pyGAPS: a Python-based framework for adsorption isotherm processing and material characterisation

Engineering Insights into Tailored Metal-Organic Frameworks for CO2 Capture in Industrial Processes

Despite the known impacts on climate change of carbon dioxide emissions, the continued use of fossil fuels for energy generation leading to the emission of carbon dioxide (CO2) into the atmosphere is evident. Therefore, innovation to address and reduce CO2 emissions from industrial operations remains an urgent and crucial priority. A viable strategy in the area is postcombustion capture mainly through absorption by aqueous alkanolamines, which focuses on the separation of CO2 from flue gas, despite its limitations. Within this context, porous materials, particularly metal-organic frameworks (MOFs), have arisen as favorable alternatives owing to their significant adsorption capacity, selectivity, and reduced regeneration energy demands. This research evaluates the engineering insights into tailored MOFs for enhanced CO2 capture, focusing on three series of MOFs (ZIF, UiO-66, and BTC) to investigate the effects of organic ligands, functional groups, and metal ions. The evaluation encompassed a range of aspects including adsorption isotherms of pure gases [CO2 and nitrogen (N2)] and mixed gas mixture (CO2 and N2 with 15:85% ratio), along with utilization of the ideal adsorbed solution theory (IAST) to simulate multicomponent gas adsorption isotherms. Moreover, the reliability of IAST for mixed gas adsorption prediction has been investigated in detail. The research offers valuable insights into the correlation between the characteristics of MOFs and their effectiveness in gas separation and how these characteristics contribute to the differences between IAST predictions and experimental results. The findings enhance the understanding of how to enhance MOF characteristics in order to reduce CO2 emissions and also highlight the need for advanced models that consider thermodynamic nonidealities to accurately predict the behavior of mixed gas adsorption in MOFs. As a result, the incorporation of MOFs with enhanced predictability and reliability into CO2 capture industrial processes is facilitated.

Machine learning and experimentally exploring the controversial role of nitrogen in CO2 uptake by waste-derived nitrogen-containing porous carbons

Waste-derived nitrogen-containing porous carbons were widely accepted as promising carbon capture materials. However, roles of nitrogen in CO2 uptake were highly controversial, posing a challenge in designing high CO2 uptake porous carbons. Herein, nitrogen-containing species was firstly introduced into machine learning (ML) models to uncover the complex relationship of nitrogen, micropore and CO2 uptake by combining ML models, DFT computations and experiments. The results revealed that micropore volume (Vmicro) was the most important property influencing CO2 uptake, but was not the only determinant factor. Nitrogen-containing species (pyrrolic/pyridonic-N (N5) and pyridinic-N (N6)) rather than total nitrogen content, also played an essential role. On the one hand, they can enhanced CO2 adsorption by Lewis acid-base and hydrogen bonding. On the other hand, they promoted development of micropores by participating in activation reactions. The model further indicated that excessive N5 (>1.5 wt%) or N6 (>1.7 wt%) led to restriction on developments of micropores, which was attributed to enlargement of pore size, collapses or blockage of micropores. The double edged-sword effect of N5 and N6 on changes of microporous structures was responsible for the long-standing controversy over nitrogen. The result was further verified by synthesizing eight porous carbons with different textural and chemical properties. This study provided not only a new perspective for resolving the controversy of nitrogen in CO2 uptake, but also a graphical user interface prediction software meaningful for designing porous carbons.

Investigating the synergy of rapidly synthesized iron oxide predecessor and plasma-gaseous species for dye-removal to reuse water in irrigation

This study explores a novel and sustainable approach to reusing textile wastewater for irrigation. This is investigated by degrading Evans blue dye, a model azo dye, in wastewater by combining iron oxide predecessor (IOP) catalyst with gaseous species generated by multi-electrode cylindrical plasma device (MCPD). Analysis of IOP-plasma gaseous species revealed the generation of different types of reactive oxygen species in solution which were responsible for degradation of model dye. Key factors influencing the degradation process were studied by performing optimization experiments that resulted in rates of up to 0.008 L mg-1 min-1, more than twice as fast as using plasma gas treatment alone. These studies included mechanistic response of MCPD generated gaseous species with the IOP. In particular, reusability testing of IOP affirmed the robustness and performance efficiency upto three cycles. Finally, toxicity analysis revealed not only reduced negative effects on plant growth by the treated wastewater, but also it can used as minerals to plants. These findings highlight the feasibility of the IOP-MCPD system as a sustainable and eco-friendly solution to reduce scarcity of water in irrigation by treating textile effluent.

