Big-Data Science in Porous Materials: Materials Genomics and Machine Learning

By combining metal nodes with organic linkers we can potentially synthesize millions of possible metal-organic frameworks (MOFs). The fact that we have so many materials opens many exciting avenues but also create new challenges. We simply have too many materials to be processed using conventional, brute force, methods. In this review, we show that having so many materials allows us to use big-data methods as a powerful technique to study these materials and to discover complex correlations. The first part of the review gives an introduction to the principles of big-data science. We show how to select appropriate training sets, survey approaches that are used to represent these materials in feature space, and review different learning architectures, as well as evaluation and interpretation strategies. In the second part, we review how the different approaches of machine learning have been applied to porous materials. In particular, we discuss applications in the field of gas storage and separation, the stability of these materials, their electronic properties, and their synthesis. Given the increasing interest of the scientific community in machine learning, we expect this list to rapidly expand in the coming years.

Isosteric Heat: Comparative Study between Clausius–Clapeyron, CSK and Adsorption Calorimetry Methods

This work presents the calorimetric study of five adsorbents with different chemical and textural characteristics: MOF-199, MCM-41, SBA-15, activated carbon prepared from corn cob (GACKP) and graphite. These solids were used to establish the differences between isosteric heats evaluated by three different methods: Clausius–Clapeyron (C-C), Chakraborty, Saha and Koyama (CSK) and Adsorption Calorimetry (A-Cal). The textural characterization results show solids that have values of specific surface area between 2271 m2·g−1 for the MOF-199 and 5.2 m2·g−1 for the graphite. According to the results obtained for the isosteric heats for each sample, the magnitude varies depending on the coverage of the adsorbate and the textural characteristics of each adsorbent. Solids with an organized structure have isosteric heat values that are coincident among the three methods. Meanwhile, heterogeneous solids such as activated carbon values evaluated by the CKS and C-C have a high dispersion method regarding the adsorption calorimetry method. The results obtained show that the adsorption calorimetry, being a direct experimental measurement method, presents less dispersed data. At low quantities, the isosteric heat of nitrogen adsorption decreased in the order MOF-199, GACKP, MCM-41, SBA-15 and Graphite. The order for the isosteric heats values was coherent with the surface characteristics of each of the solids, especially with the pore size distribution. Finally, throughout the coverage examined in this work, the isosteric heats for nitrogen adsorption determined by adsorption calorimetry (A-Cal) were larger than the evaluated by C-C and CSK indirect methods of vaporization. According to the results, it is shown that the adsorption calorimetry allows values of the isosteric heats of adsorption with an error of less than 2% to be established and also reveals the complex nature of the heterogeneity or homogeneity of the adsorbent.

Gas Adsorption at Metal Sites for Enhancing Gas Sensing Performance of ZnO@ZIF-71 Nanorod Arrays

The detection of trace amount of volatile organic compounds (VOCs) has been covered by tons of researches, which are dedicated to improve the detection limit and insensitivity to humidity. In this work, we have synthesized ZnO@ZIF-71 nanorod arrays (NRAs) equipped with the adsorption effect at metal site that promoted the detection limit of ethanol and acetone, to which also have great selectivity. The gas sensor not only exhibits shorter response/recovery time (53/55% for ethanol, 48/31% for acetone), but also excellent insensitivity to humidity and improved detection limit (10× improved at 21 ppb for ethanol, 4× at 3 ppb for acetone) at low working temperature (150 °C). By the analysis of in situ diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy and calculation of density functional theory (DFT), the mechanism of enhanced gas sensing performance from ZnO@ZIF-71 NRAs is proved. It shows ethanol and acetone gas molecules can be adsorbed at the metal sites of ZIF-71. This work provides a new idea to improve the detection limit and humidity-insensitivity of gas sensor toward specific gas molecules.

A combined experimental-computational investigation on water adsorption in various ZIFs with the SOD and RHO topologies

Our results demonstrated that the contribution of vdW interactions is negligible and the contribution of electrostatic interactions plays a dominant role in the water adsorption in ZIFs.

