Porphyrinic Zirconium Research Articles

Guest-Stimulated Nonplanar Porphyrins in Flexible Metal-Organic Frameworks.

Nonplanar porphyrins with out-of-plane distortions play crucial roles in many biological functions and chemical applications. The artificial construction of nonplanar porphyrins usually involves organic synthesis and modification, which is a highly comprehensive approach. However, incorporating porphyrins into guest-stimulated flexible systems allows to manipulate the porphyrin distortion through simple ad/desorption of guest molecules. Here, a series of porphyrinic zirconium metal-organic frameworks (MOFs) is reported that exhibit guest-stimulated breathing behavior. X-Ray diffraction analysis and skeleton deviation plots confirm that the material suffers from porphyrin distortion to form a ruffled geometry under the desorption of guest molecules. Further investigation reveals that not only the degree of nonplanarity can be precisely manipulated but also the partial distortion of porphyrin in a single crystal grain can be readily achieved. As Lewis acidic catalyst, the MOF with nonplanar Co-porphyrin exhibits active properties in catalyzing CO2 /propylene oxide coupling reactions. This porphyrin distortion system provides a powerful tool for manipulating nonplanar porphyrins in MOFs with individual distortion profiles for various advanced applications.

Spike Current Induction by Photogenerated Charge Accumulation at the Surface Sites of Porous Porphyrinic Zirconium Metal-Organic Framework Electrodes in Photoelectrochemical Cells

Abstract Photoelectrochemical (PEC) capacitors have recently garnered increasing interest based on their charge accumulation and dissipation mechanisms, particularly with respect to spike and overshoot currents, and have therefore been investigated for biomedical applications, including nerve photostimulation and biomolecular sensing. Porous metal-organic frameworks (MOFs) are capable of accumulating large amounts of photogenerated charge at their surface sites, owing to their large surface areas, and therefore may have potential as a new material for use in PEC capacitors. To explore the PEC capacitor properties of MOFs, we performed transient photocurrent measurements using PEC cells comprising porphyrinic zirconium MOF (PZ-MOF) electrodes in a phosphate-buffered saline solution. We observed a clear growth and decay of the cathodic current during light irradiation and the generation of an anodic reverse current when the light was turned off, thus inducing spike and overshoot currents. However, no spike or overshoot currents were observed when excess oxygen was introduced into the electrolyte. These results indicate that PZ-MOFs have the ability for photogenerated charge accumulation at the surface pores near the interface between the PZ-MOF electrode and the electrolyte. Thus, we have confirmed that PZ-MOFs are a promising PEC capacitor material that may be used in future biomedical applications.

Self-cleaning and regenerable nano zero-valent iron modified PCN-224 heterojunction for photo-enhanced radioactive waste reduction.

The expansion of large-scale nuclear power causes a substantial volume of radioactive wastewater containing uranium to be released into the environment. Because of uranium's toxicity and bioaccumulation, it is critical to develop the efficient and sustainable materials for selective removal of uranium (VI). Herein, a regenerable anti-biofouling nano zero-valent iron doped porphyrinic zirconium metal-organic framework (NZVI@PCN-224) heterojunction system was successfully fabricated. Due to the Schottky-junction effect at the NZVI/MOF interface, the NZVI nanomaterial immobilized on PCN-224 could improve interfacial electron transfer and separation efficiency, and enhance entire reduction of highly soluble U(VI) to less soluble U(IV), involving photocatalytic reduction and chemical reduction. Meanwhile, the photocatalytic effect also prompts the NZVI@PCN-224 to produce more biotoxic reactive oxygen species (ROS), resulting in high anti-microbial and anti-algae activities. Under dark conditions, NZVI@PCN-224 with a large specific surface area could provide sufficient oxo atoms as the uranium binding sites and show the highest uranium-adsorbing capability of 57.94mg/g at pH 4.0. After eight adsorption-desorption cycles, NZVI@PCN-224 still retained a high uranium adsorption capacity of 47.98mg/g and elimination efficiency (91.72%). This sorption/reduction/anti-biofouling synergistic strategy of combining chelation, chemical reduction and photocatalytic performance inspires new insights for highly efficient treatment of liquid radioactive waste.

