A hierarchically structured beta zeolite with intercrystalline mesopores was successfully synthesized via in situ assembly of nanoparticles by employing a simple organic molecule N2-p-N2, tailored from polyquaternium surfactant, with no hydrophobic long chain. The generated samples were studied by using powder X-ray diffraction (XRD) and nitrogen adsorption/desorption isotherms. Computer simulation, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) technologies were also used. The characterized results show that the tailored template molecule N2-p-N2 without hydrophobic long-chain tail still can direct the zeolite crystallization, while the hydrophobic long-chain tail is not necessary during the mesoporous Beta zeolite formation. The catalytic performances of the sample were studied using alkylation of benzene with propene reaction to evaluate the relationship between the structure and property. The results apparently suggested an overall improved resistance against deactivation as compared to conventional beta zeolite in reactions. Furthermore, this tailored simple organic molecule strategy from dual-functional surfactant for making mesoporous zeolite would offer a new method of synthesizing other hierarchically structured zeolites.

Hierarchical porous zeolitic imidazolate frameworks (ZIFs) have potential for adsorption, catalysis and chemical sensing applications. Ultrafast synthesis of ZIFs at room temperature and pressure is particularly desirable for large-scale industrial production. Here, we developed a green and versatile method using organic amines as supramolecular templates (organic amine-template) to rapidly synthesize hierarchical porous ZIFs (ZIF-8, ZIF-61 and ZIF-90) at room temperature and pressure. The synthesis time was reduced dramatically to within 1 min, and the resulting ZIFs had multimodal hierarchical porous structures with mesopores/macropores interconnected with micropores. Notably, the space–time yield (STY) of hierarchical porous ZIF-8 was up to 1.29×104 kg m–3 d–1, which is more than three times higher than that reported using other methods. Furthermore, the morphologies and porosities of the produced ZIFs could be readily tuned by controlling the synthesis time or type of organic amine. The organic amine played two roles in the synthesis: (1) a protonation agent to deprotonate organic ligands, facilitating the formation of ZIF crystals, and (2) an structure directing agent to direct mesopore/macropore formation. The resulting hierarchical porous ZIF-8 exhibited enhanced uptake capacities and diffusion rates for guest molecules relative to its microporous counterpart. This work provides a new direction for the green and efficient synthesis of various hierarchical porous ZIFs with high STYs for a wide range of applications.常温下快速合成具有多级孔结构的ZIFs村料具有重要的意义: 一方面, 多级孔道结构能有效地增加分子扩散速率、 降低其传质阻力, 这对于涉及大分子参与的反应具有重要意义, 扩大了村料的应用范围; 另一方面, 在常温下快速合成ZIFs村料不仅能大幅降低能源消耗, 并且能极大地提高生产效率, 是一种绿色高效的工艺路线. 本文采用有机胺类作为模板, 首次在常温下快速合成具有高空时产率的3种多级ZIFs村料(ZIF-8, ZIF-61以及ZIF-90), 村料的合成时缩短至1分钟, 同时兼具微孔, 介孔, 大孔结构. 此外, ZIFs产物的形貌和多孔性质可以通过调节胺模板的类型或者合成时间来调控. 更为重要的是, ZIFs村料的空时产率高达1.29×104 kg m−3 d—1, 比之前报导过的值高出3倍, 这为ZIFs村料的商业化生产提供了可能. 最后, 我们通过对有机胺类分子进行计算机模拟, 再结合之前文献报导的结果, 得到了一般性的合成机理: 一方面有机胺作为质子化剂使得有机配体去质子化, 被质子化的配体迅速地和金属离子结合形成金属有机骨架; 另一方面, 有机胺作为模板被用来引导介孔和大孔结构的形成.

Hierarchical porous metal–organic frameworks (HP-MOFs) with tunable porosity are highly valuable for many applications. Here, we developed a versatile solvothermal method to synthesize various HP-MOFs, such as Cu–BTC and ZIF-8, by using an organic amine as the template. The resulting HP-MOF products were characterized by a complementary combination of X-ray powder diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, nitrogen adsorption–desorption isotherms, pore size distributions analysis, thermogravimetric analysis, and density functional theory calculations. The results indicated that the obtained HP-MOF products had high thermal stability and contained multimodal hierarchically porous structures with mesopores or macropores interconnected with micropores. In addition, the porosities of the produced HP-MOFs could be easily tuned by controlling the amount of the template. The introduced organic amine served as the template to direct the formation of mesopores and macropores. Furthermore, the synthesis route is highly versatile as other organic amines (e.g., N,N-dimethylhexadecylamine and N,N-dimethyltetradecylamine) can also be used as templates to synthesize HP-MOFs. The method developed in this work may offer a new direction to synthesize various stable HP-MOFs with tunable porosities for a wide range of applications.

