Mixed-linker Metal-organic Frameworks Research Articles

Mixed-Linker Zr-Metal-Organic Framework with Improved Lewis Acidic Sites for CO2 Fixation Reaction Catalysis.

Applying the mixed-linker strategy in synthesizing metal-organic frameworks (MOFs) has drawn considerable attention as a heterogeneous catalyst owing to their easy synthesis and different functional ligands in their frameworks. Following this strategy, we have developed a mixed linker Zr(IV)-based MOF, [Zr6O4(OH)4(FUM)n(PZDC-NO2)6-n] (PZDC-NO2 = 4-nitro-3,5-pyrazoledicarboxylic acid, FUM = fumaric acid) denoted as MOF-801(PZDC-NO2) synthesized via this strategy which possess an electron-withdrawing group (-NO2) on secondary linkers. The MOF-801(PZDC-NO2) has been fully characterized via various analyses, such as Fourier transform infrared, powder X-ray diffraction, 13C/1H nuclear magnetic resonance, XPS, TGA, and N2 adsorption/desorption, SEM, EDX, etc. By considering the concurrent existence of acid-base active sites and the synergistic role of these sites, this mixed-linker MOF was used as a catalyst for the cycloaddition reaction of CO2 and epoxides under mild without-solvent conditions. MOF-801(PZDC-NO2) displays significant catalytic performance by producing the highest catalytic conversion of epoxide to cyclic carbonate (93%) with a turnover number of 130.7 in 8 h reaction time and 100 °C temperature under low-pressure CO2 pressure. The mixed-linker Zr-MOF exhibits exceptional stability and reusability, maintaining its structure and functionality after consecutive cycles of utilization. Finally, the reaction mechanism was further investigated by density functional theory calculations. The total energy of the reactants, intermediates, and products involved in the process.

Diffusional Electron Transport Coupled to Thermodynamically Driven Electron Transfers in Redox-Conductive Multivariate Metal-Organic Frameworks.

The development of redox-conductive metal-organic frameworks (MOFs) and the fundamental understanding of charge propagation through these materials are central to their applications in energy storage, electronics, and catalysis. To answer some unresolved questions about diffusional electron hopping transport and redox conductivity, mixed-linker MOFs were constructed from two statistically distributed redox-active linkers, pyromellitic diimide bis-pyrazolate (PMDI) and naphthalene diimide bis-pyrazolate (NDI), and grown as crystalline thin films on conductive fluorine-doped tin oxide (FTO). Owing to the distinct redox properties of the linkers, four well-separated and reversible redox events are resolved by cyclic voltammetry, and the mixed-linker MOFs can exist in five discrete redox states. Each state is characterized by a unique spectroscopic signature, and the interconversions between the states can be followed spectroscopically under operando conditions. With the help of pulsed step-potential spectrochronoamperometry, two modes of electron propagation through the mixed-linker MOF are identified: diffusional electron hopping transport between linkers of the same type and a second channel that arises from thermodynamically driven electron transfers between linkers of different types. Corresponding to the four redox events of the mixed-linker MOFs, four distinct bell-shaped redox conductivity profiles are observed at a steady state. The magnitude of the maximum redox conductivity is evidenced to be dependent on the distance between redox hopping sites, analogous to the situation for apparent electron diffusion coefficients, Deapp, that are obtained in transient experiments. The design of mixed-linker redox-conductive MOFs and detailed studies of their charge transport properties present new opportunities for future applications of MOFs, in particular, within electrocatalysis.

Understanding and Controlling Molecular Compositions and Properties in Mixed-Linker Porphyrin Metal-Organic Frameworks.

Porphyrin-based metal-organic frameworks (MOFs) are attractive materials for photo- and thermally activated catalysis due to their unique structural features related to the porphyrin moiety, guest-accessible porosity, and high chemical tunability. In this study, we report the synthetic incorporation of nonplanar β-ethyl-functionalized porphyrin linkers into the framework structure of PCN-222, obtaining a solid-solution series of materials with different modified linker contents. Comprehensive analysis by a combination of characterization techniques, such as NMR, UV-vis and IR spectroscopy, powder X-ray diffraction, and N2 sorption analysis, allows for the confirmation of linker incorporation. A detailed structural analysis of intrinsic material properties, such as the thermal response of the different materials, underlines the complexity of synthesizing and understanding such materials. This study presents a blueprint for synthesizing and analyzing porphyrin-based mixed-linker MOF systems and highlights the hurdles of characterizing such materials.

