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Metal-organic Frameworks – Green Materials For Sustainable Future

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According to Professor Mark Miodownik of University College London, innovation of materials in the 20th century was about how materials work, their inside structures, and their properties. However, innovation in the 21st century is about applying this knowledge to enable significant progress to solve problems pertaining to various fields such as energy, biomedical, environment, etc.1

In this context, Metal-organic frameworks (MOFs) armoured with novel functionalities are re-emerging as much sought-out green materials. The term MOF was coined by Omar Yaghi in 1995. MOFs consist of both organic and inorganic building entities, where extended framework is created by the coordination of organic ligands and metal ion clusters. The frameworks are rigid enough to form internal voids after solvent removal, forming structures with high porosity, and possess a surface area of up to ~ 7000 m2g-1.2


MOFs comprised of metal-containing nodes connected by organic links (Source)

MOFs have indefinite number of structures, thus paving way for numerous applications in many fields that exploit their cage-like structure, such as gas storage and separation, liquid separation and purification, electrochemical energy storage, catalysis, sensors, batteries, fuel cells, supercapacitors, and biomedical applications such as drug delivery and imaging.3,4


Different structures of MOFs (Source)

Even though a tremendous amount of research has been carried out over the last two decades, synthesis of countless number of MOFs at only lab scale and lack of focus on environmentally friendly synthetic routes are a few hurdles for commercialisation. Therefore, there is a need to develop sustainable, scalable and cost-effective approaches to the synthesis of MOFs. However, the difficulty is that many concepts of Green Chemistry have only recently emerged to address the unique challenges of assembling structures composed of MOFs.5


Large scale MOF production is now underway which will help secure customer confidence and open the window for other MOF-based products. BASF, MOF Technologies, NuMat Technologies, MOF Apps, ProfMOF, KRICT, Framergy Inc., STREM Chemicals Inc., Immaterial Labs Ltd., MOFWORX, MOFGen, Acsynam, Mosaic Materials, Tarsis Technology, Inmondo Tech Inc., and Promethean Particles Ltd., are a few companies that are involved in the commercial production of MOFs.

Researchers from McGill University and the University of Birmingham in collaboration with 525 Solutions Inc., have developed a strategy to design hypergolic behaviour within an MOF platform, by using simple trigger functionalities to unleash the latent and generally not recognized energetic properties of popular class of MOFs based on zeolitic imidazolate.6

Fabrication of MOF-74(Ni) and UTSA-16(Co) monoliths with loadings as high as 80 and 85 wt. % using the 3D printing technique and evaluation of their adsorptive performance for CO2 removal from air has been reported by researchers of Missouri University of Science and Technology.7


Fabrication of MOF monoliths using the 3D printing technique (Source)

One‐pot synthesis of 3D printable hydrogel ink containing zeolitic imidazolate frameworks (ZIF‐8) anchored on anionic 2,2,6,6‐tetramethylpiperidine‐1‐oxylradical‐mediated oxidized cellulose nanofibers (TOCNF) is presented by researchers of Stockholm University. This approach may open new venues for MOFs processing and its large‐scale applications.8


Photos of 3D printed scaffolds of the printed scaffolds: TOCNF (a), 4CelloZIF8 (b), and 4CelloZIF8-Cur (c). Insets are images representing the pores, with the scale bar of 0.5 mm (Source)

Zeolitic imidazole framework‐8 (ZIF‐8) based magnetic helical microrobots for drug delivery have been fabricated by researchers from ETH Zurich. This highly integrated multifunctional device can swim along predesigned tracks under the control of weak rotational magnetic fields. The proposed systems can achieve single‐cell targeting in a cell culture media and a controlled delivery of drug payloads inside a complex microfluidic channel network.9

Dr. Ryohei Mori at Green Science Alliance Co. Ltd. has developed MOF-based electrode material for lithium ion battery. Zinc-based MOF has been used to make a new type of electrode with a cell capacity of 100 mAh/g cell capacity over 50 times of cell cycles in a stable manner.10


Lithium Ion Battery Test Cell made with MOF based Electrode (Source)

Water Harvesting Inc. is working on commercializing atmospheric water harvesting systems based on MOFs. It has negotiated an exclusive licensing agreement with UC Berkeley to develop and commercialize water harvesting systems, and has also recently filed its own provisional US patent application related to details of the system design.11

