As the lockdown in Switzerland is being lifted and we are back in our office, we are busy working on customer and internal projects. Part of this is further improving our work-up and shaping, so that we can offer more solutions to our clients.

In this issue we want to highlight another Swiss startup, DePoly. They have found a way to upcycle PET bottles into raw chemicals, so that we (and other chemical companies) can close the recycling loop.

DePoly upcycles used PET bottles into terephthalic acid (TPA) and mono ethylene glycol (MEG), and the TPA we use for some of the MOFs we produce. Great startup and we are looking forward to their growth!

 

Besides that, we found the webinar by Philip L. Llewellyn on MOFs for gas separations quite worthwhile. He covers materials to potential and actual application of MOFs.

From our blog

New articles of the last quarter

Metal-Organic Framework: a versatile platform for sensing technology

Highly sensitive and selective routes to detect molecules in various media, that commonly used materials do not match.

How MOF sensors work

Several working principles allow MOFs to be used in sensing and detecting applications.

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Interesting publications

Publications related to Carbon capture, reduction, storage and alternative energy

Highly modular metal-organic framework-based materials show great potential for photocatalytic hydrogen production

A metal organic framework (MOF)-based water splitting photocatalyst, developed at KAUST, has brought researchers a step closer to generating clean hydrogen fuel using sunlight.

“Magnetic sponge” MOF captures carbon with record energy efficiency

As porous materials with incredibly high surface areas, metal-organic frameworks (MOFs) offer a huge degree of versatility that could see them used in alternative rocket fuels, advanced batteries and devices that quickly detect dangerous gases. Another area where they have real potential is in the field of carbon capture, which a team of researchers in Australia has demonstrated with a sponge-like device that adsorbs CO2 using just a third of the energy of other methods.

Ultralow Ru Loading Transition Metal Phosphides as High‐Efficient Bifunctional Electrocatalyst for a Solar‐to‐Hydrogen Generation System

Water splitting is a promising technology for sustainable conversion of hydrogen energy. The rational design of oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) bifunctional electrocatalysts with superior activity and stability in the same electrolyte is the key to promoting their large‐scale applications. Herein, an ultralow Ru (1.08 wt%) transition metal phosphide on nickel foam (Ru–MnFeP/NF) derived from Prussian blue analogue, that effectively drivies both the OER and the HER in 1 KOH, is reported. To reach 20 mA cm−2 for OER and 10 mA cm−2 for HER, the Ru–MnFeP/NF electrode only requires overpotentials of 191 and 35 mV, respectively. Such high electrocatalytic activity exceeds most transition metal phosphides for the OER and the HER, and even reaches Pt‐like HER electrocatalytic levels. Accordingly, it significantly accelerates full water splitting at 10 mA cm−2 with 1.470 V, which outperforms that of the integrated RuO2 and Pt/C couple electrode (1.560 V). In addition, the extremely long operational stability (50 h) and the successful demonstration of a solar‐to‐hydrogen generation system through full water splitting provide more flexibility for large‐scale applications of Ru–MnFeP/NF catalysts.

A Highly Water-Stable meta-Carborane-Based Copper Metal–Organic Framework for Efficient High-Temperature Butanol Separation

Biofuels are considered sustainable and renewable alternatives to conventional fossil fuels. Biobutanol has recently emerged as an attractive option compared to bioethanol and biodiesel, but a significant challenge in its production lies in the separation stage. The current industrial process for the production of biobutanol includes the ABE (acetone–butanol–ethanol) fermentation process from biomass; the resulting fermentation broth has a butanol concentration of no more than 2 wt% (the rest is essentially water). Therefore, the development of a cost-effective process for separation of butanol from dilute aqueous solutions is highly desirable. The use of porous materials for the adsorptive separation of ABE mixtures is considered a highly promising route, as these materials can potentially have high affinities for alcohols and low affinities for water. To date, zeolites have been tested toward this separation, but their hydrophilic nature makes them highly incompetent for this application. The use of metal–organic frameworks (MOFs) is an apparent solution; however, their low hydrolytic stabilities hinder their implementation in this application. So far, a few nanoporous zeolitic imidazolate frameworks (ZIFs) have shown excellent potential for butanol separation due to their good hydrolytic and thermal stabilities. Herein, we present a novel, porous, and hydrophobic MOF based on copper ions and carborane–carboxylate ligands, mCB-MOF-1, for butanol recovery. mCB-MOF-1 exhibits excellent stability when immersed in organic solvents, water at 90 °C for at least two months, and acidic and basic aqueous solutions. We found that, like ZIF-8, mCB-MOF-1 is non-porous to water (type II isotherm), but it has higher affinity for ethanol, butanol, and acetone compared to ZIF-8, as suggested by the shape of the vapor isotherms at the crucial low-pressure region. This is reflected in the separation of a realistic ABE mixture in which mCB-MOF-1 recovers butanol more efficiently compared to ZIF-8 at 333 K.

