The Preparation Of Manganese Dioxide Nanomaterials And Adsorption On Low Concentration Of Ammonium

Excessive ammonium in the water influences the growth and reproduction of aquatic organisms and causes the deterioration of water quality,and it's important to remove the ammonium in the water.Ammonium can be removed completely by ion exchange method,which has less effect of temperature and ion exchange absorbents can be utilized for cycles.With the goal from "the water with first level A GB emission standards" to "? class water" in the sewage treatment plant,the ion exchange method is especially suitable for use in such case.So we prepared ?-MnO₂,?-MnO₂ and ?-MnO₂ on the base of ion exchange method,firstly systemically researched the adsorption on ammonium of three kinds of crystalline phases of manganese dioxide,proposed a novel idea and achieved high and quick adsorption on ammonium.In this report,we synthesized ?-MnO₂ and ?-MnO₂ using different precursors with hydrothermal method and the adsorption perfermance was studied in the 40 mg·L^-1 NH₄⁺-N aqueous solution.The result shows that?-MnO₂ with the KMnO4 as the precursor has the adsorption capacity of 11.86 mg·g^-1,?-MnO₂ has little adsorption on ammonium yet.It is because that the the[2×2]tunnel of 4.6 A in the ?-MnO₂ can accommodate ammonium while the[1×1]tunnel of 1.89 A in the ?-MnO₂ can not accommodate ammonium.Then,8-Mn0₂ was manufactured by pyrolyzing MnC0₃.We studied the influence of temperature,the ritio of MnC0₃ and NaOH,heating rate and heating time on adsorption,and find that adsorption capacity of ?-MnO₂ is as high as 21.64 mg·g^-1,which ascribes the 7.2 A interlayer spacing fitting for accommodatting ammonium and ammonium hydronium ion.In the solution containing Mg²⁺,Ca²⁺,Na⁺ and NH₄⁺,8-Mn0₂ still has selective adsorption on ammonium.The ion exchange mechanism has been confirmed by comparing the amount of ion in solution before and after adsorption.Finally,on the basis of above work,we fabricated ?-MnO₂ nanoplate arrays decorated graphite felt with KMn0₄ as precursor via a facile in-situ redox process to get Mn0₂NPs/GF composite materials,which were studied by XRD,SEM,TEM and XPS,systematically.After that,we discussed the impact on concentration of precusor and preparation time,and have revealed that when the concentration of KMn0₄ is 4 g·^-1 and reaction time is 5 hours,prepared Mn0₂NPs/GF exhibits not only high adsorption capacity(15 mg·g^-1)but also quick adsorption,which reflects in the case of adsorption capacity at 3 minutes reaching up to 87.5%of equilibrium adsorption capacity.In repetitive adsorption-desorption experiments,MnO₂NPs/GF has good stability and regenerability after 20 cycles with the removal rate of 89.72%.The adsorption process corresponds to the pseudo-second-order model and the thermodynamics experiment demonstrates that the adsorption isotherm fit well with Langmuir isotherm.We made simulation flow-through adsorption experiments with utility of Mn0₂NPs/GF composite materials.The concentration of NH₄⁺-N reduces from 40 mg·^-1 to 2.52 mg·^-1 after adsorption of Mn0₂NPs/GF under the condition of short time and high flux,while to 36.56 mg·^-1 after flowing through 8-Mn0₂ plates.?-MnO₂ nanoplate arrays with high specific surface area provide accessibility with solution and high porosity of graphite felt reduces barriers of water,which make Mn0₂NPs/GF composite materials exhibit excellent instantaneous adsorption performance.