Magnetic Metal-Organic Frameworks for Efficient Carbon Dioxide Capture and Remote Trigger Release

Performance of ferrite nanoparticles in inductive heating swing adsorption (IHSA): how tailoring material properties can circumvent the design limitations of a system

Inductive heating swing adsorption (IHSA) using hybrid adsorbents incorporating a porous material and ferrite nanoparticles holds promise to be a performant, electrified alternative for conventional gas separation. Successful implementation of hybrid adsorbents in IHSA depends on achieving a maximal specific absorption rate (SAR) in the conditions and at the frequency of the induction setup. This paper outlines and demonstrates successful strategies for optimization of the particle composition, tailoring the coercivity and susceptibility of the ferrite particles to optimal performance in a given alternating magnetic field.

Fundamentals and Recent Progress in Magnetic Field Assisted CO2 Capture and Conversion

CO2 capture and conversion technology are highly promising technologies that definitely play a part in the journey towards carbon neutrality. Releasing CO2 by mild stimulation and the development of high efficiency catalytic processes are urgently needed. The magnetic field, as a thermodynamic parameter independent of temperature and pressure, is vital in the enhancement of CO2 capture and conversion process. In this review, the recent progress of magnetic field-enhanced CO2 capture and conversion is comprehensively summarized. The theoretical fundamentals of magnetic field on CO2 adsorption, release and catalytic reduction process are discussed, including the magnetothermal, magnetohydrodynamic, spin selection, Lorentz forces, magnetoresistance and spin relaxation effects. Additionally, a thorough review of the current progress of the enhancement strategies of magnetic field coupled with a variety of fields (including thermal, electricity, and light) is summarized in the aspect of CO2 related process. Finally, the challenges and prospects associated with the utilization of magnetic field-assisted techniques in the construction of CO2 capture and conversion systems are proposed. This review offers a reference value for the future design of catalysts, mechanistic investigations, and practical implementation for magnetic field enhanced CO2 capture and conversion.

Electrochemical and Biocatalytic Signal-Controlled Payload Release from a Metal-Organic Framework

A metal-organic framework (MOF), ZIF-8, which is stable at neutral and slightly basic pH values in aqueous solutions and destabilized/dissolved under acidic conditions, is loaded with a pH-insensitive fluorescent dye, rhodamine-B isothiocyanate, as a model payload species. Then, the MOF species are immobilized at an electrode surface. The local (interfacial) pH value is rapidly decreased by means of an electrochemically stimulated ascorbate oxidation at +0.4 V (Ag/AgCl/KCl). Oxygen reduction upon switching the applied potential to -0.8 V allows to return the local pH to the neutral/basic pH, then stopping rapidly the release process. The developed method allows electrochemical control over stimulated or inhibited payload release processes from the MOF. The pH variation proceeds in a thin film of the solution near the electrode surface. The switchable release process is realized in a buffer solution and undiluted human serum. As the second option, the pH decrease stimulating the release process is achieved upon an enzymatic reaction using esterase and ester substrate. This approach potentially allows the release activation controlled by numerous enzymes assembled in complex biocatalytic cascades. It is expected that related electrochemical or biocatalytic systems can represent novel signal-responding materials with switchable features for delivering (bio)molecules within biomedical applications.

Covalent organic frameworks for CO2 capture: from laboratory curiosity to industry implementation

CO2 concentration in the atmosphere has increased by about 40% since the 1960s. Among various technologies available for carbon capture, adsorption and membrane processes have been receiving tremendous attention due to their potential to capture CO2 at low costs. The kernel for such processes is the sorbent and membrane materials, and tremendous progress has been made in designing and fabricating novel porous materials for carbon capture. Covalent organic frameworks (COFs), a class of porous crystalline materials, are promising sorbents for CO2 capture due to their high surface area, low density, controllable pore size and structure, and preferable stabilities. However, the absence of synergistic developments between materials and engineering processes hinders achieving the qualitative leap for net-zero emissions. Considering the lack of a timely review on the combination of state-of-the-art COFs and engineering processes, in this Tutorial Review, we emphasize the developments of COFs for meeting the challenges of carbon capture and disclose the strategies of fabricating COFs for realizing industrial implementation. Moreover, this review presents a detailed and basic description of the engineering processes and industrial status of carbon capture. It highlights the importance of machine learning in integrating simulations of molecular and engineering levels. We aim to stimulate both academia and industry communities for joined efforts in bringing COFs to practical carbon capture.

