“Green” Synthesis of Metal-Organic Frameworks

New Insights into ZIF-90 Synthesis

Zeolitic imidazolate frameworks (ZIFs) are traditionally synthesized using N, N-dimethylformamide (DMF). However, DMF is toxic and hazardous to human health and the environment, hence other alternative solvents need to be considered. Herein, three different solvents like methanol, water and acetone were used to replace DMF and to explore the syntheses of ZIF-90 using a conventional and a microwave-assisted solvothermal method to obtain hydrothermally stable products, which also exhibit an increased water uptake. Pure ZIF-90 was synthesized under ambient pressure at 60 °C for 90 min using the conventional solvothermal method in an acetone-water solution, while under microwave irradiation it was formed in only 5 min at 80 °C. Altering methanol, water and acetone in the reaction mixture significantly affected the structural and water adsorption properties of ZIF-90s, which were monitored via PXRD, TGA, nitrogen and water sorption, and SEM. The highly efficient, less toxic, low-cost and activation-free microwave synthesis resulted in the formation of ZIF-90 nanoparticles that exhibited the highest maximum water adsorption capacity (0.37 g/g) and the best hydrothermal stability between water adsorption at 30 °C and desorption at 100 °C at 12.5 mbar among all the products obtained.

Rare-earth acetates as alternative precursors for rare-earth cluster-based metal-organic frameworks

RE-UiO-66 analogues are synthesized using RE acetates as precursors for the first time. These MOFs are fully characterized and the influence of the precursor on the materials obtained is studied. Additionally, the influence of water on the yield of the syntheses and the quality of the materials is explored.

Green synthesis of MOF-based textile composites for the degradation of a chemical warfare agent simulant

A green synthesis of UiO-66-NH2 embedded in chitosan and deposited on textiles has been investigated for the degradation of chemical warfare agents. This method requires no heating or use of toxic solvents. The composite synthesized presents an interesting efficiency in detoxifying common simulants of chemical warfare agents, such as DMNP. In parallel, resistance and permeability tests were also realized in order to confirm the suitability of the composites for further applications.

Magnetic Multienzyme@Metal-Organic Material for Sustainable Biodegradation of Insoluble Biomass

Biodegradation of insoluble biomass such as cellulose via carbohydrase enzymes is an effective approach to break down plant cell walls and extract valuable materials therein. Yet, the high cost and poor reusability of enzymes are practical concerns. We recently proved that immobilizing multiple digestive enzymes on metal-organic materials (MOMs) allows enzymes to be reused via gravimetric separation, improving the cost efficiency of cereal biomass degradation [ACS Appl. Mater. Interfaces 2021, 13, 36, 43085-43093]. However, this strategy cannot be adapted for enzymes whose substrates or products are insoluble (e.g., cellulose crystals). Recently, we described an alternative approach based on magnetic metal-organic frameworks (MOFs) using model enzymes/substrates [ACS Appl. Mater. Interfaces 2020, 12, 37, 41794-41801]. Here, we aim to prove the effectiveness of combining these two strategies in cellulose degradation. We immobilized multiple carbohydrase enzymes that cooperate in cellulose degradation via cocrystallization with Ca2+, a carboxylate ligand (BDC) in the absence and presence of magnetic nanoparticles (MNPs). We then compared the separation efficiency and enzyme reusability of the resultant multienzyme@Ca-BDC and multienzyme@MNP-Ca-BDC composites via gravimetric and magnetic separation, respectively, and found that, although both composites were effective in cellulose degradation in the first round, the multienzyme@MNP-Ca-BDC composites displayed significantly enhanced reusability. This work provides the first experimental demonstration of using magnetic solid supports to immobilize multiple carbohydrase enzymes simultaneously and degrade cellulose and promotes green/sustainable chemistry in three ways: (1) reusing the enzymes saves energy/sources to prepare them, (2) the synthetic conditions are "green" without generating unwanted wastes, and (3) using our composites to degrade cellulose is the first step of extracting valuable materials from sustainable biomasses such as plants whose growth does not rely on nonregeneratable resources.

Light-induced MOF synthesis enabling composite photothermal materials

Metal-organic frameworks (MOFs) are a class of porous materials known for their large surface areas. Thus, over the past few decades the development of MOFs and their applications has been a major topic of interest throughout the scientific community. However, many current conventional syntheses of MOFs are lengthy solvothermal processes carried out at elevated temperatures. Herein, we developed a rapid light-induced synthesis of MOFs by harnessing the plasmonic photothermal abilities of bipyramidal gold nanoparticles (AuBPs). The generality of the photo-induced method was demonstrated by synthesizing four different MOFs utilizing three different wavelengths (520 nm, 660 nm and 850 nm). Furthermore, by regulating light exposure, AuBPs could be embedded in the MOF or maintained in the supernatant. Notably, the AuBPs-embedded MOF (AuBP@UIO-66) retained its plasmonic properties along with the extraordinary surface area typical to MOFs. The photothermal AuBP@UIO-66 demonstrated a significant light-induced heating response that was utilized for ultrafast desorption and MOF activation.

