Gas Adsorption Applications Research Articles

A microporous bismuth-based MOF for efficient separation of acetylene from carbon dioxide.

The separation of acetylene from carbon dioxide is challenging due to their almost identical molecular sizes and volatilities. Metal-organic frameworks (MOFs) in general are strong candidates for the separation of gas mixtures owing to the presence of functional pore surfaces that can selectively capture specific target molecules. Herein, we report a stable and easily synthesized bismuth-based MOF, Bi-BTC, which can achieve the separation of acetylene and carbon dioxide. We performed a detailed analysis of the sorption properties of the Bi-MOF. Bi-BTC shows good adsorption capacities for C2H2 with a capacity of 53.8 cm3 g-1 at 298 K and 1.0 bar, and C2H2/CO2 selectivity of 5.14/7.69 at 298 K and 1.0/0.1 bar. IAST selectivity calculations indicate that Bi-BTC possesses good separation capacity, and dynamic breakthrough experiments were performed to prove the separation of C2H2 and CO2. Bi-MOFs as a group of relatively less studied types of MOFs have interesting adsorption characteristics, and this study on Bi-based MOF will enrich three-dimensional Bi-MOF adsorbents for gas adsorption and separation applications.

Yttrium-based metal-organic frameworks built on hexanuclear clusters.

Yttrium-based metal-organic frameworks built on hexanuclear clusters (Y6-MOFs) represent an important subgroup of MOFs that are assembled from Y6 clusters and diverse organic linkers, featuring a variety of topologies. Due to the robust Y-O bonds and high connectivity of hexanuclear SBUs, Y6-MOFs are generally thermally stable and resistant to water. Additionally, their pore structures are highly tunable through the practice of the reticular chemistry strategy, resulting in excellent performance in gas adsorption and separation related applications. Y6-MOFs are structurally analogous to Zr6-MOFs; however, the existence of charge-balancing cations in Y6-MOFs serves as an additional pore structure regulator, enhancing their tailorability with respect to pore shape and dimensions. In this Frontier article, we summarize the main advances in the design and synthesis of Y6-MOFs, with a particular focus on the precise engineering of their pore structure for gas separation. Future directions of research efforts in this field are also discussed.

A Brief Review of MoO3 and MoO3-Based Materials and Recent Technological Applications in Gas Sensors, Lithium-Ion Batteries, Adsorption, and Photocatalysis.

Molybdenum trioxide is an abundant natural, low-cost, and environmentally friendly material that has gained considerable attention from many researchers in a variety of high-impact applications. It is an attractive inorganic oxide that has been widely studied because of its layered structure, which results in intercalation ability through tetrahedral/octahedral holes and extension channels and leads to superior charge transfer. Shape-related properties such as high specific capacities, the presence of exposed active sites on the oxygen-rich structure, and its natural tendency to oxygen vacancy that leads to a high ionic conductivity are also attractive to technological applications. Due to its chemistry with multiple valence states, high thermal and chemical stability, high reduction potential, and electrochemical activity, many studies have focused on the development of molybdenum oxide-based systems in the last few years. Thus, this article aims to briefly review the latest advances in technological applications of MoO3 and MoO3-based materials in gas sensors, lithium-ion batteries, and water pollution treatment using adsorption and photocatalysis techniques, presenting the most relevant and new information on heterostructures, metal doping, and non-stoichiometric MoO3-x.

MIL-101 (Cr) hybrid nanoporous carbon derived MOF as a nano-adsorbent for dye removal using RSM-CCD

Metal-organic frameworks (MOFs) are a promising class of nanoporous crystalline materials with potential applications in gas storage, catalysis, biomedical, adsorption, and clean energy. The massive parts of commercial dyes are interring to our environment and are considered danger for humans and animals. In this research work, nanohybrids based on MOFs have been studied as a suitable nanoadsorbent for the adsorption of cationic dyes such as methylene blue (MB). In this article, a nanopore carbon (NPC) was prepared from Zn-MOF. The Zn-MOF NPC with MI-101 NPs has been used to prepare Zn-MOF NPC@MIL nanohybrid by the hydrothermal method. Various XRD, FT-IR, SEM, EDX, TEM, TGA, and BET techniques have been used to characterize the nano adsorbent. Four essential variables effective in adsorption, loading percentage of NPs, initial concentration of MB, contact time and pH, were optimized by Central Composite Response Surface Method (RSM-CCD). The removal percentage (Re%) of MB is equal to 95.7% was obtained under the following conditions: The loading value of 25Wt.%, the MB initial concentration of 50 mg. L-1, contact time 30 min and pH 8. Also, the experimental data were investigated with famous kinetic models and isotherms, and it was observed that MB removal by nanohybrid is correlated with pseudo-second-order kinetic model and Langmuir isotherm.

