Post-synthetic Methods Research Articles

Sequential Linker Installation in Metal-Organic Frameworks.

ConspectusMetal-organic frameworks (MOFs) represent a sophisticated blend of inorganic and organic components, promoting the development of coordination chemistry greatly and offering a versatile platform for tailored functionalities. By combining various metal nodes, organic linkers, and functional guests, MOFs provide numerous pathways for their design, synthesis, and customization. Among these, sequential linker installation (SLI) stands out as a novel and crucial strategy, enabling the precise integration of desired properties and functions at the atomic scale. SLI enhances structural diversity and stability while facilitating the meticulous construction of robust frameworks by leveraging open metal sites and functional organic linkers at targeted locations. Compared to the direct synthesis of MOFs, postsynthetic modification methods allow for precise regulation of their structures and corresponding properties. While unlike conventional postsynthetic modification methods, SLI requires the careful selection of linkers and framework design to ensure precise positioning for installation, which gives rise to the well-designed and ordered positions for the installed linkers, confirmed directly by X-ray diffraction technology.Recent advancements in MOF synthesis have led to the creation of increasingly tailored flexible matrix structures, particularly due to the diverse connection modes of multicore metal clusters, especially for the Zr6 cluster. The spatial hindrance of certain ligands has resulted in the formation of unsaturated metal clusters and various missing linker pockets. Examples of these advanced MOFs include PCN-606, PCN-608, PCN-609, PCN-700, and PCN-808, which feature specific open metal sites and certain framework flexibility conducive to SLI. Strategically positioned open metal sites within these frameworks serve as predetermined anchor points for desired functional molecules, while the frameworks' flexibility can accommodate molecules of varying sizes to a certain extent, enlarging the scopes of application greatly. This precise positioning of functional groups enables the creation of tailored sites for enhanced applications, such as adsorption, catalysis, and recognition.In this Account, we delve into the intricate process of designing and synthesizing MOFs with appropriate missing-linker pockets for the aforementioned applications. We discuss the meticulous selection of functional linkers and the methods used to insert them into the corresponding missing-linker pockets within the MOFs. Additionally, we explore the diverse properties and functionalities of the resulting MOFs, focusing on their adsorptive, catalytic, and recognition performance. Furthermore, we provide insights into the future trajectory of SLI methods, complemented by our recent works. This Account not only reviews the evolution of the SLI method but also underscores its practical applications across various functional domains, paving a rational pathway for the future development of advanced multifunctional MOFs through this method.

Synthetic Strategies to Extended Aromatic Covalent Organic Frameworks.

π-Conjugated materials are highly attractive owing to their unique optical and electronic properties. Covalent organic frameworks (COFs) offer a great opportunity for precise arrangement of building units in a π-conjugated crystalline matrix and tuning of the properties through choice of functionalities or post-synthetic modification. With this review, we aim at summarizing both the most representative as well as emerging strategies for the synthesis of π-conjugated COFs. We give examples of direct synthesis using large, π-extended building blocks. COFs featuring fully conjugated linkages such as vinylene, pyrazine, and azole are discussed. Then, post-synthetic modification methods that result in the extension of the COF π-system are reviewed. Throughout, mechanistic insights are presented when available. In the context of their utilization as film devices, we conduct a concise survey of the prominent COF layer deposition techniques reported and their aptness for the deposition of fused aromatic systems.