Alginate-modified surfactants functionalized metal-organic framework-based fluorescent film sensors for detection and adsorption of volatile aldehydes in water

Volatile aldehydes have an adverse impact on both human health and the environment, therefore, a fast, straightforward, highly accurate detection technique for the simultaneous detection and removal of several aldehydes is eagerly anticipated. Herein, novel APGF@ZIF-8 and APOF@ZIF-8 sensing materials were developed by coating fluorescent alginate-modified surfactants (APGF and APOF) into the ZIF-8 MOFs to produce quite porous fluorescent sensors (SBET up to 1519 m2/g). The detection capacity of the prepared sensors for benzaldehyde, glyoxal, formaldehyde, and acetaldehyde has been examined. The detection mechanism was suggested as hydrogen bonding formation between the sensors and volatile aldehydes as confirmed by Gaussian calculations. All the fluorescence spectra of aldehydes display remarkable linear detection relationships in the range of 0.05-200 μM with the limits of detection (LOD) values in the range of 0.001-0.18 μM (0.106-10.44 ppb). These sensors were utilized successfully to detect multiple volatile aldehydes in river water samples with satisfactory recoveries of 96-107 %. Interestingly, fluorescent APGF@ZIF-8/CS and APOF@ZIF-8/CS films as portable disposable removal techniques for benzaldehyde, glyoxal, formaldehyde, and acetaldehyde from water were fabricated. APOF@ZIF-8/CS exhibited an excellent formaldehyde adsorption capacity of 58.30 mg/g and an adsorption removal efficiency of 93.5 %. The adsorption process of biosorbent on various aldehydes was fitted by Freundlich adsorption isotherm. The adsorption kinetics followed Pseudo-second-order kinetic model.

The green synthesis and applications of biological metal-organic frameworks for targeted drug delivery and tumor treatments

Biological metal-organic frameworks (bio-MOFs) constitute a growing subclass of MOFs composed of metals and bio-ligands derived from biology, such as nucleobases, peptides, saccharides, and amino acids. Bio-ligands are more abundant than other traditional organic ligands, providing multiple coordination sites for MOFs. However, bio-MOFs are typically prepared using hazardous or harmful solvents or reagents, as well as laborious processes that do not conform to environmentally friendly standards. To improve biocompatibility and biosafety, eco-friendly synthesis and functionalization techniques should be employed with mild conditions and safer materials, aiming to reduce or avoid the use of toxic and hazardous chemical agents. Recently, bio-MOF applications have gained importance in some research areas, including imaging, tumor therapy, and targeted drug delivery, owing to their flexibility, low steric hindrances, low toxicity, remarkable biocompatibility, surface property refining, and degradability. This has led to an exponential increase in research on these materials. This paper provides a comprehensive review of updated strategies for the synthesis of environmentally friendly bio-MOFs, as well as an examination of the current progress and accomplishments in green-synthesized bio-MOFs for drug delivery aims and tumor treatments. In conclusion, we consider the challenges of applying bio-MOFs for biomedical applications and clarify the possible research orientation that can lead to highly efficient therapeutic outcomes.

Green valorization of PET waste into functionalized Cu-MOF tailored to catalytic reduction of 4-nitrophenol

Metal-organic frameworks (MOFs) are attractive functional materials due to their high surface area, high porosity, and flexible compositions. However, the high precursor cost and complex synthetic processes hinder their large-scale applications. Herein, a novel green approach has been developed toward the synthesis of Cu-based MOF by a solvent-free mechano-synthesis method and utilizing consumed polyethylene terephthalate (PET)-derived benzenedicarboxylate (BDC) as the linker. The as-prepared CuBDC and aminated CuBDC (CuBDC-NH2) act as green catalysts for the reduction of deleterious 4-nitrophenol (4-NP) into the value-added 4-aminophenol (4-AP). Compared with CuBDC, CuBDC-NH2 shows increased adsorption capability and reduction efficiency. The mechanism and thermodynamic studies suggest that the adsorption of 4-NP on CuBDC-NH2 is an endothermic, spontaneous, favorable, and physical adsorption process. Furthermore, CuBDC-NH2 can expedite the reduction of 4-NP by participating in an adsorptive catalytic process. With the CuBDC-NH2 catalyst, the catalytic normalized kinetic rate of 4-NP was achieved 11.28 mol/min. mg, outperforming state-of-the-art catalysts, and a complete reduction occur in 5 min for a concentrated effluent (200-ppm 4-NP). The plastic waste-derived MOF-mediated catalytic valorization of organic pollutants demonstrated here opens an avenue for the green recycling/utilization of plastic waste, providing meaningful insights into the sustainable management of organic pollutants in wastewater.