Optimizing post-synthetic metal incorporation in mixed-linker MOFs: insights from metalation studies on bipyridine-containing UiO-67 single crystals.

The postsynthetic metalation (PSM) of metal-organic frameworks (MOFs) with intrinsic metal binding sites is an intriguing strategy to introduce catalytic function into MOFs. The spatial distribution of the catalytic sites within the MOF crystal will affect the efficiency of the material, but the factors that govern depth distribution of the introduced metal sites are often not well understood. Herein, we employ Rutherford backscattering spectrometry (RBS) to investigate the metal distribution in a series of post-synthetically metalated mixed linker bpdc/BPY UiO-67 (UiO = Universitet i Oslo, bpdc = biphenyl-dicarboxylate, BPY = 2,2'-bipyridine-5,5'-dicarboxylate) single crystals as a function of linker ratio and metalation time. The RBS spectra reveal large differences in the depth distribution of inserted Ni2+ ions, and core/shell architectures are observed in high BPY materials at shorter incubation times. The incubation times to achieve uniform metal incorporation increases with increasing BPY ratios in the materials, suggesting that the presence of the BPY linkers slow down metal uptake. We propose a combination of ionic interactions and pore clogging, where coordinated ions reduce the available pore space for further ions to diffuse deeper into the framework as reasons for the observed trends. The observations are likely relevant for other mixed-linker MOF systems, and understanding the effect that linker ratios have on PSM and cation distribution will aid in future optimizations of catalytic MOFs.

A mechanochemically synthesized Schiff-base engineered 2D mixed-linker MOF for CO2 capture and cationic dye removal.

Developing synthetic strategies for smart materials for the adsorption and separation of toxic chemicals is of great importance. Metal-organic frameworks (MOFs) have been proven to be outstanding adsorbent materials that possess excellent pollutant removal performances in wastewater treatment, including dye recycling. In this work, a neutral Cd(II) based 2D framework with a dual ligand strategy involving -OH functionalized 5-hydroxyisophthalic acid (5-OH-H2IPA) and the amide decorated Schiff base ligand (E)-N'-(pyridin-4-ylmethylene)isonicotinohydrazide (L) has been synthesized by different synthetic routes and characterized by various analytical methods. Thus, crystals of {[Cd(5-OH-IPA)(L)]·CH3OH}n synthesized via diffusion (ADES-7D) and the phase pure bulk product synthesized by conventional reflux (ADES-7C) and the mechanochemical grinding method (ADES-7M) have been established using PXRD data of the respective product showing identical simulated SXRD data to those of ADES-7D. The mechanochemically synthesized ADES-7M possesses a better surface area and CO2 adsorption capability compared to ADES-7C, which is also supported by electron microscopy and particle size measurements. Furthermore, ADES-7 can be used as an efficient adsorbent material for the reversible, selective adsorption (42-99%) and separation of the cationic dyes malachite green (MG), methyl violet (MV), methylene blue (MB), and rhodamine B (RhB) from the mixture of cationic/anionic dyes (methyl orange (MO) and bromocresol green (BCG)) in the aqueous phase. Specifically, ADES-7M possesses better dye capture capability compared to ADES-7C, even in the case of the bigger dye RhB with adsorption differences of 2.38 to 1.01 mg g-1, respectively. The dye adsorption kinetics follows pseudo-second-order kinetics, and the dye adsorption isotherm fits well with the Langmuir/Freundlich adsorption isotherm models. The probable mechanism of adsorption involving the supramolecular interaction between the host MOF and the guest dye has also been proposed.

Controlled Partial Linker Thermolysis in Metal-Organic Framework UiO-66-NH2 to Give a Single-Site Copper Photocatalyst for the Functionalization of Terminal Alkynes.

Metal-organic frameworks (MOFs) with expanding porosity and tailored pore environments are intriguing for catalytic applications. We report herein a straightforward method of controlled partial linker thermolysis to introduce desirable mesopores into mono-ligand MOFs, which is different from the classical thermolyzing method that starts from mixed-linker MOFs. UiO-66-NH2 , after partial ligand thermolysis, exhibits significant mesoporosity, retained crystal structure, improved charge photogeneration and abundant anchoring sites, which is ideal to explore single-site photocatalysis. Atomically dispersed Cu is then accommodated in the tailored pore. The resulting single-site Cu catalyst exhibits excellent performance for photocatalytic alkylation and oxidation coupling for the functionalization of terminal alkynes. The study highlights the advantage of controlled partial linker thermolysis to synthesize hierarchical MOFs to achieve the advanced single-site photocatalysis.