Hierarchical zeolites are important solid catalysts for the conversion of bulky molecules according to their mesoporosities. In this study, we prepared a hierarchically structured beta zeolite by using a bifunctionalized amphiphilic surfactant, C18-6-diphe, under hydrothermal synthesis conditions. The product was characterized by a combination of X-ray powder diffraction, N2 adsorption–desorption isotherms, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, 27Al magic-angle spinning nuclear magnetic resonance spectroscopy, thermogravimetric analysis, and NH3 temperature-programmed desorption. The results indicated that the surfactant acted as a dual-functional template for generating both micropores and mesopores simultaneously and that the mesopore walls exhibited zeolite-like micropore frameworks with high hydrothermal stability. The incorporation of Al atoms and the presence of abundant mesopores did not affect the intrinsic acidity of the beta zeolite, especially for weak and medium-strong acids. The hierarchically structured beta zeolite exhibited high catalytic activity due to its mesoporous structure with abundant exposed acid sites on the external surface and short diffusion routes. This hierarchical micro/mesostructured beta zeolite may be a candidate for practical industrial applications especially in those reactions where bulky molecules are involved.

A novel hierarchically structured HKUST-1 has been synthesized under hydrothermal synthesis conditions using a mixed ligand strategy, in which benzene-1,3,5-tricarboxylic acid was partially replaced by benzoic acid. The formation of the crystalline HKUST-1 material containing mesoporosity was characterized by a complementary combination of X-ray powder diffraction, Fourier transform infrared spectroscopy, N2 adsorption–desorption isotherms, scanning electron microscopy, transmission electron microscopy and thermogravimetric analysis. These analyses indicated that incorporation of a certain amount of benzoic acid in the crystal lattice of HKUST-1 preserved its crystal structure. The benzoic acid ligand could be seen as “defect” sites that two carboxylate groups of one linker molecule are missing, leading to a distorted paddle-wheel unit, which induced the formation of an intra-crystalline mesoporous structure in HKUST-1. The hierarchically structured HKUST-1 combines the dual merits of two different pore structures, enabling it has maximum structural function in a limited space due to the enhanced diffusion through mesoporous channels. The presented method opens the door for the preparation of a variety of hierarchically structured MOFs.

Using a walnut shell as a carbon source and ZnCl2 as an activating agent, we resolved the temperature gradient problems of activated carbon in the microwave desorption process. An appropriate amount of silicon carbide was added to prepare the composite activated carbon with high thermal conductivity while developing VOC adsorption-microwave regeneration technology. The experimental results show that the coefficient of thermal conductivity of SiC-AC is three times as much as those of AC and SY-6. When microwave power was 480 W in its microwave desorption, the temperature of the bed thermal desorption was 10 °C to 30 °C below that of normal activated carbon prepared in our laboratory. The toluene desorption activation energy was 16.05 kJ∙mol−1, which was 15% less than the desorption activation energy of commercial activated carbon. This study testified that the process could maintain its high adsorption and regeneration desorption performances.

The adsorptive separation properties of M-BTC isostructural series (M = Ti, Fe, Cu, Co, Ru, Mo) for methanol–acetone mixtures were investigated by using various computational procedures of grand canonical Monte Carlo simulations (GCMC), density functional theory (DFT), and ideal adsorbed solution theory (IAST), following with comprehensive understanding of adsorbate–metal interactions on the adsorptive separation behaviors. The obtained results showed that the single component adsorptions were driven by adsorbate–framework interactions at low pressures and by framework structures at high pressures, among which the mass effects, electrostatics, and geometric accessibility of the metal sites also played roles. In the case of methanol-acetone separation, the selectivity of methanol on M-BTCs decreased with rising pressures due to the pressure-dependent separation mechanisms: the cooperative effects between methanol and acetone hindered the separation at low pressures, whereas the competitive effects of acetone further resulted in the lower selectivity at high pressures. Among these M-BTCs, Ti and Fe analogues exhibited the highest thermodynamic methanol/acetone selectivity, making them promising for adsorptive methanol/acetone separation processes. The investigation provides mechanistic insights on how the nature of metal centers affects the adsorption properties of MOFs, and will further promote the rational design of new MOF materials for effective gas mixture separation.Keywords: adsorptive separation; DFT; GCMC; IAST; metal−organic frameworks; methanol/acetone