Ferric iron loaded porphyrinic zirconium MOFs on corncob for the enhancement of diuretics extraction.

Herein, corncob waste was used as a scaffold for the fabrication of effective adsorbents. Porphyrinic zirconium metal-organic frameworks (MOFs) PCN-223 and PCN-224 constructed by different numbers of Zr6 cluster nodes were grown on the surface of the corncob. Fe (Ш) ions were implanted in the porphyrin ring by post-synthesis modification. The results showed that the extraction capacity of diuretics on PCN-224@corncob containing suitable pore size was larger than that of PCN-223@corncob. The adsorption of diuretics was further enhanced because of the electrostatic effect caused by implantation of Fe (Ш) ions. PCN-224-Fe@corncob was recyclable and selective for the extraction of furosemide (Fur) and bumetanide (Bum). Coupled in-syringe solid phase extraction (IS-SPE) with ultra-performance liquid chromatography (UPLC), an efficient, sensitive, and stable method was established. With a sensitivity between 0.6 and 1.0μg/L and a recovery between 83.2% and 119.2%, it is used for the analysis of trace amounts of Fur and Bum in weight loss products and environmental water. The functionalized corncob has potential application for the adsorption of diuretics, and the metal ions implantation in MOFs provides a promising strategy for enhancing extraction capacity.

Enhanced degradation of bisphenol F in a porphyrin-MOF based visible-light system under high salinity conditions

The efficient degradation of organic contaminants in practical water treatment is a challenge for advanced oxidation processes via such as semiconductor photocatalysis due to interference from the inhibiting influence due to the reactions between radicals and coexisting anions in the actual water column. Herein, a porphyrinic zirconium metal–organic framework (PCN-223) is used in a visible light system to effectively decompose bisphenol F (BPF) in saline water. The PCN-223/visible-light system can effectively resist the influence of environmental coexisting anions and natural organic matter (NOM), thus demonstrating excellent performance in decomposing pollutants. Furthermore, the catalytic system is able to maintain stable contaminant degradation over a wide pH range and in five water matrices. Coexisting anions promote the conductivity of electrons by forming ionic bonds with Zr, which enhances light-induced electron transfer under visible light. This work illustrates the mechanism and conditions under which porphyrin-MOF can resist high salt environments in photocatalysis, and provides a new perspective on the practical application of photocatalysis to overcome complex environmental disturbances.

Ligand-Directed Conformational Control over Porphyrinic Zirconium Metal-Organic Frameworks for Size-Selective Catalysis.

Zirconium-based metal-organic frameworks (Zr-MOFs) have aroused enormous interest owing to their superior stability, flexible structures, and intriguing functions. Precise control over their crystalline structures, including topological structures, porosity, composition, and conformation, constitutes an important challenge to realize the tailor-made functionalization. In this work, we developed a new Zr-MOF (PCN-625) with a csq topological net, which is similar to that of the well-known PCN-222 and NU-1000. However, the significant difference lies in the conformation of porphyrin rings, which are vertical to the pore surfaces rather than in parallel. The resulting PCN-625 exhibits two types of one-dimensional channels with concrete diameters of 2.03 and 0.43 nm. Furthermore, the vertical porphyrins together with shrunken pore sizes could limit the accessibility of substrates to active centers in the framework. On the basis of the structural characteristics, PCN-625(Fe) can be utilized as an efficient heterogeneous catalyst for the size-selective [4 + 2] hetero-Diels-Alder cycloaddition reaction. Due to its high chemical stability, this catalyst can be repeatedly used over six times. This work demonstrates that Zr-MOFs can serve as tailor-made scaffolds with enhanced flexibility for target-oriented functions.

Synthesis of Porphyrin Zr-MOFs for the Adsorption and Photodegradation of Antibiotics under Visible Light.

