Synthesis and Defect Characterization of Phase-Pure Zr-MOFs Based on Meso-tetracarboxyphenylporphyrin

Enhancing the Catalytic Activity of Laccase@Copper-Metal-Organic Framework Nanofractal Microspheres: Synergistic Contribution of the Mass Transfer and Electron Transfer Pathway

Metal-organic frameworks (MOFs) are limited by small pores and buried active sites, and their enzyme-like catalytic activity is still very low. Herein, laccase was employed as the organic component to construct laccase@Cu3(BTC)2 nanofractal microspheres. During the preparation process, laccase adsorbed Cu2+ by electrostatic attractive interaction, then combined with Cu2+ by coordination interaction, and finally induced the in situ growth of H3BTC2 in multiple directions by electrostatic repulsion. Interestingly, electrostatic repulsion was tuned efficiently by adjusting the Cu2+ concentration to obtain laccase@Cu3(BTC)2 nanofractal microspheres (nanosheet microspheres, nanorod microspheres, and nanoneedle microspheres). Laccase@Cu3(BTC)2 nanorod microspheres exhibited the highest catalytic efficiency, which was 14-fold higher than that of smooth microspheres. The mechanism of the improvement of catalytic activity in the degradation of BPA was proposed for the first time. The enhanced catalytic activity depended on the adsorption effect of the nanorod framework and dual cycle synergistic catalysis of Cu+/Cu2+ active sites, which accelerated substrate diffusion and electron transfer. The catalytic mechanism of enzyme@MOF nanofractal microspheres not only deepens our understanding of enzyme and MOF synergistic catalysis but also provides new insights into the design of catalysts.

Tailoring the efficiency of porphyrin molecular frameworks for the electroactivation of molecular N2

The combination of compositional versatility and topological diversity for the integration of electroactive species into high-porosity molecular architectures is perhaps one of the main appeals of metal-organic frameworks (MOFs) in the field of electrocatalysis. This premise has attracted much interest in recent years, and the results generated have also revealed one of the main limitations of molecular materials in this context: low stability under electrocatalytic conditions. Using zirconium MOFs as a starting point, in this work, we use this stability as a variable to discriminate between the most suitable electrocatalytic reaction and specific topologies within this family. Our results revealed that the PCN-224 family is particularly suitable for the electroreduction of molecular nitrogen for the formation of ammonia with faradaic efficiencies above 30% in the presence of Ni2+ sites, an activity that improves most of the catalysts described. We also introduce the fluorination of porphyrin at the meso position as a good alternative to improve both the activity and stability of this material under electrocatalytic conditions.

How Reproducible is the Synthesis of Zr-Porphyrin Metal-Organic Frameworks? An Interlaboratory Study

Metal-organic frameworks (MOFs) are a rapidly growing class of materials that offer great promise in various applications. However, the synthesis remains challenging: for example, a range of crystal structures can often be accessed from the same building blocks, which complicates the phase selectivity. Likewise, the high sensitivity to slight changes in synthesis conditions may cause reproducibility issues. This is crucial, as it hampers the research and commercialization of affected MOFs. Here, it presents the first-ever interlaboratory study of the synthetic reproducibility of two Zr-porphyrin MOFs, PCN-222 and PCN-224, to investigate the scope of this problem. For PCN-222, only one sample out of ten was phase pure and of the correct symmetry, while for PCN-224, three are phase pure, although none of these show the spatial linker order characteristic of PCN-224. Instead, these samples resemble dPCN-224 (disordered PCN-224), which has recently been reported. The variability in thermal behavior, defect content, and surface area of the synthesised samples are also studied. The results have important ramifications for field of metal-organic frameworks and their crystallization, by highlighting the synthetic challenges associated with a multi-variable synthesis space and flat energy landscapes characteristic of MOFs.