Elucidating the role of synthesis conditions on Zr-MOF properties and yield

Metal-organic frameworks (MOFs) are a new type of ultra-high surface area porous materials with applications in catalysis, energy storage, and gas adsorption. Compared to other MOFs, Zirconium-based MOFs (Zr-MOFs) demonstrate improved stability due to strong bonds between tetravalent zirconium and carboxylate ligands, making them applicable in real world conditions. This study aims to investigate optimal synthesis conditions for the solvothermal fabrication of Zr-MOFs by looking at two promising tetratopic ligand-based MOFs, Zr-TCPP and Zr-TPTC. By systematically investigating the impact of synthesis parameters on yield, crystallinity, and morphological characteristics, both general and specific trends were determined. The present work demonstrated that the ideal reactant ratio was twice the actual Zr:ligand ratio in the final structure. Stronger acid modulators were found to produce more crystalline samples for MOFs with flexible ligands (Zr-TPTC), where formic acid use resulted in more crystalline samples compared to acetic acid; however, this lowered the yield. The effect of temperature on yield was non-linearly dependent on the reactant ratio used for synthesising flexible Zr-TPTC. For MOFs with rigid ligands (Zr-TCPP), increasing synthesis temperature did not affect yield but decreased crystallite size and improved phase selectivity. Stability tests in water and acid were performed on both MOFs to assess the effect on crystallinity and morphology and the results showed expected trends for Zr-MOFs. The optimized synthesis parameters for Zr-TCPP resulted in a superior method of producing PCN-222 with higher yield and crystallinity. On the other hand, a new Zr-TPTC MOF with high yield and crystallinity was synthesised using the optimized parameters. This study thus elucidates the role of synthesis parameters on Zr-MOF properties and yield and furthers the understanding of MOF synthesis mechanisms, expanding the potential for their applicability in industry.

Robust porous hydrogen-bonded organic frameworks: Synthesis and applications in gas adsorption and separation

Being an emerging family of crystalline porous materials, hydrogen-bonded organic frameworks (HOFs) are types of ordered supramolecular structures that constructed from organic linkers (including those with organometallic units) via mainly hydrogen bonds. HOFs have now attracted increasing attention in various fields, owing to their valued features such as mild synthetic condition, convenient purification/recovery processes, high processibility and diverse functionality. Great potentials have emerged for HOFs in the field of adsorption and separation, especially for the purification of light hydrocarbons that are crucial to the petrochemical industry. Their practical applications, however, is limited as it is rather difficult to maintain their porous architectures only through hydrogen bonds after removing the lattice solvent molecules. Several types of strategies have hence been developed to solve the issue of HOF structure fragility, including introduction of stronger/different forms of intermolecular interactions, adoption of monomers with rigid backbones, integration of appropriate structural interpenetrations, formation of the cross-linked structures, etc. In this review, the common strategies for constructing HOFs and the important role of each method in enhancing the structural stability of HOFs are briefly introduced. Then, the application of robust porous HOFs in various gases adsorptions and separations is carefully summarized, as well as its mechanism is analyzed in detail from the perspective of supramolecular interactions among the frameworks and gas molecules. The current challenges and the future perspectives for HOFs are discussed with respect to the urgent demands in enhancing their performance, which propose a broader vision of HOFs in developing novel functional porous materials.

Investigation of BN modified graphene nanoribbon for gas adsorption applications: DFT study

Graphene nanoribbons that are modified using boron and nitrogen (CBN) are examined in this work for their adsorption of CO, CO2, H2, H2O, NH3, NO, and NO2 gases. A first principles approach that utilizes density functional theory (DFT) computation is employed to investigate both perfect and vacancy defected structures. The gas molecule adsorption capacity is examined in this work by determination of the adsorption energy (Ed), adsorption length (D), charge exchanged amongst the gas and CBN (ΔQ), along with the density of states (DOS). The results indicate that NO and NO2 gases have favorable adsorption on the perfect CBN, however, chemisorption is not achieved for these gases. On the other hand, NO2 and NH3 gases have favorable adsorption on the vacancy defected CBN and they establish chemical bonds with the structure. Ed is 235% and 165% for NO2 and NH3, respectively, higher for the vacancy defected nanoribbon relative to the perfect nanoribbon. Furthermore, the adsorption length of NO2 and NH3 decreases dramatically for the vacancy defected CBN to 1.55 and 1.69 Å, while the charge transferred increases to 0.326 and -0.415 e, respectively. The sensor response evaluation indicates that the vacancy defected CBN structure exhibits an enhanced response towards NO2 gas followed by that of NH3. Consequently, the introduction of a vacancy defect in the CBN structure is an efficient approach to enhance its sensitivity and selectivity, particularly, for NO2 and NH3.

