Syntheses And Properties Of Aluminophosphate-Based Molecular Sieves

Aluminophosphate molecular sieves, designated AlPO₄-n, have constructed an importantfamily of zeolitic materials since their first discover by Wilson et al. in1982. Theincorporation of heteroatoms with different valences in the framework of AlPO₄-n willgenerate Br nsted or Lewis acid sites, making MAPO （M=metal heteroatoms） molecularsieves useful in a rich range of catalytic processes. On the other hand, MAPO molecularsieves also find other applications in photoluminescence, magnetism, and so forth.Therefore, the synthesis of heteroatom-containing aluminophosphate molecular sieves withspecial structures and properties has aroused considerable interest.In this thesis, several novel heteroatom-containing aluminophosphate molecular sievesand aluminophosphate molecular sieves have been hydrothermally synthesized. Thestructures and properties of as-synthesized compounds have been studied. The main resultsare as follows:1. Three new iron aluminum phosphates|(C₂H₁₀N₂)₄|[Fe8-xAlxFx（H₂O）_2-x（PO₄）₈]·2H₂O,（=1.64,1.33,0.80） with ACO-zeotypestructures, denoted as FeAPO-CJ66（a）, FeAPO-CJ66（b） and FeAPO-CJ66（c）, respectively,have been synthesized by introducing fluorine ions in the synthetic system together withethylenediamine decomposed from diethylenetriamine （DETA） as co-templates. Theirframework structures are made of double four-ring （D4R） building units, which possessthree-dimensional intersecting8-ring channels running along the [001],[010], and [100]directions. Fluoride ions or water molecules reside in the center of D4Rs, and diprotonatedethylenediamine cations and water molecules are occluded in the free space of channels to stabilize the whole structures. Notably, the Al/Fe ratios in the frameworks can beeffectively controlled from1/3.9to1/5.0to1/9.0by adjusting the amounts of phosphoricacid and hydrofluoric acid added in the initial reaction mixture. M ssbauer and magneticmeasurements show that the Fe ions in the compounds are bivalent and undergo antiferromagnetic ordering at room temperature.2. By using two different organic amines, n-methylpiperidine and1,2-diaminocyclohexane （DACH）, as the structure-directing agents （SDAs）, twomagnesium aluminophosphate molecular sieves|(C₆H₁₄N)₂|[Mg₂Al₇（PO₄）₉] and|(C₆H₁₄N₂)_1.4（H₂O）₂H₂|[Mg₂Al₅（PO₄）₇], denoted as MgAPO-CJ67（a） and MgAPO-CJ67（b）,have been synthesized under hydrothermal conditions. They are the first example of Mgincorporated aluminophosphates with the LEV-zeotype structure. The magnesium andaluminum atoms co-occupy the same crystallographic positions in the frameworks ofMgAPO-CJ67（a） and MgAPO-CJ67（b）, but with different Mg/Al ratio of1/3.5and1/2.5,respectively. MgAPO-CJ67（a） exhibits higher thermal stability than MgAPO-CJ67（b）, andcan be stable up to650°C. After the removal of organic SDAs by calcination,MgAPO-CJ67（a） has BET surface area of386m2g–1and a medium acidity, which mightbe a potential single-site solid acid catalyst.3. A new magnesium aluminophosphateJU92(|C₅N₂H₁₄|[Mg₂Al₆（PO₄）₈（H₂O）₃])hasbeen hydrothermally prepared by using n-methylpiperazine （NMP） as thestructure-directing agent. Single-crystal structure analysis reveals that its anionicframework [Mg₂Al₆（PO₄）₂₈（H₂O）₃]^2–is constructed by alternating connection ofmetal-centered polyhedra （i.e. AlO₄, MgO₄（H₂O）/MgO₄（H₂O）2） and PO₄tetrahedra. Afterdehydration at300oC, JU92transforms to a new compound JU-300(|C₅N₂H₁₄|[Mg₂Al₆（PO₄）₈]) whose inorganic framework is built up strictly from TO₄tetrahedra （T=Al, Mg, P） and exhibits a new zeotype topology with two-dimensionalintersecting8-ring channels and a unique [6⁸.8⁴] cage. The pore sizes of8-ring openingsare5.9×1.9and6.5×1.6（O···O distances）. Mg atoms unambiguously occupy thedistinct site in the framework, and distribute along the wall of8-ring channels. Intact NMPmolecules reside in the channels of JU92and JU92-300. JU92-300exhibits a high thermalstability, and can be stable up to650°C. 4. NMP@zeolite materials with special fluorescent properties have been prepared bycalcined the as-synthesized JU92under different temperature （from300°C to450°C）.Interestingly, graphitic-like carbon dots （C-dots） are generated in the channels of JU92-300through the decomposition of organic structure-directing agent （SDA） upon heating above450°C. Such C-dots@zeolite composite material exhibits photoluminescence properties.The emission color can be finely adjusted from yellow to blue through different thermaltreatments. Furthermore, it is found that the photoluminescent brightness can be enhancedby extending the calcination time, which is reflected in the high emission quantum yields.The C-dots can be isolated from the host lattice by treated with NaOH and concentratedhydrochloric acid, and then dispersed in water. Such C-dots without surface passivationexhibit excitation-dependent photoluminecent behavior in water, as well as tunablefluorescent properties with high quantum yields in solid zeolite materials. This works notonly provides a feasible approach to prepare the luminescent C-dots confined in the voidspace of zeolite structure, but also presents an excellent solid fluorescent compositematerial.5. An aluminophosphate molecular sieve, JU93（Na[Al（PO₄）OH]·2（H₂O））, has beenhydrothermally synthesized for the first time, by using NaOH as mineralizing agent withthe absence of organic amine. The framework with two-dimensional intersecting8-ringchannels contains part of the five-coordinated aluminum. And the framework may betransformed into AEN-zeotype after removed the O atoms connected between two Alatoms through heating treatment. The reported AEN aluminophosphate molecular sieves hadbeen synthesized by using methylamine or dimethylamine as templates. This workexplores a novel method to synthesize aluminophosphate molecular sieves without organictemlates, which greatly reduces the synthetic cost.