Regulating highly photoelectrochemical activity of Zr-based mixed-linker metal-organic frameworks toward sensitive electrogenerated chemiluminescence sensing of α-glucosidase

The conductivity and emission efficiency of metal-organic frameworks (MOFs) remain challenging factors that limit their electrogenerated chemiluminescence (ECL) sensing applications. Herein, we report a facile approach to address these challenges by integrating an electroactive linker (H2-TCPP) with an ECL active electrogenerated chemiluminescence linker (H4-TBAPy) to construct a highly photoelectrochemical active mixed-linker MOFs (ML-MOFs). ECL results revealed a remarkable 15.4-fold enhancement for the top-performing ML-MOFs (M6-MOFs), surpassing the single linker MOFs. In addition, M6-MOFs also exhibit a remarkable 73-fold enhancement in ECL efficiency compared to commercial Ru (bpy)32+. This improvement should be attributed to the synergistic effects resulting from the combination of two linkers. Furthermore, M6-MOFs are found to be served as a model ECLphore for sensitive and selective detection of α-glucosidase for the first time with good potential practicability in human serum samples. This work represents a promising direction to guide for designing good conductivity and high ECL efficiency MOFs in terms of linker functionalization and thus bandgap modulation for advancing their ECL sensing applications.

Systematic Thiol Decoration in a Redox-Active UiO-66-(SH)2 Metal-Organic Framework: A Case Study under Oxidative and Reductive Conditions.

The practical applicability of thiolated metal-organic frameworks (MOFs) remains challenging due to their low crystallinity and transient stability. Herein, we present a one-pot solvothermal synthesis process using varying ratios of 2,5-dimercaptoterephthalic acid (DMBD) and 1,4-benzene dicarboxylic acid (100/0, 75/25, 50/50, 25/75, and 0/100) to prepare stable mixed-linker UiO-66-(SH)2 MOFs (ML-U66SX). For each variant, the effects of different linker ratios on the crystallinity, defectiveness, porosity, and particle size have been discussed in detail. In addition, the impact of modulator concentration on these features has also been described. The stability of ML-U66SX MOFs was investigated under reductive and oxidative chemical conditions. The mixed-linker MOFs were used as sacrificial catalyst supports to highlight the interplay of template stability on the rate of the gold-catalyzed 4-nitrophenol hydrogenation reaction. The release of catalytically active gold nanoclusters originating from the framework collapse decreased with the controlled DMBD proportion, resulting in a 59% drop in the normalized rate constants (9.11-3.73 s-1 mg-1). In addition, post-synthetic oxidation (PSO) was used to further probe the stability of the mixed-linker thiol MOFs under harsh oxidative conditions. Following oxidation, the UiO-66-(SH)2 MOF underwent immediate structural breakdown, unlike other mixed-linker variants. Along with crystallinity, the microporous surface area of the post-synthetically oxidized UiO-66-(SH)2 MOF could be increased from 0 to 739 m2 g-1. Thus, the present study delineates a mixed-linker strategy to stabilize the UiO-66-(SH)2 MOF under harsh chemical conditions through meticulous thiol decoration.

Redox-Active Mixed-Linker Metal-Organic Frameworks with Switchable Semiconductive Characteristics for Tailorable Chemiresistive Sensing.

Metal-organic frameworks (MOFs), with diverse metal nodes and designable organic linkers, offer unique opportunities for the rational engineering of semiconducting properties. In this work, we report a mixed-linker conductive MOF system with both tetrathiafulvalene and Ni-bis(dithiolene) moieties, which allows the fine-tuning of electronic structures and semiconductive characteristics. By continuously increasing the molar ratio between tetrathiafulvalene and Ni-bis(dithiolene), the switching of the semiconducting behaviors from n-type to p-type was observed along with an increase in electrical conductivity by 3 orders of magnitude (from 2.88 × 10-7 S m-1 to 9.26 × 10-5 S m-1). Furthermore, mixed-linker MOFs were applied for the chemiresistive detection of volatile organic compounds (VOCs), where the sensing performance was modulated by the corresponding linker ratios, showing synergistic and nonlinear modulation effects.

Reticular chemistry for the rational design of mechanically robust mesoporous merged-net metal-organic frameworks

Reticular chemistry for the rational design of mechanically robust mesoporous merged-net metal-organic frameworks

Imparting Multifunctionality in Zr-MOFs Using the One-Pot Mixed-Linker Strategy: The Effect of Linker Environment and Enhanced Pollutant Removal.