Recent Advances in the Support Layer, Interlayer and Active Layer of TFC and TFN Organic Solvent Nanofiltration (OSN) Membranes: A Review

Although separation of solutes from organic solutions is considered a challenging process, it is inevitable in various chemical, petrochemical and pharmaceutical industries. OSN membranes are the heart of OSN technology that are widely utilized to separate various solutes and contaminants from organic solvents, which is now considered an emerging field. Hence, numerous studies have been attracted to this field to manufacture novel membranes with outstanding properties. Thin-film composite (TFC) and nanocomposite (TFN) membranes are two different classes of membranes that have been recently utilized for this purpose. TFC and TFN membranes are made up of similar layers, and the difference is the use of various nanoparticles in TFN membranes, which are classified into two types of porous and nonporous ones, for enhancing the permeate flux. This study aims to review recent advances in TFC and TFN membranes fabricated for organic solvent nanofiltration (OSN) applications. Here, we will first study the materials used to fabricate the support layer, not only the membranes which are not stable in organic solvents and require to be cross-linked, but also those which are inherently stable in harsh media and do not need any cross-linking step, and all of their advantages and disadvantages. Then, we will study the effects of fabricating different interlayers on the performance of the membranes, and the mechanisms of introducing an interlayer in the regulation of the PA structure. At the final step, we will study the type of monomers utilized for the fabrication of the active layer, the effect of surfactants in reducing the tension between the monomers and the membrane surface, and the type of nanoparticles used in the active layer of TFN membranes and their effects in enhancing the membrane separation performance.

Evaluation of a graphitic porous carbon modified with iron oxides for atrazine environmental remediation in water by adsorption

In the last decades, the growth of world agricultural activity has significantly contributed to the increased presence of emerging pollutants such as atrazine (ATZ) in aquatic ecosystems. Due to its high stability to the natural or artificial degradation processes, the ATZ environmental remediation by adsorption has been investigated. In this study, a graphitic-porous-carbon- (GPC) based material with magnetic domains was applied to remove ATZ from aqueous solution. ATZ high adsorption efficiency in a reduced time was achieved in the presence of the GPC adsorbent, leading to a detailed investigation of the mechanisms involved in the adsorption processes. Pseudo-first-order (PFO), pseudo-second-order (PSO), Ritchie, Elovich, and Weber-Morris models were applied to calculate the kinetic process efficiency. Likewise, adsorption isotherms based on Langmuir, Freundlich, Temkin, and Redlich-Peterson models were applied for a detailed understanding of the adsorption mechanisms. GPC was successfully applied for ATZ remediation in natural waters, confirming its high potential for treating natural waters contaminated by ATZ using adsorption process. The material can also be recovered and reused for up to 4 application cycles due to its magnetic properties, showing that in addition to ATZ adsorption efficiency, its sustainable use can be achieved.

Overview on recent advances of magnetic metal-organic framework (MMOF) composites in removal of heavy metals from aqueous system

Developing a novel, simple, and cost-effective analytical technique with high enrichment capacity and selectivity is crucial for environmental monitoring and remediation. Metal-organic frameworks (MOFs) are porous coordination polymers that are self-assembly synthesized from organic linkers and inorganic metal ions/metal clusters. Magnetic metal-organic framework (MMOF) composites are promising candidate among the new-generation sorbent materials available for magnetic solid-phase extraction (MSPE) of environmental contaminants due to their superparamagnetism properties, high crystallinity, permanent porosity, ultrahigh specific surface area, adaptable pore shape/sizes, tunable functionality, designable framework topology, rapid and ultrahigh adsorption capacity, and reusability. In this review, we focus on recent scientific progress in the removal of heavy metal ions present in contaminated aquatic system by using MMOF composites. Different types of MMOFs, their synthetic approaches, and various properties that are harnessed for removal of heavy metal ions from contaminated water are discussed briefly. Adsorption mechanisms involved, adsorption capacity, and regeneration of the MMOF sorbents as well as recovery of heavy metal ions adsorbed that are reported in the last ten years have been discussed in this review. Moreover, particular prospects, challenges, and opportunities in future development of MMOFs towards their greener synthetic approaches for their practical industrial applications have critically been considered in this review.

Synergistically Enabling Fast-Cycling and High-Yield Atmospheric Water Harvesting with Plasma-Treated Magnetic Flower-Like Porous Carbons

Sorption-based atmospheric water harvesting (AWH) offers a promising solution to the water scarcity in arid regions. However, majority of the existing AWH sorbents are suffering from rather poor water productivity due to their slow water adsorption-desorption cycling capability especially when they are applied in high packing thickness. Herein, an oxygen plasma-treated magnetic flower-like porous carbon (P-MFPC) with large open surfaces, abundant surface oxygen-containing moieties, and excellent localized magnetic induction heating (LMIH) capacity is developed. These merits, together with the use of air-blowing-assisted water adsorption and LMIH-driven water desorption strategy, synergistically allow P-MFPC with 2 cm of packing thickness to complete a AWH cycling in 20 min and deliver a record 4.5 L_H2O kg^-1 day^-1 of water productivity at 30% relative humidity. Synergistically enabling such an ultrafast AWH cycling at high sorbent packing thickness provides a promising way for the scalable high-yield AWH with compact AWH systems.