Robust {Pb10}-Cluster-Based Metal-Organic Framework for Capturing and Converting CO2 into Cyclic Carbonates under Mild Conditions

Developing a highly active catalyst that can efficiently capture and convert carbon dioxide (CO2) into high-value-added energy materials remains a severe challenge, which inspires us to explore effective metal-organic frameworks (MOFs) with high chemical stability and high-density active sites. Herein, we report a robust 3D lead(II)-organic framework of {(Me2NH2)2[Pb5(PTTPA)2(H2O)3]·2DMF·3H2O}n (NUC-111) with unreported [Pb10(COO)22(H2O)6] clusters (abbreviated as {Pb10}) as nodes (H6PTTPA = 4,4',4″-(pyridine-2,4,6-triyl)triisophthalic acid). After thermal activation, NUC-111a is functionalized by the multifarious symbiotic acid-base active sites of open Pb2+ sites and uncoordinated pyridine groups on the inner surface of the void volume. Gas adsorption tests confirm that NUC-111a displays a higher separation performance for mixed gases of f CO2 and CH4 with the selectivity of CO2/CH4 at 273 K and 101 kPa being 31 (1:99, v/v), 23 (15:85, v/v), and 8 (50:50, v/v), respectively. When the temperature rises to 298 K, the selectivity of CO2/CH4 at 101 kPa is 26 (1:99, v/v), 22 (15:85, v/v), and 11 (50:50, v/v). Moreover, activated NUC-111a exhibited excellent catalytic performance, stability, and recyclability for the cycloaddition of CO2 with epoxides under mild conditions. Hence, this work provides valuable insight into designing MOFs with multifunctionality for CO2 capture, separation, and conversion.

Construction of Zn-Cu bimetallic metal-organic frameworks for carbon dioxide capture

Bimetallic metal-organic frameworks (MOFs) have shown more impressive performance in gas adsorption compared with monometallic MOFs. Herein, a Cu-Zn bimetallic metal-organic framework (Zn/Cu-BTC) was synthesized via a one-pot method, and its structure, thermal stability and CO2 adsorption property were investigated and compared with those of corresponding monometallic Cu-BTC and Zn-BTC. The results showed that Zn/Cu-BTC has a specific ortho-octahedral crystal morphology with a unique X-ray diffraction peak, the atomic ratio of Zn to Cu is about 1 : 5, and it remained stable at a temperature up to 490 K. In Zn/Cu-BTC, Cu2+ played a role in increasing the specific surface area and porosity of the MOF and improving the gas adsorption performance. The CO2 adsorption of Zn/Cu-BTC is lower than that of Cu-BTC but much higher than that of Zn-BTC, and CO2 adsorption heat was 30.52 kJ mol-1, which indicated physical adsorption. In addition, Zn/Cu-BTC had higher CO2/N2 adsorption selectivity compared with Zn-BTC and Cu-BTC, with a maximum value of 17. This study can be a reference for the research on improving the adsorption selectivity of gases by constructing bimetallic MOFs.

pyCOFBuilder: A Python Package for Automated Creation of Covalent Organic Framework Models Based on the Reticular Approach

Covalent organic frameworks (COFs) have gained significant popularity in recent years due to their unique ability to provide a high surface area and customizable pore geometry and chemistry, making them an ideal choice for a wide range of applications. However, exploring COFs experimentally can be arduous and time-consuming due to their immense number of potential structures. As a result, computational high-throughput studies have become an attractive option. Nevertheless, generating COF structures can also be a challenging and time-consuming task. To address this challenge, here, we introduce the pyCOFBuilder, an open-source Python package designed to facilitate the generation of COF structures for computational studies. The pyCOFBuilder software provides an easy-to-use set of functionalities to generate COF structures following the reticular approach. In this paper, we describe the implementation, main features, and capabilities of the pyCOFBuilder, demonstrating its utility for generating COF structures with varying topologies and chemical properties. pyCOFBuilder is freely available on GitHub at https://github.com/lipelopesoliveira/pyCOFBuilder.