The adsorption and separation properties of benzene and toluene on the zirconium-based frameworks UiO-66, -67, -68, and their functional analogues UiO-Phe and UiO-Me2 were studied using grand canonical Monte Carlo simulations, density functional theory, and ideal adsorbed solution theory. Remarkable higher adsorption uptakes of benzene and toluene at low pressures on UiO-Phe and -Me2 were found compared to their parent framework UiO-67. It can be ascribed to the presence of functional groups (aromatic rings and methyl groups) that significantly intensified the adsorption, majorly by reducing the effective pore size and increasing the interaction strength with the adsorbates. At high pressures, the pore volumes and accessible surfaces of the frameworks turned out to be the dominant factors governing the adsorption. In the case of toluene/benzene separation, toluene selectivities of UiOs showed a two-stage separation behavior at the measured pressure range, resulting from the greater interaction affinities of toluene at low pressures and steric hindrance effects at high pressures. Additionally, the counterbalancing factors of enhanced π delocalization and suitable pore size of UiO-Phe gave rise to the highest toluene selectivity, suggesting the ligand functionalization strategy could reach both high adsorption capacity and separation selectivity from aromatic mixtures at low concentrations.Keywords: adsorption and separation; aromatics; DFT; GCMC; IAST; zirconium-based metal−organic frameworks

The hierarchical zeolite with MFI nanosheet frameworks was directly prepared under hydrothermal synthesis conditions using a series of tetra-headgroup rigid bolaform quaternary ammonium surfactants, where the bolaform surfactants act as dual structure-directing functions on two different length scales (micro- and mesoporous) simultaneously. The MFI zeolite nanosheets were characterized by a complementary combination of X-ray diffraction, scanning electron microscopy, transmission electron microscopy, nitrogen adsorption isotherms, Fourier transform infrared spectroscopy, 27Al MAS NMR spectroscopy, thermogravimetric analysis and density functional theory calculations. The results suggested that the hydrophilic headgroups caused the aluminosilicate species to form MFI zeolite-like frameworks while the surfactant linkers with a rigid biphenol group directed MFI nanosheet layers into an ordered multilamellar mesostructure. The morphologies and textural properties of MFI zeolite nanosheets could be controlled with different surfactants. Since the synthesis of MFI zeolite nanosheets has great potential for industrial applications, our synthesis approach can be expected to be extended to other types of zeolites in order to improve their performance in targeted catalytic reactions.

Hierarchically structured ZSM-5 zeolites were synthesized by employing only one dual-porogenic surfactant, and the hydrothermal crystallization of hierarchical structured zeolites were investigated under rotating and static synthesis conditions. X-Ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N2 adsorption–desorption isotherms, 27Al magic-angle spinning nuclear magnetic resonance (27Al MAS NMR) and thermogravimetric analysis (TGA) were used to characterize the structural and textural features of the resultant zeolite products. By tuning the synthesis conditions from rotating to static, the morphology of the as-obtained hierarchical structure ZSM-5 zeolites changed from silk-like to nanoparticles with a disordered arrangement. Furthermore, the obtained zeolites under static conditions showed a higher BET surface area and lower total pore volume than those of zeolites synthesized under rotating conditions. In addition, quantum chemical calculation results show that the inner ammonium groups may have greater contribution in directing the zeolite structure than tailed ammonium groups. More importantly, the hierarchical structured ZSM-5 zeolites synthesized under static conditions exhibited a higher benzyl alcohol conversion rate and lower ester selectivity compared to those of the samples prepared under rotating conditions. Consideration of the effects of synthesis conditions may be useful for modulating the textural and catalytic properties of hierarchical zeolites.

Metal–organic frameworks (MOFs) are of great promises for the adsorption of volatile organic compounds (VOCs). The adsorption of methanol, aldehyde and one on IRMOF-1 and an amino-functionalized framework, IRMOF-NH2, were investigated by density functional theory. The adsorption mechanisms and the effects of amino functionalization were clarified with comparison of binding energies, optimized configurations, atomic partial charges and the electrostatic potentials. The calculated results revealed that the electron-donating effect of amino groups had great influence on the electrostatic properties of the framework. The adsorption of methanol was greatly enhanced on organic linkers of IRMOF-NH2 compared to IRMOF-1, but weakened on the metal corners, different from the adsorption behaviors of aldehyde and acetone. A plausible interaction mechanism was inferred as the VOCs adsorption might be governed by the electrostatic interaction between methyl groups of the adsorbates and the binding sites of the framework, while the polar groups of adsorbates only interacted with framework through weak interaction like H-bonding. Besides, the steric hindrance effects of the inserted amino groups should also be taken into consideration, depending on the configuration and the electrostatic properties of the adsorbates. The binding mechanisms of VOCs on IRMOF-1 and IRMOF-NH2, provide fundamental insights into the oriented design of MOFs for the adsorption of VOCs.