Capture, Storage, and Release of Oxygen by Metal–Organic Frameworks (MOFs)

Oxygen is a critical gas for medical and industrial settings. Much of today's global oxygen supply is via inefficient technologies such as cryogenic distillation, membranes or zeolites. Metal–organic frameworks (MOFs) promise a superior alternative for oxygen separation, as their fundamental chemistry can in principle be tailored for reversible and selective oxygen capture. We evaluate the characteristics for reversible and selective uptake of oxygen by MOFs, focussing on redox‐active sites. Key characteristics for separation can also be seen in MOFs for oxygen storage roles. Engineering solutions to release adsorbed oxygen from the MOFs are discussed including Temperature Swing Adsorption (TSA), Pressure Swing Adsorption (PSA) and the highly efficient Magnetic Induction Swing Adsorption (MISA). We conclude with the applications and outlooks for oxygen capture, storage and release, and the likely impacts the next generation of MOFs will have on industry and the broader community.

Magnetic Stuffed Bun-Structured Metal-Organic Framework Monoliths with Noncompromised Accessible Pores and Highly Efficient Recycling Capability

Development of industrially favorable metal-organic framework (MOF) monoliths is of paramount importance for their real-world applications. However, MOF monoliths prepared with the existing MOF shaping methods usually have seriously compromised accessible pores and suffer from inefficient and energy-intensive recycling, thereby greatly limiting their practical applications. We herein present a magnetic stuffed bun-structured MOF (mSBM) bead consisting of highly porous poly(vinyl alcohol) wraps stuffed with a binder-free powder mixture of UiO-66 and Fe₃O₄ nanoparticles. Such a unique structure and composition of the mSBM not only make its MOF component have a well-reserved crystal structure, surface area, and porosity and the corresponding accessible pores but also impart it with excellent localized magnetic induction heating (LMIH) capability that enables the sufficient heating and highly efficient recycling of the mSBM. These merits of mSBMs are further exemplified by assessing their atmospheric water adsorption and LMIH-driven water desorption performance. The mSBMs exhibit well-reserved atmospheric water adsorption capacities, up to 100% LMIH-driven water desorption, excellent reusability, and durability toward the practical applications. Our current work, therefore, demonstrates a new MOF shaping strategy to produce MOF monoliths with well-defined shapes, noncompromised accessible pores, and highly efficient recycling capabilities, paving a bright avenue to accelerate the practical applications of MOF monoliths.

Influence of Metal Identity on Light-Induced Switchable Adsorption in Azobenzene-Based Metal-Organic Frameworks

Energy-efficient capture and release of small gas molecules, particularly carbon dioxide (CO₂) and methane (CH₄), are of significant interest in academia and industry. Porous materials such as metal-organic frameworks (MOFs) have been extensively studied, as their ultrahigh porosities and tunability enable significant amounts of gas to be adsorbed while also allowing specific applications to be targeted. However, because of the microporous nature of MOFs, the gas adsorption performance is dominated by high uptake capacity at low pressures, limiting their application. Hence, methods involving stimuli-responsive materials, particularly light-induced switchable adsorption (LISA), offer a unique alternative to thermal methods. Here, we report the mechanism of a well-known LISA system, the azobenzene-based material PCN-250, for CO₂ and CH₄ adsorption. There is a noticeable difference in the LISA effect dependent on the metal cluster involved, with the most significant being PCN-250-Al, where the adsorption can change by 83.1% CH₄ and 56.1% CO₂ at 298 K and 1 bar and inducing volumetric storage changes of 36.2 and 33.9 cm³/cm³ at 298 K between 5 and 85 bar (CH₄) and 2 and 9 bar (CO₂), respectively. Using UV light in both single-crystal X-ray diffraction and gas adsorption testing, we show that upon photoirradiation, the framework undergoes a "localized heating" phenomenon comparable to an increase of 130 K for PCN-250-Fe and improves the working capacity. This process functions because of the constrained nature of the ligand, preventing the typical trans-to-cis isomerization observed in free azobenzene. In addition, we observed that the degree of localized heating is highly dependent on the metal cluster involved, with the series of isostructural PCN-250 systems showing variable performance based upon the degree of interaction between the ligand and the metal center.