The development of mixed-linker metal-organic frameworks (MOFs) is an efficient strategy to improve the performance of MOFs. Herein, we successfully integrate tetrakis(4-carboxyphenyl)porphyrin (TCPP) into different Zr-MOFs via a facile one-pot solvothermal synthesis while preserving the integrity of their frameworks. The functional groups, length of primary linkers, and the inner pore structure significantly affected the properties of the synthesized TCPP@MOFs, such as surface area, average pore size, and 1O2 productivity. Among them, TCPP@PCN-777 demonstrated the largest surface area (2386 cm2/g, as measured by N2 uptake) and the highest 1O2 generation rate (1.15 h-1, [1O2]ss = 2.66 × 10-12 M) under irradiation. The TCPP loading was also shown to affect the crystal phase, morphology, surface area, and photochemical properties of the synthesized MOFs. Therefore, TCPP@PCN-777s with various TCPP loadings were synthesized to investigate the optimum loading. The optimized TCPP@MOF, TCPP@PCN-777-30, was evaluated for its removal of model contaminant ranitidine (RND) through both adsorption and photodegradation. TCPP@PCN-777-30 showed a higher adsorption capacity toward RND than both the parent MOF (PCN-777) and commercially available activated carbon, and effectively degraded RND in aqueous solution (>99% photodegradation in 1 h). With irradiation, TCPP@PCN-777-30 showed a minimal loss in adsorption efficiency over four consecutive treatment cycles, confirming the reusability of the material enabled through the incorporation of TCPP into the MOF structure. This work not only developed an efficient multifunctional material for environmental remediation but also forwarded knowledge on the effect of linker environment (i.e., functional groups, framework structure, and linker ratio) on the properties of TCPP@MOFs to guide future research on mixed-linker MOFs.

Mixed-Linker Metal-Organic frameworks for carbon and hydrocarbons capture under moist conditions

• MOF-801-FA were synthesised via utilizing a mixed-ligand strategy. • Gas adsorption was boosted, e.g., a 2.5-fold increase for methane capture. • Prominent IAST selectivities were witnessed for CH 4 /N 2 and CO 2 /N 2 mixture. • MOF-801-FA reveal clean and sharp separations in a high relative humidity. The capture of carbon and hydrocarbons is significant to the utilization of valuable resources and the mitigation of global warming, but achieving high gas capacity and selectivity at the same time remains a challenge, especially in the presence of high humidity. In this regard, based on the building block of MOF-801, MOF-801-FA structures were synthesized with high quality and few defects through a mixed-ligand strategy, in which formate ligands were introduced into the framework apart from fumarate ligands. This brought about tremendous increases in gas adsorption capacity, e.g., ca. 2.5-fold and 1.1-fold enhancement occurred to the adsorption of CH 4 and CO 2 in MOF-801-Hf-FA than MOF-801-Hf at 298 K and 1 bar. Besides, prominent IAST selectivities were also witnessed in MOF-801-FA, higher than those in the pristine MOFs, for CH 4 /N 2 and CO 2 /N 2 mixtures under ambient conditions. We then confirmed the efficient performance of MOF-801-FA for real CH 4 /N 2 and CO 2 /N 2 mixtures using the breakthrough experiments and following cycling tests, even in a relative humidity of 90%. Thus, the mixed-linker strategy was demonstrated effective to tune the structures of MOFs, and boost their performance in gas adsorption and separation. The results also showed that, with high capacities for CH 4 and CO 2 , superior selectivities over N 2 , desirable water resistance and facile regeneration, MOF-801-M−FA (M = Zr or Hf) are promising candidates for capturing CH 4 and CO 2 from N 2 in industry.

Decarboxylation-Induced Defects in MOF-Derived Single Cobalt Atom@Carbon Electrocatalysts for Efficient Oxygen Reduction.

Developing transition metal single-atom catalysts (SACs) for oxygen reduction reaction (ORR) is of great importance. Zeolitic imidazolate frameworks (ZIFs) as a subgroup of metal-organic frameworks (MOFs) are distinguished as SAC precursors, due to their large porosity and N content. However, the activity of the formed metal sites is limited. Herein, we report a decarboxylation-induced defects strategy to improve their intrinsic activity via increasing the defect density. Carboxylate/amide mixed-linker MOF (DMOF) was chosen to produce defective Co SACs (Co@DMOF) by gas-transport of Co species to DMOF upon heating. Comparing with ZIF-8 derived SAC (Co@ZIF-8-900), Co@DMOF-900 with more defects yet one fifth Co content and similar specific double-layer capacitance show better ORR activity and eight times higher turnover frequency (2.015 e s-1 site-1 ). Quantum calculation confirms the defects can weaken the adsorption free energy of OOH on Co sites and further boost the ORR process.

