The use of nanoporous zeolitic imidazolate frameworks (ZIFs) in separation processes is attractive, but the presence of acid gases such as SO x or NO x in process streams can have detrimental effects. While we have recently developed a mechanistic picture of SO x –ZIF interactions, here we describe the remarkably different effects of NO2 on ZIFs. ZIFs with a representative range of SO x stabilities are all unstableas defined by loss of crystallinity and porosityin dry and humid NO2, whereas most ZIFs are stable in dry SO x and some even in humid SO x . A detailed mechanism is developed based on Fourier transform infrared spectroscopy and density functional theory calculations. H-abstraction by free radical NO2 and subsequent acidic species formation are the major degradation pathways, while adsorbed HNO3 formation in humid conditions is an additional pathway in hydrophilic ZIFs. These findings strongly suggest that new strategies to stabilize ZIFs/metal–organic frameworks toward NO2 attack are required.

Parent and amine-functionalized analogues of metal-organic frameworks (MOFs), UiO-66(Zr), MIL-125(Ti), and MIL-101(Cr), were evaluated for their hydrogen sulfide (HS) adsorption efficacy and post-exposure acid gas stability. Adsorption experiments were conducted through fixed-bed breakthrough studies utilizing multicomponent 1% HS/99% CH and 1% HS/10% CO/89% CH natural gas simulant mixtures. Instability of MIL-101(Cr) materials after HS exposure was discovered through powder X-ray diffraction and porosity measurements following adsorbent pelletization, whereas other materials retained their characteristic properties. Linker-based amine functionalities increased HS breakthrough times and saturation capacities from their parent MOF analogues. Competitive CO adsorption effects were mitigated in mesoporous MIL-101(Cr) and MIL-101-NH(Cr), in comparison to microporous UiO-66(Zr) and MIL-125(Ti) frameworks. This result suggests that the installation of HS binding sites in large-pore MOFs could potentially enhance HS selectivity. In situ Fourier transform infrared measurements in 10% CO and 5000 ppm HS environments suggest that framework hydroxyl and amine moieties serve as HS physisorption sites. Results from this study elucidate design strategies and stability considerations for engineering MOFs in sour gas purification applications.

Functionalization of copper carboxylate groups on a series of UiO-66 metal organic framework (MOF) analogues and their corresponding impact on humid and dry ammonia adsorption behavior were studied. Relative locations of possible carboxylic acid binding sites for copper on the MOF analogues were varied on ligand and missing linker defect sites. Materials after copper incorporation exhibited increased water vapor and ammonia affinity during isothermal adsorption and breakthrough experiments, respectively. The introduction of copper markedly increased ammonia adsorption capacities for all adsorbents possessing carboxyl binding sites. In particular, the new MOF UiO-66-(COOCu)2 displayed the highest ammonia breakthrough capacities of 6.38 and 6.84 mmol g–1 under dry and humid conditions, respectively, while retaining crystallinity and porosity. Relative carboxylic acid site locations were also found to impact sorbent stability, as missing linker defect functionalized materials degraded under humid conditions after copper incorporation. Postsynthetic metal insertion provides a method for adding sites that are analogous to open metal sites while maintaining good structural stability.

The conventional synthesis of metal-organic frameworks (MOFs) through soluble metal-salt precursors provides little control over the growth of MOF crystals. The use of alternative metal precursors would provide a more flexible and cost-effective strategy for direction- and shape-controlled MOF synthesis. Here, we demonstrate for the first time the use of insoluble metal-carbon matrices to foster directed growth of MOFs. Aluminum carbide was implemented as both the metal precursor and growth-directing agent for the generation of MIL-53(Al). A unique needle-like morphology of the MOF was grown parallel to the bulk surface in a layer-by-layer manner. Importantly, the synthesis scheme was found to be transferrable to the production of different linker analogues of the MOF and other topologies. Given the variety of metal carbides available, these findings can be used as a blueprint for controlled, efficient, and economical MOF syntheses and set a new milestone toward the industrial use of MOFs at large-scale.

Converting unconventional precursors into advanced separation materials can reduce manufacturing complexity while affording economic and environmental benefits. Here we report the conversion of various aluminum-containing commercial products, such as recycled beverage cans and aluminum foil, to both supported and nonsupported metal−organic frameworks (MOFs). Supported MOF/aluminum composites grow from and on aluminum via hydrothermal treatment to create multiple supported MOF topologies. The same precursor is also employed to generate nonsupported MOFs using HCl (aq) as an etching agent. High yields (∼83%) of MIL-53(Al) are achieved using aluminum foil, with products possessing textural properties that are consistent with conventionally synthesized materials. This study provides a synthesis methodology for enhancing the economic viability of next-generation separation materials.