Process-Oriented Smart Adsorbents: Tailoring the Properties Dynamically as Demanded by Adsorption/Desorption

Adsorptive separation plays a critical role in chemical, food, pharmaceutical, and environmental industries, as well as in many other industrial areas. Adsorbents are most important for adsorptive separation and undergo adsorption and desorption processes to accomplish the specific tasks of separation. In the process of adsorption, adsorbates diffuse into the pore spaces of adsorbents through pore openings, adsorb on active sites via physical or chemical interactions, and subsequently are regenerated by temperature or pressure swings during desorption. In the process of adsorption and desorption, however, the requirements for pore structures and surface properties of adsorbents are different. In general, adsorbents with small pore openings can realize selective adsorption and do not favor desorption; on the other hand, adsorbents with large pore openings are efficient in desorption but at the expense of adsorption selectivity. Remarkably, active sites possessing strong interactions with adsorbates contribute to high selectivity for adsorption, while desorption becomes difficult. The trade-off between adsorption and desorption presents an enormous challenge to develop high-efficiency adsorbents. Restricted by their fixed structures and surface properties, conventional adsorbents are unable to meet the demands of adsorption and desorption processes simultaneously.To confront the obstacles, the development of advanced adsorbents to meet the demand of adsorptive separation are urgent. A key strategy to address such issues lies in dynamically adjusting the pore structures or the surface properties of adsorbents with controllability according to the demands of adsorption/desorption. For instance, pursuant to the requirements of varying pore structures during adsorption/desorption, the pore openings of adsorbents can be customized through dynamic structural change of the decorated stimuli-sensitive motifs by suitable external intervention. In addition, the active sites within the adsorbents can be exposed to enhance the adsorption selectivity or sheltered to accelerate the desorption through stimuli-triggered adsorbent-adsorbate interactions. Hence, we proposed a concept of process-oriented smart adsorbents (POSAs) on the basis of the requirements of the adsorption/desorption processes. The design and development of such POSAs are based on three aspects, namely, pore openings, pore spaces, and adsorption sites of adsorbents.In this Account, we present the progress in the development of POSAs according to the demands of adsorption/desorption processes. A series of POSAs with incorporated stimuli-sensitive motifs were successfully achieved. The versatility of incorporated motifs allows them to tune the pore structures and surface properties of adsorbents dynamically and further to enhance the adsorption and desorption efficiency simultaneously. Based on the concept of POSAs, we hope that this Account could contribute to the development of high-efficiency adsorbents and ultimately promote their applications in practical industrial separation. Moreover, we present an outlook on future trends and challenges on the road toward the development and applications of POSAs.

Thermal decarboxylation for the generation of hierarchical porosity in isostructural metal-organic frameworks containing open metal sites

The effect of metal-cluster redox identity on the thermal decarboxylation of a series of isostructural metal-organic frameworks (MOFs) with tetracarboxylate-based ligands and trinuclear μ3-oxo clusters was investigated. The PCN-250 series of MOFs can consist of various metal combinations (Fe3, Fe/Ni, Fe/Mn, Fe/Co, Fe/Zn, Al3, In3, and Sc3). The Fe-based system can undergo a thermally induced reductive decarboxylation, producing a mixed valence cluster with decarboxylated ligand fragments subsequently eliminated to form uniform mesopores. We have extended the analysis to alternative monometallic and bimetallic PCN-250 systems to observe the cluster's effect on the decarboxylation process. Our results suggest that the propensity to undergo decarboxylation is directly related to the cluster redox accessibility, with poorly reducible metals, such as Al, In, and Sc, unable to thermally reduce at the readily accessible temperatures of the Fe-containing system. In contrast, the mixed-metal variants are all reducible. We report improvements in gas adsorption behavior, significantly the uniform increase in the heat of adsorption going from the microporous to hierarchically induced decarboxylated samples. This, along with Fe oxidation state changes from 57Fe Mössbauer spectroscopy, suggests that reduction occurs at the clusters and is essential for mesopore formation. These results provide insight into the thermal behavior of redox-active MOFs and suggest a potential future avenue for generating mesoporosity using controlled cluster redox chemistry.

Metal Microfibers Delivered Eddy Current Heating for Efficient Synthesis and Regeneration of Metal-Organic Framework Monoliths

On the basis of stainless-steel fiber (SSF)-delivered localized Eddy current heating (LECH) in response to an alternating magnetic field, a novel LECH-driven framework synthesis (LIFS) strategy has been developed for highly efficient metal-organic framework (MOF) synthesis, resulting in the production of a set of SSF/MOF composites consisting of MOF-coated SSF (SSF@MOF) fibers and free MOF crystals. Detailed studies on the LIFS reaction kinetics indicate that the use of LIFS can greatly promote MOF production in comparison to the conventional solvothermal reactions. To facilitate the practical applications, the resulting powder SSF/UiO-66-NH₂ composites, as a typical example, are further processed into well-shaped SSF/UiO-66-NH₂ monoliths (SUS) with varied MOF loadings. In SUSs, the embedded SSFs exhibit well-controlled LECH capacities depending on the applied magnetic field strength. Driven by LECH, SUS monoliths can be uniformly heated and fully regenerated, demonstrating a LECH-triggered framework regeneration (LIFR) process for highly efficient regenerating MOF monoliths. As LECH is delivered by the low-cost commercial SSFs and remotely triggered by an external magnetic field, our currently developed LIFS and LIFR processes provide a novel, low-cost, and energy-efficient way to highly efficiently synthesize and regenerate MOF materials.

