Preparation Of Modified Molecular Sieve Composite Flexible SiO₂ Nanofiber Membrane And Its Application In Water Treatment

Water is a vital resource for human survival.With the current vigorous development of industry and improper disposal of chemical products and raw materials,the prospect of pollution in industrial wastewater is not optimistic.Molecular sieves are widely used in water treatment as a catalytic carrier due to their large specific surface area,excellent ion exchange and adsorption properties and applicability.However,most of the traditional molecular sieve products are in powder form,which requires complicated separation and recycling operations after using in industrial wastewater,which increases additional recycling costs.When recycling is not sufficient,it is easy to cause secondary pollution to the waterbody.The flexible silica nanofiber membrane prepared by the electrostatic spinning method possesses the characteristics of high porosity,good hydrophilicity,chemical stability and excellent heat resistance,which is suitable to be a carrier of molecular sieve materials.In this paper,the molecular sieve powder is bonded to the surface of the flexible silica nanofiber membrane,so that the advantages of the two are complementary and the functional component is transformed from a powder-like substance to a flexible film-like substance.After using the molecular sieve/Si O₂ material and metal oxide@molecular sieve/Si O₂ prepared in this experiment to remove the ammonia nitrogen and phenol in the wastewater,the material can be taken out directly without other complicated separation and recycling operations,which greatly reduces recycling costs and provides great convenience for application in industrial water treatment.（1）In this paper,the flexible ceramic Si O₂ nanofiber membrane was prepared by electrospinning.First,the influence of the amount of H₃PO₄ added in the precursor solution occur on the properties of the solution,its spinnability and the final prepared flexible Si O₂ nanofiber membrane was explored,and the optimal silica sol ratio was determined to be TEOS,H₂O and H₃PO₄ at a mass ratio of 1:1:0.01.Next,the spinning process of classic Si O₂ nanofibers is improved.By adjusting the spinning distance and voltage to the corresponding level,the flexible ceramic nanofiber membrane prepared at the infusion speed of 1.5 m L h^-1has the same fiber diameter as the material prepared by the classic method,and has a uniform and smooth fiber surface,which increases the production efficiency of flexible Si O₂ nanofibers by 50%.（2）Secondly,two molecular sieves,13X and ZSM-5,are loaded on flexible Si O₂ nanofiber membranes by dipping and sintering then the molecular sieve/Si O₂ composite materials was prepared for adsorb ammonia nitrogen in wastewater.During the preparation process,the influence of the concentration of the molecular sieve dispersion on the loading capacity and performance of the composite material was mainly studied.SEM and XRD characterization proved that 13X and ZSM-5 were successfully loaded on the flexible Si O₂ nanofiber membrane,and the loading process did not change the crystal structure of the two molecular sieves.The ammonia nitrogen wastewater removal test results respectively show that under the same conditions,the ammonia nitrogen removal effect of 13X/Si O₂ material is significantly better than that ZSM-5/Si O₂material.A series of experiments have proved that the optimal molecular sieve dispersion concentration is 2 g L^-1 and the optimal material dosage is 4 g L^-1 when removing ammonia nitrogen in wastewater.Its p H is applicable in a wide range,which is conducive to its actual use.（3）Finally,Fe（NO₃）₃·9H₂O and Mn（NO₃）₂·4H₂O were used as metal sources,and metal oxides were loaded on the prepared molecular sieve/Si O₂ composite material by impregnation and high-temperature sintering methods.And eventually,we successfully prepared a metal oxide@molecular sieve/Si O₂composite catalyst to the degradation of phenol in wastewater by the persulfate advanced oxidation method.The characterizations of SEM,ICP,XRD,XPS,BET and FT-IR proved that Fe₂O₃ and Mn O₂components were successful loading on molecular sieve/Si O₂materials,and the corresponding loading amount were determined.At the same time,a series of catalysts of the prepared metal oxide@molecular sieve/Si O₂ composites were tested.The results showed that the best catalyst carrier is prepared when the molecular sieve dispersion concentration is 2g L^-1 for ZSM-5/Si O₂ material and the effect of simultaneously loading iron and manganese oxide materials at a ratio of 1:1 is better than loading separate iron or manganese oxide materials,the optimal potassium persulfate concentration is 20 m M,persulfate advanced oxidation method has a wide p H range of application,so there’s no need to perform p H adjustment steps.The prepared Fe-Mn@molecular sieve/Si O₂ composite material shows good reusability,which is significant to industrial application.