Adsorption of radon on transition metal functionalized graphene monolayer with external effects

The noble gas radon (Rn) is radioactive and can gravely harm the human body. As a result, capturing and dealing with Rn gas is an important task, in terms of radiation protection. The large specific surface area of graphene renders it a potential candidate for gas adsorption applications. Along these lines, in this work, theoretical calculations based on the density functional theory were presented to systematically explore the adsorption properties of Rn on transition metal (TM) functionalized graphene monolayer. The adsorption energies of Rn atoms on the functional graphene were estimated up to −0.873 eV, according to our computed results. The increase in the concentration of Rn atoms and the ambient temperature led to a reduction in the adsorption energy of Rn on the surface. To effectively control the adsorption characteristics, electric field and stress were externally added. The calculation results showed that a negative electric field and proper deformation could significantly improve the adsorption of Rn to TM functionalized graphene. In this work, it was demonstrated that TM functionalized graphene could be successfully used as an adsorber of Rn atoms with promising results. In addition, the adsorption properties can be controlled and enhanced under the application of an external field, as well as a stress load, which is of great significance for application in radiation protection.

Assessing CO2 Capture in Porous Sorbents via Solid-State NMR-Assisted Adsorption Techniques

Adsorption isotherms obtained through volumetric measurements are widely used to estimate the gas adsorption performance of porous materials. Nonetheless, there is always ambiguity regarding the contributions of chemi- and physisorption processes to the overall retained gas volume. In this work, we propose, for the first time, the use of solid-state NMR (ssNMR) to generate isotherms of CO2 adsorbed onto an amine-modified silica sorbent. This method enables the separation of six individual isotherms for chemi- and physisorbed CO2 components, a feat only possible using the discrimination power of NMR spectroscopy. The adsorption mechanism for each adsorbed species was ascertained by tracking their adsorption profiles at various pressures. The proposed method was validated against conventional volumetric adsorption measurements. The isotherm curves obtained by the proposed ssNMR-assisted approach enable advanced analysis of the sorbents, revealing the potential of variable-pressure NMR experiments in gas adsorption applications.

Recent Developments in Sonochemical Synthesis of Nanoporous Materials

Ultrasounds are commonly used in medical imaging, solution homogenization, navigation, and ranging, but they are also a great energy source for chemical reactions. Sonochemistry uses ultrasounds and thus realizes one of the basic concepts of green chemistry, i.e., energy savings. Moreover, reduced reaction time, mostly using water as a solvent, and better product yields are among the many factors that make ultrasound-induced reactions greener than those performed under conventional conditions. Sonochemistry has been successfully implemented for the preparation of various materials; this review covers sonochemically synthesized nanoporous materials. For instance, sonochemical-assisted methods afforded ordered mesoporous silicas, spherical mesoporous silicas, periodic mesoporous organosilicas, various metal oxides, biomass-derived activated carbons, carbon nanotubes, diverse metal-organic frameworks, and covalent organic frameworks. Among these materials, highly porous samples have also been prepared, such as garlic peel-derived activated carbon with an apparent specific surface area of 3887 m2/g and MOF-177 with an SSA of 4898 m2/g. Additionally, many of them have been examined for practical usage in gas adsorption, water treatment, catalysis, and energy storage-related applications, yielding satisfactory results.

Role of molecular modelling in the development of metal-organic framework for gas adsorption applications.

The importance of density functional theory-based molecular modeling studies in offering design clues to improve the gas adsorption and storage capacity of existing MOF architectures is discussed here. The use of DFT-based investigation in conjunction with experimental synthesis is an imperative tool in designing new-generation MOFs with enhanced uptake capacity.

Sodium Alginate-Based Carbon Aerogel-Supported ZIF-8-Derived Porous Carbon as an Effective Adsorbent for Methane Gas.