The release of antibiotics into the water environment can pose a serious threat to human and ecological health, so it is of great significance to effectively remove antibiotics from wastewater. In this work, porphyrinic zirconium metal–organic framework material, PCN-224, was first explored for the adsorption removal of antibiotics from water using tetracycline (TC) and ciprofloxacin (CIP) as examples. We prepared a series of PCN-224 with different particle sizes (150 nm, 300 nm, 500 nm, and 6 μm). Benefiting from the huge surface area (1616 m2 g–1), the 300 nm-PCN-224 sample had the best adsorption properties for TC and CIP. Remarkably, it exhibits fast removal rates and high adsorption capacities of 354.81 and 207.16 mg g–1 for TC and CIP, respectively. The adsorption of TC and CIP in 300 nm-PCN-224 is consistent with the pseudo-second-order kinetic model and Langmuir isotherm model, which indicates that the adsorption can be regarded as homogeneous monolayer chemisorption, and the adsorption is exothermic, which has been confirmed by thermodynamic studies. Under visible-light irradiation, 300 nm-PCN-224 exhibited high photocatalytic activity for TC and CIP. The adsorption studies confirmed that the adsorption of adsorbates takes place via the formation of hydrogen bonding, π–π interactions, and electrostatic attraction. In addition, the adsorbent can be simply regenerated by photocatalysis under visible light, and the adsorption–desorption efficiency is still above 85% after repeated use five times. The work of MOFs to remove antibiotics from water shows that MOFs have great potential in this field and are worthy of further study.

Effect of Topology on Photodynamic Sterilization of Porphyrinic Metal‐Organic Frameworks

Porphyrinic metal-organic frameworks (MOFs) are promising photosensitizers due to the lack of self-aggregation of porphyrin in aqueous solution. However, how the topology of porphyrinic MOFs affects the generation of singlet oxygen (1 O2 ) is unclear. Here, the effect of the topology of porphyrinic MOFs on their photodynamic performance is reported. Four porphyrinic zirconium MOFs (MOF-525, MOF-545, PCN-223 and PCN-224 with different topologies: ftw, csq, shp and she, respectively) were selected to study the influence of topology on the photodynamic antibacterial performance. The 1 O2 generation and the photodynamic antibacterial performance followed an decreasing order of MOF-545>MOF-525>PCN-224>PCN-223. The results reveal that the pore size, the distance between porphyrin, and the number of porphyrin per Zr6 O8 cluster in MOFs greatly affected 1 O2 generation. This work provides guidance for designing new MOFs for efficient photodynamic sterilization.

Porphyrinic zirconium metal-organic frameworks: Synthesis and applications for adsorption/catalysis

Zr-based porphyrinic MOFs, which have isolated porphyrin units imbedded in MOFs’ rigid structure, exhibit excellent textural properties and high stability. Among the porphyrin ligands, tetrakis(4-carboxyphenyl)-porphyrin (TCPP) is broadly employed, and so far, seven Zr-based porphyrinic MOFs of MOF-525, MOF-545 (also named PCN-222), PCN-221, PCN-223, PCN-224, PCN-225, and NU-902 have been synthesized using TCCP. The built-in TCPP ligand with various functionality and coordinatively unsaturated Zr clusters can be subjected to diverse pre- and post-synthesis functionalization or guest encapsulation. Aided by the excellent hydrothermal/chemical stability and high porosity, these Zr-based porphyrinic MOFs are gaining attention for applications in adsorption, sensors, heterogeneous catalysis for chemical conversions, photocatalysis, electrocatalysis, and others. This paper reviews the current status of research and development on the synthesis, characterization, functionalization, and adsorption/catalysis applications of Zr-based porphyrinic MOFs.

Porphyrinic Zirconium Metal–Organic Frameworks (MOFs) as Heterogeneous Photocatalysts for PET‐RAFT Polymerization and Stereolithography

