Tuning the Selectivity Between C2H2 and CO2 in Molecular Porous Materials
Tony Pham,1 Katherine A. Forrest,1 Kai-Jie Chen,2 Douglas M. Franz,1 Michael J. Zaworotko,2 and Brian Space1
1.) Department of Chemistry, University of South Florida, 4202 East Fowler Avenue, CHE205, Tampa, FL 33620-5250, United States
2.) Department of Chemical & Environmental Sciences, University of Limerick, Limerick, Republic of Ireland
Experimental and theoretical C2H2 and CO2 adsorption studies were performed in MPM-1-Cl and MPM-1-TIFSIX, two robust molecular porous materials (MPMs) with the empirical formula [Cu2(adenine)4Cl2]Cl2 and [Cu2(adenine)4(TiF6)2], respectively. Both MPMs consist of a hydrogen-bonding network that is self-assembled by dinuclear copper–adenine paddlewheel complexes. The difference between the two structures is simply the axial ligand. Experimental measurements revealed that MPM-1-Cl displays higher low-pressure uptake, isosteric heat of adsorption (Qst), and selectivity for C2H2 than CO2, whereas the opposite is true for MPM-1-TIFSIX. Dynamic breakthrough experiments and modeling studies confirmed that MPM-1-Cl is more selective toward C2H2, while MPM-1-TIFSIX is more selective toward CO2. Molecular simulations revealed that both MPMs display a greater preference for C2H2 within their large channels. However, MPM-1-TIFSIX contains a small accessible channel in the structure that is not present in MPM-1-Cl; this channel represents the primary binding site in the material. Calculation of the classical MPM–adsorbate interaction energies and diffusion barriers about the primary binding site in MPM-1-TIFSIX revealed that this site is more favorable for CO2 than C2H2, thus explaining why the selectivity in this MPM is inverted relative to MPM-1-Cl.
Molecular dynamics of metal-organic framework [(CH3)2NH2]Mn(HCOO)3 near magnetic and ferroelectric transitions using 1H, 55Mn NMR.
2. Rhea Reyes2
3. John Haddock1
4. Arneil Reyes3
5. Naresh Dalal1
1. Florida State University
2. New York University
3. National High Magnetic Field Laboratory
Dimethylammonium Manganese Formate (DMMnF) is of interest as a multiferroic metal-organic framework. For the first time, 1H and 55Mn NMR are used to study the known ferroelectric transition at TFE~184K and antiferromagnetic (AF) transition at TN ~8.5K. A broad and strong zero-field 55Mn NMR signal was found below TN, with a calculated 8T internal field due to ordered Mn moments. This signal is suppressed above 0.3T, consistent with the known spin-flop transition. Dramatic changes in 1H spectra correlate to the magnetic ordering with a critical exponent of β =1/4, in contrast to the mean field prediction’s value of 0.5. The spin-lattice relaxation T1 recovery exhibits a double exponential behavior, with the long and short components differing by 3 orders of magnitude. The long T1 component dips near 150K and 8.5K, while the short component exhibits a huge enhancement approaching the critical regime followed by an exponential decay at low temperatures. This behavior is suggestive of an opening of a spin gap, Δ ~ 4.45K, about half of TN. Implications of these results will be discussed.
Tunable Solid State Fluorescence in Isoreticular Metal Organic Frameworks
University of Central Florida
In this work highly stable zirconium based metal organic frameworks isoreticular to UiO-66 were prepared utilizing highly fluorescent links. These links allow for the systematic control over the emissive profile of the prepared material. This study shows how the tailoring of organic linkers with specific properties can be incorporated into a MOF in order to produce tunable properties. Three organic linkers were synthesized with Blue, Green, and Orange fluorescence to prepare solid solutions with properties similar to those observed in solution. This tunability allows for complete control of the emission profile as well as the temperature of the emitted white light. This careful design of organic linkers provides a strategy that can give insight into the photophysical manipulation of MOF monomers and their projected properties inside the MOF.