Remarkable water-mediated proton conductivity of two porous zirconium(IV)/hafnium(IV) metal-organic frameworks bearing porphyrinlcarboxylate ligands

Obtaining crystalline materials with high structural stability as well as super proton conductivity is a challenging task in the field of energy and material chemistry. Therefore, two highly stable metal-organic frameworks (MOFs) with macro-ring structures and carboxylate groups, Zr-TCPP (1) and Hf-TCPP (2) assembled from low-toxicity as well as highly coordination-capable Zr(IV)/Hf(IV) cations and the multifunctional linkage, meso-tetra(4-carboxyphenyl)porphine (TCPP) have attracted our strong interest. Note that TCPP as a large-size rigid ligand with high symmetry and multiple coordination sites contributes to the formation of the two stable MOFs. Moreover, the pores with large sizes in the two MOFs favor the entry of more guest water molecules and thus result in high H2O-assisted proton conductivity. First, their distinguished structural stabilities covering water, thermal and chemical stabilities were verified by various determination approaches. Second, the dependence of the proton conductivity of the two MOFs on temperature and relative humidity (RH) is explored in depth. Impressively, MOFs 1 and 2 demonstrated the optimal proton conductivities of 4.5 × 10-4 and 0.78 × 10-3 S·cm-1 at 100 °C/98 % RH, respectively. Logically, based on the structural information, gas adsorption/desorption features, and activation energy values, their proton conduction mechanism was deduced and highlighted.

Influence of Water Content on Speciation and Phase Formation in Zr-Porphyrin-Based MOFs

Controlled synthesis of phase-pure metal-organic frameworks (MOFs) is essential for their application in technological areas such as catalysis or gas sorption. Yet, knowledge of their phase formation and growth remain rather limited, particularly with respect to species such as water whose vital role in MOF synthesis is often neglected. As a consequence, synthetic protocols often lack reproducibility when multiple MOFs can form from the same metal source and linker, and phase mixtures are obtained with little or no control over their composition. In this work, the role of water in the formation of the Zr-porphyrin MOF disordered PCN-224 (dPCN-224) is investigated. Through X-ray total scattering and scanning electron microscopy, it is observed that dPCN-224 forms via a metal-organic intermediate that consists of Zr6O4(OH)4 clusters linked by tetrakis(4-carboxy-phenyl)porphyrin molecules. Importantly, water is not only essential to the formation of Zr6O4(OH)4 clusters, but it also plays a primary role in dictating the formation kinetics of dPCN-224. This multidisciplinary approach to studying the speciation of dPCN-224 provides a blueprint for how Zr-MOF synthesis protocols can be assessed and their reproducibility increased, and highlights the importance of understanding the role of water as a decisive component in Zr-MOF formation.

Rapid Exciton Transport and Structural Defects in Individual Porphyrinic Metal Organic Framework Microcrystals

To date, spectroscopic characterization of porphyrin-based metal organic frameworks (MOFs) has relied almost exclusively on ensemble techniques, which provide only structurally averaged insight into the functional properties of these promising photochemical platforms. This work employs time-resolved pump-probe microscopy to probe ultrafast dynamics in PCN-222 MOF single crystals. The simultaneous high spatial and temporal resolution of the technique enables the correlation of spectroscopic observables to both inter- and intracrystal structural heterogeneity. The pump-probe measurements show that significant differences in the excited state lifetime exist between individual PCN-222 crystals of an ensemble. On a single PCN-222 crystal, differences in excited state lifetime and photoluminescence quantum yield are found to correlate to microscale structural defects introduced at crystallization. Pump probe microscopy also enables the direct measurement of excited state transport. Imaging of exciton transport on individual MOF crystals reveals rapid, but subdiffusive exciton transport which slows on the 10s of ps time scale. Time-averaged exciton diffusion coefficients over the first 200 ps span a range of 0.27 to 1.0 cm2/s, indicating that excited states are rapidly transported through the porphyrin network of PCN-222 before being trapped. Together, these single-particle-resolved measurements provide important new insight into the role played by structural defects on the photochemical functionality of porphyrin-based MOFs.

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.

High-efficient removal of anionic dye from aqueous solution using metal-organic frameworks@chitosan aerogel rich in benzene structure