Embedding metal foam into metal-organic framework monoliths for triggering a highly efficient release of adsorbed atmospheric water by localized eddy current heating

Using metal-organic frameworks (MOFs) to harvest water from the atmosphere represents an attractive way to alleviate the global water shortage stress. However, the intrinsic thermal insulating nature of MOFs makes it rather challenging to scale-up water production by utilizing industrially favorable bulky MOF monoliths due to the insufficient water desorption triggered by the existing water desorption methods. To overcome this challenge, metal foam (MF) embedded MOF monoliths (MF@MOFs) are presented. In MF@MOFs, MF not only serves as the backbone of MOF monoliths to support them with excellent mechanical robustness, but also enables the rapid generation of enormous localized eddy current heating (LECH) upon their exposure to an alternating magnetic field. Compared with the traditional heating methods, the use of LECH can effectively overcome the thermal insulating nature of MOF monoliths and realize their rapid and uniform heating, thereby triggering a complete water desorption from MF@MOFs with significantly improved desorption kinetics. The viability of the LECH-triggered water release method for practical atmospheric water harvesting is also validated through a newly designed LECH-based atmospheric water harvester. Note that this is the first exploration that uses LECH to overcome the intrinsic insulating nature of MOF monoliths.

Recent Advances in TiO2-Based Heterojunctions for Photocatalytic CO2 Reduction With Water Oxidation: A Review

Photocatalytic conversion of CO₂ into solar fuels has gained increasing attention due to its great potential for alleviating the energy and environmental crisis at the same time. The low-cost TiO₂ with suitable band structure and high resistibility to light corrosion has proven to be very promising for photoreduction of CO₂ using water as the source of electrons and protons. However, the narrow spectral response range (ultraviolet region only) as well as the rapid recombination of photo-induced electron-hole pairs within pristine TiO₂ results in the low utilization of solar energy and limited photocatalytic efficiency. Besides, its low selectivity toward photoreduction products of CO₂ should also be improved. Combination of TiO₂ with other photoelectric active materials, such as metal oxide/sulfide semiconductors, metal nanoparticles and carbon-based nanostructures, for the construction of well-defined heterostructures can enhance the quantum efficiency significantly by promoting visible light adsorption, facilitating charge transfer and suppressing the recombination of charge carriers, resulting in the enhanced photocatalytic performance of the composite photocatalytic system. In addition, the adsorption and activation of CO₂ on these heterojunctions are also promoted, therefore enhancing the turnover frequency (TOF) of CO₂ molecules, so as to the improved selectivity of photoreduction products. This review focus on the recent advances of photocatalytic CO₂ reduction via TiO₂-based heterojunctions with water oxidation. The rational design, fabrication, photocatalytic performance and CO₂ photoreduction mechanisms of typical TiO₂-based heterojunctions, including semiconductor-semiconductor (S-S), semiconductor-metal (S-M), semiconductor-carbon group (S-C) and multicomponent heterojunction are reviewed and discussed. Moreover, the TiO₂-based phase heterojunction and facet heterojunction are also summarized and analyzed. In the end, the current challenges and future prospects of the TiO₂-based heterostructures for photoreduction of CO₂ with high efficiency, even for practical application are discussed.

Stimuli-responsive metal-organic framework nanoparticles for controlled drug delivery and medical applications

Stimuli-responsive metal-organic framework nanoparticles, NMOFs, provide a versatile platform for the controlled release of drugs and biomedical applications. The porous structure of NMOFs, their biocompatibility, low toxicity, and efficient permeability turn the NMOFs into ideal carriers for therapeutic applications. Two general methods to gate the drug-loaded NMOFs and to release the loads were developed: by one method, the loaded NMOFs are coated or surface-modified with stimuli-responsive gates being unlocked in the presence of appropriate chemical (e.g., ions or reducing agents), physical (e.g., light or heat), or biomarker (e.g., miRNA or ATP) triggers. By a second approach, the drug-loaded NMOFs include encoded structural information or co-added agents to induce the structural distortion or stimulate the degradation of the NMOFs. Different chemical triggers such as pH changes, ions, ATP, or redox agents, and physical stimuli such as light or heat are applied to degrade the NMOFs, resulting in the release of the loads. In addition, enzymes, DNAzymes, and disease-specific biomarkers are used to unlock the gated NMOFs. The triggered release of drugs for cancer therapy, anti-blood clotting, and the design of autonomous insulin-delivery systems ("artificial pancreas") are discussed. Specifically, multi-drug carrier systems and functional NMOFs exhibiting dual and cooperative therapeutic functions are introduced. The future perspectives and applications of stimuli-responsive particles are addressed.

