Syntheses And Properties Of SAPO-56 Zeolite

Carbon dioxide is a class of by-product of fossil fuel combustion which has caused great harm to the environment.Carbon capture and storage（CCS）technology is the second major measure to reduce the greenhouse effect after using new energy,which is regarded as one of the most important methods to solve environmental problems.Compared with traditional adsorption technology,physical adsorption and separation technology has the advantages of low energy consumption and simple operation.Molecular sieves are representative norganic porous solid adsorbent materials and the most intensively and widely studied gas adsorption and separation material.Molecular sieves have the characteristic of inherent molecular sieving effect,rich and adjustable pore structure,large specific surface area,excellent physical/chemical stability,controllable polarity,internal electromagnetic field gradient,adjustable and functionable channels,cheap and preparability.Separation mechanisms of molecular sieves for small molecular gases mainly include size screening effect,kinetic screening effect,thermodynamic screening effect,trapdoor effect or cation gating effect,breathing effect.The gas adsorption behavior of molecular sieves is affected by topology,pore structure,elemental composition,and guest ions.This thesis focuses on SAPO-56（AFX topology）which has a similar pore width with small gas molecular.By optimizing synthesis conditions and adjusting the ratio of silicon and aluminum to improve its CO₂adsorption and separation ability.And by introducing different inorganic cations such as alkali metal ions or rare earth ions into the molecular sieve to regulate and functionalize the molecular sieves channels.The influencing factors of guest ions on the gas adsorption and separation capacity of SAPO-56 molecular sieve were also studied.As a class of inorganic materials widely used,molecular sieves maintain stability after high temperature calcination.Using molecular sieves prepared carbon dots-based composites,its fluorescence and room temperature phosphorescence properties was investigated.The main results are as follows:1.By using N,N,N’,N’-tetramethyl-1,6-hexanediamine as an organic structure directing agent and adopting hydrothermal synthesis strategy,a series of SAPO-56molecular sieves with different silicon contents were prepared.The influence of silicon content on the acidity of SAPO-56 and the CO₂adsorption capacity was investigated.The study showed that the samples with the highest silicon content had the strongest acidity and the highest CO₂uptake.At 273 K and 101 k Pa,the CO₂adsorption capacity could reach 4.7 mmol/g.The IAST（ideal adsorbed solution theory）was used for calculated the selectivity of SAPO-56 for the separation of CO₂/N₂and CO₂/CH₄（separation ratio reached 173,64）.The sample showed excellent adsorption and separation performance.SAPO-56 was also prepared by using trimethylamine and triethylamine as organic structure directing agent.The effects of different OSDA on the adsorption performance of CO₂were investigated.The research showed that the samples with Si（4Al）distribution had higher CO₂adsorption capacity on the premise of same amount of silicon,which was increased by17.75%.This is due to the specific distribution of silicon atoms determined by the host guest interaction between the template molecule and the SAPO framework,which further affects the performance differences of SAPO-56 molecular sieves.2.The adsorption and separation performance of SAPO-56 molecular sieves was improved by using metal modification strategy.The key factors of gas adsorption and separation performance were explored,such as the means of metal ion modification,ion type.Results show that the means of metal ion modification affects the crystallinity of molecular sieve and ion type affect adsorption performance.The study showed that Na-SAPO-56 had highest CO₂and C₂H₄adsorption enthalpy at 298 K（4.0 mmol/g and 2.9 mmol/g）among all the molecular sieves which were modified with different alkali metals（Li⁺、Na⁺、K⁺、Cs⁺）.The calculation results using IAST（ideal adsorbed solution theory）showed that Na-SAPO-56 had potential C₂H₄/C₂H₆separation performance（separation ratio reached 5.6）.Sm-SAPO-56 which was modified with rare earth metals showed the highest CO₂uptake（4.3 mmol/g）at 298 K,which was 23%higher than that of H-SAPO-56.3.The CDs@M-SAPO-56（M=Li⁺,Na⁺,K⁺,Cs⁺）composites were prepared by calcination strategy.The effects of calcination temperature and metal ion types on the fluorescence and room temperature phosphorescence performance of the CDs-based composites material were studied.The two-step calcination strategy（high and low temperature）improved the luminescence properties.The SAPO-56 composites modified by Cs cation had the best fluorescence and room temperature phosphorescence properties,and the life time was up to 980 ms and 1.047 s,respectively.The quantum yield reached 18.51%.