With the exponentially increase of dye pollutants, the purification of dye wastewater has been an urgent ecological problem. As a novel type of porous adsorbent, metal-organic frameworks still face challenges in recyclability, agglomeration, and environmentally unfriendly synthesis. Herein, MOF-525 was in-situ growth onto the surface of the chitosan (CS) beads to fabricate MOF-525@CS aerogel. CS was utilized as substrate to uniformly disperse MOF-525, thereby significantly mitigating agglomeration and improving recyclability of MOF-525. The characterization results shown that MOF-525@CS aerogel had a high specific surface area of 103.0 m2·g-1, and MOF-525 was uniformly distributed in the 3D porous structure of CS, and the presence of benzoic acid was detected. The MOF-525@CS aerogel had a remarkable adsorption capacity of 1947 mg·g-1 for Congo red, which is greater than the sum of its parts. MOF-525@CS aerogel also inherited the rapid adsorption ability of MOF-525, removing 80 % of Congo red within 600 min. Such excellent adsorption performance can be attributed to the benzoic acid trapped by CS via CN band to enhance the π-π stacking interactions. Additionally, the utilization of benzoic acid makes the synthesis process of MOF-525@CS aerogel more environmentally friendly. The high-efficient MOF-525@CS aerogel is a competitive candidate for dye pollution adsorption.

Recent Progress on Phase Engineering of Nanomaterials

As a key structural parameter, phase depicts the arrangement of atoms in materials. Normally, a nanomaterial exists in its thermodynamically stable crystal phase. With the development of nanotechnology, nanomaterials with unconventional crystal phases, which rarely exist in their bulk counterparts, or amorphous phase have been prepared using carefully controlled reaction conditions. Together these methods are beginning to enable phase engineering of nanomaterials (PEN), i.e., the synthesis of nanomaterials with unconventional phases and the transformation between different phases, to obtain desired properties and functions. This Review summarizes the research progress in the field of PEN. First, we present representative strategies for the direct synthesis of unconventional phases and modulation of phase transformation in diverse kinds of nanomaterials. We cover the synthesis of nanomaterials ranging from metal nanostructures such as Au, Ag, Cu, Pd, and Ru, and their alloys; metal oxides, borides, and carbides; to transition metal dichalcogenides (TMDs) and 2D layered materials. We review synthesis and growth methods ranging from wet-chemical reduction and seed-mediated epitaxial growth to chemical vapor deposition (CVD), high pressure phase transformation, and electron and ion-beam irradiation. After that, we summarize the significant influence of phase on the various properties of unconventional-phase nanomaterials. We also discuss the potential applications of the developed unconventional-phase nanomaterials in different areas including catalysis, electrochemical energy storage (batteries and supercapacitors), solar cells, optoelectronics, and sensing. Finally, we discuss existing challenges and future research directions in PEN.

Metal Modulation: An Effortless Tactic for Refining Photoredox Catalysis in Living Cells

The remarkable impact of photoredox catalytic chemistries has sparked a wave of innovation, opening doors to novel biotechnologies in the realm of catalytic antitumor therapy. Yet, the quest for novel photoredox catalysts (PCs) suitable for living systems, or the enhancement of catalytic efficacy in existing biocompatible PC systems, persists as a formidable challenge. Within this context, we introduce a readily applicable metal modulation strategy that significantly augments photoredox catalysis within living cells, exemplified by a set of metalloporphyrin complexes termed M-TCPPs (M = Zn, Mn, Ni, Co, Cu). Among these complexes, Zn-TCPP emerges as an exceptional catalyst, displaying remarkable photocatalytic activity in the oxidation of nicotinamide adenine dinucleotide (NADH), nicotinamide adenine dinucleotide phosphate (NADPH), and specific amino acids. Notably, comprehensive investigations reveal that Zn-TCPP's superior catalytic prowess primarily arises from the establishment of an efficient oxidative cycle for PC, in contrast to previously reported PCs engaged in reductive cycles. Moreover, theoretical calculations illuminate that amplified intersystem crossing rates and geometry alterations in Zn-TCPP contribute to its heightened photocatalytic performance. In vitro studies demonstrated that Zn-TCPP exhibits therapeutic potential and is found to be effective for photocatalytic antitumor therapy in both glioblastoma G98T cells and 3D multicellular spheroids. This study underscores the transformative role of "metal modulation" in advancing high-performance PCs for catalytic antitumor therapy, marking a significant stride toward the realization of this innovative therapeutic approach.

