Synthesis, characterization, and CO2 adsorption of three metal-organic frameworks (MOFs): MIL-53, MIL-96, and amino-MIL-53

Temperature-dependent molecular sieving of fluorinated propane/propylene mixtures by a flexible-robust metal-organic framework

The electronics industry necessitates highly selective adsorption separation of hexafluoropropylene (C3F6) from perfluoropropane (C3F8), which poses a challenge due to their similar physiochemical properties. In this work, we present a microporous flexible-robust metal-organic framework (Ca-tcpb) with thermoregulatory gate opening, a rare phenomenon that allows tunable sieving of C3F8/C3F6. Remarkably, the temperature-dependent adsorption behavior enhances the discrimination between the larger C3F8 and the smaller C3F6, resulting in unprecedented C3F6/C3F8 selectivity (over 10,000) compared to other well-known porous materials at an optimal temperature (298 K). Dynamic breakthrough experiments demonstrate that high-purity C3F8 (over 99.999%) could be obtained from a C3F6/C3F8 (10:90) mixture under ambient conditions. The unique attributes of this material encompass exceptional adsorption selectivity, remarkable structural stability, and outstanding separation performance, positioning it as a highly promising candidate for C3F6/C3F8 separation. Single-crystal structural analysis of C3F6-loaded Ca-tcpb and theoretical calculations elucidate the host-guest interaction via multiple intermolecular interactions.

Physiochemical characterization of metal organic framework materials: A mini review

Metal-organic frameworks (MOFs) are promising materials offering exceptional performance across a myriad of applications, attributable to their remarkable physicochemical properties such as regular porosity, crystalline structure, and tailored functional groups. Despite their potential, there is a lack of dedicated reviews that focus on key physicochemical characterizations of MOFs for the beginners and new researchers in the field. This review is written based on our expertise in the synthesis and characterization of MOFs, specifically to provide a right direction for the researcher who is a beginner in this area. In this way, experimental errors can be reduced, and wastage of time and chemicals can be avoided when new researchers conduct a study. In this article, this topic is critically analyzed, and findings and conclusions are presented. We reviewed three well-known XRD techniques, including PXRD, single crystal XRD, and SAXS, which were used for XRD analysis depending on the crystal size and the quality of crystal morphology. The TGA profile was an effective factor for evaluating the quality of the activation process and for ensuring the successful investigation for other characterizations. The BET and pore size were significantly affected by the activation process and selective benzene chain cross-linkers. FTIR is a prominent method that is used to investigate the functional groups on pore surfaces, and this method is successfully used to evaluate the activation process, characterize functionalized MOFs, and estimate their applications. The most significant methods of characterization include the X-ray diffraction, which is utilized for structural identification, and thermogravimetric analysis (TGA), which is used for exploring thermal decomposition. It is important to note that the thermal stability of MOFs is influenced by two main factors: the metal-ligand interaction and the type of functional groups attached to the organic ligand. The textural properties of the MOFs, on the other hand, can be scrutinized through nitrogen adsorption-desorption isotherms experiments at 77 K. However, for smaller pore size, the Argon adsorption-desorption isotherm at 87.3 K is preferred. Furthermore, the CO2 adsorption isotherm at 273 K can be used to measure ultra-micropore sizes and sizes lower than these, which cannot be measured by using the N2 adsorption-desorption isotherm at 77 K. The highest BET was observed in high-valence MOFs that are constructed based on the metal-oxo cluster, which has an excellent ability to control their textural properties. It was found that the synthesis procedure (including the choice of solvent, cross-linker, secondary metal, surface functional groups, and temperature), activation method, and pressure significantly impact the surface area of the MOF and, by extension, its structural integrity. Additionally, Fourier-transform infrared spectroscopy plays a crucial role in identifying active MOF functional groups. Understanding these physicochemical properties and utilizing relevant characterization techniques will enable more precise MOF selection for specific applications.

