Great attention has been given to metal–organic frameworks (MOFs)-derived solid bases because of their attractive structure and catalytic performance in various organic reactions. The extraordinary ...skeleton structure of MOFs provides many possibilities for incorporation of diverse basic functionalities, which is unachievable for conventional solid bases. The past decade has witnessed remarkable advances in this vibrant research area; however, MOFs for heterogeneous basic catalysis have never been reviewed until now. Therefore, a review summarizing MOFs-derived base catalysts is highly expected. In this review, we present an overview of the recent progress in MOFs-derived solid bases covering preparation, characterization, and catalytic applications. In the preparation section, the solid bases are divided into two categories, namely, MOFs with intrinsic basicity and MOFs with modified basicity. The basicity can originate from either metal sites or organic ligands. Different approaches used for generation of basic sites are included, and each approach is described with representative examples. The fundamental principles for the design and fabrication of MOFs with basic functionalities are featured. In the characterization section, experimental techniques and theoretical calculations employed for characterization of basic MOFs are summarized. Some representive experimental techniques, such as temperature-programmed desorption of CO2 (CO2-TPD) and infrared (IR) spectra of different probing molecules, are covered. Following preparation and characterization, the catalytic applications of MOFs-derived solid bases are dealt with. These solid bases have potential to catalyze some well-known “base-catalyzed reactions” like Knoevenagel condensation, aldol condensation, and Michael addition. Meanwhile, in contrast to conventional solid bases, MOFs show some different catalytic properties due to their special structural and surface properties. Remarkably, characteristic features of MOFs-derived solid bases are described by comparing with conventional inorganic counterparts, keeping in mind the current opportunities and challenges in this field.
Photoresponsive metal–organic frameworks (PMOFs) are of interest for tailorable CO2 adsorption. However, modulation of CO2 adsorption on PMOFs is based on steric hindrance or structural change owing ...to weak interactions between CO2 and active sites. It is challenging to fabricate PMOFs with strong but tailorable sites for CO2 adsorption. Now, the construction of PMOFs with target‐specific (strong) active sites is achieved by introducing tetraethylenepentamine into azobenzene‐functionalized MOFs for tailorable CO2 adsorption. Amines are specific active sites for CO2, contributing to capture CO2 selectively. Cis/trans isomerization of azobenzene motifs trigged by UV/Vis light adjusts the electrostatic potential of amines significantly, leading to exposure/shelter of amines and modulation of CO2 adsorption on strong active sites. This system enables us to design adsorption processes for CO2 capture from mixtures, which is impossible to realize by traditional PMOFs.
Smart adsorbents were fabricated by introducing target‐specific active sites (amines) into photoresponsive metal–organic frameworks (PMOFs). The cis/trans isomerization of azobenzene motifs trigged by UV/Vis light irradiation adjusts the electrostatic potential of amines significantly. This leads to exposure/shelter of amines and successful modulation of CO2 adsorption on strong active sites, which is impossible to realize by traditional PMOFs.
Abstract
The zeolite Cu(I)Y is promising for adsorptive removal of thiophenic sulfur compounds from transportation fuels. However, its application is seriously hindered by the instability of Cu(I), ...which is easily oxidized to Cu(II) even under atmospheric environment due to the coexistence of moisture and oxygen. Here, we report the adjustment of zeolite microenvironment from hydrophilic to superhydrophobic status by coating polydimethylsiloxane (yielding Cu(I)Y@P), which isolates moisture entering the pores and subsequently stabilizes Cu(I) despite the presence of oxygen. Cu(I) in Cu(I)Y@P is stable upon exposure to humid atmosphere for 6 months, while almost all Cu(I) is oxidized to Cu(II) in Cu(I)Y for only 2 weeks. The optimized Cu(I)Y@P material after moisture exposure can remove 532 μmol g
−1
of thiophene and is much superior to Cu(I)Y (116 μmol g
−1
), regardless of similar uptakes for unexposed adsorbents. Remarkably, Cu(I)Y@P shows excellent adsorption capacity of desulfurization for water-containing model fuel.