Electronics

Detecting toxic PFAS with a chip-sized sensor

PNNL has patented an accurate and portable way to detect miniscule amounts of an extremely persistent toxic chemical that accumulates in our bodies and our environment.

Water Stable Zn(II) Metal–Organic Framework as a Selective and Sensitive Luminescent Probe for Fe(III) and Chromate Ions

Sensing and monitoring toxic contaminants like Fe3+, CrO42–, and Cr2O72– ions in water is very important due to their harmful effects on biological and environmental systems. Enhanced hydrolytic stability, sensitivity, and selectivity, in addition to their excellent luminescence properties, are important attributes of metal–organic framework (MOF)-based sensors for sensing applications. In this work, the water stable Zn–MOF [Zn2(tpeb)(bpdc)2] (where tpeb = 1,3,5-tri-4-pyridyl-1,2-ethenylbenzene and bpdc = biphenyl-4,4′-dicarboxylic acid) was synthesized and characterized. The framework retains its crystallinity and structural integrity in harsh acidic and basic conditions (pH 4–11). Most interestingly, the Zn–MOF demonstrates a strong blue luminescence in water that can be quenched selectively only by contaminants like Fe3+, CrO42–, and Cr2O72– ions. Higher Ksv values and low detection limits in selective luminescence quenching confirm the superior sensing performance, which is comparable to those of contemporary materials. Furthermore, in all cases, quenching efficiency remains unaltered in the presence of interfering ions, even after the compound is used in multiple cycles, which makes this MOF an attractive, reliable, and recyclable luminescent sensor material. The luminescence quenching mechanism is based on the competitive absorption and weak interactions. It is worth noting that most of the reported MOF-based sensors used for the separate sensing of Fe(III) and chromate ions are used in organic media due to their poor hydrolytic stabilities. Reports on the dual sensing of Fe(III) and chromate ions, which are also in aqueous media, are rare. Based on these results, Zn–MOF can be considered as a suitable candidate for advanced practical applications for the efficient sensing of Fe(III) and chromate ions in water.

Electrically Conductive Metal–Organic Frameworks

Metal–organic frameworks (MOFs) are intrinsically porous extended solids formed by coordination bonding between organic ligands and metal ions or clusters. High electrical conductivity is rare in MOFs, yet it allows for diverse applications in electrocatalysis, charge storage, and chemiresistive sensing, among others. In this Review, we discuss the efforts undertaken so far to achieve efficient charge transport in MOFs. We focus on four common strategies that have been harnessed toward high conductivities. In the “through-bond” approach, continuous chains of coordination bonds between the metal centers and ligands’ functional groups create charge transport pathways. In the “extended conjugation” approach, the metals and entire ligands form large delocalized systems. The “through-space” approach harnesses the π–π stacking interactions between organic moieties. The “guest-promoted” approach utilizes the inherent porosity of MOFs and host–guest interactions. Studies utilizing less defined transport pathways are also evaluated. For each approach, we give a systematic overview of the structures and transport properties of relevant materials. We consider the benefits and limitations of strategies developed thus far and provide an overview of outstanding challenges in conductive MOFs.

