What are MOFs?
Metal-Organic Frameworks (MOFs) are crystalline, hybrid materials containing metal ions and organic molecules; components that together forms a three-dimensional structure. The material is known for its high porosity and large surfaces and its components allow for various combinations of organic and inorganic blocks. These blocks give rise to millions of different structures.
The unique features of MOFs, such as their large surface-areas and diversity of structures, makes the them suitable to a broad range of industrial processes. MOFs are, for instance, very well suited for storing and transportation of gases, separation of gases, water absorption, catalysis or even adsorption cooling and drug delivery. MOFs have the highest surface-area of any known materials, they are very light, porous, and their structure can be designed for a wide specter of purposes. The MOF-structure can, for instance, be designed to captivate specific gases and chemicals, while other substances passes through. MOFs are therefore well suited for efficient separation processes. Increased efficiency of gas storage, should also be mentioned. The large surface-area of MOFs enables them to soak up large amounts of gas, greater storage capacities are therefore possible.
The latest developed MOFs, are a relatively new class of hybrid materials, these MOFs have been given immense interest the last couple of years. Their increased stability, makes them so unique that they most certainly will play an important role in future industrial processes.
How is it produced?
There are several methods used to synthesize highly functionalized MOFs. However, the most common process is called solvothermal batch reaction, a method that requires high temperature (160-250°C), long reaction time, and applying solvent such as N,N-Dimethylformamide. This method has been criticized for both environmental and economic reasons and the preparation of MOFs have been highly dependent on this method. However, an alternative method has been proven in recent years and now several promising MOF-structures have been synthesized using water as solvent and continuous flow synthesis methods to avoid the issues. A method with advanced sustainable and environmental-friendly synthesis, representing a shift towards green chemistry.
The stability of MOFs is largely determined by the structure of its bricks and the nature of the chemical bonds it forms with the organic molecules. A major concern regards industrial application of MOFs have been the poor stability of most MOFs. An issue that has been research and resolved by developing MOFs with exceptional thermal, chemical, and mechanical stability. These type of MOFs are developed by scientists at Universitetet i Oslo (UiO) and is called UiO-66. These MOFs are comprised of the Zr₆(O)₄(OH)₄ building blocks. The UiO-66 MOFs are stable up to 400 degrees and can have surface-areas from 800 to 7000 m²/g.