Ionic Liquids Hybridization for Carbon Dioxide Capture: A Review

CO2 absorption has been driven by the need for efficient and environmentally sustainable CO2 capture technologies. The development in the synthesis of ionic liquids (ILs) has attracted immense attention due to the possibility of obtaining compounds with designated properties. This allows ILs to be used in various applications including, but not limited to, biomass pretreatment, catalysis, additive in lubricants and dye-sensitive solar cell (DSSC). The utilization of ILs to capture carbon dioxide (CO2) is one of the most well-known processes in an effort to improve the quality of natural gas and to reduce the green gases emission. One of the key advantages of ILs relies on their low vapor pressure and high thermal stability properties. Unlike any other traditional solvents, ILs exhibit high solubility and selectivity towards CO2. Frequently studied ILs for CO2 absorption include imidazolium-based ILs such as [HMIM][Tf2N] and [BMIM][OAc], as well as ILs containing amine groups such as [Cho][Gly] and [C1ImPA][Gly]. Though ILs are being considered as alternative solvents for CO2 capture, their full potential is limited by their main drawback, namely, high viscosity. Therefore, the hybridization of ILs has been introduced as a means of optimizing the performance of ILs, given their promising potential in capturing CO2. The resulting hybrid materials are expected to exhibit various ranges of chemical and physical characteristics. This review presents the works on the hybridization of ILs with numerous materials including activated carbon (AC), cellulose, metal-organic framework (MOF) and commercial amines. The primary focus of this review is to present the latest innovative solutions aimed at tackling the challenges associated with IL viscosity and to explore the influences of ILs hybridization toward CO2 capture. In addition, the development and performance of ILs for CO2 capture were explored and discussed. Lastly, the challenges in ILs hybridization were also being addressed.

π-π stack driven competitive /complementary adsorption of aromatic compounds on MIL-53(Al)

In this study, the selective adsorption of aromatic compounds on mesoporous MIL-53(Al) was investigated, and followed the order: Biphenyl (Biph) > Triclosan (TCS) > Bisphenol A (BPA) > Pyrogallol (Pyro) > Catechol (Cate) > Phenol (Phen), and exhibited high selectivity toward TCS in binary compounds. In addition to hydrophobicity and hydrogen bonding, π-π interaction/stacking predominated, and more evidently with double benzene rings. TCS-containing halogens could increase π interaction on the benzene rings via forming Cl-π stacking with MIL-53(Al). Moreover, site energy distribution confirmed that complementary adsorption mainly occurred in the Phen/TCS system, as evidenced by ΔQ^pri (the decreased solid-phase TCS concentration of the primary adsorbate) < Q^sec (the solid-phase concentrations of the competitor (Phen)). In contrast, competitive sorption occurred in the BPA/TCS and Biph/TCS systems within 30 min due to ΔQ^pri = Q^sec, followed by substitution adsorption in the BPA/TCS system, but not for the Biph/TCS system, likely attributed to the magnitude of energy gaps (E_g) and bond energy of TCS (1.80 eV, 362 kJ/mol) fallen between BPA (1.74 eV, 332 kJ/mol) and Biph (1.99 eV, 518 kJ/mol) according to the density-functional theory of Gaussian models. Biph with a more stable electronic homeostasis than TCS lead to the occurrence of substitution adsorption in the TCS/BPA system, but not in the TCS/Biph system. This study provides insight into the mechanisms of different aromatic compounds on MIL-53(Al).

One-Pot Synthesis Method of MIL-96 Monolith and Its CO2 Adsorption Performance

A novel preparation method was proposed for a metal-organic framework (MOF) monolith using a simple one-pot synthesis method. A MOF tubular monolith was successfully prepared by the hydrothermal treatment for an α-Al₂O₃ monolith in an aqueous solution of 1,3,5-benzenetricarboxylic acid and nitric acid without the addition of a metal source. The effects of temperature and the HNO₃ concentration in the synthesis solution on the crystallization behavior of MIL-96 were studied. HNO₃ enhanced the dissolution of the α-Al₂O₃ monolith and the growth of MIL-96. The growth rate of MIL-96 was also influenced by the synthesis temperature; a synthesis temperature of over 453 K was required for crystallization. The CO₂ adsorption capacity of the prepared MIL-96 monoliths was evaluated and found to be comparable to that of the well-grown MIL-96 powdery crystal. Furthermore, the MIL-96 monoliths demonstrated good stability as their adsorption properties were retained even after 2 months of storage under atmospheric conditions.