A highly fluorescent covalent organic framework as a hydrogen chloride sensor: roles of Schiff base bonding and π-stacking

In this paper we report the extremely crystalline structures, high thermal stabilities, and strong fluorescence emissions of covalent organic frameworks (COFs) based on linked carbazole units. We have synthesized three stable luminescent carbazole-linked COFs, namely, BCTB–PD, BCTA–TP, and BCTB–BCTA, through Schiff base condensations of 4,4′,4′′,4′′′-([9,9′-bicarbazole]-3,3′,6,6′-tetrayl)tetrabenzaldehyde (BCTB-4CHO) with p-phenylenediamine (PD), of 4,4′,4′′,4′′′-([9,9′-bicarbazole]-3,3′,6,6′-tetrayl)tetraaniline (BCTA-4NH2) with terephthalaldehyde (TP), and of BCTB-4CHO with BCTA-4NH2, respectively. These COFs had large Brunauer–Emmett–Teller surface areas (up to 2212 m2 g−1) and outstanding thermal stabilities (decomposition temperatures of up to 566 °C). Interestingly, the intramolecular charge transfer (ICT) and fluorescence properties of these COFs were strongly influenced by their types of Schiff base bonding (BCTB-4CH[double bond, length as m-dash]N or BCTA-4N[double bond, length as m-dash]CH) and the degrees of π-stacking between their COF layers. For example, ICT from the electron-donating carbazole group to the acceptor through the Schiff base units of the type BCTB-4CH[double bond, length as m-dash]N and increasing the π-stacking distance enhanced the fluorescence emission from the COF. Moreover, BCTB–BCTA, the most fluorescent of our three COFs, functioned as a fluorescent chemosensor for HCl in solution, with outstanding sensitivity and a rapid response.

Gas separation/storage and degradation

Discovery of Record-Breaking Metal-Organic Frameworks for Methane Storage using Evolutionary Algorithm and Machine Learning

In the past decade, there has been a rise in a number of computational screening works to facilitate finding optimal metal-organic frameworks (MOF) for variety of different applications. Unfortunately, most of these screening works are limited to its initial set of materials and result in brute-force type of a screening approach. In this work, we present a systematic strategy that can find materials with desired property from an extremely diverse and large MOF set of over 100 trillion possible MOFs using machine learning and evolutionary algorithm. It is demonstrated that our algorithm can discover 964 MOFs with methane working capacity over 200 cm3 cm−3 and 96 MOFs with methane working capacity over 208 cm3 cm−3, which is the current world record. We believe that this methodology can facilitate a new type of a screening approach that takes advantage of the modular nature in MOFs, and can readily be extended to other important applications as well.

Porous Carbon Derived from Metal Organic Framework for Gas Storage and Separation: The Size Effect

Metal organic framework (MOF) derived carbon is an important kind of carbons with various potential applications. The structure of MOF precursor plays a key role in the proprieties of their derived carbon. Herein, the size effect of a Zn-MOF on the porosity and gas uptake of its derived carbon are investigated in detail. We found that the large-size MOF tend to form porous carbons with higher specific surface area as well as large pore size, while the carbon derived from small-size MOF shows lower specific surface area and more micropores as well as higher gas uptake. Especially, the CS-1000 derived from Zn-MOF-small shows a high CO2 uptake of 129.2 cm3 g−1 at 273 K and 1 bar, a high H2 uptake of 241.6 cm3 g−1 at 77 K and 1 bar, and a high CH4 uptake of 58.3 cm3 g−1 at 273 K and 1 bar, making it very potential for carbon capture and sequestration and clean energy storage.

A novel polyoxovanadate-based Co–MOF: highly efficient and selective oxidation of mustard gas simulant by two sites synergetic catalysis

Two novel polyoxovanadate-based metal–organic frameworks (MOFs), [Co(bib)]{V2O6} (V–Co-MOF) and [Ni(en)(bib)]{V2O6}·2H2O (V–Ni-MOF) (bib = 1,4-bis(1H-imidazoly-1-yl)benzene, en = ethylenediamine) were facilely synthesized under mild hydrothermal conditions. Single-crystal X-ray diffraction analysis shows that the V sites in both compounds adopt {VO4} tetrahedral coordination geometries, and the Co center in the V–Co-MOF presents a four-coordinated distorted tetrahedron configuration (coordinatively unsaturated metal sites, CUMS), while the Ni center in the V–Ni-MOF exhibits six-coordinated octahedral geometry (coordinatively saturated metal sites, CSMS). Given that the CUMS can generally be used as active sites for catalytic reactions, we explored the catalytic activities of these two compounds for the oxidation of a mustard gas simulant, 2-chloroethyl ethyl sulfide (CEES). The experimental results indicate that they can catalyze the oxidation of CEES to give the only nontoxic product, 2-chloroethyl ethyl sulfoxide (CEESO). Significantly, the V–Co-MOF exhibits higher catalytic activity; it converts 100% of CEES in 10 min, whereas V–Ni-MOF converts only 47.5% of CEES under identical conditions. Researching the mechanism of the catalytic reaction revealed that the excellent catalytic performance of the V–Co-MOF was attributed to the two-site synergetic effect: (1) the oxidant H2O2 interacts with the V site to produce peroxovanadium with higher oxidation activity; (2) the S atom in CEES coordinates with the four-coordinated Co(II) center to obtain 2-chloroethyl ethyl sulfonium cation (CEES+), which makes the CEES more easily oxidize to CEESO based on the oxidation mechanism of peroxovanadium and shortens the molecular size distance between CEES and the obtained peroxovanadium, thereby greatly improving the rate of the catalytic reaction. To our knowledge, this is the first dual-active-site polyoxometalate-based MOF catalyst for catalysing the oxidative detoxification of CEES.