The Role of Water in Carbon Dioxide Adsorption in Porphyrinic Metal-Organic Frameworks

Capturing and converting CO2 through artificial photosynthesis using photoactive, porous materials is a promising approach for addressing increasing CO2 concentrations. Porphyrinic Zr-based metal-organic frameworks (MOFs) are of particular interest as they incorporate a photosensitizer in the porous structure. Herein, the initial step of the artificial photosynthesis is studied: CO2 sorption and activation in the presence of water. A combined vibrational and visible spectroscopic approach was used to monitor the adsorption of CO2 into PCN-222 and PCN-223 MOFs, and the photophysical changes of the porphyrinic linker as a function of water concentration. A shift in CO2 sorption site and bending of the porphyrin macrocycle in response to humidity was observed, and CO2/H2O competition experiments revealed that the exchange of CO2 with H2O is pore-size dependent. Therefore, humidity and pore-size can be used to tune CO2 sorption, CO2 capacity, and light harvesting in porphyrinic MOFs, which are key factors for CO2 photoreduction.

Improving the molecular spin qubit performance in zirconium MOF composites by mechanochemical dilution and fullerene encapsulation

Enlarging the quantum coherence times and gaining control over quantum effects in real systems are fundamental for developing quantum technologies. Molecular electron spin qubits are particularly promising candidates for realizing quantum information processing due to their modularity and tunability. Still, there is a constant search for tools to increase their quantum coherence times. Here we present how the mechanochemical introduction of active spin qubits in the form of 10% diluted copper(ii)-porphyrins in the diamagnetic PCN-223 and MOF-525 zirconium-MOF polymorph pair can be achieved. Furthermore, the encapsulation of fullerene during the MOF synthesis directs the process exclusively toward the rare PCN-223 framework with a controllable amount of fullerene in the framework channels. In addition to the templating role, the incorporation of fullerene increases the electron spin-lattice and phase-memory relaxation times, T1 and Tm. Besides decreasing the amount of nuclear spin-bearing solvent guests in the non-activated qubit frameworks, the observed improved relaxation times can be rationalized by modulating the phonon density of states upon fullerene encapsulation.

Removal of diclofenac by adsorption process studied in free-base porphyrin Zr-metal organic frameworks (Zr-MOFs)

As the world population continues to grow, there is also a rising concern regarding water pollution since this condition could negatively impact the supply of clean water. One of the most recent concerns is related to the pollution that comes from various pharmaceuticals, in particular non-steroidal anti-inflammatory drugs (NSAIDs) since they have been industrially produced at large scale and can be easily purchased as an over-the-counter medicine. Diclofenac is one of the most popular NSAIDs because of its high-effectiveness, which leads to its excessive consumption. Consequently, its presence in water bodies is also continuously increasing. An adsorption process could then be employed as a highly effective method to address this issue. In comparison to other conventional adsorbents such as activated carbon, the use of metal-organic frameworks (MOFs) as an alternative adsorbent is very attractive since it can offer various advantages such as tailorability and high adsorption capacity. In this study, the performance of three water-stable, free-base porphyrin MOFs assembled using zirconia-based nodes, namely MOF-525, MOF-545, and NU-902, for diclofenac adsorption was thoroughly investigated. Interestingly, although all three free-base porphyrin MOFs are assembled using the same building block and have a similar specific surface area (based on the experimental argon physisorption and calculation based on non-localized density functional theory), their diclofenac adsorption capacity is substantially different from one another. It is found that the highest diclofenac adsorption capacity is shown by MOF-525, which has maximum capacity around 792 mg g^-1. This is then followed by MOF-545 and NU-902 that have adsorption capacities around 591 and 486 mg g^-1, respectively. Some possible adsorption mechanisms are then thoroughly discussed that might contribute to this phenomenon. Lastly, their performance is also compared with other MOFs that are also studied for this purpose to show their performance superiority not only in terms of adsorption capacity but also their affinity towards the diclofenac molecule, which might be useful as an adsorption performance indicator in the real condition where the contaminant concentration is considerably low.

Defective Homojunction Porphyrin-Based Metal-Organic Frameworks for Highly Efficient Sonodynamic Therapy

