Commentary - (2021) Volume 9, Issue 3
Metal organic frameworks
Leila Azadeh*
Description
Metal-organic frameworks (MOFs) are organic-inorganic hybrid crystalline a porous material that contains a daily array of charged metal ions surrounded by organic 'linker' molecules. The metal ions form nodes that fix the arms of the linkers together to make a repeating, cage-like structure. Due to this hollow structure, MOFs have a huge internal area. Researchers have synthesized MOFs that feature an area of quite 7800 square meters per gram. To put this into context, if you'll lay out the available area during a teaspoon of this material, it might cover a whole soccer field.
MOFs offer unique structural diversity in contrast to other porous materials uniform pore structures; atomic-level structural uniformity; tunable porosity; extensive varieties; and
adaptability in topology, geometry, dimension, and chemical functionality. This enables researchers to control the framework of topology, porosity, and functionality. MOFs are composed of couple of components: a metal ion or bunch of metal ions and an organic particle called a linker. For this reason, the materials are often mentioned as hybrid organic-inorganic materials; however, this terminology has recently been openly discouraged. The organic units are characteristically mono-, di-, tri-, or tetravalent ligands. The choice of metal and linker orders the structure and later properties of the MOF. For example, the metal's organization preference effects the dimensions and form of pores by dictating what percentage ligands can bind to the metal and in which location.
The study of MOFs established from coordination chemistry and solid state chemistry, particularly the zeolites. Except for the utilization of preformed ligands, MOFs and zeolites are produced completely by hydrothermal or solvothermal methods, where crystals are gradually grown from a hot solution. In contrast with zeolites, MOFs are built from bridging organic ligands that remain intact during the synthesis.
Zeolite synthesis often marks use of a "template". Templates are ions that impact the structure of the growing inorganic framework. Typical templating ions are quaternary ammonium cations, which are detached later. In MOFs, the framework is templated by the SBU (secondary building unit) and therefore the organic ligands. A templating tactic that's beneficial for MOFs intended for gas storage is that the usage of metal-binding solvents like N,Ndiethylformamide and water. In these situations, metal sites are exposed when the solvent is evacuated, permitting hydrogen to bind at these sites. A recent progression in the solvent-free research of MOF films and composites is their synthesis by chemical vapor deposition. This procedure, MOF-CVD, was first confirmed for ZIF-8 and comprises two steps. During an initiative, metal oxide precursor coatings are placed. In the second step, these precursor layers are out to sublimed ligand molecules that make a phase alteration to the MOF space lattice. Creation of water during this reaction plays a significant role in guiding the conversion. This method was successfully scaled up to an integrated cleanroom process, conforming to industrial microfabrication values.
Conclusion
Many methods have been stated for the growth of MOFs as concerned with thin films. However, these methods are appropriate only for the synthesis of a lesser number of MOF topologies. One such example being the Vapor Assisted Conversion (VAC) which can be used for the thin film synthesis of several UiO-type MOFs.