Deciphering supramolecular isomerization in coordination polymers: connected molecular squares vs. fused hexagons

The self-assembly of Mn(ii), bis(tridentate) ligands and bent dicarboxylate linkers under ambient conditions has been exploited to generate a series of 1D coordination polymers in good yields. For a set of seven compounds, structural isomerization of these architectures is demonstrated through the variation of length and nature of the spacer between the tridentate capping sites of the bis(tridentate) ligands, such as tpbn (N,N',N'',N'''-tetrakis-(2-pyridylmethyl)-1,4-diaminobutane), tphxn (N,N',N'',N'''-tetrakis-(2-pyridylmethyl)-1,6-diaminohexane), and tpxn (N,N',N'',N'''-tetrakis-(2-pyridylmethyl)-xylylamine) or by varying the bent dicarboxylate linker 4,4'-(dimethylsilanediyl)bis-benzoic acid (H2L1) or 4,4'-oxybis-benzoic acid (H2L2). These compounds have been structurally characterized by single-crystal and powder X-ray diffraction, FTIR, and thermogravimetric and elemental analyses. This study reveals that the supramolecular structural variation can be precisely controlled either by a judicious selection of reaction conditions or linker/ligand combinations. For example, the self-assembly of Mn(ii), tpbn and H2L1 in DMF/EtOH/water affords a mixture of products (1 and 1a) while changing the solvent combination to EtOH/water results in the generation of a single isomer (1a) in a highly selective manner. On the other hand, for the Mn(ii)-tphxn system, different structural isomers have been isolated by varying the dicarboxylates, H2L1 and H2L2 (2vs.5). Similarly, for the Mn(ii)-H2L2 system, a variation in the spacer chain length of bis(tridentate) ligands, tpbn and tphxn resulted in the formation of different structural isomers (4vs.5).

Label-free visualization of heterogeneities and defects in metal-organic frameworks using nonlinear optics

Defects influence the properties of metal-organic frameworks (MOFs), such as their storage amount and the diffusion kinetics of gas molecules. However, the spatial distribution of defects is still poorly understood due to a lack of visualization methods. Here, we present a new method using nonlinear optics (NLO) that allows the visualization of defects within MOFs.

Performance evaluation of CuBTC composites for room temperature oxygen storage

Oxygen is commonly separated from air using cryogenic liquefaction. The inherent energy penalties of phase change inspire the search for energy-efficient separation processes. Here, an alternative approach is presented, where we determine whether it is possible to utilise simpler, stable materials in the right process to achieve overall energy efficiency. Adsorption and release by Metal-Organic Frameworks (MOFs) are an attractive alternative due to their high adsorption and storage capacity at ambient conditions. Cu-BTC/MgFe2O4 composites were prepared, and magnetic induction swing adsorption (MISA) used to release adsorbed oxygen quickly and efficiently. The 3 wt% MgFe2O4 composites exhibited an oxygen uptake capacity of 0.34 mmol g-1 at 298 K and when exposed to a magnetic field of 31 mT, attained a temperature rise of 86 °C and released 100% of adsorbed oxygen. This water vapor stable pelletized system, can be filled and emptied within 10 minutes requiring around 5.6 MJ kg-1 of energy.

Gas Sensors Based on Chemi-Resistive Hybrid Functional Nanomaterials

Chemi-resistive sensors based on hybrid functional materials are promising candidates for gas sensing with high responsivity, good selectivity, fast response/recovery, great stability/repeatability, room-working temperature, low cost, and easy-to-fabricate, for versatile applications. This progress report reviews the advantages and advances of these sensing structures compared with the single constituent, according to five main sensing forms: manipulating/constructing heterojunctions, catalytic reaction, charge transfer, charge carrier transport, molecular binding/sieving, and their combinations. Promises and challenges of the advances of each form are presented and discussed. Critical thinking and ideas regarding the orientation of the development of hybrid material-based gas sensor in the future are discussed.