Chemical surface modification of mesoporous SiO2-based membranes for fine-tuning of drug loading and release properties

Transdermal Drug Delivery Systems (TDDS) show significant advantages over other forms of drug application. Despite their clinical use for decades, these drug delivery devices have yet to reach their full potential. While polymer matrices are most commonly used as transdermal patches so far, inorganic carriers like mesoporous silica membranes offer several advantages, including chemical stability and their tunable porous system, with adjustable pore sizes, pore volumes and surface chemistries. In this study, we chemically modified high and low porosity mesoporous silica membranes by post-synthetic methods and compared the effects of different surface modifications on loading efficacies and release profiles of different pharmacologically relevant drugs with different chemical properties. Drug loading capacities and release profiles were substantially affected by pore structure and surface modifcations with strongly acidic SO3H groups or hydrophobic methyl groups, while weakly acidic COOH groups or nitrile groups showed little effects. SO3H modification of low porosity (LP) membranes led to markedly increased loading capacity and a more sustained release profile of anastrozole. The latter was also observed for xylazine, but associated with lesser drug loading. Likewise, the SO3H modification also slowed down the release of imiquimod or flunixin. Increasing LP membrane hydrophobicity by methyl modification essentially abolished anastrozole drug loading. In high porosity (HP) membranes, effects of chemical surface modifications were overall weaker. This led to particularly slow anastrozole or xylazine release profiles from methyl-modified membranes. Biocompatibility studies showed some cell-inhibitory effects of CN functionalization, but full biocompatibility of SO3H functionalized membranes as indicated by efficient cell attachment and high viability. Both parameters, pore structure and chemical surface modifcations, drug-dependently affect drug loading and release properties. Since they can be precisely fine-tuned in mesoporous silica membranes, this allows for the development of optimized TDDS providing high drug loading and the desired release profile of a given drug. Our results presented here indicate that the SO3H modification is particularly useful in this regard.

Carbon nano-onions: Individualization and enhanced water dispersibility

Carbon nano-onions (CNOs) are a unique class of carbon nanomaterials, with a concentric fullerene-like structure and sp2-hybridized carbon atoms. Onions present high mechanical strength, good conductivity, the capability to intercalate alkali metals, showing promising applications in diverse fields, such as tribology, energy storage, and nanomedicine. Their production has been developed by several techniques, with the most interesting being the thermal annealing of carbon nanodiamonds because of the easy scalability (gram-scale) and morphologic control (size and shape form perfectly spherical to polygonal). However, this synthesis is commonly affected by the formation of strong aggregates larger than 100 nm, attributed to carbon soot formation or strong van der Waals interactions, hindering the work with small and individual particles, leading to an altered yield of functionalization. In this study we propose a method for CNO individualization based on strong acid treatment, yielding highly water dispersible nanoparticles. Analytical ultracentrifugation (AUC) analysis is employed as a technique to investigate the particle dimensions directly in dispersion, permitting an ensemble analysis free from further sample preparation bias. Moreover, we also provide a comprehensive evaluation of the common post-synthetic treatment methods, and their effects. By means of scanning transmission electron microscopy with medium angle annular dark field detector and electron energy loss spectroscopy (STEM-MAADF and EELS) we have shown images of individual CNOs. Their successful separation achieved in this study is significant for future research and applications in nanomedicine, electrochemistry, and materials composites, where sample homogeneity is critical.

Hierarchical Porous Amidoximated Metal-Organic Framework for Highly Efficient Uranium Extraction.

With the rapid development of industry and technology, high-efficiency extraction of uranium from seawater is a research hotspot from the aspect of nuclear energy development. Herein, a new amidoximated metal-organic framework (UiO-66-DAMN-AO) constructed through a novel organic ligand of 2-diaminomaleonitrile-terephthalic acid (BDC-DAMN) is designed via one-step post-synthetic methods (PSM), which possess the merit of abundant multiaffinity sites, large specific surface area, and unique porous structure for efficient uranium extraction. Adopting one-step PSM can alleviate the destruction of structural stability and the reduction of the conversion rate of amidoxime groups. Meanwhile, introducing the BDC-DAMN ligand with abundant multiaffinity sites endow UiO-66-DAMN-AO with excellent adsorption ability (Qm=426.3mgg-1) and selectivity. Interestingly, the UiO-66-DAMN-AO has both micropores and mesopores, which may be attributed to the partial etching of UiO-66-DAMN-AO during the amidoximation. The presence of mesopores improves the mass transfer rate of UiO-66-DAMN-AO and provides more exposed active sites, favoring the adsorption of uranium on UiO-66-DAMN-AO. Thus, this study provides a feasible strategy for modifying metal-organic framework (MOFs) with plentiful amidoxime groups and the promising prospect for MOF-based materials to adsorb uranium from ocean.