A dual purpose aluminum-based metal organic framework for the removal of chloramphenicol from wastewater

The presence of antibiotics in the aquatic environment can cause significant environmental and human health problems even at trace concentrations. Conventional treatment systems alone are ineffective in removing these resistant antibiotics. To address this problem, oxidation and adsorption techniques were used to explore the removal of recalcitrant antibiotic chloramphenicol (CAP). An aluminum-based metal-organic framework (Al-MIL) with high surface area and extended porosity, was prepared and used both as adsorbent and catalyst for the oxidation of CAP. Characterization of the Al-MIL revealed a large surface area of 1137 m² g^-1, a homogeneous microporous structure, good crystallinity, and particle size in the range of 200-400 nm. Adsorption of CAP on Al-MIL achieved equilibrium after 1 h, reaching a maximum adsorption capacity of 96.1 mg g^-1 at the optimum pH value of 5.3. The combination of adsorption and oxidation did not improve the % TOC reduction considerably, indicating an antagonistic rather than synergistic effect between the two processes. Oxidation alone in the presence of persulfate, achieved a % TOC reduction of 71% after 2 h, compared to 56% achieved by adsorption alone at the same duration. The optimum persulfate concentration was determined as 2.5 mM. The Al-MIL structure did not demonstrate any substantial deterioriation after six repeated runs, according to the reusability experiments.

Combined and Single Doxorubicin/Naproxen Drug Loading and Dual-Responsive pH/Ultrasound Release from Flexible Metal-Organic Framework Nanocarriers

In this study, the flexible aluminum-based MIL-53(Al) metal-organic framework was loaded with doxorubicin (DOX) and naproxen (NAP) and was examined as a promising pH/ultrasound dual-responsive drug delivery system. The two drugs were encapsulated in MIL-53(Al) individually to produce the DOX@MIL-53(Al) and NAP@MIL-53(Al) nanocarriers. They were also encapsulated as a dual-drug formulation to produce the DOX* + NAP*@MIL-53(Al) nanocarrier. The MOF nanoparticles were characterized using the Scanning Electron Microscopy (SEM), X-ray diffraction (XRD), Fourier Transform Infrared spectroscopy (FTIR), and Dynamic Light Scattering (DLS) techniques. In the case of the DOX@MIL, the nanocarriers’ drug Encapsulation Efficiency (EE) and Encapsulation Capacity (EC) were 92% and 16 wt.%, respectively, whereas, in the case of NAP@MIL-53(Al), the average NAP EE and EC were around 97.7% and 8.5 wt.%, respectively. On the other hand, in the DOX* + NAP*@MIL-53(Al) nanoparticles, the average DOX* EE and EC were 38.9% and 6.22 wt.%, respectively, while for NAP*, the average EE and EC were 70.2% and 4.49 wt.%, respectively. In vitro release experiments demonstrated the good pH and Ultrasound (US) dual-responsiveness of these nanocarriers, with a maximum US-triggered DOX and NAP release, at a pH level of 7.4, of approximately 53% and 95%, respectively. In comparison, the measured release was around 90% and 36% at pH 5.3 for DOX and NAP, respectively. In the case of the dualdrug formulation, the nanocarrier displayed similar pH/US dual-responsive behavior. Finally, the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) results confirmed the biocompatibility and low cytotoxicity of MIL-53(Al) at concentrations up to 1000 μg/ml.

Scalable Formation of Diamine-Appended Metal-Organic Framework Hollow Fiber Sorbents for Postcombustion CO2 Capture

We describe a straightforward and scalable fabrication of diamine-appended metal-organic framework (MOF)/polymer composite hollow fiber sorbent modules for CO₂ capture from dilute streams, such as flue gas from natural gas combined cycle (NGCC) power plants. A specific Mg-MOF, Mg₂(dobpdc) (dobpdc^4- = 4,4'-dioxidobiphenyl-3,3'-dicarboxylate), incorporated into poly(ether sulfone) (PES) is directly spun through a conventional "dry-jet, wet-quench" method. After phase separation, a cyclic diamine 2-(aminomethyl)piperidine (2-ampd) is infused into the MOF within the polymer matrix during postspinning solvent exchange. The MOF hollow fibers from direct spinning contain as high as 70% MOF in the total fibers with 98% of the pure MOF uptake. The resulting fibers exhibit a step isotherm and a "shock-wave-shock" breakthrough profile consistent with pure 2-ampd-Mg₂(dobpdc). This work demonstrates a practical method for fabricating 2-ampd-Mg₂(dobpdc) fiber sorbents that display the MOF's high CO₂ adsorption capacity while lowering the pressure drop during operation.