High Refractive Index Polymer Composites
Florida State University
Hybrid organic/inorganic thermoset polymers synthesized through the thiol-ene coupling reaction have proved to produce materials with a high refractive index (n) making them potentially suitable for optical applications. A series of hard transparent polymer composites were made from tetravinylsilane (TVS) and 1.3-Benzenedithiol (BDTH) with varying concentrations of zirconium oxo-cluster Zr6(OH)4O4(OMc)12 (ZOC) incorporated. The resulting polymers exhibited a significant improvement in the refractive index relative to the parent polymer, TVS and BDTH (n = 1.693). This improvement reaches a maximum value of 1.719 at a loading of 2.5 wt.% ZOC and then decreased as the concentration of ZOC in the polymer matrix increased. The refractive index of ZOC itself was determined to be 1.539 by the Becke Line method which is well below the observed refractive index of the polymer composites. The trend in the refractive index of the composites as a function of ZOC loading and the high refractive index achieved (1.719), despite the low inherent refractive index of the ZOC itself, was found to be due to changes in the bulk density of the composites. Finally, the glass transition temperatures (Tg) of the polymers seemed to decrease as the mole fraction of ZOC increases, resulting in a compromise of its hardness. Solid state Si29 NMR and RAMAN spectra show evidence that a significant amount of unreacted vinyl groups are left over when high concentration of ZOC is present in the polymer matrix.
Synthesis of High Refractive Index Lens Materials
Yue Su, Albert Stiegman
Florida State University
High refractive index polymer materials are synthesized from with the self-initiating thiol-ene coupling reaction between the trivinylphosphine derivatives and selected dithiols. The presence of highly polarizable elements of P, S and Se in P=S/P=Se bonds in the vinyl monomers and the presence of aromatic structures and S in thiols generates polymers exhibiting high refractive indices ranging from 1.64 to 1.75. The polymers also have Abbe Numbers from 22.73 to 37.18 depending on the composition. After undergoing a slow graduated curing process that reached a final temperature of 120, hard, transparent optical materials were obtained. Solid-state 31P NMR was performed to characterize the the degree of cross-linking in the thiol-ene polymer. DSC and DMA are used to measure Tg and Young’s modulus respectively. The transmittance over visible range of the spectrum was carried out by UV-vis spectroscopy and other physical properties such as the density were measured.
The pH Effect in Seed-Mediated Growth of Gold Nanorods
Gang Chen, Reese Gallagher, Xing Zhang
Department of Chemistry, University of Central Florida
Although various gold nanorods (AuNRs) have been produced with different aspect ratio, current synthesis methods through seed-mediated growth are far from ideal, sharing the same drawbacks, such as low yield of gold conversion (~20%), poor shape uniformity and reproducibility, due to a lack of understanding of the reaction mechanism. While the mechanism of the anisotropic growth of AuNRs is not clear yet, the experimental detail in the literature show that the final products depend on the rate of chemical reduction of metal ion. Basically, the reduction rate depends on both the reactivity and concentration of the reactants (gold salts and ascorbic acid (AA)). The concentration of AA is commonly utilized to control the reduction rate. For example, to decrease the reduction rate, the ratio of AA to gold ion has been optimized to be 1.1 which is far below the stoichiometric ratio (1.5), giving extremely poor yield of gold conversion (~20%). In this research, to achieve a high gold conversion yield, we keep the stoichiometric ratio of AA to gold ion (1.5) but tuning the reduction rate by reactivity. As a polyol compound, the reactivity of AA depends on the pH of the system. At stoichiometric ratio (1.5), the optimal pH range for AA has been discovered to get prefect AuNRs with improved uniformity, reproducibility and gold conversion yield (> 80%). The gold conversion yield can be improved further at higher ratio of AA to gold ion than the stoichiometry. With the same idea, the PI has extended the reducing agent to other polyol compounds, such as phenol, hydroquinone, catechol, resorcinol, and phloroglucinol.