| Mesoporous materials refers to the pore size range of 2-50nm synthetic synthetic material, and has a large specific surface area, pore volume and a relatively large pore size, it is mainly applied to the fields of ion exchange, gas separation, adsorption and catalysis. In recent years, mesoporous materials as the main body, the encapsulated nano composites are paid more and more attention by people; As a magnetic nanomaterial, magnetic nano Fe3O4 has some excellent performances such as adjustable electromagnetic parameters, lower dielectric parameters, uniform size and good absorbing properties, it is widely used in the fields of communications, computers, biotechnology and stealth materials. In this topic, the preparation and characterization of the mesoporous materials and the nano Fe3O4 were completed through the National Natural Science Foundation-funded project " the nano-magnetic composite encapsulated by modified zeolite and the response behavior of electromagnet (project grant No.:50972026)", as well as the research on the compound of mesoporous materials and nano Fe3O4, the absorbing performance of nano composites and the corresponding mechanism of preparation are also studied.(1) Preparation of the mesoporous materials:This article adoption triblock copolymer (abbreviate P123) composite beer yeast as a templating agent,Hydrothermal method obtained average pore size of 12nm、Specific surface area 327.366m2/g; The dielectric loss tangent value is 0.098, and the hysteresis loss tangent value of 0.23 (Absorbing performance parameters)of the mesoporous material.The synthetic samples were characterized by The specific surface area and pore size determination (N2 adsorption/desorption instrument), scanning electron microscope (SEM), X-ray diffraction (XRD), thermogravimetric (TG) and infrared spectroscopy (IR). During the preparation of the mesoporous materials, six factors which have an influence on the specific surface area, pore volume, average pore size and morphology of the mesoporous materials are discussed systematically in the paper. They are types of template, concentration of template, crystallization temperature, crystallization time and the adding amount of swelling agent.The results show that water glass is adopted as silicon source, sodium aluminate as aluminum source, P123 composite beer yeast as a templating agent and the concentration of beer yeast is 2.4g/L.Put them into stainless steel reactor with strong acidic system and crystallize, the crystallization temperature is 110℃, crystallization time is 72h, then mesoporous materials of which average pore diameter is 12nm and of which specific surface area is 327.366m2/g can be prepared, and the average pore diameter of preparative samples can reach to 29nm by adding a swelling agent in the template solution-mesitylene.In this paper the preparation mechanism of mesoporous zeolite was studied, by theories of the effect among silicon source, aluminum source and templating agent, the self-assembly of mesoporous zeolite, the growth of mesoporous zeolite during crystallization process and the calcination for removing the template.(2) Preparation of nano Fe3O4:By co-precipitation prepared classes spherical、about 10nm; The dielectric loss tangent value of 0.085, hysteresis loss tangent value of 0.22 (absorbing performance parameters) Fe3O4 nanoparticles. The particle size, morphology and absorbing properties of the nano particles also have been characterized by the method of X-ray diffractometer (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and complex permeability. Factors such as molysite species, molysite concentration, precipitating agent species, precipitating agent concentration, reaction time, crystallization time, reaction temperature, crystallization temperature and crystal shape controlling agent types are taken into account, effects of the particle size, morphology and absorbing properties of the nano particles are discussed.The study results show that ferrous sulphate is adopted as iron source, sodium hydroxide as precipitation agent, oxalic acid as polymorph control agent, molysite concentration is 0.4 mol/L, precipitating agent concentration is 0.8 mol/L, reaction temperature is 50℃, crystallization temperature is 60℃, reaction time is 20 min, crystallization time is 20 min. finally, about 10nm spherical nanometer triiron tetraoxide is obtained, which the absorbing propertie is better.This article calculated by the reaction kinetics,Nano ferroferric oxide generation process, the Gibbs free energy-3059.86J.mol-1,Study the formation mechanism of nano ferroferric oxide generated; By crystal growth kinetic theory and molecular orbital theory to study the formation mechanism of iron oxide nano morphology.(3) Mesoporous materials encapsulates the nano Fe3O4:This article was first realized skeleton mesoporous materials dispersed nano-Fe3O4,To solve the agglomeration in the nano Fe3O4 utilization process. In this paper, the chemical co-precipitation method and suspension polymerization are adopted to complete the preparation of the nano magnetite composites encapsulated by mesoporous material. The particle size, morphology and absorbing properties of the composite are characterized with the method of N2 adsorption/desorption, X-ray diffractometer (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and the data of complex permeability.The results showed that:Chemical coprecipitation nano four iron oxide encapsulated into mesoporous material within get the specific surface area of the composite material 181.155m2 /g, and the specific surface area of the raw materials of mesoporous materials 327.366 m2/g, Specific surface area reduced 146.211 m2/g, The average pore size is reduced by 12.18nm to 1.72nm, reduced 10.46nm; Suspension polymerization use nano iron oxide encapsulated into mesoporous materials to get The specific surface area of the composite material 104.048m2/g, and the raw mesoporous materials specific surface area of 327.366 m2/g, Specific surface area reduced 223.318 m2/g, The average pore size is reduced by 12.18nm to 1.54nm, reduced 10.64nm. The suspension polymerization encapsulated is better than the chemical coprecipitation method.The use of chemical co-precipitation、ion effect theory to study the mechanism of the preparation of nanocomposites.(4) Composite absorbing performance study:By microwave absorbing properties analysis of the composite material that synthesis of Mesoporous materials, nano iron oxide and mesoporous materials encapsulated nano iron oxide,Encapsulated obtained composite material hysteresis loss tangent value of 0.24, Higher than the before encapsulation nano Fe3O4 hysteresis loss tangent of 0.22 and mesoporous materials hysteresis loss tangent of 0.23, the encapsulated after microwave absorbing properties of composite materials has been strengthened.Using chemical co-precipitation, ion effect related theories for the study of Nanocomposite preparation mechanism.Using surface effect、microstructure caused loss the theory of resonance loss and coated structures to the research of mesoporous zeolite Nano ferroferric oxide and composite absorbing mechanism,Proposed for the first time"Microstructure caused the resonance loss" is the key to the composite absorbing, Calculated Fe3O4 intrinsic vibration frequency:... |
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