Effect Of Inorganic Anions On The Synthesis Of Inorganic Porous Materials

Inorganic porous materials refer to inorganic nonmetallic materials with micropore,mesoporous or macropore.The typical representatives are zeolites and ordered mesoporous materials.Zeolites have been widely used in energy sources,chemical industry,environmental protection and biomedicine due to their regular channel structure,adjustable acidity and high thermal and chemical stability.How to accurately regulate the synthesis of porous materials has attracted widely attention.Studies have shown that adding inorganic ions(cations and anions)into the synthesis systems of zeolites and mesoporous materials is an effective method to adjust the crystallization process and the properties of the products.However,the mechanisms of ionic influence on the formation of zeolites and mesoporous materials are still not clear due to the complex synthesis system and strict reaction conditions of high temperature and high pressure for in-situ monitoring.Thus,it is necessary to understand the mechanism of the inorganic ionic effects on the synthesis of porous materials in order to modulate the synthesis of porous materials via inorganic ions.In this thesis,we take silicalite-1,aluminosilicate zeolites(including MOR,Na Y and ZSM-5)and mesoporous silica materials as research systems,and systematically study the effect of inorganic anions on the synthesis of these inorganic porous materials.The detailed results are summarized below:1.Na₂SO₄,Na F,Na Cl,Na Br,Na I or Na SCN was separately introduced to the initial reaction mixture of silicalite-1(MFI)and the effect of anions on the synthesis of silicalite-1 was investigated.The result showed that the crystallization of silicalite-1 was remarkably sped up by the salt in the sequence of Na₂SO₄>Na F>Na Cl>Na Br>Na I>Na SCN.The sequence is exactly the same as that of Hofmeister series.The liquid ¹H NMR and the radial distribution function(RDF)analyses revealed that the anions were located around the template cation TPA⁺with a distance to the N atom of TPA⁺in the sequence of SO₄^2->F^->Cl^->Br^->I^->SCN^-.Combining the analyses on ¹H NMR and the charge density of anions,it was discovered that the anions affected the release of the water molecules by activating the hydration spheres around TPA⁺cation at a different degree,thus regulating the zeolite crystallization.This work provides a new insight into the zeolite crystallization via introducing anion additives.2.Different amounts of Na I were introduced to the the initial mixture of MOR zeolites(Si O₂-Al₂O₃-Na₂O-H₂O-seed)and the effect of Na I on the SAR of MOR zeolites was investigated.The results indicated that the addition of Na I increased SARs of MOR zeolites.When Na I/Al₂O₃=4.8,the largest increase was obtained in the SAR of MOR zeolite(6.55%).The effect of Na I on the SAR of Na Y(FAU)and ZSM-5(MFI)was also investigated and the result showed introduction of Na I could also increase the SARs of Na Y(FAU)and ZSM-5(MFI).Density functional theory(DFT)calculations suggested that Na I can significantly decrease the free energy barriers for the formation of Si-O-Si bonds but increase the free energy barriers for the formation of Si-O-Al bonds,thus leading to an increase of the SAR of zeolites.This work provided a new method to regulate the SAR of zeolites.3.Different anions was introduced to the initial mixture of mesoporous silica(Si O₂-CTEABr-H⁺-H₂O,CTEABr:cetyltriethylammonium bromide)by using various acids(H₂SO₄,HCl,HBr and HNO₃)and the effect of anions on the synthesis of the formation of mesoporous silica was investigated.The results showed that different acids could lead to different mesoporous silica that corresponded to different packing parameter(g).The values of g of these mesoporous materials followed the order of g(3D hexagonal P6₃/mmc)<g(cubic Pm3?n)<g(2D-hexagonal p6mm).The results indicated that SO₄^2-was favorable for the formation of 3D hexagonal P6₃/mmc with low g value,Cl^-was favorable for the formation of cubic Pm3?n,while Br^-and NO₃^- was favorable for the formation of 2D-hexagonal p6mm with high g value.It could be seen that the effect of anions on g value of mesoporous materials conformed with Hofmeister series(SO₄^2-,Cl^-,Br^-,NO₃^-).The effect of anions on mesoporous materials was investigated by liquid ¹H NMR.It was found that the anions were located in different spatial regions of CTEA⁺.SO₄^2-was near the hydrophilic head group of CTEA⁺,while Cl^-,Br^-and NO₃^-could penetrate into the hydrophilic head group of CTEA⁺and enter the vicinity of the hydrophobic chain of CTEA⁺,thus affecting the g of micelles and leading to different mesoporous materials.This work provided an in-depth understanding on the role of anions in the formation of mesoporous materials.