Localized Electrical Induction Heating for Highly Efficient Synthesis and Regeneration of Metal-Organic Frameworks

Based on carbon fibers (CFs) delivered localized electrical induction heat, a novel electrical induction framework synthesis (EIFS) strategy has been developed to in-situ grow versatile metal-organic frameworks (MOFs) on CFs, resulting in the production of a set of MOF-coated CF (MOF@CF) fibers. Detailed studies on the production of UiO-66-NH₂@CFs indicate that the use of EIFS leads to dramatically accelerated MOF growth at dozen times higher reaction rate than that of the conventional solvothermal reaction. By periodically switching anodes during EIFS reactions, uniform MOF@CF fibers with well-controlled MOF loadings have been achieved depending on the reaction conditions. Mediated by the embedded CFs in the resulting MOF@CFs, MOF@CFs exhibit well-regulated electrical induction heating capacities depending on MOF loadings and the applied voltages. Driven by such localized heat, up to 100% of the adsorbed CO₂ in UiO-66-NH₂@CF can be rapidly released, demonstrating an electrical induction framework regeneration (EIFR) process for highly efficient regeneration of MOFs. As CFs enable to rapidly deliver localized electrical induction with over 90% of electrothermal conversion efficiency and at rather low operation voltage, currently developed EIFS and EIFR process provide a highly efficient, low-energy, low operation cost, and safe way to highly efficient synthesis and regeneration of MOF materials.

Construction of 3D lanthanide based MOFs with pores decorated with basic imidazole groups for selective capture and chemical fixation of CO2

Rational construction of three new 3D lanthanide-based MOFs exhibiting selective CO₂ capture and conversion to value-added cyclic carbonates under mild conditions is reported.

Bottom-Up Formation of Carbon-Based Magnetic Honeycomb Material from Metal-Organic Framework-Guest Polyhedra for the Capture of Rhodamine B

Three-dimensional carbon-based porous materials have proven to be quite useful for tailoring material properties in the energy conservation and environmental protection applications. In view of the three-dimensional and well-defined structure of metal-organic frameworks (MOFs), a novel carbon-based magnetic porous material (HKUST-Fe₃O₄) has been designed and constructed by MOF-guest interactions of high-temperature pyrolysis. The obtained HKUST-Fe₃O₄ exhibited the unique features of superparamagnetism, a macro/mesoporous structure, environmental protection (inexistence of toxic heavy metal ions), and physicochemical stability and has shown high adsorption capacity and rapid adsorption for carcinogenic organic pollutants (for example, rhodamine B) with an environmentally friendly character and excellent reusability. We demonstrate that the unique/superior advantages of HKUST-Fe₃O₄ could meet the requirements of environment cleaning, especially for removing the targeted organic pollutant from water. Moreover, the specific HKUST-Fe₃O₄ and organic pollutant interaction mechanism has been analyzed in detail via parameter-free calculations. This study proposes a promising strategy for constructing novel carbon-based magnetic nanomaterials for various applications, not limitated to pollutant removal.

Metallopolymers for advanced sustainable applications

Since the development of metallopolymers, there has been tremendous interest in the applications of this type of materials. The interest in these materials stems from their potential use in industry as catalysts, biomedical agents in healthcare, energy storage and production as well as climate change mitigation. The past two decades have clearly shown exponential growth in the development of many new classes of metallopolymers that address these issues. Today, metallopolymers are considered to be at the forefront for discovering new and sustainable heterogeneous catalysts, therapeutics for drug-resistant diseases, energy storage and photovoltaics, molecular barometers and thermometers, as well as carbon dioxide sequesters. The focus of this review is to highlight the advances in design of metallopolymers with specific sustainable applications.

Biowaste-derived 3D honeycomb-like N and S dual-doped hierarchically porous carbons for high-efficient CO2 capture

Considering the characteristics of abundant narrow micropores of <1 nm, appropriate proportion of mesopores/macropores and suitable surface functionalization for a highly-efficient carbon-based CO₂ adsorbent, we proposed a facile and cost-effective strategy to prepare N and S dual-doped carbons with well-interconnected hierarchical pores. Benefiting from the unique structural features, the resultant optimal material showed a prominent CO₂ uptake of up to 7.76 and 5.19 mmol g⁻¹ at 273 and 298 K under 1 bar, and importantly, a superb CO₂ uptake of 1.51 mmol g⁻¹ at 298 K and 0.15 bar was achieved, which was greatly significant for CO₂ capture from the post-combustion flue gases in practical application. A systematic study demonstrated that the synergetic effect of ultramicroporosity and surface functionalization determined the CO₂ capture properties of porous carbons, and the synergistic influence mechanism of nitrogen/sulfur dual-doping on CO₂ capture performance was also investigated in detail. Importantly, such as-prepared carbon-based CO₂ adsorbents also showed an outstanding recyclability and CO₂/N₂ selectivity. In view of cost-effective fabrication, the excellent adsorption capacity, high selectivity and simple regeneration, our developed strategy was valid and convenient to design a novel and highly-efficient carbonaceous adsorbent for large-scale CO₂ capture and separation from post-combustion flue gases.

