flower-like microspheres with a diameter of 5-6?m.?2?The effects of Ni/Co ratio,pH,temperature and concentration on the methyl orange?MO?adsorption were studied,found that the best adsorption performance were obtained at the Ni/Co=1:1,pH⁷ and high temperature?15-55??environment.Due to the porous structure of flower-like microspheres,the adsorption equilibrium time was shortened to 5-50 min and the maximum theoretical adsorption capacity of Ni₁Co₁-LDH was 497 mg g^-1,which was higher than that of conventional adsorbents and bulk LDH materials.Meanwhile,the adsorption process is mainly monolayer adsorption controlled by chemical reaction;the adsorption mainly results from the synergistic effect of surface adsorption and anion exchange of LDH.?3?High aspect ratio of Ag nanowires with a diameter of 100 nm and length few micrometers were prepared by solvothermal method.On this basis,Ag nanowires and NiCo-LDH nanosheets were sequentially deposited on the nickel foam?NF?via dip-coating and hydrothermal method to obtain NiCo-LDH/Ag/NF composite electrode.the intervention of Ag nanowires makes the thickness of LDH nanoplatelets reduce from³0 nm to¹5 nm,the electrode conductivity enhance and the electrochemical active sites increase.Therefore the specific capacitance of NiCo-LDH/Ag composite was increased 2920.6 F g^-1 at the current density of 5 A g^-1,about 1.4 times than that of the NiCo-LDH electrode,and the stability was also significantly improved?89.8%after2000 cycles?,revealing that the composite electrode has excellent electrochemical performance.In addition,the asymmetric supercapacitor with NiCo-LDH/Ag/NF as the positive electrode and activated carbon?AC?as the negative electrode displays high power density,energy density(42.9 Wh kg^-1 at 800 W kg^-1)and electrochemical stability.?4?Different morphology Graphene?Gr film,and Gr nanowall?were grown on nickel foam substrate via CVD method.On this basis,NiCo-LDHs nanosheet arrays were grown on NF,GF/NF and GW/NF substrates using hydrothermal method to form three-dimensional porous NiCo-LDH/NF,NiCo-LDH/GF/NF and NiCo-LDH/GW/NF composite electrodes.?5?Due to the improvement of its conductivity,porosity and surface area,the NiCo-LDH/GF/NF composite electrode has the most excellent capacitance performance(2690 F g^-1 at 5 A g^-1),about 1.3 times that of NiCo-LDH/NF(1158.8 F g^-1)and 1.2times than that of NiCo-LDH/GW/NF(1532.6 F g^-1).In addition,the asymmetric supercapacitor with NiCo-LDH/GF/NF as the positive electrode and activated carbon?AC?as the negative electrode displays high power density and energy density(50.2 Wh kg^-1at 800 W kg^-1)and electrochemical stability.NiCo-LDH and its nanocomposites were synthesized by a facile hydrothermal method and the application in the pollutants adsorption and supercapacitors was discussed.These research results provide important instructional significance for the preparation of LDH-based novel efficient adsorbents,high-performance energy storage devices and the application of LDH.