Properties of Aliphatic Ligand-Based Metal-Organic Frameworks

Ligands with a purely aliphatic backbone are receiving rising attention in the chemistry of coordination polymers and metal-organic frameworks. Such unique features inherent to the aliphatic bridges as increased conformational freedom, non-polarizable core, and low light absorption provide rare and valuable properties for their derived MOFs. Applications of such compounds in stimuli-responsive materials, gas, and vapor adsorbents with high and unusual selectivity, light-emitting, and optical materials have extensively emerged in recent years. These properties, as well as other specific features of aliphatic-based metal-organic frameworks are summarized and analyzed in this short critical review. Advanced characterization techniques, which have been applied in the reported works to obtain important data on the crystal and molecular structures, dynamics, and functionalities, are also reviewed within a general discussion. In total, 132 references are included.

Sonocrystallization of a novel ZIF/zeolite composite adsorbent with high chemical stability for removal of the pharmaceutical pollutant azithromycin from contaminated water

Water pollution management, reduction, and elimination are critical challenges of the current era that threaten millions of lives. By spreading the coronavirus in December 2019, the use of antibiotics, such as azithromycin increased. This drug was not metabolized, and entered the surface waters. ZIF-8/Zeolit composite was made by the sonochemical method. Furthermore, the effect of pH, the regeneration of adsorbents, kinetics, isotherms, and thermodynamics were attended. The adsorption capacity of zeolite, ZIF-8, and the composite ZIF-8/Zeolite were 22.37, 235.3, and 131 mg/g, respectively. The adsorbent reaches the equilibrium in 60 min, and at pH = 8. The adsorption process was spontaneous, endothermic associated with increased entropy. The results of the experiment were analyzed using Langmuir isotherms and pseudo-second order kinetic models with a R2 of 0.99, and successfully removing the composite by 85% in 10 cycles. It indicated that the maximum amount of drug could be removed with a small amount of composite.

Metal-organic frameworks and plastic: an emerging synergic partnership

Mismanagement of plastic waste results in its ubiquitous presence in the environment. Despite being durable and persistent materials, plastics are reduced by weathering phenomena into debris with a particle size down to nanometers. The fate and ecotoxicological effects of these solid micropollutants are not fully understood yet, but they are raising increasing concerns for the environment and people's health. Even if different current technologies have the potential to remove plastic particles, the efficiency of these processes is modest, especially for nanoparticles. Metal-organic frameworks (MOFs) are crystalline nano-porous materials with unique properties, have unique properties, such as strong coordination bonds, large and robustus porous structures, high accessible surface areas and adsorption capacity, which make them suitable adsorbent materials for micropollutants. This review examines the preliminary results reported in literature indicating that MOFs are promising adsorbents for the removal of plastic particles from water, especially when MOFs are integrated in porous composite materials or membranes, where they are able to assure high removal efficiency, superior water flux and antifouling properties, even in the presence of other dissolved co-pollutants. Moreover, a recent trend for the alternative preparation of MOFs starting from plastic waste, especially polyethylene terephthalate, as a sustainable source of organic linkers is also reviewed, as it represents a promising route for mitigating the impact of the costs deriving from the widescale MOFs production and application. This connubial between MOFs and plastic has the potential to contribute at implementing a more effective waste management and the circular economy principles in the polymer life cycle.

Salicylaldehydate coordinated two-dimensional-conjugated metal-organic frameworks

A novel class of copper-based 2D-c-MOF was synthesized from 1,3,5-triformylphloroglucinol using green mechano-chemistry. Herein, metal coordination with the salicylaldehyde functional moiety was explored for the first time in MOFs. Moreover, an intrinsic semiconductive copper-based SA-MOF thin film was fabricated using an in situ salt-free method at room temperature.