Chemoinformatics at IFP Energies Nouvelles: Applications in the Fields of Energy, Transport, and Environment

The objective of the present paper is to summarize chemoinformatics based research, and more precisely, the development of quantitative structure property relationships performed at IFP Energies nouvelles (IFPEN) during the last decade. A special focus is proposed on research activities performed in the "Thermodynamics and Molecular Simulation" department, i. e. the use of multiscale molecular simulation methods in responses to projects. Molecular simulation techniques can be envisaged to supplement dataset when experimental information lacks, thus the review includes a section dedicated to molecular simulation codes, development of intermolecular potentials, and some of their possible applications. Know-how and feedback from our experiences in terms of machine learning application for thermophysical property predictions are included in a section dealing with methodological aspects. The generic character of chemoinformatics is emphasized through applications in the fields of energy, transport, and environment, with illustrations for three IFPEN business units: "Transports", "Energy Resources", and "Processes". More precisely, the review focus on different challenges such as the prediction of properties for alternative fuels, the prediction of fuel compatibility with polymeric materials, the prediction of properties for surfactants usable in chemical enhanced oil recovery, and the prediction of guest-host interactions between gases and nanoporous materials in the frame of carbon dioxide capture or gas separation activities.

Differential Heat of Adsorption and Isosteres

Heat of adsorption is a basic thermodynamic property extensively used not only for understanding thermal effects and heat management in industrial gas storage and separation processes but also for development and validation of adsorption models and materials force fields. Despite a long history of theoretical studies and a vast experimental literature, controversies often arise in the thermodynamic analysis of heat effects due to various assumptions used to describe gas adsorption and inconsistencies between direct calorimetric measurements and isosteric heat obtained from various adsorption isotherms. Here we present a rigorous theoretical procedure for predicting isosteric heat without any assumption about the geometry of porous adsorbents or operating conditions. Quantitative relations between the differential heat and various isosteres have been established with the grand-canonical Monte Carlo simulation for gas adsorption in amorphous as well as crystalline porous materials. The inconsistencies and practical issues with conventional methods for the analysis of the heat effect have been clarified in the context of the exact results for model systems. Via the resolution of a number of controversies about heat analysis, we hope that the new theoretical procedure will be adopted for both fundamental research and industrial applications of gas adsorption processes.

The synthesis and tribological properties of small- and large-sized crystals of zeolitic imidazolate framework-71

Crystals of ZIF-71 with different particle sizes were synthesized using different strategies. The small- and large-sized crystals of ZIF-71 showed different lubrication effects.

High-throughput computational screening of metal-organic frameworks

There is an almost unlimited number of metal-organic frameworks (MOFs). This creates exciting opportunities but also poses a problem: how do we quickly find the best MOFs for a given application? Molecular simulations have advanced sufficiently that many MOF properties - especially structural and gas adsorption properties - can be predicted computationally, and molecular modeling techniques are now used increasingly to guide the synthesis of new MOFs. With increasing computational power and improved simulation algorithms, it has become possible to conduct high-throughput computational screening to identify promising MOF structures and uncover structure-property relations. We review these efforts and discuss future directions in this new field.

Biofuel purification in zeolitic imidazolate frameworks: the significant role of functional groups

A molecular simulation study is reported for biofuel purification in six zeolitic imidazolate frameworks (ZIF-8, -25, -71, -90, -96 and -97) with different functional groups. For pure ethanol and water, the predicted adsorption isotherms agree fairly well with experimental data. Hydrogen bonding has an important effect on the adsorption of ethanol and water. In hydrophilic ZIFs (ZIF-90, -96 and -97) with polar groups, adsorption capacities are higher than in hydrophobic counterparts (ZIF-8, -25 and -71). The atomic charges in symmetrically functionalized ZIF-8, -25, and -71 are found to have an indiscernible effect on adsorption, in remarkable contrast to asymmetrically functionalized ZIF-90, -96 and -97. For ethanol-water mixtures representing the biofuel, the selectivity of ethanol-water drops with increasing ethanol in mixtures. It is revealed that the selectivity is determined primarily by framework hydrophobicity as well as the cage size. Among the six ZIFs, ZIF-8 exhibits the highest selectivity. This simulation study provides a microscopic insight into the adsorption of ethanol and water in various ZIFs, reveals the significant role of functional groups in governing biofuel purification, and would facilitate the development of new nanoporous materials for high-efficacy liquid separation.