Bandgap Modulation in Zr-Based Metal-Organic Frameworks by Mixed-Linker Approach.

Metal-organic frameworks (MOFs) have been a promising material for many applications, e.g., photocatalysis, luminescence-based sensing, optoelectronics, and electrochemical devices, due to their tunable electronic properties through linker functionalization. In this work, we investigate the effect of mixed organic linkers on the bandgap modulation of polymorphic zirconium-based MOFs, UiO-66 and MIL-140A using density functional theory (DFT) calculations. We show that the electronic properties of both MOFs are in contrast to Vegard's law for semiconductors, that is, mixed-linker systems exhibit bandgaps not intermediate within the range of single-linker systems. Calculations of the total and partial density of states revealed the formation of mid-gap states in mixed-linker MOFs, causing the bandgap reduction. Interestingly, although both MOFs have similar composition, the effect is more significant in MIL-140A than in UiO-66. This is due to the presence of π-π stacking interactions in MIL-140A, which does not occur in UiO-66. The simulation results reveal a direct relationship between the strength of π-π interactions and the bandgap. This illustrates that distinct structural features, particularly the orientation of organic linkers can give rise to different consequences in bandgap modulation. Moreover, this computational work highlights the possibility to engineer the electronic properties of MOFs through a mixed-linker approach.

Photoelectrochemical alcohol oxidation by mixed-linker metal-organic frameworks.

Metal-organic frameworks (MOFs) provide a suitable platform for stable and efficient heterogeneous photoelectrochemical oxidation catalysis due to their highly ordered structure, large surface area, and synthetic tunability. Herein, a mixed-linker MOF comprising of a photosensitizer [Ru(dcbpy)(bpy)2]2+ (bpy = 2,2'-bipyridine, dcbpy = 5,5'-dicarboxy-2,2'-bipyridine) and catalyst [Ru(tpy)(dcbpy)Cl]+ (tpy = 2,2':6',2''-terpyridine) that were incorporated into the UiO-67 framework and grown as thin films on a TiO2-coated, fluorine-doped tin oxide (FTO) electrode (RuB-RuTB-UiO-67/TiO2/FTO). When used as an electrode for the photoelectrochemical oxidation of benzyl alcohol, the mixed-linker MOF film showed a faradaic efficiency of 34%, corresponding to a 3-fold increase in efficiency relative to the RuB-UiO-67/TiO2/FTO control. This increase in catalytic efficiency is ascribed to the activation of RuTB moieties via oxidation by photogenerated RuIIIB. Transient absorption spectroscopy revealed the delayed appearance of RuIIITB* or RuIIITB formation, occurring with a lifetime of 21 ns, due to energy and/or electron transfer. The recovery kinetics of the charge separated state was increased (283 μs) in comparison to single-component control experiments (105 μs for RuB-UiO-67/TiO2/FTO and 7 μs for RuTB-UiO-67/TiO2/FTO) indicating a cooperative effect that could be exploited in chromophore/catalyst MOF motifs.

Flexible and porous 2D layered structures based on mixed-linker metal-organic frameworks for gas sorption studies.

Layered structures of flexible mixed-linker metal-organic frameworks termed IRHs-(4 and 5) (IRH = Institut de Recherche sur l'Hydrogène) were synthesized by mixing cyclam, tetrakis(4-carboxyphenyl)benzene (TCPB), and copper and zinc metal salts respectively. The new materials characterized by single-crystal X-ray diffraction exhibited the features of HOFs and MOFs. Their structures are formed by coordination and hydrogen bonds that link metallocyclam (with Cu or Zn) and TCPB to a 2D sheet which is further packed to form a 3D structure with 1D microchannels. Remarkably, the as-synthesized IRHs-(4 and 5) contain DMF in the channels that can be exchanged with DCM and afterward removed from the framework by heating without losing their single-crystallinity. This enabled an easy elucidation of the structural transformations by single-crystal and powder X-ray diffraction analyses. Experimental studies of single-component adsorption isotherms of pure CO2, CH4, and N2 gases have been carried out for all activated IRHs. Based on the obtained adsorption isotherms, theoretical calculations using Ideal Adsorbed Solution Theory (IAST) have been performed to predict the selectivity of equimolar CO2/CH4 and CO2/N2 (1 : 1) binary mixtures. The simulations predicted outstanding selectivity for CO2/N2 than for CO2/CH4 at low pressures, reaching 185 for IRH-4 and 130 for IRH-5 at 1 bar.