Nanoporous adsorbents are highly efficient in selectively capturing aromatic sulfur compounds such as thiophene, benzothiophene, dibenzothiophene, and 4,6-dimethyldibenzothiophene that are refractory ...to remove by traditional techniques from liquid hydrocarbon fuels. In the past decades, great progress has been made in design and fabrication of nanoporous adsorbents as well as the judicious strategies of promoting their performance for deep desulfurization. However to the best of our knowledge, a comprehensive review from this perspective has never been reported until now. Therefore, a review summarizing these nanoporous adsorbents and advanced strategies is highly anticipated. In this review, we provide an overview of the synthesis methods, improvement strategies, and prospective of the nanoporous adsorbents for applications with adsorptive desulfurization. The concerned materials cover most of the traditional and recently emerged nanoporous materials, and are introduced and basically grouped by material type. Each category is illustrated with some typical examples, and the fundamental principles on how to design and fabricate nanoporous adsorbents are highlighted. The adsorption mechanism is discussed in detail as well.
Traditional and recently emerged nanoporous adsorbents for deep desulfurization of liquid hydrocarbon fuels are summarized.
Hierarchically porous metal–organic frameworks (HP‐MOFs) have attracted great attention owing to their advantages over microporous MOFs in some applications. Despite many attempts, the development of ...a facile approach to generate HP‐MOFs remains a challenge. Herein we develop a new strategy, namely the modulation of cation valence, to create hierarchical porosity in MOFs. Some of the CuII metal nodes in MOFs can be transformed into CuI via reducing vapor treatment (RVT), which partially changes the coordination mode and thus breaks coordination bonds, resulting in the formation of HP‐MOF based on the original microporous MOF. Both the experimental results and the first‐principles calculation show that it is easy to tailor the amount of CuI and subsequent hierarchical porosity by tuning the RVT duration. It is found that the resultant HP‐MOFs perform much better in the capture of aromatic sulfides than the original microporous MOF.
Making the cut: Some of CuII nodes in the metal–organic framework (MOF) HKUST‐1 can be transformed into CuI by a reducing vapor treatment (RVT). This treatment partially changes the coordination mode of the Cu nodes and thus breaks coordination bonds, resulting in the formation of hierarchical pores from the original microporous HKUST‐1.
Hierarchically porous metal–organic frameworks (HP‐MOFs) are promising in various applications. Most reported HP‐MOFs are prepared based on the generation of mesopores in microporous frameworks, and ...the formed mesopores are connected by microporous channels, limiting the accessibility of mesopores for bulky molecules. A hierarchical structure is formed by constructing microporous MOFs in uninterrupted mesoporous tunnels. Using the confined space in as‐prepared mesoporous silica, highly dispersed metal precursors for MOFs are coated on the internal surface of mesoporous tunnels. Ligand vapor‐induced crystallization is employed to enable quantitative formation of MOFs in situ, in which sublimated ligands diffuse into mesoporous tunnels and react with metal precursors. The obtained hierarchically porous composites exhibit record‐high adsorption capacity for the bulky molecule trypsin. The thermal and storage stability of trypsin is improved upon immobilization on the composites.
Hierarchical structures were constructed using microporous metal–organic frameworks (MOFs) in uninterrupted mesoporous tunnels. Highly dispersed metal precursors are coated on the internal surface of mesoporous tunnels, followed by ligand vapor‐induced crystallization to form MOFs. The obtained composites show high adsorption capacity for trypsin.
Porous Liquids Responsive to Light Dinker, Manish Kumar; Zhao, Kan; Dai, Zhengxing ...
Angewandte Chemie International Edition,
December 12, 2022, Letnik:
61, Številka:
50
Journal Article
Recenzirano
Odprti dostop
A porous liquid is a unique liquid medium that combines the cavity of porous solids with the fluidity of liquids. This special characteristic offers potential in various applications. Here we report ...a type II photoresponsive porous ionic liquid (PPIL) from dissolving a photoresponsive metal‐organic polyhedron (PMOP, constructed from dicopper and azobenzene‐containing carboxylate) in a polyethylene‐glycol‐functionalized bulky ionic liquid (IL). Owing to favorable ion interactions, bulky IL molecules encircle outside PMOP, and the inter cavities are maintained. The azobenzene moieties can be isomerized freely in the PPILs to expose and shelter active sites upon visible and UV light irradiation. Hence, the adsorption capacity of PPILs is controllable by light irradiation, and the change in CO2 uptake is up to 30 % compared to neat IL. This study may inspire the development of new adsorption process regulated by light instead of pressure and temperature swing adsorption.
