Preparation Of Manganese Oxide/Carbon Composite Hollow Nanotubes And Their Adsorption Performance Of Lead Ions

Electrospun carbon nanofibers(ECNF)are prepared by pre-oxidation and carbonization methods using electrospinning technology.The method has the advantages of high specific surface area,high porosity,small diameter and continuous uniformity.However,the adsorption effect of ECNF on heavy metals is generally suitable,but it is very suitable for supporting materials,and often other metal oxides are supported on its surface to improve the adsorption performance to removal the heavy metals in water.Manganese dioxide(MnO2)is a typical transition metal oxide,because of its high negative charge,low charge point,as an adsorbent to the heavy metal ions,it have a good adsorption effect.Combined with carbon nanofibers,the new material own large surface area.As a result,the adsorption capacity increases dramatically.Based on the redox reaction principle between potassium permanganate and carbon,ECNF was immersed in potassium permanganate(KMnO4)solution,MnO2 was modified on the surface of ECNF,and then the composite fibers were annealed to obtain manganese oxide / carbon composite nanotubes(MnO2 / CNTs).In the solution reaction stage,the loading of manganese dioxide is controlled by adjusting the concentration of potassium permanganate and the reaction time in the solution.During the annealing process,the formation process of the hollow tube is controlled by annealing times.The surface morphology and micro-pore structure of the composites formed in the reaction process,the thermal change of the composite nanotubes,the crystal structure of the manganese dioxide,the element composition and the valence of the elements were analyzed.The main factors affecting the adsorption of lead on MnO2/CNTs were studied,including pH value,adsorption time and initial lead concentration.The adsorption process was analyzed by various adsorption thermodynamics and adsorption kinetics model.Field emission scanning electron microscopy(SEM)and transmission electron microscopy(TEM)shows that the change of the content of the composite material from the nanofibers to the nanotubes with the increase of potassium permanganate concentration and reaction time.Energy Dispersive Spectrometer(EDS)shows the reaction time has a greater effect on the deposition of MnO2.When the concentration of potassium permanganate is 10 mmol / L and the reaction time is 24 h,the hollow nanotube structure with granular granules can be obtained successfully.X-ray diffraction(XRD)and TEM characterization show that the deposited layer on the surface of ECNF contains birnessite-MnO2.After the ECNF / MnO2 composite fiber is further heat treated,the structure of MnO2 is changed from nanofiber to nanotube.Thermogravimetric analysis(TGA)and X-ray photoelectron spectroscopy(XPS)analysis showed that the annealing process promoted the reaction of MnO2 and carbon and produced low-valent manganese.The main factors influencing the adsorption of lead on MnO2 / CNTs were studied,including pH value,adsorption time,initial lead concentration and so on,and the adsorption process was analyzed.The adsorption rate of the lead ions increased from 68% to 90%,and the adsorption rate increased with the increase of pH(2-6)in the system.The adsorption rate is related to the initial concentration of lead ions in the solution.The higher the concentration and the lower the adsorption rate,the reason is that the adsorption sites on the surface of MnO2 / CNTs are fully bound and can not be further adsorbed.MnO2 / CNTs adsorption in the solution of lead ions in two stages,rapid adsorption stage and slow adsorption stage.The adsorption kinetics coincides with the quasi-second-order kinetics equation,and the fitted correlation coefficient approaches 0.9998.The adsorption thermodynamics accorded with Langmuir adsorption isotherm model,and the fitted correlation coefficient approached 0.9996.The maximum adsorption capacity of MnO2 / CNTs measured in practical experimental data is 285.5mg / g,which is very close to the calculated theoretical capacity.The results of adsorption experiments show that the material has a good application prospect and potential,and its preparation process also provides some new ideas and methods for the synthesis of new nanotube materials.