Water harvesting / water purification

Water and Metal–Organic Frameworks: From Interaction toward Utilization

The steep stepwise uptake of water vapor and easy release at low relative pressures and moderate temperatures together with high working capacities make metal–organic frameworks (MOFs) attractive, promising materials for energy efficient applications in adsorption devices for humidity control (evaporation and condensation processes) and heat reallocation (heating and cooling) by utilizing water as benign sorptive and low-grade renewable or waste heat. Emerging MOF-based process applications covered are desiccation, heat pumps/chillers, water harvesting, air conditioning, and desalination. Governing parameters of the intrinsic sorption properties and stability under humid conditions and cyclic operation are identified. Transport of mass and heat in MOF structures, at least as important, is still an underexposed topic. Essential engineering elements of operation and implementation are presented. An update on stability of MOFs in water vapor and liquid systems is provided, and a suite of 18 MOFs are identified for selective use in heat pumps and chillers, while several can be used for air conditioning, water harvesting, and desalination. Most applications with MOFs are still in an exploratory state. An outlook is given for further R&D to realize these applications, providing essential kinetic parameters, performing smart engineering in the design of systems, and conceptual process designs to benchmark them against existing technologies. A concerted effort bridging chemistry, materials science, and engineering is required.

Ultrathin water-stable metal-organic framework membranes for ion separation

Owing to the rich porosity and uniform pore size, metal-organic frameworks (MOFs) offer substantial advantages over other materials for the precise and fast membrane separation. However, achieving ultrathin water-stable MOF membranes remains a great challenge. Here, we first report the successful exfoliation of two-dimensional (2D) monolayer aluminum tetra-(4-carboxyphenyl) porphyrin framework (termed Al-MOF) nanosheets. Ultrathin water-stable Al-MOF membranes are assembled by using the exfoliated nanosheets as building blocks. While achieving a water flux of up to 2.2 mol m−2 hour−1 bar−1, the obtained 2D Al-MOF laminar membranes exhibit rejection rates of nearly 100% on investigated inorganic ions. The simulation results confirm that intrinsic nanopores of the Al-MOF nanosheets domain the ion/water separation, and the vertically aligned aperture channels are the main transport pathways for water molecules.

Filtering out toxic chromium from water

Hexavalent chromium continues to contaminate water sources around the world, with one US company fined just this February for having put employees at risk. Hexavalent chromium is considered to be extremely toxic, especially when inhaled or ingested, and its use is regulated in Europe and in many countries around the world. It is thought to be genotoxic, leading to DNA damage and the formation of cancerous tumors.

Now, chemists at EPFL are developing energy efficient processes for removing contaminants, this time hexavalent chromium, from water.

Pharmaceuticals / biomedical applications

A new way to deliver drugs in MOFs

Scientists from the Institute of Physical Chemistry of the Polish Academy of Sciences (IPC PAS) in cooperation with the Faculty of Chemistry of the Warsaw University of Technology (WUT) have developed a new, solvent-free method for the encapsulation of drug molecules in MOF (metal-organic framework) porous materials.

MOF delivers cancer drug candidate straight to mitochondria

A metal-organic framework (MOF) has been created to effectively smuggle drugs into mitochondria, which are where cancers often begin. The researchers have also revealed the mechanism cells use to ‘swallow’ MOFs – an important first step towards developing more efficient drug delivery systems.