Tracking Lattice Distortion Induced by Defects and Framework Tin in Beta Zeotypes.

The use of powder X-ray diffraction (PXRD) coupled with lattice parameter refinement is used to investigate the crystal structure of Sn-Beta materials. A newly developed semiempirical PXRD model with a reduced tetragonal unit cell is applied to obtain the characteristic crystallographic features. There is a robust correlation between lattice parameters and the concentration of tin and defects for materials prepared via hydrothermal (HT) and postsynthetic (PT) methods. With tin incorporation, PT Sn-Beta samples, which possess a more defective structure, exhibit an extended interlayer distance in the stacking sequence and expansion of the translation symmetry within the layers, leading to larger unit cell dimensions. In contrast, HT Sn-Beta samples, having fewer defects, show a minimal effect of tin site density on the unit cell volume, whereas lattice distortion is directly correlated to the framework tin density. Furthermore, density functional theory (DFT) studies support an identical trend of lattice distortion following the monoisomorphous substitution of T sites from silicon to tin. These findings highlight that PXRD can serve as a rapid and straightforward characterization method to evaluate both framework defects and heteroatom density, offering a novel approach to monitor structural changes and the possibility to evaluate the catalytic properties of heteroatom-incorporated zeotypes.

Utilization of Physical Anisotropy in Metal-Organic Frameworks via Post-Synthetic Alignment Control with Liquid Crystal.

Metal-organic frameworks (MOFs) represent crystalline materials constructed from combinations of metal and organic units to often yield anisotropic porous structures and physical properties. Postsynthetic methods to align the MOF crystals in bulk remain scarce yet tremendously important to fully utilize their structure-driven intrinsic properties. Herein, we present an unprecedented composite of liquid crystals (LCs) and MOFs and demonstrate the use of nematic LCs to dynamically control the orientation of MOF crystals with exceptional order parameters (as high as 0.965). Unique patterns formed through a facile multidirectional alignment of MOF crystals exhibit polarized fluorescence with the fluorescence intensity of a pattern dependent on the angle of a polarizer, offering potential use in various optical applications such as an optical security label. Further, the alignment mechanism indicates that the method is applicable to numerous combinations of MOFs and LCs, which include UV polymerizable LC monomers used to fabricate free-standing composite films.

Incorporated Metal–Organic Framework Hybrid Materials for Gas Separation, Catalysis and Wastewater Treatment

The special features of metal–organic frameworks (MOFs), namely, tunable porosity, exceptional structure, high surface area and high adsorption capability enable them to be widely studied in many applications including carbon capture and storage (CCS), biomedical engineering, catalysis and pollutant treatment. Despite these remarkable properties, MOFs are known to be moisture-sensitive, hardly recyclable and expensive in fabrication cost which limits their breakthrough performance in more efficient uses. Recently, extensive studies have been devoted to counter those shortcomings by embedding MOFs with support materials using various series of synthetic designs to yield incorporated MOF hybrid materials to counter their limitations. In view of this interest, this review summarizes the latest developments of incorporated MOFs with various materials, namely, ionic liquids (ILs), membranes and metal species. Pre-synthetic and post-synthetic synthesis methods are also discussed. This review also aims to highlight the factors associated with incorporated MOF performance such as materials selection and mass ratio which could have favorable effects in gas separation, catalysis and wastewater treatment applications. The data indicate that incorporated MOF hybrid materials exhibit exceptional properties including excellent robustness and stability. Correspondingly, in comparison to pristine MOFs, incorporated MOF hybrid materials significantly improve, among others, the gas selectivity, catalyst activity and dye removal efficiency in gas separation, catalysis and wastewater treatment, respectively. In addition, the challenge related to the utilization of this newly incorporated material is mentioned.

