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Nanotechnology Paper Metal Organic Frameworks By: Daniel Johnston In our Nano technology class we examine a number of different Nano scale structures such as carbon Nanotubes, silver Nano wires, and the composition and construction of diodes. But I believe that I know of another beneficial material, Metal Organic frameworks or MOFs. (I also did extensive research on MOFs in 2012.) MOFs are a crystalline mix of organic and inorganic chemicals and are truly intriguing. They can be constructed, modified, and functionalized into custom built chemical lattices or cages similar to C60 or Bucky Balls, which can be highly porous and react in specially designed manners. In this way the material can be designed and used in applications ranging from gas storage and catalysis to electronic components. Typically a MOF is a highly ordered nanoporous crystalline material with a structure that is composed of metal cluster centers connected by organic ligands in a grid or lattice type fashion (similar to a scaffolding setup to paint a building). The functionality and usage of the MOF can be custom tailored for the application desired. For instance by changing out the metal cluster from say a cobalt based compound with a nickel based one, we can cause its reactivity to be altered for different things. And also by changing out the ligand with say an optically reactive ligand that will change shape when exposed to UV light or a longer ligand, we can modify the pore size within the crystal lattice of the MOF, thereby selectively creating the correct pore and active site for the desired application. The characteristic creation of a MOF is typically by the use of solvothermal techniques. This procedure is usually completed by mixing the ligand of desire and the metal organic center of choice within a solvent then placed inside a pressure vessel and heated to high temperatures for 36+ hours in a programmable oven. Where in after the solution is removed from the oven and has returned to room temperature the crystals of the MOFs can be extracted and analyzed via Powder X-ray diffraction, Infrared spectroscopy, Ultraviolet spectroscopy, and H Proton NMR. The practice of using a MOF for gas storage is the topic that originally caught my interest when deciding on a research project with my professor whom headed my research. Gas storage is an important topic when energy storage is considered. An example being either hydrogen or Natural gas powered cars, how can we store enough gas on board to travel a given distance? One possible solution would be by using MOFs that have been designed to maximize the storage capacity of a given container of gas. This sounds counter intuitive that by placing a material inside of a gas cylinder that we can increase its storage capacity. But this is possible because of the absorbent and highly porous nature of MOFs. By adding in a specific MOF to a gas container one can add from 3-10% extra storage capacity. This can occur because with such a huge surface area there are many open areas within the MOFs’ crystalline structure that can sequester the gas thereby increasing the overall storage capacity. I believe that with further research and development on these materials, I can imagine that we could safely double our gas storage ability via the use of MOFs and their Nano porosity.1 However, the focus of my research was in regards to the MOFs ability of being used as a catalyst. Typically a good catalyst is one that reacts very fast with a substrate and brings about the reaction. But as we try to make the catalyst more reactive, the catalyst, itself, becomes prone to degradation. For Metal based organometallic 1 Mendoza-Cortes, Jose L.; Han, Sang Soo; Goddard Wa, William A.: High H2Uptake in Li-, Na-, K- Metalated Covalent Organic Frameworks and Metal Organic Frameworks at 298 K. The Journal of Physical Chemistry., 2012, A116, 1621-31 DOI: 10.1021/jp206981d catalysts, moisture becomes a big problem for the stability of the metal site, especially if the metal site is designed to bind to the substrate fast. To analyze the stability of these different structures, I constructed a number of different MOFs and created their appropriate molecular variations. In particular I synthesized MOFs with various different metal sites; Such as Cu(II), Zn(II), Ni(II), Cr(III), Ru(II), Co(II). Also, I synthesized the molecular complexes of the respective metal sites with similar coordination environments to their corresponding MOF. I then explored immersion testing in H2O/Non-aqueous medium of both the molecular and MOF form of the different metal sites. I immersed the chosen chemical in various concentrations of water and nonaqueous solvents for 12+ hours and then removed the molecular complex/MOFs. I then examined the MOFs via powder x-ray diffraction (PXRD), and the molecular complex via UV-spectroscopy and H NMR.2 I discovered that the MOF version of the catalyst was indeed many times (>103 times) more structurally stable and catalytically active. Using the information that the MOF bolstered catalyst is many times more resilient to degradation then the pure molecular version, one could think of many applications for MOF stabilized compounds, especially where highly reactive, robust and cheap catalysts are required. Next with MOFs as electronic components, there has been interest for their application in 4 main areas, sensors, passive electronics, active electronics, and as support structures. 