A type II photoresponsive porous ionic liquid (PPIL) with permanent cavities is formed by dissolving Cu‐based metal‐organic polyhedron (MOP) in bulky ionic liquid .The MOP carries azobenzene moieties as pendant groups which undergo trans‐ and cis‐isomerization under visible and UV light irradiation and thus, a controlled CO2 uptake and release is realized.
Stimuli‐responsive metal–organic polyhedra (srMOPs) functionalized with azobenzene showed UV‐irradiation‐induced isomerization from the insoluble trans‐srMOP to the soluble cis‐srMOP, whereas ...irradiation with blue light reversed this process. Guest molecules were trapped and released upon cis‐to‐trans and trans‐to‐cis isomerization of the srMOPs, respectively. This study provides a new direction in the ever‐diversifying field of MOPs, while laying the groundwork for a new class of optically responsive materials.
Lock in the guests, later set them free: Stimuli‐responsive metal–organic polyhedra (srMOPs) functionalized with azobenzene showed UV‐light‐induced isomerization from insoluble srMOPs substituted with trans‐azobenzene to soluble srMOPs with cis‐azobenzene units; irradiation with blue light reversed this process (see picture). Guest molecules were trapped upon cis‐to‐trans and released upon trans‐to‐cis isomerization of the azobenzene units.
Because of their abundant porosity, tunable surface properties, and high stability, N-doped porous carbons (NPCs) are highly promising for CO2 capture. Carbonization of N-containing polymers is ...frequently used for the preparation of NPCs, while such an approach is hindered by the high cost of some polymer precursors. In the present study, we report for the first time the fabrication of NPCs through the rational choice of the low-cost, N-rich polymer NUT-2 (NUT indicates Nanjing Tech University) as the precursor, which was obtained from polymerization of easily available monomers under mild conditions in the absence of any catalysts. Through carbonization at different temperatures (500–800 °C), NPCs with various porosity and nitrogen contents are obtained. The pore structure and CO2-philic (N-doped) sites are responsible for the adsorption performance, while the highest surface area does not lead to the highest CO2 adsorption capacity. For the sample carbonized at 600 °C (NPC-2-600), the adsorption capacity on CO2 is as high as 164.7 cm3 g–1 at 0 °C and 1 bar, which is much better than that of the benchmarks, such as activated carbon (62.5 cm3 g–1) and 13X zeolite (91.8 cm3 g–1), as well as most reported carbon-based adsorbents. We also demonstrate that the present NPCs can be regenerated completely under mild conditions. The present adsorbents may provide promising candidates for the capture of CO2 from various mixtures, such as flue gas and natural gas.
Because of their diverse structure, high porosity, and tunable functionality, metal–organic frameworks (MOFs) are of great interest for diverse applications, including catalysis. However, the poor ...hydrostability of most reported MOFs hinders their catalytic applications seriously. In addition, the development of an effective method to improve the catalytic activity of MOFs is another challenge. Here, we report for the first time the development of a double-solvent strategy to fabricate MOFs inside silica nanopores. A typical MOF (MOF-5) and a mesoporous silica with two-dimensional hexagonal pore regularity (SBA-15) were first attempted. The double-solvent strategy is based on a hydrophobic solvent and a hydrophilic solution containing MOF precursors with a volume equal to or less than the pore volume of the support so that the MOF can be formed selectively in the channels of support. Our results show that upon confinement in silica nanopores the hydrostability of MOF-5 is apparently improved. The framework of MOF-5 is destroyed obviously in a humid environment for 15 min, but that confined in SBA-15 is well preserved after 8 h. Moreover, the catalytic activity of the composite MOF-5@SBA-15 is superior to that of pure MOF-5 regarding activity and reaction rate. Under the catalysis of MOF-5@SBA-15, the conversion of benzyl bromide in the Friedel–Crafts alkylation reaction can reach 100% at 80 °C for 3 h, which is much higher than that of pure MOF-5 (61%) and SBA-15 (0%). We also demonstrate that the double-solvent strategy can be successfully extended to other MOFs, such as HKUST-1 and ZIF-8. Our work might open up an avenue for the improvement of stability and performance of MOFs, which is highly expected for a variety of applications.
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