Epitaxial Growth of Two-Dimensional MWW Zeolite

Two-dimensional (2D) zeolite, with a high aspect ratio, has more open skeletons and accessible active sites than its three-dimensional (3D) counterpart. However, traditional methods of obtaining 2D zeolites often cause structural damage and widespread skeleton defects, hindering efficient selectivity in molecular separation. In this study, we present, for the first time, a direct epitaxial synthesis of 2D zeolite (Epi-MWW) guided by hexagonal boron nitride (h-BN) with a coincidence matching of site lattices to MWW zeolite. The as-grown Epi-MWW zeolite possesses a high crystallinity and intact hexagonal 2D morphology, with an average thickness of 10 nm and an aspect ratio of over 50. Thanks to its excellent molecular accessibility, the diffusion time constants of o-xylene (OX) and p-xylene (PX) are as 12 and 133 times higher than those of conventional MCM-22, respectively; the PX/OX selectivity of Epi-MWW is 7.4 times better than MCM-22 as calculated by the ideal adsorbed solution theory.

Unraveling the role of internal-external metal substitution in Zn3[Co(CN6)]2 for the styrene oxide-CO2 cycloaddition reaction

We investigated the influence of the structural and textural properties along with the chemical environment of pure Zn3[Co(CN)6]2 in comparison with the modified phases on the catalytic performance in the cycloaddition reaction between styrene oxide and CO2. We relate these to the proposed reaction pathways and mechanisms. The natural cubic phase (ZnCoCn) was dehydrated to obtain the rhombohedral phase (ZnCoRn), while the stabilized cubic phase (ZnCoCs) was synthesized by substituting external zinc atoms with cadmium atoms. The rhombohedral stabilized phase (ZnCoRs) was achieved by the internal cobalt change with iron. All the materials were extensively characterized using X-ray diffraction (XRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), X-ray photoelectron spectroscopy (XPS), and N2 adsorption. The catalytic behavior of the four phases was tested. The crystalline structure of each phase was obtained, and by XPS, it was demonstrated that the chemical environments of all elements conforming to the rhombohedral stabilized phase are different from those of all other materials owing to the exchange of internal metals. The bulk textural properties were similar; only the ZnCoRs presented more micropore area but did not exceed the total surface area of the other materials. The product distribution and yield at reaction times of 2 h and 6 h were closer to those of the cubic phases. The natural rhombohedral phase exhibits the best performance. The tetrabutylammonium bromide (TBAB) and rhombohedral stabilized phase work together to yield a bigger copolymer quantity at the expense of the styrene carbonate (StCO3) production. From the proposed mechanism, the TBAB cation (TBA+) has a "protection" function that drives the closing of the StCO3 ring; however, the charge distribution anisotropy in the four nitrogen atoms generated by Co replacement in ZnCoRs could hold TBA+ as the reaction time progressed, causing an unavailability that triggered the copolymerization propagation step.

Robust Carborane-Based Metal-Organic Frameworks for Hexane Separation

Hexane isomers play a vital role as feedstocks and fuel additives in the petrochemical industry. However, their similar physical and chemical properties lead to significant challenges in the separation process. Traditional thermal separation techniques are energy-intensive and lead to significant carbon footprint penalties. As such, there is a growing demand for the development of less energy-intensive nonthermal separation methods. Adsorption-based separation methods, such as using solid sorbents or membranes, have emerged as promising alternatives to distillation. Here, we report the successful synthesis of two novel metal-organic frameworks (MOFs), NU-2004 and NU-2005, by incorporating a carborane-based three-dimensional (3D) linker and using aluminum and vanadium nodes, respectively. These MOFs exhibit exceptional thermal stability and structural rigidity compared to other MIL-53 analogues, which is further corroborated using synchrotron studies. Furthermore, the inclusion of the quasi-spherical 3D linker in NU-2004 demonstrates significant advancements in the separation of hexane isomers compared to other MIL MOFs containing two-dimensional (2D) and aliphatic 3D linkers.