Fluorescence Enhancement in the Solid State by Isolating Perylene Fluorophores in Metal–Organic Frameworks

Polycyclic aromatic hydrocarbons such as perylene and pyrene and their derivatives are highly emissive fluorophores in solution. However, the practical applications of these materials in the field of molecular electronic and light-emitting devices are often hindered by self-quenching effects because of the formation of nonfluorescent aggregates in concentrated solutions or in the solid state. Herein, we demonstrate that aggregation-caused quenching of perylenes can be minimalized by molecular incorporation into metal-organic frameworks (MOFs). This study utilized a stable Zr6 cluster-based MOF, UiO-67, as a matrix. Linear linkers containing photoresponsive moieties were designed and incorporated into the parent UiO-67 scaffold through the partial replacement of the nonfluorescent linkers of a similar length, forming mixed-linker MOFs. The average distance between perylene moieties was tuned by changing the linker ratios, thus controlling the fluorescence intensity, emission wavelength, and quantum yield. Molecular modeling was further adopted to correlate the number of isolated perylene linkers within the framework with the ratio between the two linkers, thereby rationalizing the change in the observed fluorescent properties. Taking advantage of the tunable fluorescence, inherent porosity, and high chemical stability of this MOF platform, it was applied as a fluorescent sensor for oxygen detection in the gas phase, a model reaction, showing fast response and good recyclability.

Dimension Control in Mixed Linker Metal-Organic Frameworks via Adjusting the Linker Shapes.

In this context, we describe a novel method to control the dimensionality and, further, the morphology in three mixed linker metal-organic frameworks (MOFs) TMU-70, TMU-71, and TMU-49 via altering the linker shapes. The compatibility between the shape of linkers used in the mixed linker framework, specifically linker angles, can directly affect the dimensionality of the resulting networks from 2D to 3D. Using incompatible linkers (one bent and one linear) together with binodal SBU directed the structure to form 2D networks, while 3D networks were obtained through applying linkers with the same shape. Further, the 2D and 3D MOFs were fabricated through the coordination modulation strategy. The impact of various modulators on the size and morphology of the structures has been examined. The 2D MOFs produced only nanorods through application of different capping agents owing to their preferred crystal growth, while the 3D networks led to rod and plate morphologies. Also, the catalytic performance of MOFs in an aldol-type condensation reaction was estimated. High and fast catalytic activity is detected in nanoscale rod-shaped catalysts.

Synthetic Strategies and Structural Arrangements of Isoreticular Mixed-Component Metal-Organic Frameworks.

In recent years, the synthesis of mixed-metal and mixed-linker metal-organic frameworks with multiple metals and/or linker molecules combined in one framework has become a growing field of interest. These mixed-component or multivariate metal-organic framework materials provide the possibility to introduce multiple functionalities inside one framework. The interaction of guest molecules with different functionalities in the same material is a promising approach in the fields of gas storage, separation, catalysis and drug delivery. Furthermore, the combination of different components may lead to synergistic effects that cannot be achieved otherwise. These mixed-component approaches open up new pathways to an even larger range of possible customizations in the field of metal-organic frameworks.

Synthesis of Cu-Trimesic Acid/Cu-1,4-Benzenedioic Acid via Microdroplets: Role of Component Compositions

Mixed-linker metal–organic frameworks (MOFs) offer great tunability in both pore structures and surface chemistry. This study reports the synthesis and characterization of model mixed-linker MOFs (i.e., Cu-TMA/Cu-BDC; BDC = 1,4-benzenedioic acid, TMA = trimesic acid) via a microdroplet-based spray process, to unravel the relationship between the properties of mixed-linker MOFs and the component compositions. The as-prepared mixed-linker MOFs exhibited distinct properties in terms of morphology, crystalline phase, surface chemistry, and pore structure. In particular, two-dimensional correlation spectroscopy (2D-COS) analysis was conducted to analyze the correlational features among surface functional groups, which are unattainable from traditional infrared and Raman spectra. The results from the 2D-COS analysis also suggest that the surface chemistry of the mixed-linker MOFs is adjustable by controlling the precursor conditions. Measurements of CO2 adsorption on the mixed-linker MOFs demonstrated the tunab...