Zirconium-based metal organic framework (Zr-MOF), UiO-66 and UiO-67, were synthesized and used as adsorbents of NO(2) at ambient temperatures in either dry or moist conditions. The samples were characterized before and after exposure to NO(2) by X-ray diffraction, scanning electron microscopy, N(2)-adsorption at 77 K, thermal analysis, and infrared spectroscopy. The results indicate the important effect of a ligand size on the adsorption of NO(2) on Zr-MOF materials. While the large size of the 4,4-benzenebiphenyldicarboxylic acid (BDPC) ligand has a positive impact on the adsorption of NO(2) on UiO-67 in moist conditions, the opposite effect is found in dry conditions. The large pore volume of UiO-67 enhances the adsorption of moisture and formation of nitric and nitrous acids. The small pore sizes of UiO-66 favor the NO(2) removal in dry conditions via dispersive forces. Upon interaction of NO(2) molecules with the Zr-MOF in dry conditions, the bond between the organic linker and metallic oxide center is broken, leading to the formation of nitrate and nitrite species. Moreover, organic ligands also contribute to the NO(2) reactive adsorption via nitration reaction.

New hybrid cerium modified zirconium based metal-organic frameworks (MOFs) were synthesized. The as-received materials were evaluated as adsorbents of NO2 in either moist or dry conditions. The surface of the initial and exhausted samples was characterized using XRD, SEM-EDX, nitrogen adsorption, thermal analysis, and FTIR. It was found that the addition of Ce(+3) slightly affects the growth of the framework and introduces new features to Zr-MOF. The shapes of the octahedral crystals are changed, and they are interwoven with rod-flake-like sheets. The extent of the interconnection, and thus the extent of the hybrid MOF formation, depends on the Zr to Ce ratio. The alterations in the surface chemistry and texture are reflected in the amount of NO2 adsorbed. The narrow pore channels present in these new materials enhance adsorption in either moist or dry conditions. The amount of NO2 adsorbed on the Ce-doped MOF increases over 25% in dry conditions in comparison with the unmodified MOF. Exposure of Ce-UiO-66 to NO2 results in a development of porosity. Regardless the conditions, the XRD patterns indicate the stability of this new hybrid MOF upon NO2 adsorption. Interactions of NO2 with MOF result in the formation of nitrate and nitrite species associated either with metals or with organic ligands.

Amorphous molybdenum sulfides (a-MoS x ) are known to be active electrocatalysts for the hydrogen evolution reaction (HER), but the role stoichiometry of the sulfur atoms plays in the HER activity remains unclear. In this work, we deposited thin films of a-MoS x from two thiomolybdate deposition baths with different sulfur ratios (MoS 4 2− and Mo 2 S 12 2− ) and showed that the sulfur stoichiometry, as determined by X-ray photoelectron spectroscopy, is controlled by the precursor of choice and the electrochemical method used to deposit the thin films. Using the Mo 2 S 12 2− precursor allows access to a MoS 6 thin film, with a higher S/Mo ratio compared with that of any previously reported electrodeposited films. We also examined the effect of electrochemistry on the resulting S/Mo ratio in the as-prepared a-MoS x thin films. Samples with S/Mo ratios ranging from 2 to 6 were electrodeposited on glassy carbon (GC) substrates by using anodic, cathodic, or cyclic voltammetry deposition. The a-MoS x thin films deposited on GC substrates were tested as HER catalysts in acidic electrolytes. The overpotentials needed to drive current densities of 10 mA/cm 2 ranged from 160 mV for MoS 6 samples to 216 mV for MoS 2 samples, signifying the important role sulfur content plays in HER activity of the prepared films. Furthermore, we characterized the deactivation of the a-MoS x films and found that the sulfur content is gradually depleted over time, leading to a slow deactivation of the a-MoS x thin-film catalysts. We showed a facile procedure that affords a-MoS x films with high sulfur content by using S-rich precursors and highlighted the role of sulfur in the prepared films for HER.

Development of technologies for protection against chemical warfare agents (CWAs) is critically important. Recently, polyoxometalates have attracted attention as potential catalysts for nerve-agent decomposition. Improvement of their effectiveness in real operating conditions requires an atomic-level understanding of CWA decomposition at the gas–solid interface. We investigated decomposition of the nerve agent Sarin and its simulant, dimethyl chlorophosphate (DMCP), by zirconium polytungstate. Using a multimodal approach, we showed that upon DMCP and Sarin exposure the dimeric tungstate undergoes monomerization, making coordinatively unsaturated Zr­(IV) centers available, which activate nucleophilic hydrolysis. Further, DMCP is shown to be a good model system of reduced toxicity for studies of CWA deactivation at the gas–solid interface.

We report the first study of a gas‐phase reaction catalyzed by highly dispersed sites at the metal nodes of a crystalline metal–organic framework (MOF). Specifically, CuRhBTC (BTC3−=benzenetricarboxylate) exhibited hydrogenation activity, while other isostructural monometallic and bimetallic MOFs did not. Our multi‐technique characterization identifies the oxidation state of Rh in CuRhBTC as +2, which is a Rh oxidation state that has not previously been observed for crystalline MOF metal nodes. These Rh2+ sites are active for the catalytic hydrogenation of propylene to propane at room temperature, and the MOF structure stabilizes the Rh2+ oxidation state under reaction conditions. Density functional theory calculations suggest a mechanism in which hydrogen dissociation and propylene adsorption occur at the Rh2+ sites. The ability to tailor the geometry and ensemble size of the metal nodes in MOFs allows for unprecedented control of the active sites and could lead to significant advances in rational catalyst design.