Application Of Hydrothermal/Solvothermal Combinatorial Technique To The Synthesis Of Inorganic Microporous Compounds

In the last few decades, extensive research has been focused on the exploration of new microporous materials because of their wide applications in the field of catalysis, environment and functional material. However, the formation of these materials, which is normally facilitated by organic templates, is not yet well understood due to the complexity of hydrothermal or solvothermal reactions. The reaction systems for these kinetic crystalline compounds are very complex and their crystallization processes are manipulated by various factors, such as gel composition, organic template, pH value, temperature and crystallization time. So far the preparations of microporous materials are still through traditional trial and error method, this means, in a sense, the synthesis is blindness. Compared to the traditional synthesis methods for materials, the combinatorial approach has been proven as a fast experimentation method for the discovery of new materials. In addition, the systematic investigation of large parts of the respective parameter space in made possible and thus reaction trends are easily established. The advantages of the application of the combinatorial methodology can be summarized as follows: The combinatorial method allows the fast and systematic investigation of a large number of reactions since automatic dispensing, mixing of reagents, as well as automatic separation and identification of the products are possible; The use of minimal amounts of starting materials leads to a cost and waste reduction and makes systematical investigations using expensive or hard to be synthesized starting materials feasible; The use of parallel reactors guarantees that all samples are treated identically, e.g., the same solutions are used, reacted at the same temperature and for the identical time. Thus it is possible to find optimum reaction conditions and evaluate reaction trends in parameter space. 1) Synthesis new phases Applying combinatorial approach, in the Zn(OAc)2·2H2O-H3PO4-N, N'-dimethylpiperazine-H2O/EG system, four open-framework zinc phosphates and an amine phosphate cluster have been obtained. A ([C6H16N2]0.5·[C5H14N2]·[Zn6(PO4)5(H2O)]·3H2O), with a novel three-dimensional open-framework architecture containing intersecting 16-, 10-and 8-membered ring channels. Diprotonated N, N'-dimethylpiperazine and N-methylpiperazine molecules reside in the pores, balance the framework charge. N-methylpiperazine molecules are believed to be decomposed from the N, N'-dimethylpiperazine molecules in the reaction mixture under hydrothermal conditions. Compound A transforms to another new phase (compound A-200) upon calcination at 200-350°C with the removal of the coordinated water to Zn atoms in the lattice. The structure of A-200, as well as the phase transformation, has been further studied. C ([C4H14N2]·[Zn5(PO4)4(H2O)]), is built up by ZnO4, ZnO3(H2O), PO4 and PO3(=O) units via vertex oxygen atoms forming an open-framework with 10-membered ring channels along the [010] direction. Diprotonated N, N'-dimethylethylenediamine molecules balance the framework charge, which is believed to be decomposed from the N, N'-dimethylpiperazine molecules under hydrothermal conditions. D ([C6H16N2]·[Zn2(HPO4)3]), is built up by ZnO4, PO3(OH) and PO2(OH)(=O) tetrahedral units via Zn-O-P linkages forming an open-framework with intersecting 8-membered ring channels along the [100], [010], and [101] direction, respectively. The charge balance is achieved by diprotonated N, N'-dimethylpiperazine. By a solvothermal combinatorial approach,a new 2D layered compound[C2H8N]2·[Al2(HPO4)(PO4)2] (named AlPO-DMF) are obtained. It exhibits distinctive H-bonded chains formed by the organic templates and the inorganic network, which is believed to be responsible for the intriguing packing mode of the inorganic-organic assembly. It has an intriguing ABCD sheet stacking sequence along the c axis. Its structure has been predicted before by us. The combinatorial method provides a rapid approach for the discovery of new materials with designed structures and properties. 2) Study the synthesis rulers Applying combinatorial approach, various synthetic factors are studied, such as the gel compositions, crystallization temperature, and solvent on the influence of the crystallization of zinc phosphates in the Zn(OAc)2·2H2O-H3PO4-N, N'-dimethylpiperazine-H2O/or EG system. Four open-framework zinc phosphates including phase A ([C6H16N2]0.5·[C5H14N2]·[Zn6(PO4)5(H2O)]·3H2O), B (Zn3(PO4)2(H2O)), and C ([C4H14N2]·[Zn5(PO4)4(H2O)]), D ([C6H16N2]·[Zn2(HPO4)3]), and an amine phosphate cluster E ([C6H16N2]·[H2PO4]0.5), are obtained in above system in the presence of N, N'-dimethylpiperazine as the structure-directing agent. Analysis of the structures of these phases will give some insight into the influence of various synthetic factors on the nature of resulting crystalline products. It is noted that the organic template agent added in the initial reaction system for all above compounds is N, N'-dimethylpiperazine, however, it is partially decomposed to N-methylpiperazine in A crystallized at 180?C in H2O system, and to N, N'-dimethylethylenediamine in C crystallized at 200?C in H2O system, but kept intact in D crystallized at 180?C in EG system and in E crystallized at 140 ?C in EG system. It appears that N, N'-dimethylpiperazine is easily decomposed in H2O system at 180-200?C, but kept intact in EG system at 140-180?C. Above results reflect that the crystallization products are greatly dependent on the organic amine species that are affected by the crystallization temperature, as well as the type of solvent under solvothermal conditions. 3) Towards Rational Synthesis of Microporous Aluminophosphate AlPO4-21 byHydrothermal Combinatorial Approach The templating abilities of organic amines for the synthesis of AlPO4-21 can be reasonably evaluated in terms of the nonbonding interaction energies of host-guest. The study shows that the organic amines having lower interaction energies with framework, such as ethanolamine and trimethylamine, are suitable templates that can successfully direct the formation of aluminophosphate AlPO4-21. The larger organic amines like N, N, N', N'-tetramethylethylenediamine and N, N, N', N'-tetramethyl-1,3-propanediamine tend to decompose to small and suitable amines to direct the formation of AlPO4-21. Furthermore, the organic amines with higher interaction energies with the framework are indeed not favorable for the formation of AlPO4-21. Once the organic templates are selected, the combinatorial approach is found to be an efficient method for rapid search of the crystallization conditions to the synthesis of target products. This work further demonstrates that the application of computational simulation approaches and combinatorial approach will be helpful for the rational synthesis of materials with special structures or properties. 4) Study of low-dimensional aluminophosphates as precursors Three-dimensional (3D) zeolite type structure GIS has been successful prepared both from 1D chain aluminophosphate AlPO-ESC and 2D layered aluminophosphate AlPO-DMF as precursors through metal cations M2+ (M=Mn, Co, Mg). This work provides a new approach to the synthesis of higher open-framworks through the low-dmensional structures via metal cations. Employing triethylenetramine (TETA) as the structure-directing agent, a layered aluminophosphate [C6N4H21][Al3P4O16] (named TETA-1) has been solventhermally prepared. The alternation of tetrahedral AlO4 and PO3(=O) units forms an anionic 2-D layered aluminophosphate. It contains 4, 6-net sheets. Applying combinatorial approach, various synthetic factors are investigated. When adding some transitional metal cations to the reaction system, the TETA become 4-(2-aminoethyl)diethyenetriamine (TREN), then 3-D open-framework alnminophosphate [[C24N16H91][Al9-xMx(PO4)12]?nH2O (named TETA2) (M=Zn2+,...