A Route to Understanding the Ethane Adsorption Selectivity of the Zeolitic Imidazolate Framework-8 in Ethane-Ethylene Mixtures

Ethylene production has a negative environmental impact, with its separation step being one of the major contributors of pollution. This has encouraged the search for energy-efficient alternatives, among which the adsorptive separation of ethane and ethylene stands out. ZIF-8 is a molecular sieve that is potentially useful for this purpose. It is selective to ethane, an exceptional property that remains unexplained. Furthermore, the adsorption of ethane and ethylene above room temperature, such as at steam cracking process outlet temperatures, has not been addressed either. This work aims to fill this knowledge gap by combining experiments at very low volumetric fillings with density-functional theory modelling methods. Adsorption isotherms of ethane and ethylene on ZIF-8 at pressures below 0.3 bar and 311 K, 333 K, and 363 K were measured using zero-length column chromatography. The low-pressure domain of the isotherms contains information on the interactions between the adsorbate molecules and the adsorbent. This favors the understanding of their macroscopic behavior from simulations at the atomic level. The isosteric enthalpy of adsorption of ethane remained constant at approximately -10 kJ/mol. In contrast, the isosteric enthalpy of adsorption of ethylene decreased from -4 kJ/mol to values akin to those of ethane as temperature increased. ZIF-8 selectivity to ethane, estimated from ideal adsorbed solution theory, decreased from 2.8 to 2.0 with increasing pressure up to 0.19 bar. Quantum mechanical modelling suggested that ethylene had minimal interactions with ZIF-8, while ethane formed hydrogen bonds with nitrogen atoms within its structure. The findings of this research are a platform for designing new systems for the adsorptive separation of ethane and ethylene and thus, reducing the environmental impact of ethylene production.

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.

Design of biomass-based N, S co-doped porous carbon via a straightforward post-treatment strategy for enhanced CO2 capture performance

Biomass-based adsorbents are considered to have great potential for CO₂ capture due to their low cost, high efficiency and exceptional sustainability. The aim of this work is to design a simple method for preparing biomass-based adsorbents with abundant active sites and large numbers of narrow micropores, so as to enhance CO₂ capture performance. Herein, N, S co-doped porous carbon (NSPC) was created utilizing walnut shell-based microporous carbon (WSMC) as the main framework and thiourea as N/S dopant through physical grinding and post-treatment process at a moderate temperature without any other reagents and steps. By altering the post-treatment parameters, a series of porous carbons with varying physico-chemical properties were prepared to discuss the roles of microporosity and N/S functional groups in CO₂ adsorption. NSPC with narrow micropore volume of 0.74 cm³ g^-1, N content of 4.89 % and S contents of 0.71 % demonstrated the highest CO₂ adsorption capacity of 7.26 (0 °C) and 5.51 mmol g^-1 (25 °C) at 1 bar. Meanwhile, a good selectivity of binary gas mixture CO₂/N₂ (15/85) of 29.72 and outstanding recyclability after ten cycles of almost 100 % adsorption capacity retention were achieved. The proposed post-treatment method was beneficial in maintaining the narrow micropores and forming N/S active sites, which together improve the CO₂ adsorption performance of NSPC. The novel NSPC displays amazing CO₂ adsorption characteristics, and the practical, affordable synthetic approach exhibits significant potential to produce highly effective CO₂ adsorbents on a broad scale.

CRAFTED: An exploratory database of simulated adsorption isotherms of metal-organic frameworks

Grand Canonical Monte Carlo is an important method for performing molecular-level simulations and assisting the study and development of nanoporous materials for gas capture applications. These simulations are based on the use of force fields and partial charges to model the interaction between the adsorbent molecules and the solid framework. The choice of the force field parameters and partial charges can significantly impact the results obtained, however, there are very few databases available to support a comprehensive impact evaluation. Here, we present a database of simulations of CO₂ and N₂ adsorption isotherms on 690 metal-organic frameworks taken from the CoRE MOF 2014 database. We performed simulations with two force fields (UFF and DREIDING), six partial charge schemes (no charges, Qeq, EQeq, MPNN, PACMOF, and DDEC), and three temperatures (273, 298, 323 K). The resulting isotherms compose the Charge-dependent, Reproducible, Accessible, Forcefield-dependent, and Temperature-dependent Exploratory Database (CRAFTED) of adsorption isotherms.