Adsorption natural gas (ANG) is a technology in which natural gas is stored on the surface of porous materials at relatively low pressures, which are promising candidates for adsorption of natural gas. Adsorbent materials with a large surface area and porous structure plays a significant role in the ANG technology, which holds promise in increasing the storage density for natural gas while decreasing the operating pressure. Here, we demonstrate a facile synthetic method for rational construction of a sodium alginate (SA)/ZIF-8 composite carbon aerogel (AZSCA) by incorporating ZIF-8 particles into SA aerogel through a directional freeze-drying method followed by the carbonization process. The structure characterization shows that AZSCA has a hierarchical porous structure, in which the micropores originated from MOF while the mesopores are derived from the three-dimensional network of the aerogel. The experimental results show that AZSCA achieved high methane adsorption of 181 cm3·g-1 at 65 bar and 298 K, along with higher isosteric heat of adsorption (Qst) throughout the adsorption range. Thus, the combination of MOF powders with aerogel can find potential applications in other gas adsorption.

Facile Synthesis of Two-Dimensional (2D) Boron Carbonitride and 2D Porous Boron Carbonitride for Excellent Energy Storage and Gas Adsorption Applications

Facile Synthesis of Two-Dimensional (2D) Boron Carbonitride and 2D Porous Boron Carbonitride for Excellent Energy Storage and Gas Adsorption Applications

Control of the pore chemistry in metal-organic frameworks for efficient adsorption of benzene and separation of benzene/cyclohexane

Control of the pore chemistry in metal-organic frameworks for efficient adsorption of benzene and separation of benzene/cyclohexane

Catalyst controlled synthesis of porous organic polymers and their SWCNT composites for high performance supercapacitor applications

The present study discusses the importance of catalyst selectivity for the preparation of homocoupling polymers for CO2 gas adsorption and supercapacitor applications. N, N′-bicarbazole based conjugated porous organic polymers (TGs) have been synthesized through sonogashira (TGPd/Cu), glaser (TGCuCl) and Eglington (TGCu(OAc)2) protocols. Here, TGPd/Cu acquired high specific surface area (923 m2 g−1), uniform pores (2 nm), and excellent CO2 adsorption (16.1 wt%). The synthesized TG polymers was utilized as efficient electrode for supercapacitor studies. TGPd/Cu exhibits a maximum capacitance of 248 F g−1 at 0.5 A g−1 current density. To enhance the electrochemical performances, the prepared TGs melded with single walled carbon nanotubes (SWCNT) and the fabricated TGPd/Cu/SWCNT electrode demonstrates a maximum specific capacitance of 523 F g−1 at 0.5 A g−1 current density with an outstanding cycling stability of 98.1% after 5000 cycles in three electrode system. The fabricated TGPd/Cu/SWCNT device showed a capacitance of 129 F g−1 at 0.5 A g−1 with high-capacity retention of 82.5% after 5000 cycles in two electrode system. Consequently, TGPd/Cu/SWCNT appear to be promising electroactive material for use as electrode in electrochemical energy storage systems. The satisfactory electrochemical performance can be attributed to the successfully π- π stacking of the TGPd/Cu onto the nanotube surface and the synergy between TGPd/Cu and highly conductive SWCNT which significantly advanced the electron transport properties of the explored composites.

ZIF-8@Zn-MOF-74 core–shell metal–organic framework (MOF) with open metal sites: Synthesis, characterization, and gas adsorption performance

In this paper, an efficient hierarchical metal–organic framework (MOF), namely ZIF-8@Zn-MOF-74 with core–shell structure and coordinately open/unsaturated metal sites (OMS) was successfully synthesized. For this purpose, the facile post-synthetic ligand exchange (PSE) method at ambient temperature was applied. In the fabricated core–shell porous structure, the SOD-type ZIF-8 acts as the core, providing molecular sieving features, resulting in greater adsorption selectivity values. On the other hand, Zn-MOF-74 as the shell part, owing to the larger pore size, makes entrance and diffusion of the guest gas molecules more convenient. In addition, due to the presence of OMS in the Zn-MOF-74 structure, a greater adsorption capacity would be achieved. The prepared MOFs were characterized by FESEM, EDS, HRTEM, FTIR, XRD, BET, and TGA analyses, and formation of the core–shell structure was confirmed. The FESEM and HRTEM images demonstrated rather smooth coverage of the core (ZIF-8) with a layer of the shell (Zn-MOF-74). The rather high BET surface area (633.2 m2/g) and total pore volume (0.671 cm3 g−1) of the core–shell structure, make it promising for gas adsorption applications. The gas adsorption measurements were conducted for CO2, N2, H2, O2, CH4, C2H6, C3H8, C2H4, and C3H6 pure gases at 308 K and equilibrium pressures up to 4 bar. It was found that the CO2 adsorption capacity of ZIF-8@Zn-MOF-74 nanoparticles (3.27 mmol g−1) has enhanced ∼63.5 % compared to the pristine ZIF-8 (∼2 mmol/g). The CO2/N2 and CO2/CH4 selectivity values were also increased by 85.4 % and 74.4 %, respectively, that indicates overcoming the trade-off between adsorption capacity and selectivity.

