Matthew A. Browe

The effect of water adsorption on the structure of the carboxylate containing metal–organic frameworks Cu-BTC, Mg-MOF-74, and UiO-66

Metal–organic frameworks (MOFs) with metal–carboxylate bonds, including Cu-BTC (HKUST-1), Mg-MOF-74 (Mg/DOBDC), and UiO-66, have been shown to have varying degrees of water stability. The three MOFs in this study are three of the most highly studied MOFs in the literature. We investigate here how each MOF degrades at several temperature and humidity conditions over the course of 28 days. At conditions of 90% relative humidity (RH) and 25 °C, water uptake for Cu-BTC is shown to be higher than at 90% RH and 40 °C, causing the degradation of the inner structure of Cu-BTC to occur more readily at the lower temperature. However the external surfaces of Cu-BTC degrade more readily, as shown through SEM images, at conditions of 90% RH and 40 °C. Mg-MOF-74 has a nearly complete loss of surface area after just one day of exposure to each of the conditions studied, however the PXRD patterns show only a change in the [100] peak. We offer here a novel mechanism for the degradation of Mg-MOF-74, involving a 6-coordinate Mg intermediate, which leaves the 1-dimensional channels of Mg-MOF-74 intact. Furthermore, we conclude that UiO-66 is stable to each of the aging conditions for the full 28 days of this study.

Conformal and highly adsorptive metal–organic framework thin films via layer-by-layer growth on ALD-coated fiber mats

Integration of metal–organic frameworks (MOFs) on textiles shows promise for enabling facile deployment and expanding MOF applications. While MOFs deposited on flat substrates can show relatively smooth surface texture, most previous reports of MOFs integrated on fibers show poor conformality with many individual crystal domains. Here we report a new low-temperature (<70 °C) method to deposit uniform and smooth MOF thin films on fiber surfaces using an energy enhanced layer-by-layer (LbL) method with an ALD Al2O3 nucleation layer. Cross-sectional TEM images show a well-defined core@shell structure of the MOF-functionalized fiber, and SEM shows a flat MOF surface texture. We analyze the thickness and mass increase data of LbL HKUST-1 MOF thin films on ALD-coated polypropylene fibers and find the growth rate to be 288–290 ng cm−2 per LbL cycle. Unlike planar LbL MOF embodiments where adsorption capacities are difficult to quantify, the large volume quantity on a typical fiber mat enables accurate surface area measurement of these unique MOF morphologies. After 40 LbL cycles the MOFs on fibers exhibit N2 adsorption BET surface areas of up to 93.6 m2 gMOF+fiber−1 (∼535 m2 gMOF−1) and breakthrough test results reveal high dynamic loadings for NH3 (1.37 molNH3 kgMOF+fiber−1) and H2S (1.49 molH2S kgMOF+fiber−1). This synthesis route is applicable to many polymer fibers, and the fiber@ALD@MOF structure is promising for gas filtration, membrane separation, catalysis, chemical sensing and other applications.

Adsorption of ammonia by sulfuric acid treated zirconium hydroxide.

The adsorption of ammonia on Zr(OH)(4), as well as Zr(OH)(4) treated with sulfuric acid, were examined. The results show that treating Zr(OH)(4) with sulfuric acid leads to the formation of a sulfate on the surface of the material, and that the sulfate contributes to the ammonia adsorption capacity through the formation of an ammonium sulfates species. Calcination of Zr(OH)(4) decreases the ammonia adsorption capacity of the material and limits the formation of sulfate species. NMR and FTIR spectroscopy results are presented that show the presence of two distinct ammonium species on the surface of the material. The adsorption capacity of the materials is shown to be a complex phenomenon that is impacted by the surface area, the sulfur content, and the pH of the material. The results illustrate that Zr(OH)(4), which is known to adsorb acidic gases, can be modified and used to adsorb basic gases.

Removal of airborne toxic chemicals by porous organic polymers containing metal–catecholates

Porous organic polymers bearing metal-catecholate groups were evaluated for their ability to remove airborne ammonia, cyanogen chloride, sulphur dioxide, and octane by micro-breakthrough analysis. For ammonia, the metal-catecholate materials showed remarkable uptake under humid conditions.

Filtration of chlorine and hydrogen chloride gas by engineered UiO-66-NH2 metal-organic framework

Chlorine (Cl2) and hydrogen chloride (HCl) are heavily utilized industrial chemicals that present significant respiratory health risks. The metal-organic framework UiO-66-NH2 has shown an unprecedented ability in powder form to remove chlorine gas. Here, we engineered UiO-66-NH2 into 20×40 mesh granules and evaluated their ability to remove chlorine and hydrogen chloride gas challenges. The exposed materials were characterized with nitrogen isotherms, powder X-ray diffraction, and attenuated total reflectance - Fourier transform infrared spectroscopy. Breakthrough results revealed that UiO-66-NH2 sorption of chlorine and hydrogen chloride met or exceeded sorption of state-of-the-art metal-impregnated activated carbon materials on a mass and volume basis in engineered form.