Transition‐metal‐incorporated molybdenum phosphide nanocatalysts synthesized through post‐synthetic transformation for the hydrogen evolution reaction

Post-synthetic chemical transformation is a recently emerging nanomaterial manufacturing method for obtaining materials with precisely modulated properties. Through post-synthetic transformation methods, foreign elements are exchanged or incorporated into presynthesized nanoparticles (NPs). However, metal phosphides have not been primarily used as starting materials because of their strong bonding characteristics. In this study, we synthesized bimetallic transition metal phosphide (TMP) NPs through a cation addition reaction using amorphous molybdenum phosphide (MoP) as the starting material, which is a promising catalyst for the hydrogen evolution reaction (HER). The additional metal elements, namely Co and Ni, were successfully incorporated into the parent MoP NPs, which led to only marginal changes in size or shape, even after 12 hours of reaction. Because morphological factors strongly influence catalytic activity, nanocatalysts with identical morphologies provide a direct comparison among NPs with various chemical properties. The Co- and Ni-incorporated MoP NPs exhibited significantly enhanced catalytic activities for the HER, with similar electrochemically active surface areas. In particular, Co-1.5 h-MoP showed the highest HER activity (167 mV at −10 mA cm−2) and durability among the samples in 0.5 M H2SO4. Such an improvement in catalytic activity through the cation addition reaction may be ascribed to the difference in the electronegativities of the original and newly added metal cations, as confirmed by X-ray photoelectron spectroscopy (XPS), resulting in abundant metal-P bonding and oxidation resistivity. This study provides a new advanced platform for directly analyzing the inherent characteristics of nanomaterials for diverse applications, especially electrocatalysis.

Cu2+–diethylaminosalicylaldehyde self-dimer for regulation of DNA amplification with changes in fluorescence

In this study we developed a new green-fluorescent nucleoside (dUHzDESA) by attaching a diethylaminosalicylaldehyde (DESA) unit to deoxyuridine (dU) through a hydrazone (Hz) linker. Interestingly, dUHzDESA chelated selectively with Cu2+ ions to form dimer pairs in DNA duplexes with a change in fluorescence. We used this property of Cu2+-induced dUHzDESA dimer pairing to regulate DNA amplification processes [i.e., the polymerase chain reaction (PCR) of linear DNA and the rolling circle amplification (RCA) of circular DNA] by exploiting corresponding changes in conformation. We synthesized DNA containing hydrazone–DESA (HyDESA) functional groups by applying stepwise enzymatic syntheses and post-synthetic methods using deoxyuridine triphosphate (dUHzTP) and DESA, producing the linear templates DESAHzDNA1 and DESAHzDNA2 and the cyclic template C-Hz9-DNA-DESA. PCR amplification of DESAHzDNA1 and DESAHzDNA2 and RCA of the circular DNA C-Hz9-DNA-DESA could be regulated reversibly, by adding Cu2+ ions for switching off and glutathione for switching on. The fluorescence of the HzDESA functional group allowed us to monitor the switching off and on of these amplification processes. Thus, coordination chemistry has potential for application in the regulation of amplification of DNA.

Revisiting Vibrational Spectroscopy to Tackle the Chemistry of Zr6O8 Metal-Organic Framework Nodes.