Sonodynamic therapy (SDT) with non-invasiveness and high tissue-penetrating ability has attracted widespread interest in treating deep-seated tumors or infections. To enhance the treatment efficacy of SDT, the development of high-efficiency and stable sonosensitizers are still needed. Herein, a defective homojunction porphyrin-based metal-organic framework (MOF) with greatly enhanced sonocatalytic ability is easily prepared and used for SDT of osteomyelitis infected by methicillin-resistant Staphylococcus aureus (MRSA). Acetic acid and benzoic acid are chosen as modulators during the hydrothermal synthesis of porphyrin-based MOF. It is found that the crystal structure of MOF shifts from PCN-222 to PCN-224 as the amount of acetic acid increases. Interestingly, the defective PCN (D-PCN) contains a two-phase homojunction structure of PCN-222/PCN-224. The sonocatalytic reactive oxygen species production presents a volcano-type trend with increased acetic acid, among which D-PCN-2 with more content of PCN-224 has the best sonocatalytic antibacterial ability. The reduced band gap introduced a defect, and type-II homojunction structures of D-PCN-2 improve the separation of the ultrasound-triggered electron hole, which significantly enhances the SDT effect. Through a mixed linker approach, this work develops a new defect-induced homojunction MOF with great performance for SDT of MRSA-infected osteomyelitis.

Metal-porphyrinic framework nanotechnologies in modern agricultural management

Metal-porphyrinic frameworks are an important subclass of metal-organic frameworks (MOFs). These porous materials exhibit a large number of applications for sustainable development and related environmental considerations. Their attractive features include (1) as a free base or metalated with zinc(II) or iron(II or III), they are environmentally benign, and (2) they absorb visible light and are emissive and semi-conducting, making them convenient tools for sensing agrochemicals. But the key feature that makes these nano-sized pristine materials or their composites in many ways superior to most MOFs is their ability to photo-generate reactive oxygen species with visible light, including singlet oxygen. This review describes important issues related to agriculture, including controlled delivery of pesticides and agrochemicals, detection of pesticides and pathogenic metals, elimination of pesticides and toxic metals, and photodynamic antimicrobial activity, and has an important implication for food safety. This comprehensive review presents the progress of the rather rapid developments of these functional and increasingly nano-sized materials and composites in the area of sustainable agriculture.

Precise regulation of defect concentration in MOF and its influence on photocatalytic overall water splitting

In this work, the defective Cu-BDC with different defect concentration and Cu¹⁺/Cu²⁺ coordinatively unsaturated sites (CUS) content were designed and synthesized by introducing defective linkers with different pK_a values. The low-concentration defects in Metal-organic frameworks (MOFs) structure act as the active sites to enhance their photocatalytic activity. In contrast, the high concentration defects serve as the recombination centers of photogenerated electrons and holes to decrease the transfer efficiency of charge carriers. Cu-BDC-FBA shows an excellent bifunctional photocatalytic performance for overall water splitting due to the suitable defect concentration, which gives an oxygen production rate of 3114 μmol g^-1 h^-1 and hydrogen production rate of 16 829 μmol g^-1 h^-1, respectively. It is expected that this study can deepen the understanding of the relationship between defects and photocatalytic activity, and provide a new idea for the design and synthesis of defective MOFs photocatalysts with excellent performance.

Exploring ionic liquid-laden metal-organic framework composite materials as hybrid electrolytes in metal (ion) batteries

This review focuses on the combination of metal-organic frameworks (MOFs) and ionic liquids (ILs) to obtain composite materials to be used as solid electrolytes in metal-ion battery applications. Benefiting from the controllable chemical composition, tunable pore structure and surface functionality, MOFs offer great opportunities for synthesizing high-performance electrolytes. Moreover, the encapsulation of ILs into porous materials can provide environmentally benign solid-state electrolytes for electrochemical devices. Due to the versatility of MOF-based materials, in this review we also explore their use as anodes and cathodes in Li- and Na-ion batteries. Finally, solid IL@MOF electrolytes and their implementation into Li and Na batteries have been analyzed, as well as the design and advanced manufacturing of solid IL@MOF electrolytes embedded on polymeric matrices.

Effective Removal of Tetracycline from Water Using Copper Alginate @ Graphene Oxide with In-Situ Grown MOF-525 Composite: Synthesis, Characterization and Adsorption Mechanisms