Rapid synthesis of bismuth-organic frameworks as selective antimicrobial materials against microbial biofilms

Antibiotic resistance is a global public health threat, and urgent actions should be undertaken for developing alternative antimicrobial strategies and approaches. Notably, bismuth drugs exhibit potent antimicrobial effects on various pathogens and promising efficacy in tackling SARS-CoV-2 and related infections. As such, bismuth-based materials could precisely combat pathogenic bacteria and effectively treat the resultant infections and inflammatory diseases through a controlled release of Bi ions for targeted drug delivery. Currently, it is a great challenge to rapidly and massively manufacture bismuth-based particles, and yet there are no reports on effectively constructing such porous antimicrobial-loaded particles. Herein, we have developed two rapid approaches (i.e., ultrasound-assisted and agitation-free methods) to synthesizing bismuth-based materials with ellipsoid- (Ellipsoids) and rod-like (Rods) morphologies respectively, and fully characterized physicochemical properties. Rods with a porous structure were confirmed as bismuth metal-organic frameworks (Bi-MOF) and aligned with the crystalline structure of CAU-17. Importantly, the formation of Rods was a 'two-step' crystallization process of growing almond-flake-like units followed by stacking into the rod-like structure. The size of Bi-MOF was precisely controlled from micro-to nano-scales by varying concentrations of metal ions and their ratio to the ligand. Moreover, both Ellipsoids and Rods showed excellent biocompatibility with human gingival fibroblasts and potent antimicrobial effects on the Gram-negative oral pathogens including Aggregatibacter actinomycetemcomitans, Porphyromonas gingivalis and Fusobacterium nucleatum. Both Ellipsoids and Rods at 50 ​μg/mL could disrupt the bacterial membranes, and particularly eliminate P. gingivalis biofilms. This study demonstrates highly efficient and facile approaches to synthesizing bismuth-based particles. Our work could enrich the administration modalities of metallic drugs for promising antibiotic-free healthcare.

A critical review on the synthesis of NH2-MIL-53(Al) based materials for detection and removal of hazardous pollutants

Nowadays, emerging hazardous pollutants have caused many harmful effects on the environment and human health, calling for the state of the art methods for detection, qualification, and treatment. Metal-organic frameworks are porous, flexible, and versatile materials with unique structural properties, which can solve such problems. In this work, we reviewed the synthesis, activation, and characterization, and potential applications of NH₂-MIL-53(Al). This material exhibited intriguing breathing effects, and obtained very high surface areas (182.3-1934 m²/g) with diverse morphologies. More importantly, NH₂-MIL-53(Al) based materials could be used for the detection and removal of various toxic pollutants such as organic dyes, pharmaceuticals, herbicides, insecticides, phenols, heavy metals, and fluorides. We shed light on plausible adsorption mechanisms such as hydrogen bonds, π-π stacking interactions, and electrostatic interactions onto NH₂-MIL-53(Al) adsorbents. Interestingly, NH₂-MIL-53(Al) based adsorbents could be recycled for many cycles with high stability. This review also recommended that NH₂-MIL-53(Al) based materials can be a good platform for the environmental remediation fields.

Efficient Activation of Peroxymonosulfate by Biochar-Loaded Zero-Valent Copper for Enrofloxacin Degradation: Singlet Oxygen-Dominated Oxidation Process

The removal of contaminants of emerging concern (CECs) has become a hot research topic in the field of environmental engineering in recent years. In this work, a simple pyrolysis method was designed to prepare a high-performance biochar-loaded zero-valent copper (CuC) material for the catalytic degradation of antibiotics ENR by PMS. The results showed that 10 mg/L of ENR was completely removed within 30 min at an initial pH of 3, CuC 0.3 g/L, and PMS 2 mmol/L. Further studies confirmed that the reactive oxygen species (ROS) involved in ENR degradation are ·OH, SO4-·, ¹O₂, and O2-. Among them, ¹O₂ played a major role in degradation, whereas O2-· played a key role in the indirect generation of ¹O₂. On the one hand, CuC adsorbed and activated PMS to generate ·OH, SO4-· and O2-·. O2-· was unstable and reacted rapidly with H₂O and ·OH to generate large amounts of ¹O₂. On the other hand, both the self-decomposition of PMS and direct activation of PMS by C=O on biochar also generated ¹O₂. Five byproducts were generated during degradation and eventually mineralized to CO₂, H₂O, NO3-, and F^-. This study provides a facile strategy and new insights into the biochar-loaded zero-valent transition-metal-catalyzed PMS degradation of CECs.

