Needs and trends in rational synthesis of zeolitic materials

Zeolites are an important class of materials which are widely used in industry as catalysts, adsorbents and ion-exchangers. Their superior properties are closely related to their unique porous framework structure, as well as composition and morphology. The ever-growing needs for zeolitic materials in applications inspire us to think of the rational synthesis of zeolites with desired structures and properties. However, rationalization of zeolitic materials remains one of the most challenging issues in the zeolite research field due to their unclear formation mechanism. Despite this, many efforts have been devoted to synthesize zeolites in a more rational way. In this tutorial review, first, we demonstrate how the geometrical characteristics of zeolite frameworks affect the catalytic performances of the resulting materials; then, we present recent advances in synthetic innovations to target materials, and we further highlight the developments in computer simulations toward ab initio design and synthesis; finally, the future perspective on the rational synthesis of zeolitic materials with desired functions and structures will be described.     

离子热法合成沸石咪唑骨架材料及其溶解-结晶机理研究

基于沸石咪唑骨架材料在离子液体和低共熔溶剂中冷却结晶的析出方式,开发了一种离子热法合成沸石咪唑骨架材料的新途径,采用X射线衍射、扫描电镜、核磁共振光谱、红外光谱以及热重分析等方法对制备的产物进行了表征,研究了合成条件对产物结晶度、尺寸和形貌的影响,探讨了沸石咪唑骨架材料在离子热合成体系中的溶解-结晶析出机理.研究发现,冷却速率能够影响产物形貌,急速冷却时,sod(RCSR代码)型产物的形貌为球形,zni(RCSR代码)型产物为棒状或平板状;程序控制冷却时,sod型产物的形貌为多面体,zni型产物呈团簇状.     

Design and synthesis of hierarchical materials from ordered zeolitic building units

The crystallization of colloidal silicalite-1 from clear solution is one of the best understood zeolite formation processes. Colloidal silicalite-1 formation involves a self-assembly process in which nanoslabs and nanotablets with a silicalite-1 type connectivity are formed at intermediate stages. During the assembly process, with strongly anisometric particles present, regions appear with orientational correlations, as evidenced with measurements of dynamic light scattering, viscosity, and rotation of polarized light. The presence of such regions rationalizes the unexpected differences between the crystallization kinetics under microgravity and on earth. The discovery of the locally oriented regions sheds new light on currently poorly understood hydrodynamic effects on the zeolite formation processes, such as the influence of stirring on the phases obtained and the subsequent kinetics. Addition of surfactants or polymers modifies the ordering of the zeolitic building units in the correlated regions, and new types of hierarchical materials named zeogrids and zeotiles can be obtained.     

新型三维开放骨架磷酸铝化合物的合成及晶化过程中的共模板效应

以1,2-丙二胺(1,2-DAP)为结构导向剂,在180℃加热摩尔组成为n(Al_2O_3)∶n(P_2O_5)∶n(1,2-DAP)∶n(H_2O)=1∶6∶5.5∶139的初始混合物,合成了具有AlPO-CJ31骨架结构的新型三维开放骨架磷酸铝化合物(1);加热摩尔组成为n(Al_2O_3)∶n(P_2O_5)∶n(1,2-DAP)∶n(H_2O)=1∶6∶7.5∶139的初始混合物,合成了二维层状磷酸铝化合物APDAP_(12)-150.利用X射线粉末衍射分析(XRD)、元素分析、热重/差热分析等表征手段确认了化合物1的分子式为[Al_4P_5O_(20)·H_3O·H_2O]·[H_3NCH_2CHNH_3CH_3],质子化的水分子与双质子化的1,2-丙二胺共同起到了导向化合物1的作用.调变初始混合物中1,2-丙二胺的比例可显著影响其模板效应.1,2-丙二胺比例较低[n(1,2-DAP)=5.5]时,产物为三维开放骨架化合物,而当其比例较高[n(1,2-DAP)=7.5]时,产物为二维层状化合物.     

Controlling phase formation in solids: rational synthesis of phase separated Co@Fe2O3 heteroparticles and CoFe2O4 nanoparticles

A wet chemical approach from organometallic reactants allowed the targeted synthesis of Co@Fe(2)O(3) heterodimer and CoFe(2)O(4) ferrite nanoparticles. They display magnetic properties that are useful for magnetic MRI detection.     