2 Das, S.; Johnston, D. E.; Das, S.: Structural Bolstering of Metal Sites as Nodes in Metal Organic Frameworks. CrystEngComm, 2012, 14, 61366139 DOI: 10.1039/C2CE25555C (among the top 10 most highly accessed papers in Aug, 2012) As a sensor a silicon cantilever would be coated on one side with a MOF designed to react to a certain condition. When this sensor is exposed to the condition it would change shape by absorbing the particles or reacting with the condition and deflect the cantilever which in turn would cause a laser to register the deflection (similar to an AFM tip in contact mode). These sensors could be custom made to register different condition changes such as temperature, pressure, radiation, magnetic field, electric potential, acoustic waves, and chemical presence. This condition sensitivity is of course based on the chemical composition and design of the MOF used on the sensor. As a passive electronic component the MOF would not play a major role in transport or control of electrons but rather would function as a dielectric in different components such as transistors. As a component in a transistor the MOF material is placed between the source, gate, and the drain connections. In this way the MOF would assist in decreasing the size of transistors, due to a MOF dielectric material being better suited then the current dielectric materials in regards to electron flow. As an active electronic component the MOF would serve as a part of the P-Njunction in say a solar cell. In this application the MOF would be made semi conducting and would be treated in a way that allows the capture and transport of the electron excitations to the terminals of the solar cell. This application would be a very good for a MOF because a MOF can be custom made in extremely thin and flexible layers that could be treated in a number of different solutions or chemicals to functionalize the MOF for a desired task or wavelength of light. As a support structure a MOF lattice could be formed and then for example silver nanowires or carbon nanotubes could be grown within the crystal lattice allowing the formation of a composite material that would be highly conductive but also structurally strong. Essentially this use of MOFs would allow for the design and utilization of single digit Nano scale arrays of Nano wires which could lead to the further shrinking of electronic components.3 In conclusion I believe that MOFs have a very big future and huge potential in energy storage and as a viable electronics addition, as well as to science as a whole. I believe that these materials are versatile and due to their moldable properties, they are highly customizable and configurable for a range of desired applications. Additionally with their highly organized self-assembly structure they could be made cheaply and efficiently, when the desired MOF is formulated. It is in this fashion that I believe that they are noteworthy and a fantastic addition to Nano scale material science in general. Also furthermore, some of the crystals are very nice looking as well such as Co-Zif-9 which reminds me of tiny amethyst crystals. 3 Mark D. Allendorf, Adam Schwartzberg, Vitalie Stavila, A. Alec Talin.: A roadmap of Implementing Metal-Organic Frameworks in Electronic Devices: Challenges and Critical Directions. Chem.. Eur. J., 2011, 17, 11372 – 11388. DOI: 10.1002/chem.201101595 References: Mendoza-Cortes, Jose L.; Han, Sang Soo; Goddard Wa, William A.: High H2Uptake in Li-, Na-, K- Metalated Covalent Organic Frameworks and Metal Organic Frameworks at 298 K. The Journal of Physical Chemistry., 2012, A116, 1621-31 DOI: 10.1021/jp206981d 2 Das, S.; Johnston, D. E.; Das, S.: Structural Bolstering of Metal Sites as Nodes in Metal Organic Frameworks. CrystEngComm, 2012, 14, 6136-6139 DOI: 10.1039/C2CE25555C 3Mark (among the top 10 most highly accessed papers in Aug, 2012) D. Allendorf, Adam Schwartzberg, Vitalie Stavila, A. Alec Talin.: A roadmap of Implementing Metal-Organic Frameworks in Electronic Devices: Challenges and Critical Directions. Chem.. Eur. J., 2011, 17, 11372 – 11388. DOI: 10.1002/chem.201101595