Understanding the ZIF-L to ZIF-8 transformation from fundamentals to fully costed kilogram-scale production

The production of MOFs at large scale in a sustainable way is key if these materials are to be exploited for their promised widespread application. Much of the published literature has focused on demonstrations of preparation routes using difficult or expensive methodologies to scale. One such MOF is nano-zeolitic imidazolate framework-8 (ZIF-8) - a material of interest for a range of possible applications. Work presented here shows how the synthesis of ZIF-8 can be tracked by a range of methods including X-ray diffraction, thermo gravimetric analysis and inelastic neutron scattering - which offer the prospect of in-line monitoring of the synthesis reaction. Herein we disclose how the production of nano-ZIF-8 can be conducted at scale using the intermediate phase ZIF-L. By understanding the economics and demonstrating the production of 1 kg of nano-ZIF-8 at pilot scale we have shown how this once difficult to make material can be produced to specification in a scalable and cost-efficient fashion.

Green Synthesis of Zeolitic Imidazolate Frameworks: A Review of Their Characterization and Industrial and Medical Applications

Metal organic frameworks (MOF) are a class of hybrid networks of supramolecular solid materials comprising a large number of inorganic and organic linkers, all bound to metal ions in a well-organized fashion. Zeolitic imidazolate frameworks (ZIFs) are a sub-group of MOFs with imidazole as an organic linker to metals; it is rich in carbon, nitrogen, and transition metals. ZIFs combine the classical zeolite characteristics of thermal and chemical stability with pore-size tunability and the rich topological diversity of MOFs. Due to the energy crisis and the existence of organic solvents that lead to environmental hazards, considerable research efforts have been devoted to devising clean and sustainable synthesis routes for ZIFs to reduce the environmental impact of their preparation. Green chemistry is the key to sustainable development, as it will lead to new solutions to existing problems. Moreover, it will present opportunities for new processes and products and, at its heart, is scientific and technological innovation. The green chemistry approach seeks to redesign the materials that make up the basis of our society and our economy, including the materials that generate, store, and transport our energy, in ways that are benign for humans and the environment and that possess intrinsic sustainability. This study covers the principles of green chemistry as used in designing strategies for synthesizing greener, less toxic ZIFs the consume less energy to produce. First, the necessity of green methods in today's society, their replacement of the usual non-green methods and their benefits are discussed; then, various methods for the green synthesis of ZIF compounds, such as hydrothermally, ionothermally, and by the electrospray technique, are considered. These methods use the least harmful and toxic substances, especially concerning organic solvents, and are also more economical. When a compound is synthesized by a green method, a question arises as to whether these compounds can replace the same compounds as synthesized by non-green methods. For example, is the thermal stability of these compounds (which is one of the most important features of ZIFs) preserved? Therefore, after studying the methods of identifying these compounds, in the last part, there is an in-depth discussion on the various applications of these green-synthesized compounds.

The chemistry behind room temperature synthesis of hafnium and cerium UiO-66 derivatives

RT formation of Hf and Ce UiO-66 derivatives is investigated using a one-step method where the linker and metal salt are simply combined, and a two-step method where the inorganic component is pre-heated to form metal clusters.

"Shake 'n Bake" Route to Functionalized Zr-UiO-66 Metal-Organic Frameworks

We report a novel synthetic procedure for the high-yield synthesis of metal-organic frameworks (MOFs) with fcu topology with a UiO-66-like structure starting from a range of commercial ZrIV precursors and various substituted dicarboxylic linkers. The syntheses are carried out by grinding in a ball mill the starting reagents, namely, Zr salts and the dicarboxylic linkers, in the presence of a small amount of acetic acid and water (1 mL total volume for 1 mmol of each reagent), followed by incubation at either room temperature or 120 °C. Such a simple "shake 'n bake" procedure, inspired by the solid-state reaction of inorganic materials, such as oxides, avoids the use of large amounts of solvents generally used for the syntheses of Zr-MOF. Acidity of the linkers and the amount of water are found to be crucial factors in affording materials of quality comparable to that of products obtained under solvo- or hydrothermal conditions.

Proof of concept for CUK family metal-organic frameworks as environmentally-friendly adsorbents for benzene vapor

The utility of metal-organic frameworks (MOFs) such as the CUK family (CUK - Cambridge University-KRICT) has been explored intensively for adsorption/separation of airborne volatile organic compounds (VOCs). In this article, three M-CUK analogs (M = Mg, Co, or Ni) were synthesized hydrothermally under similar conditions to assess the effects of their isostructural properties and metal centers on adsorption of benzene vapor (0.05-1 Pa). A list of performance metrics (e.g., breakthrough volume (BTV) and partition coefficient (PC)) were used to assess the role of the metal type (in M-CUK-1s) in the adsorption of VOCs. Specifically, Co-CUK-1 (average pore size of 8.98 nm) showed 2-3 times greater performance (e.g., in terms of 10% BTV (2012 L atm g^-1) and PC (6 mol kg^-1 Pa^-1)) over other analogs when exposed up to 0.05 Pa benzene vapor. The superiority of mesoporous Co-CUK-1 (e.g., enhanced adsorption diffusion mechanism through favorable metal-π and π- π interactions) can be attributed to the presence of cobalt metal centers (e.g., in reference to Mg- or Ni-CUK-1).