Karlsruhe Institute of Technology (KIT) of Germany and Center for Materials Science, Zewail City of Science and Technology of Egypt jointly worked on a novel approach to produce a composite of the HKUST-1 metal–organic framework (MOF) and graphene, which is suited for the fabrication of monolithic coatings of solid substrates. These monolithic coatings exhibited high surface areas (1156–1078 m2/g) and high electrical conductivity (7.6 × 10–6 S m–1 ~ 6.4 × 10–1 S m–1).12


Composite of the HKUST-1 metal–organic framework (MOF) and graphene (Source)

Researchers at the Indian Institute of Technology Guwahati have recently developed a novel water-stable Sn(ii) based mesoporous metal–organic framework (MOF) using benzene-1,3,5-tricarboxylic acid (TMA) as an organic linker via an eco-friendly solvothermal route. This Sn(II)-TMA MOF is used in fluoride removal from water and the material showed excellent aqueous stability even after prolonged exposure to water.13


Sn(II)-TMA MOF displaying positive zeta potential over a broad pH range (3-10) for selective fluoride adsorption from water (Source)

Qian-Qian Zhu et al., from Tianjin Normal University, designed and synthesized a dendritic aromatic 6-carboxyl linker (H6TDCPB), which is successfully assembled with Cd(II) ion to construct a porous metal−organic framework with a raw Cd6 cluster, {[Cd3(TDCPB)·2DMAc]·DMAc·4H2O}n. The as synthesized sample not merely owns an excellent detectable ability but also possesses an outstanding selectivity for nitrofurans, a popular category of antibiotics containing five-membered furan rings that have been widely applied in the clinical treatment of bacterial infections, particularly nitrofurazone (NFZ) and nitrofurantoin (NFT).14

Fabrication of a novel MOF(Fe)@NaAlg aerogels loaded by ammonium (NH4+) by a facile method of ion cross-linking for the slow-release fertilizer (SRF) was reported by Chengyi Wu et al.15


Researchers from the University of Cambridge have used machine learning tools to predict the mechanical properties of MOFs, which could be used to store harmful gases, power hydrogen-based cars or extract water from air. They employed a multi-level computational methodology in order to build an interactive map of the structural and mechanical landscape of MOFs. First, they used high-throughput molecular simulations for nearly 3,385 MOFs. Later, they developed a freely-available machine learning algorithm to predict the mechanical properties of existing and yet-to-be-synthesised MOFs automatically.16

Researchers from the University of Michigan gathered information on all available MOFs, those previously constructed as well as those that remain hypothetical, into a database. High-throughput computer simulations were then used to scour the resulting databank of nearly 500,000 MOFs to identify those having promising capacities. Out of these, three candidates have surpassed the previous records for hydrogen storage, and established a new high-water mark for usable hydrogen capacities in MOFs.17

An algorithmic study published in Nature Communications by a KAIST research team presents a clue for finding the perfect pairs. The team, led by Professor Ji-Han Kim from the Department of Chemical and Biomolecular Engineering, developed a joint computational and experimental approach to rationally design MOF@MOFs, a composite of MOFs where one MOF is grown on a different MOF.18

Experiments show that machine learning can use a large amount of unreported data on failed chemical reactions to optimize the synthesis of porous MOF materials. Moosavi et al., focused on the dominant reaction parameters identified by machine learning, and discovered two sets of conditions that produce Zn-HKUST-1 after carrying out just 20 trial reactions. The authors suggest that taking a completely unguided approach would have required thousands of reactions to achieve the same result.19


WO2018065555A1 from Immaterial Labs Ltd. discloses an MOF body which comprises MOF crystallites adhered to each other via an MOF binder. The MOF crystallites and the MOF binder are formed of HKUST-1 i.e., Cu3(BTC)2-3H2O. The MOF body has utility for storing and/or separating gases such as CH4, CO2, O2, NH3, Ar, CO, N2 and C2H4, toxic industrial gases such as benzene, toluene, xylenes, sulphur dioxide, ethylene oxide; and warfare agents such as sarin, mustard gas, etc.


Schematic representation of monolithic and powder MOF synthesis

WO2018197715A1 from Cambridge Enterprise Ltd. discloses the sol-gel synthesis of a mechanically and chemically robust monolithic MOF composite body which comprises MOF crystallites adhered to each other via a binder comprising MOF; and at least 0.15 vol % photolytic nanoparticles, of particle size in the range 3-200 nm, encapsulated in the MOF body. The MOF composite body can be used for treating water containing an organic dye, the reaction supported by the photocatalytic nanoparticles is a degradation reaction of the organic dye.