The metal-organic framework MOF-808 contains Zr6O8 nodes with a high density of vacancy sites, which can incorporate carboxylate-containing functional groups to tune chemical reactivity. Although the postsynthetic methods to modify the chemistry of the Zr6O8 nodes in MOFs are well known, tackling these alterations from a structural perspective is still a challenge. We have combined infrared spectroscopy experiments and first-principles calculations to identify the presence of node vacancies accessible for chemical modifications within the MOF-808. We demonstrate the potential of our approach to assess the decoration of MOF-808 nodes with different catechol–benzoate ligands. Furthermore, we have applied advanced synchrotron characterization tools, such as pair distribution function analyses and X-ray absorption spectroscopy, to resolve the atomic structure of single metal sites incorporated into the catechol groups postsynthetically. Finally, we demonstrate the catalytic activity of these MOF-808 materials decorated with single copper sites for 1,3-dipolar cycloadditions.

Tuning Lewis acid sites in TS-1 zeolites for hydroxylation of anisole with hydrogen peroxide

One-step direct hydroxylation of aromatics is an atom-economic way for phenols production. Ti-containing MFI zeolite is considered to be one of the most potential catalysts for hydroxylation of aromatics to phenols under mild condition with aqueous H 2 O 2 as the oxidant. However, the products are often a mixture of mono- or multi-phenols. Designing TS-1 zeolite catalyst with high yield and selectivity to the target phenols remains a challenging task. Here TS-1 zeolites are prepared by direct hydrothermal and post-synthetic methods. Multiple spectroscopic characterizations show that the crystallinity and Ti-Lewis acid sites (Ti-LASs) distribution of TS-1 zeolite can be controlled by the synthetic approach. The structure-activity relationship of TS-1 zeolite is established in the catalytic hydroxylation of anisole, revealing that Ti-LASs concentration determines the conversion of anisole, while both the crystallinity and Ti-LASs distribution significantly influence the selectivity to the desired product para -hydroxyanisole. •The Ti-Lewis acid properties of TS-1 zeolites can be precisely modulated by the sample preparation. •The concentration of Ti-LASs in TS-1 determines the conversion of anisole hydroxylation. •Introducing Ti-LASs into the well-crystalized TS-1 channels facilitates the selective production of para-isomers in the hydroxylation of anisole. •This work provides insights into the understanding of the catalytic properties of TS-1 zeolites towards the selective hydroxylation of anisole to phenols.

Room temperature fabrication and post-annealing treatment of amorphous Ga2O3 photodetectors for deep-ultraviolet light detection

This work fabricates deep-ultraviolet (DUV) photodetectors (PDs) with a metal-semiconductor-metal structure based on radio-frequency sputtered amorphous Ga2O3 films at room temperature. The Ga2O3-based PD exhibits a low dark current of 1.41 × 10−11 A, a responsivity of 1.77 A W−1 and a fast rise response time of 114 ms. A series of annealing treatments with different atmospheres have been found effective to reduce the oxygen vacancy concentration, exhibiting a trade-off effect between the responsivity and the response time. These results demonstrate a cost-effective room-temperature approach for fabricating amorphous Ga2O3-based PDs and developing possible post-synthetic methods for tuning the PD performance.

UiO-66-NH-(AO) MOFs with a New Ligand BDC-NH-(CN) for Efficient Extraction of Uranium from Seawater.

Metal-organic frameworks (MOFs) with a high surface area and excellent stability are potential candidates for uranium (U) adsorption. Amidoxime (AO) is the most widely used functional group to extract U, which is usually introduced into MOFs by two-step post-synthetic methods (PSMs). Herein, MOF UiO-66-NH-(AO) was obtained by a one-step PSM with amidoximation from UiO-66-NH-(CN), which was synthesized by a new organic ligand of 2-cyano-terephthalic acid and whose morphology was octahedron and could be well controlled with the new ligand. The one-step PSM can greatly maintain the octahedron of the MOFs. What is more, UiO-66-NH-(AO) showed good adsorption performance for U, the adsorption equilibrium was obtained within 1500 min, and the adsorption capacity of U was calculated to be 134.1 mg/g according to the Langmuir model. It also had excellent selectivity for U in the presence of high concentrations of vanadium (V), ferrum (Fe), magnesium (Mg), calcium (Ca), and zirconium (Zr). The adsorption capacity of U in natural seawater was determined to be 5.2 mg/g within 8 days. The recyclability of UiO-66-NH-(AO) in simulated seawater was demonstrated for at least four adsorption/desorption cycles. The binding mechanism was investigated by the extended X-ray absorption fine structure spectroscopy, revealing that U binding occurs in a fashion η2 motif. This study provides a reliable idea for the modification of MOFs and the potential for MOF-based materials to extract U from seawater.