Sano-Tachiya-Noolandi-Hong versus Onsager modelling of charge photogeneration in organic solids

We have studied the electric field dependence of charge photogeneration efficiency in organic solids for various radial distribution functions (Dirac delta, Gaussian, exponential) of initial e-h pairs in the framework of Sano-Tachiya-Noolandi-Hong (STNH) theory assuming that the final recombination (capture reaction) proceeds on a sphere of finite radius (a) with a finite velocity (κ). We compare the STNH results with the conventional Onsager theory assuming a = 0. We show that charge photogeneration is more enhanced, especially in low-electric field range, for broader initial pair distributions and for smaller final recombination velocities. We compare theoretical results with experimental data taken from electromodulation of photoluminescence (EML) for two archetypical organic photoconductors, Alq₃ and Ir(ppy)₃, commonly used as emitters in organic LEDs. From analysis of our results we infer the lower limit of final recombination velocity, κ = 0.2-2 cm/s, in vacuum evaporated films of Alq₃ and Ir(ppy)₃ which compares favorably with an evaluation of this quantity in amorphous solids.     

Aqueous room temperature synthesis of cobalt and zinc sodalite zeolitic imidizolate frameworks

Sodalite zeolitic imidazolate frameworks containing Co (ZIF-67) and Zn (ZIF-8) were synthesized at room temperature under aqueous conditions in 10 min. A trialkylamine deprotonated the 2-methylimidazole ligand and nucleated the frameworks. Furthermore, the ligand acted as a structure directing agent in place of an organic solvent.     

Computational modelling of the YAG synthesis

Mathematical and numerical models of the yttrium aluminium garnet (YAG) synthesis are presented in the article. The models allow the effective computer simulation of the YAG synthesis. The synthesis by sol–gel and solid-state reaction methods is considered in the article. The question concerning the reasons for the observed changes in the preparation temperature by changing synthesis method is answered. The inverse modelling problem is solved: using known experimental data (synthesis time, dimensions of reactants) the unknown input parameters of the model (diffusion and reaction rate coefficients) are calculated.     

Autowave exothermic organic synthesis in the mixes of organic solids

The autowave modes of organic exothermic synthesis in the mixes of organic solids were studied. A traveling wave of exothermic reaction of organic synthesis appeared in the mixes at local thermal ignition. Useful low‐molecular organic compounds having, at least, synthetic value were found out with good yields after the reactions. Autowave modes were observed in different classes of organic reactions – red‐ox, halogenation, protonation, acylation, imination etc. The possibility to organize the autowave modes is determined by the exothermic nature of the reaction (≥20 kJ/mol), phase condition and thermal stability of the reagents and products. Main peculiarities, kinetics and mechanisms of the reactions in autowave modes were investigated. The basic advantages of autowave exothermic synthesis in organic solids were analyzed.     

Co-templating synthesis of highly dispersed 1D ZnO nanostructures in amorphous SiO2 under hydrothermal condition

One-dimensional (1D) ZnO nanostructures were grown in amorphous SiO₂ matrix by a co-templating method under hydrothermal condition. Using ethylenediamine (EDA) groups grafted mesoporous silica MCM-41 as a co-template, the growth of 1D ZnO nanostructures was oriented by soft EDA groups and confined inside the hard mesochannels of MCM-41. The microstructure and morphology of the 1D-ZnO-nanostructures/SiO₂ composite were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and X-ray energy dispersive spectroscopy (EDS). All these results indicate that the 1D ZnO nanostructures were synthesized and highly dispersed in the amorphous SiO₂ matrix. Blue-shifted exciton absorption was observed from the co-templating synthesized sample.     

Design and generation of extended zeolitic metal-organic frameworks (ZMOFs): synthesis and crystal structures of zinc(II) imidazolate polymers with zeolitic topologies

Attempts to create metal-organic frameworks (MOFs) with zeolitic topologies, metal (zinc(II) and cobalt(II)) imidazolates have repeatedly been used as the metal-organic motifs of inorganic silicate analogues. By modulating the synthetic strategy based on the solvothermal and liquid diffusion method, seven further MOFs (including at least three zeolitic MOFs) of zinc(II) imidazolates, [Zn(im)2.x G] (G=guest molecule, x=0.2-1) 1 a-7 a, have been successfully synthesized. Of these, 1 a-3 a are isostructural with the previously reported cobalt analogues 1 b-3 b, respectively, while 4 a-7 a are new members of the metal imidazolate MOF family. Complex 4 a exhibits a structure related to silicate CaAl2Si2O8 of CrB4 topology, but with a higher network symmetry; complex 5 a has a structure with zeolitic DFT topology that was discovered in zeolite-related materials of DAF-2, UCSB-3, and UCSB-3GaGe; complex 6 a demonstrates an unprecedented zeolite-like topology with one dimensional channels with 10-rings; and 7 a displays a structure of natural zeolite GIS (gismondine) topology. All of these polymorphous MOFs were created only by using certain solvents as structure-directing agents (SDAs). Further extensive metal-organic frameworks with zeolitic topologies can be envisaged if other solvents were to be used.     