Pure ZI F-8 monoliths (monoZIF-8) are
transparent (Fig. 1); SnO2@monoZIF-8 appears white (Fig. 2)

US10260148B2 from NuMat Technologies, Inc. discloses a porous material, including novel metal organic framework (MOFs) and porous organic polymer (POP), that provides reactivity with or sorptive affinity towards electronic gas to substantially remove or abate electronic gas in an electronic gas-containing effluent. The MOFs or POPs provided in the container can be formed in various shapes, such as pellets, disks, or a monolithic body, in a method that gives optimal diffusion characteristics, reactivity, and efficiency for electronic gas abatement.


Schematic illustration of an abatement and purification system with a pellet-filled (left), disk-filled (center) and monolithic MOF-filled (right) container of MOFs or POPs.

US2019039047A from BASF discloses carbon dioxide and volatile organic compound sorbents that include a porous support, comprising MOF, impregnated with an amine compound.

WO2019086542A1 from Cambridge Enterprise Ltd. discloses MOF materials for delivering RNAi molecules for therapeutic use, in particular for cancer treatment.


NuMat is poised to expand the global reach of its molecularly engineered products platform to Europe, East Asia and beyond, by closing a $12.4 million financing round led by OS Fund, with participation from Osage University Partners, Tin Shed Ventures and other existing investors.20

MOF Technologies is working with many partners such as General Motors on natural gas storage, IBM on heat pumps for data center temperature management, and industrial gas companies for managing specialty gases used in the manufacture of electronics.21

Versum Materials Inc., a leading materials supplier to the semiconductor industry and NuMat Technologies, announced a commercial agreement to offer a new product line called ION-X® which can be utilized for the safe storage and delivery of dopant gases such as arsine, phosphine and boron trifluoride. ION-X® offers potential advantages over traditional carbon-based adsorbent technologies that are employed in the ion implant processes for the manufacture of semiconductor devices.22


NuMat’s Cylinders use a metal–organic framework to more safely store toxic gases to process semiconductors (Source)

Mosaic Materials which uses porous, crystalline solid MOFs for the separation of CO2 from air or flue gas has partnered with ExxonMobil to pursue carbon capture technology.23

Climeworks AG and Antecy B.V. have joined forces for removing climate-relevant amounts of CO2 from the atmosphere. It is expected that the combination of their technologies will result in even more powerful solutions for both direct air capture and utilization of CO2.24

NuMat Technologies, in association with Northwestern University, is evaluating the potential of MOFs in CO2 scrubbing systems utilized by NASA. This work builds upon existing expertise at Northwestern University and NuMat Technologies in the areas of MOF synthesis and formation.25

MOF Technologies announced the start of MOF4AIR, an €11 million H2020 EU project aimed at the reduction of energy intensity and cost of the CO2 capture process for the commercial deployment of CCS technology. It has secured €800K funding to work along 14 partners from 8 countries to develop and demonstrate the performance of MOF-based CO2 capture technologies in power plants and energy intensive industries.26


Metal organic frameworks are re-emerging as a promising tool for green materials in order to attain sustainable future technologies. Currently, commercialization of MOFs is still in its infancy and requires extensive and careful evaluation of scalable synthetic methods that cater to both environmental and economic factors. Novel methodologies such as artificial intelligence, machine learning, etc., aided by fabrication techniques such as 3D printing could help in achieving large scale productivity. This realization will bring about important developments towards implementing MOFs in technologies oriented towards applications ranging from energy to biomedical technology.

  2. Johnson Matthey Technol. Rev., 2015, 59, (2), 123–125
  4. Biomaterials, Volume 230, February 2020, 119619
  5. Green Chem., 2017, 19, 2729–2747
  6. Science Advances, 2019, 5, 4, 9044
  7. ACS Appl. Mater. Interfaces, 2017, 9, 41, 35908-35916
  8. Adv. Funct. Mater.2018, 1805372
  9. Adv.Mater.2019, 31, 1901592
  12. ACS Appl. Mater. Interfaces, 2019, 116, 6442-6447
  13. New J. Chem., 2020, Advance Article
  14. Inorg. Chem. 2020, 59, 2, 1323-1331
  15. International Journal of Biological Macromolecules, Volume 145, 15 February 2020, Pages 1073-1079
  19. Nature, 2019, 566, 464-465
  21. Chemical and engineering news, 2017, 95, 24, 18-19
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Dr. Siva Prasad

Dr. John Kathi