Engineering Metal-Organic Frameworks for Selective Separation of Hexane Isomers Using 3-Dimensional Linkers

Metal-organic frameworks (MOFs) are highly tunable materials with potential for use as porous media in non-thermal adsorption or membrane-based separations. However, many separations target molecules with sub-angstrom differences in size, requiring precise control over the pore size. Herein, we demonstrate that this precise control can be achieved by installing a three-dimensional linker in an MOF with one-dimensional channels. Specifically, we synthesized single crystals and bulk powder of NU-2002, an isostructural framework to MIL-53 with bicyclo[1.1.1]pentane-1,3-dicarboxylic acid as the organic linker component. Using variable-temperature X-ray diffraction studies, we show that increasing linker dimensionality limits structural breathing relative to MIL-53. Furthermore, single-component adsorption isotherms demonstrate the efficacy of this material for separating hexane isomers based on the different sizes and shapes of these isomers.

Hierarchical Metal-Organic Aerogel as a Highly Selective and Sustainable CO2 Adsorbent

Typical amorphous aerogels pose great potential for CO₂ adsorbents with high surface areas and facile diffusion, but they lack well-defined porosity and specific selectivity, inhibiting utilization of their full functionality. To assign well-defined porous structures to aerogels, a hierarchical metal-organic aerogel (HMOA) is designed, which consists of well-defined micropores (d ∼ 1 nm) by coordinative integration with chromium(III) and organic ligands. Due to its hierarchical structure with intrinsically flexible coordination, the HMOA has excellent porous features of a high surface area and a reusable surface with appropriate binding energy for CO₂ adsorption. The HMOA features high CO₂ adsorption capacity, high CO₂/N₂ IAST selectivity, and vacuum-induced surface regenerability (100% through 20 cycles). Further, the HMOA could be prepared via simple ambient drying methods while retaining the microporous network. This unique surface-tension-resistant micropore formation and flexible coordination systems of HMOA make it a potential candidate for a CO₂ adsorbent with industrial scalability and reproducibility.

A three dimensional graphdiyne-like porous triptycene network for gas adsorption and separation

Graphdiyne, an emerging carbon allotrope, has attracted many researchers devoted to the study of its synthesis and application. The utilization of graphdiyne in gas adsorption and separation has been predicted by computer simulation with many examples. In this work, the triangular basic unit of graphdiyne was introduced into a triptycene-based porous organic polymer to obtain a three dimensional graphdiyne-like porous triptycene network named G-PTN. With high surface area and a microporous structure, G-PTN exhibited convincing application potential for the storage of gas molecules, especially for the selective adsorption of acetylene over ethylene. Computational simulation proved the importance of the triptycene units and three dimensional structure to the selectivity, as well as the potential of graphdiyne units as selective binding sites, suggesting that through judicious design, new three-dimensional porous graphdiyne could be acquired with better gas adsorption and separation performance.

Multifunctionality of weak ferromagnetic porphyrin-based MOFs: selective adsorption in the liquid and gas phase

Ferromagnetic [Ni₅(H₂TCPP)₂O(H₂O)₄]·nS exhibits selective adsorption towards cationic dyes in solution and gas separation calculations predict promising values for gas mixtures.

Pulling Simulations and Hydrogen Sorption Modelling on Carbon Nanotube Bundles

Recent progress in molecular simulation technology has developed an interest in modernizing the usual computational methods and approaches. For instance, most of the theoretical work on hydrogen adsorption on carbon nanotubes was conducted a decade ago. It should be insightful to reinvestigate the field and take advantage of code improvements and features implemented in contemporary software. One example of such features is the pulling simulation modules now available in many molecular dynamics programs. We conduct pulling simulations on pairs of carbon nanotubes and measure the inter-tube distance before they dissociate in water. We use this distance to set the interval size between adjacent nanotubes as we arrange them in bundle configurations. We consider bundles with triangular, intermediate and honeycomb patterns, and armchair nanotubes with a chiral index from n = 5 to n = 10. Then, we simulate low pressure hydrogen adsorption isotherms at 77 K, using the grand canonical Monte Carlo method. The different bundle configurations adsorb great hydrogen amounts that may exceed 2% wt at ambient pressures. The computed hydrogen capacities are considered large for physisorption on carbon nanostructures and attributed to the ultra-microporous network and extraordinary high surface area of the configured models.