A Showcase of Green Chemistry: Sustainable Synthetic Approach of Zirconium-Based MOF Materials

Zirconium-based metal-organic framework materials (Zr-MOFs) have more practical usage over most conventional benchmark porous materials and even many other MOFs due to the excellent structural stability, rich coordination forms, and various active sites. However, their mass-production and application are restricted by the high-cost raw materials, complex synthesis procedures, harsh reaction conditions, and unexpected environmental impact. Based on the principles of "Green Chemistry", considerable efforts have been done for breaking through the limitations, and significant progress has been made in the sustainable synthesis of Zr-MOFs over the past decade. In this review, the advancements of green raw materials and green synthesis methods in the synthesis of Zr-MOFs are reviewed, along with the corresponding drawbacks. The challenges and prospects are discussed and outlooked, expecting to provide guidance for the acceleration of the industrialization and commercialization of Zr-MOFs.

Green synthesis of olefin-linked covalent organic frameworks for hydrogen fuel cell applications

Green synthesis of crystalline porous materials for energy-related applications is of great significance but very challenging. Here, we create a green strategy to fabricate a highly crystalline olefin-linked pyrazine-based covalent organic framework (COF) with high robustness and porosity under solvent-free conditions. The abundant nitrogen sites, high hydrophilicity, and well-defined one-dimensional nanochannels make the resulting COF an ideal platform to confine and stabilize the H3PO4 network in the pores through hydrogen-bonding interactions. The resulting material exhibits low activation energy (Ea) of 0.06 eV, and ultrahigh proton conductivity across a wide relative humidity (10-90 %) and temperature range (25-80 °C). A realistic proton exchange membrane fuel cell using the olefin-linked COF as the solid electrolyte achieve a maximum power of 135 mW cm-2 and a current density of 676 mA cm-2, which exceeds all reported COF materials.

A Facile One-Pot Approach to the Synthesis of Gd-Eu Based Metal-Organic Frameworks and Applications to Sensing of Fe3+ and Cr2O72- Ions

Gadolinium metal-organic frameworks (Gd-MOFs) and Eu-doped Gd-MOFs have been synthesized through a one-pot green approach using commercially available reagents. The 1,4-benzenedicarboxylic acid (H2-BDC) and 2,6-naphthalenedicarboxylic acid (H2-NDC) were chosen as ditopic organic linkers to build the 3D structure of the network. The Gd-MOFs were characterized using powder X-ray diffraction (XRD), FT-IR spectroscopy, field emission scanning electron microscopy (FE-SEM) and N2 adsorption-desorption analysis. The Gd-MOF structures were attributed comparing the XRD patterns, supported by the FT-IR spectra, with data reported in the literature for Ln-MOFs of similar lanthanide ionic radius. FE-SEM characterization points to the effect of the duration of the synthesis to a more crystalline and organized structure, with grain dimensions increasing upon increasing reaction time. The total surface area of the MOFs has been determined from the application of the Brunauer-Emmett-Teller method. The study allowed us to correlate the processing conditions and ditopic linker dimension to the network surface area. Both Gd-MOF and Eu-doped Gd-MOF have been tested for sensing of the inorganic ions such as Fe3+ and Cr2O72-.

Porphyrin and phthalocyanine-based metal organic frameworks beyond metal-carboxylates

Given the ubiquitous role of porphyrins in natural systems, these molecules and related derivatives such as phthalocyanines are fascinating building units to achieve functional porous materials. Porphyrin-based MOFs have been developed over the past three decades, yet chemically robust frameworks, necessary for applications, have been achieved much more recently and this field is expanding. This progress is partially driven by the development of porphyrins and phthalocyanines bearing alternative coordinating groups (phosphonate, azolates, phenolates…) that allowed moving the related MOFs beyond metal-carboxylates and achieving new topologies and properties. In this perspective article we first give a brief outline of the synthetic pathways towards simple porphyrins and phthalocyanines bearing these complexing groups. The related MOF compounds are then described; their structural and textural properties are discussed, as well as their stability and physical properties. An overview of the resulting nets and topologies is proposed, showing both the similarities with metal-carboxylate phases and the peculiarities related to the alternative coordinating groups. Eventually, the opportunities offered by this recent research topic, in terms of both synthesis pathways and modulation of pore size and shape, stability and physical properties, are discussed.

