Study On Preparation,Adsorption And Electrochemistry Properties Of NiFe-LDH

Now 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 hydroxide(LDH),also known as anionic clay or hydrotalcite-like compound,is comprised of positively-charged hydroxide sheets and interlayer anions.Because of its unique layer structure,the special performance of controllable metal ions in layer plate and exchangeable interlayer anion,LDH become a research hotspot in water environment treatment and electrochemical energy storage.In this work,through a variety of inspection and feasibility analysis,based on NiFe-LDH,NiFe-X-LDH with four different interlayer anions(X=Cl-,NO3-,SO42-,CO32-)and La/Mo/W-doped NiFe-LDH were synthesized by a facile co-precipitation method.Hydrothermal method of growing La/Mo/W-doped NiFe-LDH arrays on nickel foam was adopted.The synthesis of materials are characterized through the X-ray diffraction(XRD),Fourier infrared absorption spectrum(FT-IR),scanning electron microscope(SEM),X-ray photoelectron spectroscopy(XPS)and specific surface area analyzer tester test(BET).The influence of different factors on the NiFe LDH adsorption of methyl orange and heavy metal Cr(VI)were systematically explored,adsorption mechanism were further analyzed.In addition,the adsorption methyl orange performance contrast of the La,Mo,W-doped and undoped NiFe-LDH were discussed.Also the supercapacitor performances of La/Mo/W-doped NiFe-LDH array were investigated by cyclic voltammetry and constant current charge-discharge test.The main results are as follows:(1)NiFe Layered double hydroxide with four different interlayer anions(NiFe-X-LDH,X=Cl-,NO3-,SO42-,CO32-)were synthesized by co-precipitation method.Their adsorption performance of methyl orange(MO)was studied.It is found that the different interlayer anions strongly affected the MO adsorption capacity,and the adsorption amount of NiFe-X-LDH follows the order of interlayer anions: CO32-< SO42-< NO3-< Cl-,which attributed to the synergistic effect of specific surface area,pore size and ion exchange capability.(2)The adsorption behavior of NiFe-Cl-LDH for MO in various parameters was further systemically investigated.It shows that the adsorbent presents good performance within the pH range of 5 to 6.The adsorption capacity increase with solution temperature and the thermodynamic data indicate that the adsorption is spontaneous and endothermic.The adsorption isotherm data are well fitted with the Langmuir model and the pseudo-second-order model,and the maximum MO adsorption capacity of NiFe-Cl-LDH is 769.23 mg/g.Weber’s intraparticle diffusion model reveals that the adsorption behavior includes two processes: external surface adsorption and intraparticle diffusion.(3)Due to expand the application scope of NiFe-Cl-LDH,the high adsorptive capacity of Ni Fe-Cl-LDH was also reflected in the Cr(VI)adsorption.The reaction time,initial concentration and pH on the adsorption were explored.It is found that the adsorption curve are rapidly growing in the first five minutes then slowed progressively until it reached equilibrium,and the higher concentration of adsorption needs the longer equilibrium.The removal percentage is up to 100% for 2-4 mg/L of Cr2O7-and the optimal adsorption Cr2O7-pH is about 5.5.The equilibrium adsorption data fits the Langmuir isotherm well,the theoretical maximum adsorption capacity(60.24 mg/g)was correspond to the experimental data(60.14 mg/g).The adsorption date fit the pseudo-second-order kinetics,which can be inferred that the adsorption is mainly by the chemical adsorption process.And analysis result of the intraparticle diffusion model is consistent with the adsorption of methyl orange.(4)Based on the properties of lanthanum(La),molybdenum(Mo),tungsten(W),the effect of doped NiFe-LDH on adsorption methyl orange were studied.The results show that the adsorption performance of tungsten-doped sample is best,which can be interpreted that its high charge enhances adsorption ability of layer sheet.(5)The growing La/Mo/W-doped NiFe-LDH arrays on nickel foam was prepared by hydrothermal method,and a series of electrochemical test(cyclic voltammograms,constant current charge-discharge test and cycle stability testing)were used to explore the effects of doping element on the electrochemical performance.The study found that doped La sample can obtain the highly oriented layered structure and ultrathin nature nanosheets,which lead to more electrochemical active site,make its electrochemical properties of doping NiFe-LDH arrays is best,its specific capacitance in 2.5 A/g can reach 1668 F/g,in addition,doped La samples also show good rate capability,but the cycle stability needs to be improved.In conclusion,NiFe-Cl-LDH and NiFeW-Cl-LDH have excellent performance in the adsorption of dye and heavy metals,which can be used as a kind of promising material to remove pollutants in water.The supercapacitors performance of Lanthanum-doped NiFe-LDH is outstanding,it can be developed and applied as energy storage materials.These results of adsorption and electrochemical experiments offer a valuable reference for explore the application of LDH.