AbstractIn this study, porphyrinic zirconium (Zr) MOFs were investigated as heterogeneous photocatalysts for photoinduced electron transfer‐reversible addition‐fragmentation chain transfer (PET‐RAFT) polymerization of various monomers under a broad range of wavelengths, producing polymers with high monomer conversions, narrow molecular weight distributions, low dispersity and good chain‐end fidelity. Screening of various porphyrinic Zr‐MOFs (Zn) containing Zn‐metalled porphyrinic ligands demonstrated that MOF‐525 (Zn) with the smallest size had the best photocatalytic activity in PET‐RAFT polymerization, due to enhanced dispersion and light penetration. Oxygen tolerance and temporal control were also demonstrated during MOF catalysed PET‐RAFT. Results suggested that the polymerization rates were significantly affected by changing the size and surface area of MOFs, and the heterogeneous MOF photocatalysts could be easily separated and recycled for up to five independent PET‐RAFT polymerizations without an obvious decrease in efficiency. Finally, the MOF photocatalysts were utilized to create three‐dimensional polymeric objects with high resolution via visible light mediated stereolithography in an open‐air environment.

Porphyrinic Zirconium Metal-Organic Frameworks (MOFs) as Heterogeneous Photocatalysts for PET-RAFT Polymerization and Stereolithography.

In this study, porphyrinic zirconium (Zr) MOFs were investigated as heterogeneous photocatalysts for photoinduced electron transfer-reversible addition-fragmentation chain transfer (PET-RAFT) polymerization of various monomers under a broad range of wavelengths, producing polymers with high monomer conversions, narrow molecular weight distributions, low dispersity and good chain-end fidelity. Screening of various porphyrinic Zr-MOFs (Zn) containing Zn-metalled porphyrinic ligands demonstrated that MOF-525 (Zn) with the smallest size had the best photocatalytic activity in PET-RAFT polymerization, due to enhanced dispersion and light penetration. Oxygen tolerance and temporal control were also demonstrated during MOF catalysed PET-RAFT. Results suggested that the polymerization rates were significantly affected by changing the size and surface area of MOFs, and the heterogeneous MOF photocatalysts could be easily separated and recycled for up to five independent PET-RAFT polymerizations without an obvious decrease in efficiency. Finally, the MOF photocatalysts were utilized to create three-dimensional polymeric objects with high resolution via visible light mediated stereolithography in an open-air environment.

Construction of an Asymmetric Porphyrinic Zirconium Metal-Organic Framework through Ionic Postchiral Modification.

Herein, one kind of neutral chiral zirconium metal-organic framework (Zr-MOF) was reported from the porphyrinic MOF (PMOF) family with a metallolinker (MnIII-porphyrin) as the achiral polytopic linker [free base tetrakis(4-carboxyphenyl)porphyrin] and chiral anions. Achiral Zr-MOF was chiralized through the exchange of primitive anions with new chiral organic anions (postsynthetic exchange). This chiral functional porphyrinic MOF (CPMOF) was characterized by several techniques such as powder X-ray diffraction, Fourier transform infrared spectroscopy, ultraviolet-visible spectroscopy, 1H NMR, energy-dispersive X-ray spectroscopy, scanning electron microscopy, and Brunauer-Emmett-Teller measurements. In the resulting structure, there are two active metal sites as Lewis acid centers (Zr and Mn) and chiral species as Brønsted acid sites along with their cooperation as nucleophiles. This CPMOF shows considerable bimodal porosity with high surface area and stability. Additionally, its ability was investigated in asymmetric catalyses of prochiral substrates. Interactions between framework chiral species and prochiral substrates have large impacts on the catalytic ability and chirality induction. This chiral catalyst proceeded asymmetric epoxidation and CO2 fixation reactions at lower pressure with high enantioselectivity due to Lewis acids and chiral auxiliary nucleophiles without significant loss of activity up to the sixth step of consecutive cycles of reusability. Observations revealed that chiralization of Zr-MOF could happen by a succinct strategy that can be a convenient method to design chiral MOFs.