Zeolitic imidazolate frameworks: next-generation materials for energy-efficient gas separations

Industrial separation processes comprise approximately 10% of the global energy demand, driven largely by the utilization of thermal separation methods (e.g., distillation). Significant energy and cost savings can be realized using advanced separation techniques such as membranes and sorbents. One of the major barriers to acceptance of these techniques remains creating materials that are efficient and productive in the presence of aggressive industrial feeds. One promising class of emerging materials is zeolitic imidazolate frameworks (ZIFs), an important thermally and chemically stable subclass of metal organic frameworks (MOFs). The objectives of this paper are (i) to provide a current understanding of the synthetic methods that enable the immense tunability of ZIFs, (ii) to identify areas of success and areas for improvement when ZIFs are used as adsorbents, (iii) to identify areas of success and areas for improvement in ZIF membranes. A review is given of the state-of-the-art in ZIF synthesis procedures and novel ZIF formation pathways as well as their application in energy efficient separations.

Adsorptive characterization of the ZIF-68 metal-organic framework: a complex structure with amphiphilic properties

In this experimental study, the adsorption behavior of the ZIF-68 heterolinked zeolitic imidazolate framework has been explored. Vapor phase adsorption isotherms of linear C1-C6 alcohols, C6 alkane isomers, aromatics (benzene, toluene, xylene isomers, 1,3,5-trimethylbenzene, and 1,3,5-triisopropylbenzene), and polar adsorbates (water, acetonitrile, and acetone) are reported and discussed. The complex pore structure of ZIF-68, with two one-dimensional channels, each with a different polarity, displays an overall hydrophobic character. Its two-pore system results in S-shaped isotherms for small polar adsorbates (small alcohols, acetone, and acetonitrile), while longer alcohols and nonpolar molecules, such as aromatics and C6 alkane isomers, lead to type I adsorption isotherms. Bulky molecules, with a kinetic diameter significantly larger than the pore windows, are adsorbed in large amounts, which gave reason to think that this ZIF-68 material has a certain degree of framework flexibility to enlarge the free aperture of the channels. Besides, diffusion coefficients from vapor phase uptake and infrared experiments point to a different adsorption mechanism for polar and nonpolar adsorbates. Liquid phase adsorption experiments demonstrated the separation of alcohol mixtures (ethanol/1-butanol) at low concentration from water, with a clear preference for 1-butanol.

Simultaneous spray self-assembly of highly loaded ZIF-8-PDMS nanohybrid membranes exhibiting exceptionally high biobutanol-permselective pervaporation

The ability to obtain a maximum loading of inorganic nanoparticles while maintaining uniform dispersion in the polymer is the key to the fabrication of mixed-matrix membranes with high pervaporation performance in bioalcohol recovery from aqueous solution. Herein, we report the simultaneous spray self-assembly of a zeolitic imidazolate framework (ZIF)-polymer suspension and a cross-linker/catalyst solution as a method for the fabrication of a well-dispersed ZIF-8-PDMS nanohybrid membrane with an extremely high loading. The ZIF-8-PDMS membrane showed excellent biobutanol-permselective pervaporation performance. When the ZIF-8 loading was increased to 40 wt%, the total flux and separation factor could reach 4846.2 g m(-2) h(-1) and 81.6, respectively, in the recovery of n-butanol from 1.0 wt% aqueous solution (80 °C). This new method is expected to have serious implications for the preparation of defect-free mixed-matrix membranes for many applications.

Advancement of sorption-based heat transformation by a metal coating of highly-stable, hydrophilic aluminium fumarate MOF

A 300 μm thick, polycrystalline, thermally well coupled coating of microporous aluminium fumarate was deposited on a metal substrate and found to be stable for at least 4500 ad-/desorption cycles with water vapour.