Study On Synthesis Of Microporous Aluminophosphates In Concentrated Fluorine System

Porous materials constitute an important class of materials in the field of materials science. Their unique pore architectures have made them popular in a wide range of applications in catalysis, adsorption, separation and host-guest assemblies. Aluminophosphates constitute an important class of materials in the field of zeolites. The diverse arrangement of AlO4, AlO5and AlO6polyhedral units and P(Ob)n(Ot)4-n polyhedral units (b: bridging, t: terminal, n = 1, 2, 3, 4) results in their fascinating structural architectures with 0-D clusters, 1-D chains, 2-D layers, and 3-D open-frameworks and diverse stoichiometries with different Al/P ratios. In the last decades, our research group has synthesized a variety of aluminophosphates with diverse dimensions and stoichiometries by using hydrothermal or solvethermal technique, which extremely enriches the structure database and synthesis database of aluminophosphates, and supply theoretical foundation for the rational design and synthesis of aluminophosphates with special structures. However, we still need to synthesize more aluminophosphates with novel structures in order to study the relationship between synthesis conditions and resulting structure.Flanigen E. M.'s group introducted fluorine into the system, they used F^- ions instead of OH-ions to synthesize the zeolites under hydrothermal condition. After that, Guth J. L. and Kesser H performanced the systmetic research in this field. F^- ions are frequently employed in the reaction mixture to promote the formation of large single crystals or novel structures. Three roles for F- ions in the synthesis of microporous solids have been described by Guth et al., such as (a) mineralizing, (b) charge balancing, and (c) structure directing. The method of fluoride in concentrated reaction mixtures has been discovered in the end of 90's by M.A.Camblor. Many high silica and pure silica zeolites had been synthesised in this system. But the method has not been attempted in the synthesis of aluminophosphates.In the thesis, we study the influence of the concentration of reactants on the final structure in the synthesis of aluminophosphates by using hydrothermal techniques, and synthesize some aluminophosphates by using two methods in concentrated fluorine system, and discuss the difference of these two metheds.(1) In the Al(OPri)3-H3PO4-HF-organic amine-water system, we have synthesized an unknown phase by using the template of di-n-propylamine. It is a low-dimensional compound, but now it's crystal structure is not obtained; we have synthesized the known compound of fluoride AlPO4-34 by using the template of tri-n-propylamine, while protonated trimethylamine decomposed from tri-n- propylamin is located in the structure of AlPO₄-34.(2) By using different kinds of template, we studied the phase transition of product synthesized in difference concentration. We found that in fluorine system some metastable structures will occur when the concentration of reaction become higher.(3) Through a method similar to boric acid"flux"method (don't stir and direct put the reaction mixtures into Teflon-lined stainless steel autoclave), we synthesized a known 1-D aluminophosphates chain by using 1,2-PDA as the template. This chain can also be obtained in hydrothermal system; we synthesized a now 1-D fluoride aluminophosphates chain by using DETA as the template, which is the second aluminophosphates chain with Al/P ratio of 1, and its structure is the simplest. This structure has a rare AlO2F2 tetrahedron formed by two bridging O atoms and two terminal F atoms. (4) We found a similar result by changing the kinds of templates: some products don't occur in the hydrothermal system can be obtained through this method. The study of XRD patterns of these compounds show that they are maybe low-dimensional or large-pore compounds. Regretfully, these unknown phases are powder now, so their structures can not be decided.This method is similar to the solvothermal method by using the organic amine as the sovlent, but also has some differences: firstly, all kinds of organic amines can be used in this system while only some organic amines are suitable to be as the solvent; secondly, only little amount of amine is used in this system, avoiding the waste of a large number of amine; finaly, using the organic amine as the solvent, Al(OPri)3 already be hydrolyzed in the course of stiring, the appearance of nucleus and growth of crystal will not proceed in the meanwhile.Based on our experiments, we found that the method could let the reaction occurs in a concentrated fluorine system. In such system, organic amine template play the di-roles of sovlent and template, a small amount of water imported by H3PO4 and HF can hydrolyze Al(OPri)3 and transfer the protons, the fluorine ion may play the role of mineralizing and bond with Al atoms in the inorganic framework. Some compounds which are not prepared in the hydrothermal system can be prepared in such , and they maybe the precursors of some open-framework structure. This kind of method is simple and convenient, and reacted completely, which maybe suitable in the synthesis of aluminophosphates substituted by metal and other microporous compounds (such as GaPO4, InPO4, et al).