For nanomaterials, such as GO and MOF-525, aggregation is the main reason limiting their adsorption performance. In this research, Alg-Cu@GO@MOF-525 was successfully synthesized by in-situ growth of MOF-525 on Alg-Cu@GO. By dispersing graphene oxide (GO) with copper alginate (Alg-Cu) with three-dimensional structure, MOF-525 was in-situ grown to reduce aggregation. The measured specific surface area of Alg-Cu@GO@MOF-525 was as high as 807.30 m²·g^-1, which is very favorable for adsorption. The synthesized material has affinity for a variety of pollutants, and its adsorption performance is significantly enhanced. In particular, tetracycline (TC) was selected as the target pollutant to study the adsorption behavior. The strong acid environment inhibited the adsorption, and the removal percentage reached 96.6% when pH was neutral. Temperature promoted the adsorption process, and 318 K adsorption performance was the best under experimental conditions. Meanwhile, 54.6% of TC could be removed in 38 min, and the maximum adsorption capacity reached 533 mg·g^-1, far higher than that of conventional adsorption materials. Kinetics and isotherms analysis show that the adsorption process accords with Sips model and pseudo-second-order model. Thermodynamic study further shows that the chemisorption is spontaneous and exothermic. In addition, pore-filling, complexation, π-π stack, hydrogen bond and chemisorption are considered to be the causes of adsorption.

Rapid Generation of Metal-Organic Framework Phase Diagrams by High-Throughput Transmission Electron Microscopy

Metal-organic frameworks (MOFs) constructed from Zr₆ nodes and tetratopic carboxylate linkers display high structural diversity and complexity in which various crystal topologies can result from identical building units. To determine correlations between MOF topologies and experimental parameters, such as solvent choice or modulator identity and concentration, we demonstrate the rapid generation of phase diagrams for Zr₆-MOFs with 1,4-dibromo-2,3,5,6-tetrakis(4-carboxyphenyl)benzene linkers under a variety of conditions. We have developed a full set of methods for high-throughput transmission electron microscopy (TEM), including automated sample preparation and data acquisition, to accelerate MOF characterization. The use of acetic acid as a modulator yields amorphous, NU-906, NU-600, and mixed-phase structures depending on the ratio of N,N-dimethylformamide to N,N-diethylformamide solvent and the quantity of the modulator. Notably, the use of formic acid as a modulator enables direct control of crystal growth along the c direction through variation of the modulator quantity, thus realizing aspect ratio control of NU-1008 crystals with different catalytic hydrolysis performance toward a nerve agent simulant.

The role of the metal center on charge transport rate in MOF-525: cobalt and nickel porphyrin

Metal-organic Frameworks (MOFs) have emerged as promising materials for different electrochemical applications. Their low conductivity, however, is a major challenge to overcome. Therefore, a deeper understanding on the charge transfer mechanism is needed to improve the conductivity of MOF-based electrodes. For this contribution, we focused on metalated MOF-525 and found that the nature of the metal center is one of the many factors contributing to the charge transfer kinetics, which is attributed to differences in redox behaviour, affecting the hopping distance and the electron transfer rate. These results highlight the importance of the nature of the redox active site to optimize charge transfer in MOF-based electrodes.

Screening and Discrimination of Perfluoroalkyl Substances in Aqueous Solution Using a Luminescent Metal-Organic Framework Sensor Array

The extensive production and large-scale use of perfluoroalkyl substances (PFASs) have raised their presence in aquatic environments worldwide. Thus, the facile and reliable screening of PFASs in aqueous systems is of great significance. Herein, we designed a novel fluorescent sensor array for the rapid screening and discrimination of multiple PFASs in water. The sensor array comprised three highly stable zirconium porphyrinic luminescent metal-organic frameworks (i.e., PCNs) with different topological structures. The sensing mechanism was based on the static fluorescence quenching of PCNs by PFASs upon their adsorptive interactions. The fluorescence response patterns were characteristic for each PFAS because of their different adsorption affinities toward different PCNs. Through the interpretation of response patterns by statistical methods, the proposed PCN array successfully discriminated six different kinds of PFASs, each PFAS at different concentrations and PFAS mixtures at different molar ratios. The practicability of this array was further verified by effectively discriminating PFASs in two real water samples. Remarkably, the PCN sensors exhibited a very short response time toward PFASs (within 10 s) due to the ordered pore structure allowing fast PFAS diffusion. This study not only provides a facile method for rapid PFAS screening in waters but also broadens the application of luminescent metal-organic frameworks and array techniques in sensing fields.