The mesoporous zeolite is a novel porous material possessing mesopores as well as the inherent micropores of zeolites. This material can exhibit the dual merits of two different pore structures and enable zeolites to have maximum structural functions. During the past few decades, various synthetic strategies have been well developed. However, up to now, there has only been a few attempts to model mesoporous zeolites. In this paper, the structural properties of a mesoporous ZSM-5 type molecular sieve, which has mesopore walls that are made up of ZSM-5 zeolite-like frameworks, were studied using an atomistic model. The full-atom model of the mesoporous ZSM-5 type molecular sieve was constructed using a molecular modeling technique. The structure model was characterized by estimating the nitrogen accessible solvent surface area, small-angle and wide-angle X-ray diffraction patterns, toluene and benzene adsorption. It was found that these simulated results match well with the experimental data. Furthermore, the present approach can be extended to construct other micro-mesoporous molecular sieve structure models in the future.

Hierarchical zeolites have emerged as an important class of materials for applications in adsorption, separation and catalysis. Herein, hierarchical zeolite Y was hydrothermally synthesized using an organosilane surfactant, which was added into the conventional synthesis composition for crystalline microporous aluminosilicates as mesopore-generating agent. X-Ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR) (with KBr and pyridine), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), 27Al magic-angle spinning nuclear magnetic resonance (27Al MAS NMR) and N2 adsorption–desorption isotherms were used to characterize structural and textural features of the hierarchical zeolite Y. In addition, the molecular properties of the organosilane surfactant were investigated by density functional theory calculation. The hierarchical zeolite Y with mesoporous characteristics and the microporous crystalline structure of zeolites exhibited high catalytic activity and resistance to deactivation in the aldol condensation of benzaldehyde with n-butyl alcohol, as compared with conventional zeolite Y. This phenomenon could be attributed to improved mass transport ability of guest species through the interconnected micropore-to-mesopore networks. Such a hierarchical zeolite Y, that combines the advantages of two different pore structures, may find potential applications as advanced materials in various fields such as adsorption, separation and catalysis.

ZIF-8 has been rapidly developed as a potential candidate for CO2 capture due to its low density, high surface area, and robust structure. Considering the electron-donating effect of amino functional groups, amino-modification is expected to be an efficient way to improve CO2 adsorption of ZIF-8. In this work, grand canonical Monte Carlo (GCMC) simulation was performed to study the CO2 adsorption isotherm based on ZIF-8, ZIF-8-NH2, and ZIF-8-(NH2)2. ZIF-8 was synthesized and CO2 adsorption isotherms based on ZIF-8 was measured. The experimental surface area, pore volume, and CO2 adsorption isotherm were used to validate the force field. Adsorptive capacity of ZIF-8-NH2, and ZIF-8-(NH2)2 were first estimated. The GCMC simulation results indicated that the order of increasing CO2 capacity of the ZIF-8 in the lower pressure regime is: ZIF-8 < ZIF-8-NH2 < ZIF-8-(NH2)2, and in the high pressure is: ZIF-8 < ZIF-8-(NH2)2 < ZIF-8-NH2. New adsorption sites can be generated with the existence of-NH2 groups. In addition, for non-modified and amino-modified ZIF-8, it was the first time to use density functional theory (DFT) calculations to investigate their CO2 adsorption sites and CO2 binding energies. The present work indicates that appropriate amine-functionalized can directly enhanced CO2 capacity of ZIF-8.

Hierarchically structured beta zeolite has been prepared under hydrothermal synthesis conditions by employing only one dual-porogenic hexaquaternary ammonium type surfactant. The resulting mesoporous molecular sieve was characterized by a complementary combination of X-ray powder diffraction, N2 adsorption–desorption isotherms, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, 27Al MAS NMR spectroscopy, thermogravimetric analysis and density functional theory calculation. These analyses indicated that the mesopore walls were zeolite-like microporous crystalline aluminosilicate frameworks. The surfactant acts as a dual-functional template for the generation of both micropores and mesopores simultaneously. Due to the short diffusion routes and abundant exposed acid sites on the external surface, the hierarchically structured beta zeolite displayed a clear advantage for catalysis reactions of large molecules compared to conventional zeolites and traditional mesoporous materials. Furthermore, this effective approach can be extended to the synthesis of other hierarchical zeolites.