Ship-in-a-Bottle Preparation of Long Wavelength Molecular Antennae in Lanthanide Metal–Organic Frameworks for Biological Imaging

While metal–organic frameworks (MOFs) have been identified as promising materials for sensitizing near-infrared emitting lanthanide ions (Ln3+) for biological imaging, long-wavelength excitation of such materials requires large, highly delocalized organic linkers or guest-chromophores. Incorporation of such species generally coincides with fewer Ln3+ emitters per unit volume. Herein, the excitation bands of ytterbium-based MOFs are extended to 800 nm via the postsynthetic coupling of acetylene units to form a high density of conjugated π-systems throughout MOF pores. The resulting long wavelength excitation/absorption bands are a synergistic property of the composite material as they are not observed in the individual organic components after disassociation of the MOFs, thus circumventing the need for large organic chromophores. We demonstrate that the long wavelength excitation and emission properties of these modified MOFs are maintained in the biological conditions of cell culture (aqueous environment, salts, heating), pointing toward their promising use for biological imaging applications.

Oxygen Self-Sufficient Core–Shell Metal–Organic Framework-Based Smart Nanoplatform for Enhanced Synergistic Chemotherapy and Photodynamic Therapy

The abnormal angiogenesis and insufficient oxygen supply in solid tumors lead to intratumoral hypoxia, which severely limits the efficacy of traditional photodynamic therapy (PDT). Here, a multifunctional nanoplatform (ZDZP@PP) based on a zeolitic imidazolate framework-67 (ZIF-67) core as a hydrogen peroxide catalyst, a zeolitic imidazolate framework-8 (ZIF-8) shell with a pH-responsive property, and a polydopamine–poly(ethylene glycol) (PDA–PEG) layer for improving the biocompatibility is fabricated for not only relieving tumor hypoxia but also enhancing the efficacy of combination chemo–photodynamic therapy. The chemotherapy drug doxorubicin (DOX) and photosensitizer protoporphyrin IX (PpIX) are encapsulated in different layers independently; thus, a unique two-stage stepwise release becomes possible. Moreover, the nanoplatform can effectively decompose hydrogen peroxide to produce oxygen and thus relieve tumor hypoxia, which further facilitates the production of cytotoxic reactive oxygen species (ROS) by PpIX under laser irradiation. Both in vitro and in vivo experimental results confirm that the combination chemo–photodynamic therapy  withthe ZDZP@PP nanoplatform can provide more effective cancer treatment than chemotherapy or PDT alone. Consequently, the oxygen self-sufficient multifunctional nanoplatform holds promising potential to overcome hypoxia and treat solid tumors in the future.

Metal–Organic Framework Traps with Record-High Bilirubin Removal Capacity for Hemoperfusion Therapy

Adsorption-based hemoperfusion has been widely used to remove toxins from the blood of patients suffering acute liver failure (ALF). However, its detoxification effect has been severely hampered by the unsatisfactory adsorption performance of clinically used porous adsorbents, such as activated carbon (AC) and adsorption resin. Herein, two cage-based metal–organic frameworks (MOFs), PCN-333 (constructed from 4,4,4-s-triazine-2,4,6-triyl-tribenzoic acid (H3TATB) ligands and Al3 metal clusters) and MOF-808 (constructed from 1,3,5-benzenetricarboxylic acid (H3BTC) ligands and Zr6 metal clusters), are introduced for highly efficient hemoperfusion. They possess negligible hemolytic activity and can act as “bilirubin traps” to achieve outstanding adsorption performance toward bilirubin, a typical toxin related to ALF. Notably, PCN-333 shows a record-high adsorption capacity (∼1003.8 mg g–1) among various bilirubin adsorbents previously reported. More importantly, they can efficiently adsorb bilirubin in bovine serum albumin (BSA) solution or even in 100% fetal bovine serum (FBS) due to their high selectivity. Strikingly, the adsorption rate and capacity of PCN-333 in biological solutions are approximately four times faster and 69 times higher than those of clinical AC, respectively. Findings in this work pave a new avenue to overcome the challenge of low adsorption efficiency and capacity in hemoperfusion therapy.

Niklas

Author Niklas

Absolutely amazed by MOFs and their applications.

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