Predicting Low-Pressure O2Adsorption in Nanoporous Framework Materials for Sensing Applications

Room-Temperature Monitoring of CH4 and CO2 Using a Metal-Organic Framework-Based QCM Sensor Showing Inherent Analyte Discrimination

The detection of methane and carbon dioxide is of growing importance due to their negative impact on global warming. This is true for both environmental monitoring and leak detection in industrial processes. Although solid-state sensors are technologically mature, they have limitations that prohibit their use in certain situations, e.g., explosive atmospheres. Thus, there is a need to develop new types of sensor materials. Herein, we demonstrate a simple, low-cost, metal-organic framework (MOF)-based gas leak detection sensor. The system is based on gravimetric sensing by using a quartz crystal microbalance. The quartz crystal is functionalized by layer-by-layer growth of a thin metal-organic framework film. This film shows selective uptake of methane or carbon dioxide under atmospheric conditions. The hardware has low cost, simple operation, and theoretically high sensitivity. Overall, the sensor is characterized by simplicity and high robustness. Furthermore, by exploiting the different adsorption kinetics as measured by multiple harmonic analyses, it is possible to discriminate whether the response is due to methane or carbon dioxide. In summary, we demonstrate data relevant toward new applications of metal-organic frameworks and microporous hybrid materials in sensing.

Intelligent Selection of Metal-Organic Framework Arrays for Methane Sensing via Genetic Algorithms

Gas sensor arrays, also called electronic noses, use many chemically diverse materials to adsorb and subsequently identify gas species in complex mixture environments. Ideally these materials should have maximally complementary adsorption profiles to achieve the best sensing performance, but in practice they are selected by trial-and-error. Thus current electronic noses do not achieve optimal detection. In this work, we employ metal-organic frameworks (MOFs) as sensing materials and leverage a genetic algorithm to identify optimal combinations of them for detecting methane leaks in air. We build on our previously reported computational design methodology, which ranked MOF arrays by their Kullback-Liebler divergence (KLD) values for probabilistically describing the concentrations of each gas species in an unknown mixture. We ran the genetic algorithm to find optimal MOF arrays of various sizes when selecting from a library of 50 different MOF materials. The genetic algorithm was able to accurately predict the best arrays of any desired size when compared to brute-force screening. Thus, this search optimization can be integrated into the efficient design of MOF-based electronic noses.

Ab initio molecular dynamics determination of competitive O₂ vs. N₂ adsorption at open metal sites of M₂(dobdc)

The separation of oxygen from nitrogen using metal-organic frameworks (MOFs) is of great interest for potential pressure-swing adsorption processes for the generation of purified O2 on industrial scales. This study uses ab initio molecular dynamics (AIMD) simulations to examine for the first time the pure-gas and competitive gas adsorption of O2 and N2 in the M2(dobdc) (M = Cr, Mn, Fe) MOF series with coordinatively unsaturated metal centers. Effects of metal, temperature, and gas composition are explored. This unique application of AIMD allows us to study in detail the adsorption/desorption processes and to visualize the process of multiple guests competitively binding to coordinatively unsaturated metal sites of a MOF.

Theoretical prediction of the mechanical properties of zeolitic imidazolate frameworks (ZIFs)

The mechanical properties of Zeolitic Imidazolate Frameworks (ZIFs) was controlled by the electronegativity of the terminal groups.

High-symmetry hydrogen-bonded organic frameworks: air separation and crystal-to-crystal structural transformation

A columnar supramolecular structure can reversibly transform to a porous HOF, which can selectively adsorb O₂ over Ar and N₂.