Abundant defects of zirconium-organic xerogels: High anhydrous proton conductivities over a wide temperature range and formic acid impedance sensing

There exists a challenge to develop solid-state proton conductors with high conductivity not only at high working temperatures (>353 K) but at start-up temperature and even at subzero temperature (<273 K) in cold climates or high-altitude drones. Here we present a series of zirconium-organic xerogels (Zr/Fum-xerogels) with porosity and defectivity, supported by N₂ sorption, thermogravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS), exhibiting a high anhydrous proton conductivity over the temperature range of 233 to 433 K. The anhydrous conductivity of Zr/Fum-xerogel-0.04 reaches 5.68 × 10^-4 (233 K) and 2.5 × 10^-2 S cm^-1 (433 K), situating in the leading level of all anhydrous conductors reported to date. Further, the defective effects on acidities and conductive mechanisms of xerogels, especially structural changes of water clusters generated by varying temperatures are investigated by ion exchange capacity (IEC), X-ray photoelectron spectroscopy (XPS), temperature programmed desorption of NH₃ (NH₃-TPD) and in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The zirconium-organic xerogels with outstanding conducting performance is further implemented as impedance sensor towards formic acid.

Understanding disorder and linker deficiency in porphyrinic zirconium-based metal-organic frameworks by resolving the Zr8O6 cluster conundrum in PCN-221

Porphyrin-based metal–organic frameworks (MOFs), exemplified by MOF-525, PCN-221, and PCN-224, are promising systems for catalysis, optoelectronics, and solar energy conversion. However, subtle differences between synthetic protocols for these three MOFs give rise to vast discrepancies in purported product outcomes and description of framework topologies. Here, based on a comprehensive synthetic and structural analysis spanning local and long-range length scales, we show that PCN-221 consists of Zr₆O₄(OH)₄ clusters in four distinct orientations within the unit cell, rather than Zr₈O₆ clusters as originally published, and linker vacancies at levels of around 50%, which may form in a locally correlated manner. We propose disordered PCN-224 (dPCN-224) as a unified model to understand PCN-221, MOF-525, and PCN-224 by varying the degree of orientational cluster disorder, linker conformation and vacancies, and cluster–linker binding. Our work thus introduces a new perspective on network topology and disorder in Zr-MOFs and pinpoints the structural variables that direct their functional properties.

Zirconium-based metal–organic frameworks have defective structures that are useful in catalysis and gas storage. Here, the authors study the interplay between cluster disorder and linker vacancies in PCN-221 and propose a new structure model with tilted Zr₆O₄(OH)₄ clusters rather than Zr₈O₆ clusters.

Advanced applications of Zr-based MOFs in the removal of water pollutants

The global water pollution is caused by the increase of industrial and agricultural activities, which have produced various toxic pollutants. Pollutants in water generally consist of metal ions, pharmaceuticals and personal care products (PPCPs), oil spills, organic dyes, and other organic pollutants. Amongst the adsorbents that have been developed to deal with pollutants in water, Zr-based metal-organic frameworks (MOFs) have drawn scientists' great attention due to their excellent stability and adjustable functionalization. Herein, the present review article introduces the synthetic methods of functionalized Zr-based MOFs and summarizes their applications in water pollution treatment. It also clarifies the interactions and removal mechanisms between pollutants and Zr-based MOFs. The use of these MOFs with eminent adsorption ability and recycling performance have been discussed in detail. Zr-based MOFs also face some challenges such as high cost, lack of real water environment applications, selective removal of pollutants, and low ability to remove composite pollutants. Future research should focus on addressing these issues. Although there is still a blank of the practical utility of Zr-based MOFs on a commercial scale, the research reported to date clearly shows that they are very promising materials for the water treatment.

Boosting free radical type photocatalysis over Pd/Fe-MOFs by coordination structure engineering

The development of novel heterogeneous photocatalytic systems, along with a deep understanding of the relationship between the catalytic center chemical environment and the catalytic performance, is of great significance.

Structural Diversity of Zirconium Metal-Organic Frameworks and Effect on Adsorption of Toxic Chemicals