Using Postsynthetic X-Type Ligand Exchange to Enhance CO2 Adsorption in Metal-Organic Frameworks with Kuratowski-Type Building Units.

Postsynthetic modification methods have emerged as indispensable tools for tuning the properties and reactivity of metal-organic frameworks (MOFs). In particular, postsynthetic X-type ligand exchange (PXLE) at metal building units has gained increasing attention as a means of immobilizing guest species, modulating the reactivity of framework metal ions, and introducing new functional groups. The reaction of a Zn-OH functionalized analogue of CFA-1 (1-OH, Zn(ZnOH)4(bibta)3, where bibta2- = 5,5'-bibenzotriazolate) with organic substrates containing mildly acidic E-H groups (E = C, O, N) results in the formation of Zn-E species and water as a byproduct. This Brønsted acid-base PXLE reaction is compatible with substrates with pKa(DMSO) values as high as 30 and offers a rapid and convenient means of introducing new functional groups at Kuratwoski-type metal nodes. Gas adsorption and diffuse reflectance infrared Fourier transform spectroscopy experiments reveal that the anilide-exchanged MOFs 1-NHPh0.9 and 1-NHPh2.5 exhibit enhanced low-pressure CO2 adsorption compared to 1-OH as a result of a Zn-NHPh + CO2 ⇌ Zn-O2CNHPh chemisorption mechanism. The MFU-4l analogue 2-NHPh ([Zn5(OH)2.1(NHPh)1.9(btdd)3], where btdd2- = bis(1,2,3-triazolo)dibenzodioxin), shows a similar improvement in CO2 adsorption in comparison to the parent MOF containing only Zn-OH groups.

Trisequential Postsynthetic Modification of a Tagged IRMOF-9 Framework.

Tailoring the pore environments of metal-organic frameworks (MOFs) is key to improving their performance and expanding their applicability. Postsynthetic methods, wherein an already synthesized MOF undergoes further chemical reactions, present many advantages for such tailoring and lead to much interesting new chemistry. However, this method has seldom been pushed farther than two reaction steps on the organic component. Here we report a three-step sequence starting from an alkenyl group on the biphenyl backbone of an IRMOF-9 analogue. The alkene is converted to an oxirane group and subsequently to a 1,2-azidoalcohol. The ultimate product is a framework functionalized with an aziridine ring. The reaction efficiency of each step is high, which suppresses the formation of undesired functional groups and the buildup of unintended multivariate frameworks. The synthesis of each framework was attempted via a direct synthetic method employing the appropriately functionalized biphenyldicarboxylate ligand. In general, this met with failure, which demonstrates the power and utility of postsynthetic methods for preparing new materials.

Covalent organic framework-based materials: Synthesis, modification, and application in environmental remediation

• Significance and advantages of COFs for environmental remediation are discussed. • Synthesis and modification of COF-based materials are briefly described. • COF-derived materials including COF-derived carbons were also dealt. • The environmental remediation applications of COFs are discussed in detail. • The outcomes and future directions in synthesis and application are presented. Covalent organic framework (COF) is a group of porous organic polymeric materials obtained from covalently attached organic building blocks. They exhibit positional control in two- or three-dimensional spaces through the predesigned and specified bonding of the monomer linkers. COFs are contemporary materials, and the recent identification of various synthesis and linking procedures has allowed their preparation with many advantageous properties and their usage in various applications. They can also be postsynthetically modified or converted to other materials of specific interest, thereby achieving materials with improved physical and chemical properties. COFs are considered as one of the most promising materials for applications in environmental remediation because of their ordered geometry, high porosity, functionality, high stability, and postsynthetic tunability in various physical and chemical forms. This review highlights the basic state-of-the-art in the advancement of stable COFs and their postsynthetic modification methods. The environmental remediation applications of COFs, which include adsorption, filtration, separation, catalysis, and sensing, will also be discussed in detail. Finally, the outcomes will be summarized and future directions will be discussed, indicating their promise for specialists in various research fields.

