Research Project: Studies of Reactive Amorphous Compounds and Surfaces: Their Pathways to Crystallinity and Surface Functionality
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Mapping the pathway from amorphous to Crystalline
There are many groups of compounds that do not form crystals. Yet they may have interesting properties such as porosity, ion exchange and proton conductivity. They are said to be amorphous with only short range order. If their structure were known it would allow chemists to better develop uses for these compounds. We have chosen to study two types of layered amorphous materials, that on heating for long periods approach crystalline structures.
The first type of compounds are layered zirconium and tin phosphates, M(HPO4)2∙H2O, for short, ZrP and SnP. The crystallization is a slow process with the surface changing from highly disordered nanoparticles to single crystals. We have found that many compounds may be bonded to the POH groups that are on the surfaces of the layers. Our intention is to affix MOFs to the surfaces. MOFs are a combination of metals and organic compounds (Metal-Organic Frameworks) that exhibit ultra-high porosity and enormous internal surface areas. Many applications have been suggested but there is a problem with stability. We believe that MOFs bonded to our surfaces will be studier than the normally prepared MOFs.
The crystallization of ZrP is a slow process with the surfaces changing as the crystallinity increases. This change is observed by the change in the sodium ion exchange curves as the particles become more crystalline. We propose to determine the changes in the MOFs made on the surfaces of ZrP from amorphous in increments to complete crystallinity. The tin compounds remain amorphous unless treated with 10-12 M H3PO4 and high temperatures (180o C). This provides us the opportunity to study the changes in the amorphous phases and how this effects the MOF structures. To aid in this endeavor we will team with Prof. Simon Billinge at Columbia University who is an expert in determining structures of non-crystalline materials.
A second group of compounds are the phenyl phosphonates of Zr and Sn and their mixed derivatives such as Zr(O3PC6H5)2-x(HPO4)x. All these compounds are nanoparticles from as small at 10 nm to start and micron sized when near crystalline. Surely the surfaces can be prepared as different by degrees so that the MOFs or other reactive compounds may have their structures controlled by the nature of the surface. We use a layer by layer process so that we can increase the porosity depending upon the number of layers added. Furthermore, mixed MOFs may be prepared by changing the ion charge or ligand from layer to layer. We envision a new strategy controlling the nature of the surface and the composition to produce more robust MOFs with applications as catalysts, proton conductors, electron donors, molecules for separation, and drug delivery.
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