While linkers with various conformations pose challenges in the design and prediction of metal-organic framework (MOF) structures, they ultimately provide great opportunities for the discovery of novel structures thereby enriching structural diversity. Tetratopic carboxylate linkers, for example, have been widely used in the formation of Zr-based MOFs due to the ability to target diverse topologies, providing a promising platform to explore their mechanisms of formation. However, it remains a challenge to control the resulting structures when considering the complex assembly of linkers with unpredicted conformations and diverse Zr₆ node connectivities. Herein, we systematically explore how solvents and modulators employed during synthesis influence the resulting topologies of Zr-MOFs, choosing H₄TCPB-Br₂ (1,4-dibromo-2,3,5,6-tetrakis(4-carboxyphenyl)benzene) as a representative tetratopic carboxylate linker. By modulating the reaction conditions, the conformations of the linker and the connectivities of the Zr₆ node can be simultaneously tuned, resulting in four types of structures: a new topology (NU-500), she (NU-600), scu (NU-906), and csq (NU-1008). Importantly, we have synthesized the first 5-connected Zr₆ node to date with the (4,4,4,5)-connected framework, NU-500. We subsequently performed detailed structural analyses to uncover the relationship between the structures and topologies of these MOFs and demonstrated the crucial role that the flexible linker played to access varied structures by different degrees of linker deformation. Due to a variety of pore structures ranging from micropores to hierarchical micropores and mesopores, the resulting MOFs show drastically different behaviors for the adsorption of n-hexane and dynamic adsorption of 2-chloroethyl ethyl sulfide (CEES) under dry and humid conditions.

Structure-directing role of immobilized polyoxometalates in the synthesis of porphyrinic Zr-based metal-organic frameworks

We evidence the structure-directing role of the PW12O403- polyoxometalate in porphyrinic MOF synthesis whereby it promotes the formation of the kinetic topology. Its immobilization into the MOF is successfully achieved at a high temperature yielding the kinetic MOF-525/PCN-224 phases, while prohibiting the formation of the thermodynamic MOF-545 product. A combined experimental/theoretical approach uses differential PDF and DFT calculations along with solid-state NMR to show the structural integrity of the POM and its location next to the Zr-based nodes.

Iron-Based Metal-Organic Frameworks as Platform for H2S Selective Conversion: Structure-Dependent Desulfurization Activity

Three classical Fe-MOFs, viz., MIL-100(Fe), MIL-101(Fe), and MIL-53(Fe), were synthesized to serve as platforms for the investigation of structure-activity relationship and catalytic mechanism in the selective conversion of H₂S to sulfur. The physicochemical properties of the Fe-MOFs were characterized by various techniques. It was disclosed that the desulfurization performances of Fe-MOFs with well-defined microstructures are obviously different. Among these, MIL-100(Fe) exhibits the highest catalytic performance (ca. 100% H₂S conversion and 100% S selectivity at 100-180 °C) that is superior to that of commercial Fe₂O₃. Furthermore, the results of systematic characterization and DFT calculation reveal that the difference in catalytic performance is mainly because of discrepancy in the amount of Lewis acid sites. A plausible catalytic mechanism has been proposed for H₂S selective conversion over Fe-MOFs. This work provides critical insights that are helpful for rational design of desulfurization catalysts.

Substrate templated synthesis of single-phase and uniform Zr-porphyrin-based metal–organic frameworks

We successfully demonstrate that the chemical bath deposition (CBD) method is a versatile method for synthesizing phase-pure and uniform MOFs by controlling their nucleation stages and pore structures.

Controlling Charge-Transport in Metal-Organic Frameworks: Contribution of Topological and Spin-State Variation on the Iron-Porphyrin Centered Redox Hopping Rate

Metal-organic frameworks (MOFs) are an emerging class of compositions for electro- and photoelectrocatalytic energy conversion processes. Understanding and improving the charge-transport processes within these high surface area molecular redox catalyst assemblies are critical since the charge carrier conductivity is inherently limited in MOFs. Here, we examine a series of four chemically identical but structurally different hydrolytically robust Zr^IV-MOFs constructed from tetrakis(4-carboxyphenyl)porphyrinato iron(III), TCPP(Fe^III) to understand how their topological construction affects redox hopping conductivity. While a structural variation fixes center-to-center distances to define the hopping rate, we probe that altering the central metal spin-state can further tune the TCPP(Fe^III/II) reorganization energy of the self-exchange process. Significant increase in the hopping rate was observed upon axial coordination of 1-methyl imidazole (MIM), which converts a weakly halide bound high-spin (HS) TCPP(Fe^III/II) to the six-coordinated low-spin (LS) complex. Our electrochemical and resonance Raman data reveal that pore geometry that defines the Fe-Fe distance in these frameworks dictate the steric demand to accommodate two MIM-molecules, and thus, the population of LS vs HS species is a function of topology in the presence of an excess ligand.