Biocompatibility and biodegradability of metal organic frameworks for biomedical applications

Metal organic frameworks (MOFs) are a unique class of smart hybrid materials that have recently attracted significant interest for catalysis, separation and biomedical applications. Different strategies have been developed to overcome the limitations of MOFs for bio-applications in order to produce a system with high biocompatibility and biodegradability. In this review, we outline the chemical and physical factors that dictate the biocompatibility and biodegradability characteristics of MOFs including the nature of the metal ions and organic ligands, size, surface properties and colloidal stability. This review includes the in vitro biodegradation and in vivo biodistribution studies of MOFs to better understand their pharmacokinetics, organ toxicity and immune response. Such studies can guide the design of future bio-friendly systems that bring us closer to safely translating these platforms into the pharmaceutical consumer market.

Deep eutectic solvents for the preparation and post-synthetic modification of metal- and covalent organic frameworks

The use of deep eutectic solvents (DES) as media for the preparation of metal- and covalent organic frameworks (MOFs and COFs) and their post-synthetic modification towards composites is reviewed.

Benign Integration of a Zn-Azolate Metal-Organic Framework onto Textile Fiber for Ammonia Capture

Ammonia (NH₃) exposure has a serious impact on human health because of its toxic and corrosive nature. Therefore, efficient personal protective equipment (PPE) such as masks is necessary to eliminate and mitigate NH₃ exposure risks. Because economically and environmentally viable conditions are of interest for large-scale manufacture of PPE, we herein report a benign procedure to synthesize a Zn-azolate metal-organic framework (MOF), MFU-4, for NH₃ capture. The surface area and morphology of MFU-4 obtained in alcohol solvents at room temperature is consistent with that of traditionally synthesized MFU-4 in N,N-dimethylformamide at 140 °C. In addition to its large NH₃ uptake capacity at 1 bar (17.7 mmol/g), MFU-4 shows outstanding performance in capturing NH₃ at low concentration (10.8 mmol/g at 0.05 bar). Furthermore, the mild synthetic conditions implemented make it facile to immobilize MFU-4 onto cotton textile fiber. Enhanced NH₃ capture ability of the MFU-4/fiber composite was also attributed to the well-exposed MOF particles. The benign synthetic MFU-4 procedure, high NH₃ uptake, and easy integration onto fiber pave the way toward implementation of similar materials in PPE.

Aqueous Flow Reactor and Vapour-Assisted Synthesis of Aluminium Dicarboxylate Metal-Organic Frameworks with Tuneable Water Sorption Properties

Energy-efficient indoors temperature and humidity control can be realised by using the reversible adsorption and desorption of water in porous materials. Stable microporous aluminium-based metal-organic frameworks (MOFs) present promising water sorption properties for this goal. The development of synthesis routes that make use of available and affordable building blocks and avoid the use of organic solvents is crucial to advance this field. In this work, two scalable synthesis routes under mild reaction conditions were developed for aluminium-based MOFs: (1) in aqueous solutions using a continuous-flow reactor and (2) through the vapour-assisted conversion of solid precursors. Fumaric acid, its methylated analogue mesaconic acid, as well as mixtures of the two were used as linkers to obtain polymorph materials with tuneable water sorption properties. The synthesis conditions determine the crystal structure and either the MIL-53 or MIL-68 type structure with square-grid or kagome-grid topology, respectively, is formed. Fine-tuning resulted in new MOF materials thus far inaccessible through conventional synthesis routes. Furthermore, by varying the linker ratio, the water sorption properties can be continuously adjusted while retaining the sigmoidal isotherm shape advantageous for heat transformation and room climatisation applications.

Polymorphous Indium Metal-Organic Frameworks Based on a Ferrocene Linker: Redox Activity, Porosity, and Structural Diversity