Topological Strain-Induced Regioselective Linker Elimination in a Chiral Zr(IV)-Based Metal-Organic Framework

Summary Zr-carboxylate metal-organic frameworks (MOFs) are structurally robust materials, in part due to their strong coordination bonds. The regioselective Zr–O bond cleavage and formation between 3D architectures are thus challenging and are heretofore unexplored. In this work, by introducing highly flexible 18-crown-6-ether functionalities into a homochiral Zr-MOF, we report an unprecedented topology transition in which a 4,10-connected framework undergoes a rapid solid-state transition into a thermodynamically more stable 4,8-connected analog by a regioselective-linker-elimination under ambient conditions. The transition process was unambiguously unraveled by single-crystal and powder X-ray diffraction studies, and we proposed a possible transition mechanism based on various control experiments and theoretical calculations. The excellent chemical stability and substantially expanded porosity and pore apertures endowed the transformed chiral MOF with an exceptional capacity for the enantioadsorptive and solid-phase extractive separation of the racemic drug molecule of lansoprazole with 98% ee and 93% ee, respectively.

Open versus Interpenetrated: Switchable Supramolecular Trajectories in Mechanosynthesis of a Halogen-Bonded Borromean Network

Summary Precise control over topologically intricate molecular architectures remains an open challenge for chemists due to their inherent structural complexity. We report a simple solvent-free strategy to selectively prepare two multi-component supramolecular crystalline systems based on the halogen bond, endowed with either an unknot topology or a Borromean-type entanglement. Real-time in situ monitoring of the solvent-free mechanochemical synthesis of these three-component halogen-bonded ionic co-crystals reveals that the choice of milling conditions leads to a switch in the supramolecular reaction trajectory, resulting in the selective formation of an open halogen-bonded network or a halogen-bonded Borromean-type assembly.

A Porphyrinic Zirconium Metal-Organic Framework for Oxygen Reduction Reaction: Tailoring the Spacing between Active-Sites through Chain-Based Inorganic Building Units.

The oxygen reduction reaction (ORR) is central in carbon-neutral energy devices. While platinum group materials have shown high activities for ORR, their practical uses are hampered by concerns over deactivation, slow kinetics, exorbitant cost, and scarce nature reserve. The low cost yet high tunability of metal–organic frameworks (MOFs) provide a unique platform for tailoring their characteristic properties as new electrocatalysts. Herein, we report a new concept of design and present stable Zr-chain-based MOFs as efficient electrocatalysts for ORR. The strategy is based on using Zr-chains to promote high chemical and redox stability and, more importantly, tailor the immobilization and packing of redox active-sites at a density that is ideal to improve the reaction kinetics. The obtained new electrocatalyst, PCN-226, thereby shows high ORR activity. We further demonstrate PCN-226 as a promising electrode material for practical applications in rechargeable Zn-air batteries, with a high peak power density of 133 mW cm–2. Being one of the very few electrocatalytic MOFs for ORR, this work provides a new concept by designing chain-based structures to enrich the diversity of efficient electrocatalysts and MOFs.

Controlling the Polymorphism and Topology Transformation in Porphyrinic Zirconium Metal-Organic Frameworks via Mechanochemistry.

Tetratopic porphyrin-based metal-organic frameworks (MOFs) represent a particularly interesting subclass of zirconium MOFs due to the occurrence of several divergent topologies. Control over the target topology is a demanding task, and reports often show products containing phase contamination. We demonstrate how mechanochemistry can be exploited for controlling the polymorphism in 12-coordinated porphyrinic zirconium MOFs, obtaining pure hexagonal PCN-223 and cubic MOF-525 phases in 20-60 min of milling. The reactions are mainly governed by the milling additives and the zirconium precursor. In situ monitoring by synchrotron powder X-ray diffraction revealed that specific reaction conditions resulted in the formation of MOF-525 as an intermediate, which rapidly converted to PCN-223 upon milling. Electron spin resonance measurements revealed significant differences between the spectra of paramagnetic centers in two polymorphs, showing a potential of polymorphic Zr-MOFs as tunable supports in spintronics applications.

