Joseph A. Rossin

Extraordinary NO2 Removal by the Metal–Organic Framework UiO-66-NH2

Here we discuss the removal of nitrogen dioxide, an important toxic industrial chemical and pollutant, from air using the MOF UiO-66-NH2 . The amine group is found to substantially aid in the removal, resulting in unprecedented removal capacities upwards of 1.4 g of NO2  /g of MOF. Furthermore, whereas NO2 typically generates substantial quantities of NO on sorbents, the amount generated by UiO-66-NH2 is significantly reduced. Of particular significance is the formation of a diazonium ion on the aromatic ring of the MOF, and the potential reduction of NO2 to molecular nitrogen.

The catalytic decomposition of CHF3 over ZrO2-SO4

Abstract The destruction of CHF3 over ZrO2 and ZrO2-SO4 was studied in a fixed bed catalytic reactor system in dry and humid air streams. The addition of sulfate to the zirconia greatly improved the catalytic activity, decreasing the light-off temperature by approximately 40°C. The destruction of CHF3 proceeded according to a catalyzed hydrolysis reaction, rather than an oxidation reaction, thereby necessitating that water be present in the feed stream. The presence of water in the feed stream had a significant effect on the stability of the catalyst. In dry air, the catalyst rapidly deactivated. Deactivation is attributed to the fluorination of the zirconium, which results in a loss of oxygen and sulfur from the catalyst and a significant decrease in surface area. The addition of 2.5% water to the feed stream greatly improves the catalyst’s stability; however, some deactivation was observed. Deactivation in humid air was attributed to a gradual accumulation of fluorine on the catalyst, which resulted in a loss of sulfate and oxygen from the zirconia, and a decrease in the surface area of the catalyst.

Adsorption of sulfur dioxide by CoFe2O4 spinel ferrite nanoparticles and corresponding changes in magnetism.

Adsorption of sulfur dioxide on 10 nm CoFe(2)O(4) spinel ferrite nanoparticles was examined. Adsorption loadings of sulfur dioxide at breakthrough conditions were determined to be approximately 0.62 mol/kg, which is significant given the 150 m(2)/g surface area of the nanoparticles. Adsorption proceeds through a chemisorption mechanism with sulfur dioxide forming a sulfate upon adsorption on the particle surface, which leads to a 23% decrease in the remnant magnetization, a 20% decrease in the saturation magnetization, and a 9% decrease in the coercivity of the magnetic nanoparticles. Adsorbent materials that provide a magnetic signal when adsorption occurs could have broad implications on adsorption-based separations.

Effect of Reduction Treatment on Copper Modified Activated Carbons on NOx Adsorption at Room Temperature

Activated carbon was impregnated with copper salt and then exposed to reductive environment using hydrazine hydrate or heat treatment under nitrogen at 925 °C. On the obtained samples, adsorption of NO(2) was carried out at dynamic conditions at ambient temperature. The adsorbents before and after exposure to nitrogen dioxide were characterized by X-ray diffraction (XRD), thermal analysis, scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM-EDX), X-ray photoelectron spectroscopy (XPS), N(2)-sorption at -196 °C, and potentiometric titration. Copper loading improved the adsorption capacity of NO(2) as well as the retention of NO formed in the process of NO(2) reduction on the carbon surface. That improvement is linked to the presence of copper metal and its high dispersion on the surface. Even though both reduction methods lead to the reduction of copper, different reactions with the carbon surface take place. Heat treatment results in a significant percentage of metallic copper and a reduction of oxygen functional groups of the carbon matrix, whereas hydrazine, besides reduction of copper, leads to an incorporation of nitrogen. The results suggest that NO(2) mainly is converted to copper nitrates although the possibility to its reduction to N(2) is not ruled out. A high capacity on hydrazine treated samples is linked to the high dispersion of metallic copper on the surface of this carbon.

Effects of environmental weathering on the properties of ASC-whetlerite

Abstract Activated, impregnated carbon from a radial flow air purification filter was separated into fractions after the filter had been exposed to shipboard environmental conditions for 21 months. Carbon samples from the discrete filter locations were analyzed using surface analysis methods. Breakthrough times of the segregated carbon fractions were recorded for a cyanogen chloride challenge. The inlet portion of the filter was most severely affected by the weathering. For carbon removed from the filter inlet, the weathering process caused impregnants to leach from the granules and form metal sulfates, presumably by reaction with atmospheric SO x . No sulfur was detected on carbon samples removed from the center and outlet portions of the filter; however, a significant fraction of the chromium(VI) impregnant had been reduced to chromium(III). In all cases, breakthrough times recorded for a cyanogen chloride challenge were significantly less than that recorded for the unweathered carbon sample.

Spectroscopic analysis and performance of an experimental copper/zinc impregnated, activated carbon

Abstract An experimental copper/zinc/silver/triethylenediamine-impregnated, activated carbon formulation has been developed for removal of hydrogen cyanide from streams of air. The material consists of a zinc phase highly concentrated at the external surface of the granule and a copper phase distributed throughout the granule. This material performed well when first exposed to a hydrogen cyanide feed. Following prolonged humid exposure, cyanogen, a reaction product of hydrogen cyanide, broke through the carbon bed prematurely. The premature cyanogen breakthrough was attributed to the migration of copper to the external surface of the carbon granule. Results of this paper demonstrate the importance of the impregnant distribution within the granule on the carbons performance against a hydrogen cyanide feed.

Hierarchical Pore Development by Plasma Etching of Zr-Based Metal-Organic Frameworks.

The typically stable Zr-based metal-organic frameworks (MOFs) UiO-66 and UiO-66-NH2 were treated with tetrafluoromethane (CF4 ) and hexafluoroethane (C2 F6 ) plasmas. Through interactions between fluoride radicals from the perfluoroalkane plasma and the zirconium-oxygen bonds of the MOF, the resulting materials showed the development of mesoporosity, creating a hierarchical pore structure. It is anticipated that this strategy can be used as a post-synthetic technique for developing hierarchical networks in a variety of MOFs.