Investigation Of The Factors Affecting The Strucutre-directing Effect Of Piperazine,2-methylpiperazine And1,3-d Ipropanea Mine

Zeolites and related materials with open-framework have been widely used incatalysis, ion-exchange, adsorption, chemical separation, and host/guest chemistry.Even though numerous zeolitic structures have been successfully synthesized viaempirical findings or the exploration of synthesis parameters by trial and error, it is ofsignificance to rationally design and synthesize more zeolitic structures with desiredarchitectures and properties, which requires a clear understanding of their formationmechanism and crystallization process. So far, different mechanisms related to thespecific synthesis systems have been discussed regarding nucleation and crystalgrowth. However, the understanding on the formation mechanism of zeolitic is stillvery limited due to the intrinsic complexity of the synthesis system and imaging theinitial stage of zeolite formation has not previously been possible.In the synthesis of zeolites and related materials with open-framework, thestructure-directing agent is the most important factor. Without the structure-directingagent, the corresponding zeolites or materials with open-framework cannot beobtained. The role played by these extra introduced chemicals in the formation ofzeolites or open-frameworks is denoted as the template effect or thestructure-directing effect. It has been demonstrated that the structure-directing effectcan be affected by many factors. However, how these factors affect or determine thestructure-directing effect remains unclear. The nature of the template effect or thestructure-directing effect is not yet clearly understood.In this thesis, we investigated the factors affecting the structure-directing effectof piperazine,2-methylpiperazine, and1,3-dipropaneamine. 1. By heating the same initial mixture with the molar ratio of Al2O3: P2O5:1.52-methylpiperazine:125H2O at150and200oC respectively, two layeredaluminophosphates were obtained (APMeP150in150C and APMeP200in200C).The crystallization processes of these layered aluminophosphates were investigatedby using multiple techniques. The change in the pH values of the solutions, theconcentrations of Al and P in the liquid phases, and the evolution of the coordinationstates of Al and P in the solid products were monitored. The―reverse temporalevolution‖analyses of each structure showed that the core units or the possible onsets(nuclei) of crystallization of each structure were significantly different from eachother. The results showed that the heating temperature altered the structure-directingeffect of2-methylpiperazine and the crystallization process of the initial mixture viachanging the structure and chemical properties of the structure-directing agent of2-methylpiperazine, the equilibrium of the reactions occurredamong the sourcematerials, so that the self-assembling of the inorganic oligomers had changed.2. By heating the initial mixture with the composition of Al2O3:1.5P2O5: R:125H2O at160oC，where R is the structure-directing agent of2-methylpiperazine orpiperazine, layered aluminophosphates APMeP150(R=2-methylpiperazine) andAP2pip (R=piperazine) were obtained. When the same initial reaction mixture washeated at190oC, layered aluminophosphates APMeP200(R=2-methylpiperazine)and AP2pip (R=piperazine) were crystallized. APMeP200and AP2pip have thesame inorganic sheet topology. We investigated the crystallization processes of thefour open-framework aluminophosphates and the evolution of the pH and theconcentrations of Al and P in the liquid phases as well as the evolution of thecoordination states of Al and P in the solid products. The non-bonding interactionsbetween the experimental and theoretically generated structure-directing agents andthe inorganic layers of the four open-framework aluminophosphates were calculated.The possible starting points of the crystallization of the four open-frameworkaluminophosphates were analyzed and compared to each other. Thetemperature-dependence of the influence of the position-2-methyl group on the structure-directing effect of piperazine revealed that the structure-directing effect, themost important factor in the synthesis of zeolites and related open-frameworkmaterials, is determined by many factors.3. The molar rario of the initial mixture investigated is Al2O3:2.8P2O5:4.2/7.4R:125H2O (R=N-methylpiperazine or piperazine). Heating the initial mixture with themolar composition of Al2O3:2.8P2O5:4.2R:125H2O at180C, N-methylpiperazine and piperazine directed the layered aluminophosphate AlPO-CJ9andthree-dimensional open-framework aluminophosphate AlPO-CJ11/AlPO-CJB2,respectively, suggesting that the position-1-methyl group affected thestructure-directing effect of piperazine under present condition. Heating the initialmixture with the molar composition of Al2O3:2.8P2O5:7.4R:125H2O at180C,N-methyl piperazine and piperazine directed the three-dimensional open-frameworkaluminophosphate AlPO-JU88and AlPO-CJ11/AlPO-CJB2, respectively, indicatingthat the position-1-methyl group also affected the structure-directing effect ofpiperazine under present condition. The data show that the structure-directing effectof piperazine depends on the molar composition of the initial mixture, while suchdependence is eliminated by the position-1-methyl group.4. Upon heating the same initial mixture with the molar ratio of Al2O3:2.0P2O5:2.81,3-diaminopropane/DAP:125H2O at150and200oC, two open-frameworkaluminophosphates were obtained (UiO-18at150C and UiO-26at200C). Thecrystallization processes of these aluminophosphates were investigated by usingmultipletechniques. The change that in the pH values of the solutions, concentrationsof Al and Pin the liquid phases, and the evolution of the coordination states of Al andP in the solid products were monitored. The―reverse temporal evolution‖analyses ofeach structure showed that the core units or the possible onsets (nuclei) ofcrystallization of each structure were significantly different from eachother. Theresults showed that the heating temperature altered the structure-directing effect of1,3-dipropaneamine and the crystallization process of the initial mixture via changingthe structure and chemical properties of the structure-directing agent of 1,3-dipropaneamine, the equilibrium of the reactions occurring among the sourcematerials, and the self-assembling of the inorganic oligomers.