Preparation And Properties Of Magnetic Molecular Sieve Composite Fe₃O₄@SAPO-5

The core-shell magnetic nanocomposite is a new type of material composed of two or more functional materials,and has a wide range of applications in many fields.Nano-Fe₃O₄ has the characteristics of simple preparation,low cost,low toxicity and excellent magnetic properties,and is often used as the core of core-shell composite materials.The nano-Fe₃O₄ has superparamagnetism,and the coated magnetic nanocomposite material still has superparamagnetism.If a strong magnetic field is applied,it can be quickly separated from the liquid,therefore,nano-Fe₃O₄ and its composite materials are widely used in many fields.SAPO-5 molecular sieves are often used in isomerization of alkanes and catalytic cracking of n-hexane because of their large 12-membered ring pores.Therefore,in this dissertation,Fe₃O₄nanoparticles were used as the core and coated with SAPO-5 molecular sieves to form Fe₃O₄@SAPO-5 core-shell magnetic nanocomposites.It can integrate separation and recovery with the catalytic performance of SAPO-5 molecular sieves.The main work is as follows:In this paper,triethylamine as a template agent,silica sol as a silicon source,phosphoric acid as a phosphorus source,pseudo-boehmite as aluminum source,the use of an improved hydrothermal synthesis method successfully prepared SAPO-5molecular sieve.The size of synthesized molecular sieves is between 2μm-20μm,the specific surface area is distributed at 148.99-266.74m²/g;the pore volume is distributed at 0.19-0.49cm³/g;the pore size of micropores is distributed at0.56-0.70nm.Using XRD,SEM,N₂ adsorption desorption analysis and other characterization methods,the effect of template dosage,crystallization temperature,and crystallization time on the synthesis,morphology,and pore structure of SAPO-5zeolite was studied.When the molar ratio of the template to the aluminum source is0.95,the crystallization time is 12h,and the crystallization temperature is lower than200°C,SAPO-34 heterocrystals are formed.With the increase of the crystallization temperature,there is no longer the generation of the miscellaneous crystals,and the SAPO-5 molecular sieve with pure phase is synthesized.Therefore,200°C.is the suitable crystallization temperature for the synthesis of the SAPO-5 molecular sieve.When the amount of templating agent and the crystallization temperature are the same,the particle size increases with the extension of the crystallization time and gradually changes from hexagonal to spherical.At the same temperature（180°C,190°C,200°C）,as the amount of templating agent increases,the shorter the crystallization time,the larger the specific surface area.2.When the molar ratio of template to aluminum source is 0.95,crystallization temperature,time is 200^oC,and time is 24h,Core-shell structure of Fe₃O₄@SAPO-5composites is synthesized using Fe₃O₄ particles of two different sizes（20nm and100-300nm）.The effect of different addition amount of Fe₃O₄ on the structure,morphology,magnetic properties and adsorption performance of Fe₃O₄ was studied.XRD and IR spectra showed that the effect of Fe₃O₄ on the structure of SAPO-5zeolite was small,and SAPO-5 molecular sieve with pure phase could be synthesized,and no impurity peak was generated.From the N₂ adsorption test,Fe₃O₄ has a greater influence on the specific surface area,microporous surface area and pore volume of SAPO-5 zeolite.The specific surface area of the synthesized SAPO-5 molecular sieve was 207.43m²/g when the molar ratio of template to aluminum source was 0.95,and the crystallization temperature and time were 200^oC and 24h.After coating Fe₃O₄,the specific surface area of the composite was significantly reduced（Below 104.49 m²/g）.It may be that Fe₃O₄ causes damage to the pore structure of the SAPO-5 molecular sieve,resulting in a lower specific surface area.From the hysteresis loop,it can be seen that the Fe₃O₄@SAPO-5 composite has a certain magnetic properties,and as the amount of Fe₃O₄ added increases,the saturation magnetization increases.