Designed synthesis of mesoporous solids via nonionic-surfactant-templating approach

The continual needs for improved performances in applications derived by diversified compositions and mesostructures have pushed forward the development of mesoporous solids. The nonionic-surfactant-templating approach has been a critical route in this advancement. A large number of nonionic surfactants widely used in industries and featured with low cost, low toxicity, bio-degradation and ordered microdomains can be utilized as effective templates to the design and synthesis of abundant mesoporous solids. This feature article provides recent reports on the use of nonionic surfactant self-assembly as examples to fabricate high-quality ordered mesoporous solids which illustrates advances in synthesis and understanding of formation mechanisms. It includes the selection of surfactants, a summary of the effects of synthetic parameters, the current understanding of the synthetic pathways and related mechanisms with some emphasis on evaporation induced self-assembly (EISA), as well as the design and synthesis on the microscale (atomic and molecular compositions) and mesoscale (mesostructures). Preliminary applications of mesoporous solids particularly in optical devices, electrodes and biomaterials are also presented.     

A rational approach to the design and synthesis of chiral organopalladium-amine complexes

A new chiral auxiliary, (+/-)-N,N-dimethyl-1-(2,5-dimethylphenyl)ethylamine, was designed and synthesized in two steps from 1-acetyl-2,5-dimethylbenzene. Its cyclopalladated dimeric complex could be efficiently resolved via the formation of (S)-prolinate derivatives. Both hand forms of the complex could be obtained in similar yields. Despite the enormous inter-chelate steric constraints, the bulky monodentate ligand 3,4-dimethyl-1-phenylphosphole (DMPP) is able to coordinate regiospecifically to the orthopalladated 2,5-dimethylbenzylamine unit trans to the NMe(2) group. Compared to its naphthylamine analogue, the orthopalladated 2,5-dimethylbenzylamine complex exhibits a significantly higher stereoselectivity in the chiral template promoted asymmetric cycloaddition reaction between DMPP and ethyl vinyl ketone.     

Kinetics of proton transfer in the zeolitic tuff

The kinetics of a proton transfer into dilute acid solutions containing natural zeolitic tuff was studied by following the pH evolution of the liquid phase. Four different solutions with tuff contents of 9, 3, 1 and 0.5 (% wt) and three different particle size fractions (≤ 2000 μm) were studied. The proton concentration of the solution was decreased by increasing the zeolite amount and decreasing the particle size fraction. The proton transfer reaction was analyzed with chemical reactions and diffusion model equations. Analysis shows that the adsorption and/or ion exchange are possible mechanisms and are expressed by a second order reaction model.     

Rapid synthesis of zeolitic imidazolate framework-8 (ZIF-8) nanocrystals in an aqueous system

We report here the first example of ZIF materials synthesized in aqueous solution. The synthesis was performed at room temperature and typically took several minutes compared to hours and days in non-aqueous conditions. The obtained product were ZIF-8 nanocrystals having size of ~85 nm and showed excellent thermal, hydrothermal and solvothermal stabilities.     

A novel template-free sol–gel synthesis of silica materials with mesoporous structures and zeolitic walls

Hierarchical porous materials with zeolite structures show great promise in catalysis due to combining the advantages of zeolites and mesoporous materials. Here a novel template-free sol–gel method is developed to synthesize hierarchical porous silica materials. This method involves solvothermal recrystallization of the xerogel converted from uniform silicalite-1 precursor sol via vacuum drying process. The zeolite sol and the solid samples were characterized by laser light scattering, XRD, N₂ adsorption/desorption isotherm, FTIR, SEM, TEM and thermal analysis technologies. The results show that we obtain two novel materials with different mesoporous structures and silicalite-1 walls by using different recrystallization media, one of which has irregular arrays of mesopores, the other possesses 3D wormhole mesoporous structure. We speculate that formation of different mesoporous structures results from different nucleation and growth process of materials     

Hetero-arylboroxines: the first rational synthesis, X-ray crystallographic and computational analysis

A novel series of hetero-arylboroxines were synthesized and structurally characterized by X-ray diffraction, NMR and computational analysis. The solid-state structures of the hetero-arylboroxines represent the first report of AB(2)-type hetero-arylboroxines.     

About the inclusion of an insecticide in zeolitic materials

The commercial product Supercypermetrin (3-phenoxy--cyanobenzyl-3-(2,2-dichlorovinyl)-2-(2,2-dimetyl)-cyclopropanecarboxylate) [SCM] in the liquid form was included in the zeolitic host. A natural zeolitic material of clinoptilolite type [CT] from a Slovakian deposit was used. The chemical control of the guest desorption was used for checking the existence of a new inclusion compound. The desorption of the insecticide under relatively drastic conditions (12 g of product in 200 ml H₂O) showed a hindered and regulated release of the insecticide. Thermal curves obtained by means of a derivatograph and IR spectra were used for the study of the insecticide [SCM] enclosed (10%) in the zeolitic host and its desorption.