We proposed a facile and cost-effective strategy to prepare N/S dual-doped carbons with abundant micropores of <1 nm, appropriate proportion of meso/macropores and suitable surface functionalization for highly efficient CO₂ capture.

Construction of a 3D porous Co(ii) metal–organic framework (MOF) with Lewis acidic metal sites exhibiting selective CO2 capture and conversion under mild conditions

The application of a 3D Co(ii)-MOF as a recyclable heterogeneous catalyst for conversion of CO₂ to cyclic carbonates is reported.

Construction of bifunctional 2-fold interpenetrated Zn(ii) MOFs exhibiting selective CO2 adsorption and aqueous-phase sensing of 2,4,6-trinitrophenol

Design of Zn(ii) MOFs, [{Zn(BINDI)_0.5(bpa)_0.5(H₂O)}·4H₂O]_n (MOF1) and [{Zn(BINDI)_0.5(bpe)}·3H₂O]_n (MOF2) for selective CO₂ storage and aqueous-phase detection of TNP is demonstrated.

Tetranuclear cobalt(ii)-isonicotinic acid frameworks: selective CO2 capture, magnetic properties, and derived "Co3O4" exhibiting high performance in lithium ion batteries

Two new 3D cobalt metal-organic frameworks (MOFs), [Co4(CH3COO)(in)5(μ3-OH)2]·2H2O (1) and [Co4(SO4)2(in)4(DMF)2]·3DMF (2) (Hin = isonicotinic acid), have been prepared through the anion template method. Compound 1 consists of rare odd-number connected (9-connected) cubane-like SBUs, while compound 2 consists of 8-connected high-symmetry square-planar clusters. Magnetic studies indicate that compound 1 exhibits spin-canting antiferromagnetic ordering, while compound 2 shows antiferromagnetic behavior. At 273 K and 1 bar, compound 1 exhibits a high CO2 selectivity over CH4 and a significant CO2 uptake of 13.6 wt%, which is higher than that of 2 (8.5 wt%). Furthermore, compound 1 was then transformed into ultrasmall Co3O4 nanoparticles via simple but effective annealing treatment. Electrochemical measurements show that the Co3O4 nanospheres derived from compound 1 exhibited high and stable lithium storage properties (1100 mA h g-1 after 100 cycles at 200 mA g-1) and excellent rate capabilities.

Anisotropic Thermal and Guest-Induced Responses of an Ultramicroporous Framework with Rigid Linkers

The interdependent effects of temperature and guest uptake on the structure of the ultramicroporous metal-organic framework [Cu₃ (cdm)₄ ] (cdm=C(CN)₂ (CONH₂ )^- ) were explored in detail by using in situ neutron scattering and density functional theory calculations. The tetragonal lattice displays an anisotropic thermal response related to a hinged "lattice-fence" mechanism, unusual for this topology, which is facilitated by pivoting of the rigid cdm anion about the Cu nodes. Calculated pore-size metrics clearly illustrate the potential for temperature-mediated adsorption in ultramicroporous frameworks due to thermal fluctuations of the pore diameter near the value of the target guest kinetic diameter, though in [Cu₃ (cdm)₄ ] this is counteracted by a competing contraction of the pore with increasing temperature as a result of the anisotropic lattice response.

A Versatile Route toward the Electromagnetic Functionalization of Metal-Organic Framework-Derived Three-Dimensional Nanoporous Carbon Composites

Designable electromagnetic parameters accompanied by a low density of metal-organic framework (MOF)-derived metal/carbon composites are essential prerequisites for excellent microwave-absorbing materials. However, the conventional route is confined to slight modification of the physicochemical properties of metal species and carbon, which also restricts the functionalization of MOF-derived materials. Here, a facile technique has been improved by making full use of highly porous structure to uniformly introduce metallic Co nanoparticles into carbon matrix derived from Cu₃(btc)₂. Through changing the starting amount of Co sources, the composition of the final products can be tuned, offering an effective route to control electromagnetic properties. Multiple attenuation mechanisms are employed to realize excellent reflection loss performance, which can be clarified by modified equivalent circuit mode. Effective frequency bandwidth ( f_e) over the whole X band can be obtained by optimizing interfacial polarization through changing interface area and electrical conductivity. Broad f_e covering almost the whole K_u band from 12.3 to 18 GHz with a thin thickness of 1.85 mm can be gained through improving impedance matching and enhancing conduction loss. The present work not only sheds light on the easy fabrication of high-performance lightweight microwave-absorbing materials but also paves the way for extending functionalities of MOF-derived carbon composites.