Ordered mesoporous silica SBA-15 with uniform hexagonal tunable mesopore channels attracts significant interest of the intensive studies and finds numerous applications in adsorption, catalysis, controlled release and drug delivery, etc. It is generally considered that such a unique hexagonal mesopore system of SBA-15 is formed via the cooperative self-assembly of partially protonated nonionic surfactants and positively charged silicate oligomers. However, the information about the assembly mechanism and the phase transformation at mesoscopic level is still insufficient due to the limitation of experimental technology. In this paper, Mesoscopic Dynamics (MesoDyn) simulation method is employed to investigate the phase transformation in the synthesis of SBA-15 with a simple Gaussian model, and a successive phase transition process composed of various mesophases of SBA-15 including spheroidal, columnar, and hexagonal phase are obtained. Moreover, the effects of charge matching interactions between surfactants and silicate species on the mesophase morphology of SBA-15 are further discussed. The obtained results are in good agreement with the ab initio calculations and the experimental results reported before, which indicates that the MesoDyn simulation method can be used to fundamentally validate and interpret the “surfactant/silicate species cooperative formation mechanism” of ordered mesoporous materials.Graphical abstractHighlights► Successive phase transition process composed of various mesophases of SBA-15. ► Charge matching interactions determine the mesophase structure of SBA-15. ► Charge matching interactions promote the homogeneous dispersion of silica species.

Micro-mesoporous molecular sieves are novel porous materials which are equipped with long-range parallel mesopore channels like periodic mesoporous silica (PMS) materials, and its adjacent mesopores are connected to each other through micropore walls of zeolites. Such materials can be used as highly functional adsorbents, catalyst supports and nanoreactors, because micropores and mesopores play a cooperative role as gas or fluid paths and molecular adsorption sites or reservoirs. Furthermore, the introduction of the zeolite structure provided micro-mesoporous molecular sieves significantly more acidity sites than those of PMS. In this paper, ZSM-5-MCM-41 micro-mesoporous composites are synthesized by a two-step crystallization process based on the polymerization of ZSM-5 nanocluster precursors confined to the MCM-41 structure-directing agent, and microwave radiation crystallization technology is chosen in synthesis process. In addition, the structure model of ZSM-5-MCM-41 is built by using molecular modeling technique, and then characterized by calculating the accessible solvent surface area, total pore volume, small-angle and wide-angle X-ray diffraction patterns, and toluene adsorption. The calculated results are proved and compared with corresponding experiment results, such as N2 adsorption–desorption isotherms, X-ray power diffraction patterns, and toluene adsorption.

The mesoporous zeolite is a novel porous material possessing mesopores as well as the inherent micropores of zeolites. This material can exhibit the dual merits of two different pore structures and enable zeolites to have maximum structural functions. During the past few decades, various synthetic strategies have been well developed. However, up to now, there has only been a few attempts to model mesoporous zeolites. In this paper, the structural properties of a mesoporous ZSM-5 type molecular sieve, which has mesopore walls that are made up of ZSM-5 zeolite-like frameworks, were studied using an atomistic model. The full-atom model of the mesoporous ZSM-5 type molecular sieve was constructed using a molecular modeling technique. The structure model was characterized by estimating the nitrogen accessible solvent surface area, small-angle and wide-angle X-ray diffraction patterns, toluene and benzene adsorption. It was found that these simulated results match well with the experimental data. Furthermore, the present approach can be extended to construct other micro-mesoporous molecular sieve structure models in the future.

Hierarchically structured beta zeolite has been prepared under hydrothermal synthesis conditions by employing only one dual-porogenic hexaquaternary ammonium type surfactant. The resulting mesoporous molecular sieve was characterized by a complementary combination of X-ray powder diffraction, N2 adsorption–desorption isotherms, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, 27Al MAS NMR spectroscopy, thermogravimetric analysis and density functional theory calculation. These analyses indicated that the mesopore walls were zeolite-like microporous crystalline aluminosilicate frameworks. The surfactant acts as a dual-functional template for the generation of both micropores and mesopores simultaneously. Due to the short diffusion routes and abundant exposed acid sites on the external surface, the hierarchically structured beta zeolite displayed a clear advantage for catalysis reactions of large molecules compared to conventional zeolites and traditional mesoporous materials. Furthermore, this effective approach can be extended to the synthesis of other hierarchical zeolites.