Influence of drying methods on the physical properties of bacterial nanocellulose

Bacterial nanocellulose (BNC) is a promising material for the use in medical implants. BNC does not induce unwanted reactions in vivo, is long term stable and possesses unique mechanical properties. However, to make the most of these features, BNC must be carefully processed. Details of the cultivation and post-synthetic methods offer various ways to control the properties of BNC. The focus of this work is put on drying of the BNC. Different unconstrained drying methods (climate chamber at 23°C, oven at 100°C, freeze-drying) and constrained drying under excertion of uniaxial pressure at various temperatures have been investigated. The reduction of the high water content of native BNC (≈98%) causes a thickness reduction of the samples. For oven or climate chamber drying a thickness reduction of 98% is observed, while freeze-drying widely preserves the nano- or micro-structure of the fibrous material and leads to a thickness reduction of only ≈13%. During drying or pressing at high temperature (100°C), i.e. by evaporation of the water, intermolecular hydrogen bonds are formed and interconnect the individual fibres and strands. Consequently mechanical stiffening is observed in tensile tests at small strains. After drying, a densified cellulose nano-fibre network is observed by scanning electron microscopy. Due to the irreversibility of drying by evaporation, the water content and water retention capacity of BNC are not recovered by rehydration. Applying uniaxial pressure before drying further enhances the irreversible reinforcement of the fibre network, while this is not the case when pressing the samples after drying. The presented results show that the properties of BNC can be widely controlled by post-processing steps. Thus, taylor-made BNC can be produced for biomedical applications.

A Comparative Study on Mesoporous Y Zeolites Prepared by Hard-Templating and Post-Synthetic Treatment Methods

Mesoporous Y zeolites were prepared comparatively using the bottom-up templating (with carbon nanotubes, CNTs, and nanocrystalline cellulose, NCC, as the templates) and the top-down post-synthetic treatment (with the sequential chemical and alkaline treatment) methods and characterised comprehensively using various techniques. The relevant findings show that the mesoporous Y zeolites with the intercrystal mesoporosity were prepared by the templating methods, and the NCC is the more effective, economic and sustainable hard template than the CNTs for promoting the formation of intercrystal mesoporosity. While for the post-synthetic strategy, the microwave (MW)-assisted chemical treatment (using ethylenediaminetetraacetic acid, EDTA, as the chemical agent for dealumination) was much more effective than the conventional hydrothermal (HT) treatment for introducing intracrystalline mesoporosity under the comparable condition, e.g. the external surface area: 287 m2 g−1 by 1 min MW treatment vs. 205 m2 g−1 by 6 h HT treatment. The prepared mesoporous Y zeolites, along with the parent Y, were assessed using the catalytic cracking of 1,3,5 triisopriopylbenzene (TiPBz). It was found that the well-developed intracrystalline mesoporosity promoted by the effective MW-assisted post-synthesis method is highly beneficial to the catalysis involving the bulky molecules, and accordingly showed the comparatively best catalytic performance (regarding the conversion and selectivity) among all zeolites under study in this work.

Alterations to secondary building units of metal–organic frameworks for the development of new functions

Post-synthetic modification methods for the secondary building units in MOFs facilitate unique structures and properties that are impossible to accessviadirect syntheses, which can be classified as four categories.