Olefin-linked covalent organic frameworks: synthesis and applications.

Covalent organic frameworks (COFs) with high specific porosity, easy functionalization, and tailored structure are an emerging class of crystalline porous polymers that have been extensively exploited as ideal materials in various fields. Among them, sp2-carbon linked COFs with high chemical stability, porous backbone, and unique π-electron conjugated architectures structure have raised widespread attention. Specifically, the porous channels of olefin-linked COFs could be packed with active sites for catalysis and guest molecules, while π-π stacking interactions and conjugation systems pave the way for electron transfer. In recent years, many efforts have been devoted to the development of sp2-carbon linked COFs for applications in catalysis, energy storage, gas adsorption, and separation. In this review, we highlight the design principles, synthesis strategies, and impactful applications of olefin-linked COFs. We are looking forward to this review to deepen the understanding of the synthesis of olefin-linked COFs and motivate the further development of these novel conjugated organic materials with distinctive physicochemical properties, as well as their applications in a variety of fields.

Synthesis of a Highly Crystalline Amide‐Linked Covalent Organic Framework

Comprehensive SummaryThe dilemma for the synthesis of covalent organic frameworks (COFs) is crystallinity and stability. Herein, we present the synthesis of a single‐crystalline amide‐linked COF, and demonstrate its excellent chemical as well as thermal stabilities. This study will inspire the synthesis of a wide spectrum of highly crystalline and stable COFs, promote their structure‐property investigations and boost their applications in selective gas adsorption, storage and separation.

In Situ Synthesis of Hierarchical Porous Zr-MOFs on Columnar Activated Carbon and Application in Toxic Gas Adsorption.

Metal organic frameworks (MOFs) have been explored as adsorption materials owing to their diversity, controllable structure, high specific surface area, and abundant active sites. However, the shaping of MOFs has become a critical issue hindering their commercial application. A binder or high pressure is commonly used in traditional powder shaping, causing pores to be blocked or collapsed and porosity to be decreased, eventually leading to the degradation of adsorption performance. In this paper, Zr-MOFs were in situ grown on a columnar activated carbon (CAC) matrix, and a series of Zr-MOFs/CAC composites were prepared. The adsorption properties for SO2 and NO2 were measured by dynamic adsorption tests, and the Wheel-Jonas model was used to calculate the saturated adsorption capacity. Abundant mesopores can be formed between MOF crystals and activated carbon particles, and the mesoporosity of Zr-MOFs/CAC composites reached over 50%. Owing to the abundant mesoporous, increased activated sites as well as the synergistic effect between MOFs and activated carbon, the as-obtained HP-Zr-MOFs/CAC exhibited the best adsorption performance both for SO2 and NO2, which are 34.2 and 17.4 mg g-1, respectively, while the adsorption capacities of CAC for SO2 and NO2 are 20.9 and 6.6 mg g-1, respectively. The outstanding performance and facile synthesis process of HP-Zr-MOFs/CAC composites could provide ideas to develop other hierarchical porous MOFs/activated carbon composites.

SnAu clusters as detectors of CO and NO gases: A DFT study

Monitoring and control of CO and NO gases are now considered important for public health. These can be achieved by the research and development of novel sensors. Bimetallic Au–Me clusters such as Au-Pt, Au-Pd, and Au-Pb exhibit extremely high sensitivity, making them suitable for application in gas adsorption and sensing. Here, the ground-state structure, average binding energy, fragmentation energy, second-order energy difference, HOMO–LUMO gap, and average charge of SnnAun (n: 2–12) clusters were evaluated using density functional theory calculations. It was found that the SnnAun (n = 3, 8) clusters exhibited optimal performance in terms of chemical stability and charge transfer dynamics. Furthermore, the efficiency of CO and NO adsorption on the SnnAun (n = 3, 8) clusters was investigated in terms of the geometric, energetic, and electronic properties of the clusters. The results showed that CO and NO molecules chemisorb on the SnnAun (n = 3, 8) clusters, thereby allowing limited charge transfer, which significantly affects the physical properties and HOMO–LUMO gap of CO and NO molecules. These results suggest that the SnnAun (n = 3, 8) clusters can act as gas adsorbents for CO and NO molecules, and also can be used as effective sensors for NO detection.