Highly selective adsorption separation of light hydrocarbons with a porphyrinic zirconium metal-organic framework PCN-224

Light hydrocarbons are important raw materials in the petrochemical industry, mainly achieved by a cost-intensive and energy-consuming cryogenic distillation. In this work, we reported a porphyrinic zirconium metal-organic framework material, PCN-224, for the adsorption separation of C2 (ethane, C2H6) and C3 (propane, C3H8) hydrocarbons over C1 (methane, CH4). The Brunauer-Emmett-Teller (BET) surface area of the synthesized PCN-224 was 2704 m3·g−1 and the pores were mainly centered at 12 and 16 Å. Gas adsorption experiments revealed that PCN-224 exhibited much higher adsorption capacities of C2H6 and C3H8 (2.94 and 8.25 mmol·g−1) than that of CH4 (0.47 mmol·g−1) at 298 K and 100 kPa. The corresponding adsorption selectivity of C2H6/CH4 predicted by the ideal adsorbed solution theory (IAST) was 12. Particularly, the C3H8/CH4 selectivity reached up to 609 at the same conditions. Furthermore, the breakthrough experiments results showed favorable dynamic performance of PCN-224 for efficient separation of C2/C1 and C3/C1 mixtures. Additionally, PCN-224 exhibited excellent water stability after retaining its framework in water for 48 h. Therefore, PCN-224 is a promising material for the separation of C1-C3 hydrocarbons.

In situ hydrothermal growth of a zirconium-based porphyrinic metal-organic framework on stainless steel fibers for solid-phase microextraction of nitrated polycyclic aromatic hydrocarbons

The authors describe the in-situ hydrothermal growth of a porphyrinic zirconium metal-organic framework (MOF), referred to as PCN-222(Zr), on stainless steel fibers. The PCN-222(Zr) is uniformly deposited on the fiber and displays exceptional thermal and chemical stability. The coated fiber was used for the solid-phase microextraction of nitrated polycyclic aromatic hydrocarbons (NPAHs) in water sample prior to their quantitation by gas chromatography in combination with negative chemical ionization mass spectrometry. Limits of detection (S/N = 3) of 17 selected analytes ranged from 0.10 to 20 ng·L−1. Linear range was from 0.4 to 400 ng·L−1. Intra- and inter-day reproducibility values obtained from a single fiber (six replicates) ranged from 2.2–12.8% and 3.6–12.1%, respectively. Fiber-to-fiber reproducibility for six parallel fibers ranged from 3.3% to 10.3% under the same working conditions. The method was successfully applied to determine NPAHs in environmental water, atmospheric particulate matter (PM2.5), and soil samples. This work demonstrated a prominent prospect of this kinds of stable MOF for applications in extraction techniques.

The Mesoporous Porphyrinic Zirconium Metal-Organic Framework for Pipette-Tip Solid-Phase Extraction of Mercury from Fish Samples Followed by Cold Vapor Atomic Absorption Spectrometric Determination

In this study, the highly stable mesoporous porphyrinic zirconium metal-organic framework, namely PCN-222/MOF-545 (Zr-MOF), was prepared and used for pipette-tip solid-phase extraction of Hg(II). As a high-capacity sorbent, 4 mg of the Zr-MOF was placed into a conventional pipette tip and used, for the first time, for the fast extraction and preconcentration of mercury ions. For desorption, 50 μL of 10% HCl was used by 15 repeated aspirating/dispensing cycles, and Hg ions in elusion were measured by a cold vapor atomic absorption spectrometer. Affecting parameters on extraction efficiency were studied, and optimum conditions were established as amount of sorbent 2 mg, pH was adjusted to 5.0, the eluting volume was 15 μL, and extraction was performed on 1.8 mL of the sample. The optimal number of aspirating/dispensing cycles for extraction and desorption of analytes was found to be 10 and 15 cycles, respectively. The limit of detection of the method was found to be 20 ng L−1 with a relative standard deviation of ≤3.1% (for seven replicate analyses of 20 μg L−1 of mercury). Adsorption capacity and enrichment factor were 35.5 mg g−1 and 120-fold, respectively. The proposed method was successfully applied for the determination of Hg(II) ions in fish samples.

High-throughput synthesis and characterization of nanocrystalline porphyrinic zirconium metal-organic frameworks.

We describe and employ a high-throughput screening method to accelerate the synthesis and identification of pure-phase, nanocrystalline metal-organic frameworks (MOFs). We demonstrate the efficacy of this method through its application to a series of porphyrinic zirconium MOFs, resulting in the isolation of MOF-525, MOF-545, and PCN-223 on the nanoscale.