The metallocene-based linker molecule 1,1'-ferrocenedicarboxylic acid (H₂FcDC) was used to synthesize four different polymorphs of composition [In(OH)(FeC₁₂H₈O₄)]. Using conventional solvent-based synthesis methods and varying the synthetic parameters such as metal source, reaction temperature, and solvent, two different MOFs and one 1D-coordination polymer denoted as CAU-43 (1), In-MIL-53-FcDC_a (2), and In-FcDC (3) were obtained. Furthermore, thermal treatment of CAU-43 (1) at 190 °C under vacuum yielded a new polymorph of 2, In-MIL-53-FcDC_b (4). Both MOFs 2 and 4 crystallize in a MIL-53 type structure, but in different space groups C2/m for 2 and P1̅ for 4. The structures of the four title compounds were determined by single-crystal X-ray diffraction (SCXRD), powder X-ray diffraction (PXRD), or a combination of three-dimensional electron diffraction measurements (3D ED) and PXRD. N₂ sorption experiments of 1, 2, and 4 showed specific surface areas of 355 m² g^-1, 110 m² g^-1, and 140 m² g^-1, respectively. Furthermore, the electronic properties of the title compounds were characterized via Mössbauer and EPR spectroscopy. All Mössbauer spectra showed the characteristic doublet, proving the persistence of the ferrocene moiety. In the cases of 1, 3, and 4, appreciable impurities of ferrocenium ions could be detected by electron paramagnetic resonance spectroscopy. Cyclovoltammetric experiments were performed to demonstrate the accessible redox activity of the linker molecule of the title compounds. A redox process of FcDC^2- with oxidation (between 0.86 and 0.97 V) and reduction wave (between 0.69 and 0.80 V) was observed.

Conversion of a microwave synthesized alkali-metal MOF to a carbonaceous anode for Li-ion batteries

Hierarchical carbon-rich materials have shown immense potential for various electrochemical applications. Metal-organic frameworks (MOFs) are well suited precursors for obtaining such templated carbon matrices. Usually these conversions are carried out by energy intensive processes and lead to the presence of toxic transition metal residues. Herein, we demonstrate the green, scalable, microwave-assisted synthesis of a three-dimensional s-block metal based MOF and its efficient transformation into a carbonaceous material. The MOF-derived solid functions as a negative electrode for lithium-ion batteries having moderate low-rate capacities and cycling stability.

Spectroscopy, microscopy, diffraction and scattering of archetypal MOFs: formation, metal sites in catalysis and thin films

A comprehensive overview of characterization tools for the analysis of well-known metal–organic frameworks and physico-chemical phenomena associated to their applications.

Exploring thiophene-2-acetate and thiophene-3-acetate binding modes towards the molecular and supramolecular structures and photoluminescence properties of Pb(ii) polymers

The isomeric ligands thiophene-2(3)-acetate as linkers were used to construct Pb(ii) coordination polymers with an intriguing structure, noncovalent interactions, topology and interesting photoluminescence properties.

Coordinatively unsaturated metal sites (open metal sites) in metal–organic frameworks: design and applications

The defined synthesis of OMS in MOFs is the basis for targeted functionalization through grafting, the coordination of weakly binding species and increased (supramolecular) interactions with guest molecules.

Green synthesis and biological evaluation of novel 5-fluorouracil derivatives as potent anticancer agents

This study reports the formation of 5-FU co-crystals with four different pharmacologically safe co-formers; Urea, Thiourea, Acetanilide and Aspirin using methanol as a solvent. Two fabrication schemes were followed i.e., solid-state grinding protocol, in which API and co-formers were mixed through vigorous grinding while in the other method separate solutions of both the components were made and mixed together. The adopted approaches offer easy fabrication protocols, no temperature maintenance requirements, no need of expensive solvents, hardly available apparatus, isolation and purification of the desired products. In addition, there is no byproducts formation, In fact, a phenomenon embracing the requirements of green synthesis. Through FTIR analysis; for API the N-H absorption frequency was recorded at 3409.02 cm-1 and that of -C[bond, double bond]O was observed at 1647.77 cm-1. These characteristics peaks of 5-FU were significantly shifted and recorded at 3499.40 cm-1 and 1649.62 cm-1 for 5-FU-Ac (3B) and 3496.39 cm-1 and 1659.30 cm-1 for 5-FU-As (4B) co-crystals for N-H and -C[bond, double bond]O groups respectively. The structural differences between API and co-crystals were further confirmed through PXRD analysis. The characteristic peak of 5-FU at 2θ = 28.79918o was significantly shifted in the graphs of co-crystals not only in position but also with respect to intensity and FWHM values. In addition, new peaks were also recorded in all the spectra of co-formers confirming the structural differences between API and co-formers. In addition, percent growth inhibition was also observed by all the co-crystals through MTT assay against HCT 116 colorectal cell lines in vitro. At four different concentrations; 25, 50, 100 and 200 µg/mL, slightly different trends of the effectiveness of API and co-crystals were observed. However; among all the co-crystal forms, 5-FU-thiourea co-crystals obtained through solution method (2B) proved to be the most effective growth inhibitor at all the four above mentioned concentrations.