The Diffusion Behavior of CO2 Adsorption from a CO2/N2 Gas Mixture on Zeolite 5A in a Fixed-Bed Column

The objective of this research was to investigate the behavior and conditions for CO2 adsorption using a mixture of CO2/N2 over a fixed-bed column of zeolite 5A. The study was performed with a variation in gas composition of CO2/N2 as a 20/80, 50/50, and 80/20 volume %, the adsorption temperatures as 298, 333, and 373 K and the total feed flow rates as 1, 2, and 4 L/h under 100 kPa pressure. The Bohart–Adams, Yoon–Nelson, and Thomas models were used to predict the breakthrough behavior of CO2 adsorption in a fixed column. Furthermore, the adsorption mechanism has been investigated using the kinetics adsorption of pseudo-first-order, pseudo-second-order, Boyd model, and intraparticle model. Increasing the CO2 composition of a gas mixture resulted in a high CO2 adsorption capacity because of the high partial pressure of CO2. The capacity of CO2 adsorption was decreased with increasing temperature because of physical adsorption with an exothermic reaction. The CO2 adsorption capacity was also decreased with increasing feed flow rates with inadequate time for CO2 adsorbates diffusion into the pores of the adsorbent before exiting the packed bed. The CO2 adsorption by zeolite 5A confirmed that the physical adsorption with intraparticle diffusion was the rate-controlling step of the whole process.

Comparative Study of Zn Loading on Advanced Functional Zeolite NaY from Bagasse Ash and Rice Husk Ash for Sustainable CO2 Adsorption with ANOVA and Factorial Design

The objectives of the research were to develop synthesis and estimation of each factor on carbon dioxide adsorption of advanced functional zeolite NaY material derived from bagasse ash and rice husk ash with different crystallization temperatures and weight percentages of zinc by the ion exchange method. The adsorbents were tested in a packed bed reactor at different temperatures and flow rates of carbon dioxide. The Minitab program was used to estimate the effects of each factor on carbon dioxide adsorption properties. The results showed that extracted silicon dioxide from bagasse ash and rice husk ash could be successfully used as raw material for zeolite NaY synthesis with a crystallization temperature of 298.15 K. The zeolite NaY crystalline structure was well-preserved after ion exchange. The highest capacity of carbon dioxide adsorption was at 10.33 mmol/g with zeolite 5B298-373-1. The results of the Minitab program showed that the carbon dioxide adsorption decreased with increasing crystallization temperature and carbon dioxide flow rate parameters. However, the increased weight percentage of zinc loading on zeolite NaY resulted in better carbon dioxide adsorption. The factors of the types of adsorbents and adsorption temperature showed interaction with each other.

Design of a metal-organic framework with flame-retardant performance and bionic hydrophobic surface inspired by lotus leaf

This research proposes a simple and feasible method to prepare hydrophobic structures and it is a fortuitous finding. In our previous publication, triethyl phosphate is adsorbed on porous metal-organic framework...

CO2 uptake prediction of metal–organic frameworks using quasi-SMILES and Monte Carlo optimization

The first report of quasi-SMILES-based QSPR models for CO2 capture of MOFs based on experimental data.

Applications of water-stable metal-organic frameworks in the removal of water pollutants: A review

Because the pollutants produced by human activities have destroyed the ecological balance of natural water environment, and caused severe impact on human life safety and environmental security. Hence the task of water environment restoration is imminent. Metal-organic frameworks (MOFs), structured from organic ligands and inorganic metal ions, are notable for their outstanding crystallinity, diverse structures, large surface areas, adsorption performance, and excellent component tunability. The water stability of MOFs is a key requisite for their possible actual applications in separation, catalysis, adsorption, and other water environment remediation areas because it is necessary to safeguard the integrity of the material structure during utilization. In this article, we comprehensively review state-of-the-art research progress on the promising potential of MOFs as excellent nanomaterials to remove contaminants from the water environment. Firstly, the fundamental characteristics and preparation methods of several typical water-stable MOFs include UiO, MIL, and ZIF are introduced. Then, the removal property and mechanism of heavy metal ions, radionuclide contaminants, drugs, and organic dyes by different MOFs were compared. Finally, the application prospect of MOFs in pollutant remediation prospected. In this review, the synthesis methods and application in water pollutant removal are explored, which provide ways toward the effective use of water-stable MOFs in materials design and environmental remediation.

Dissecting the effects of water guest adsorption and framework breathing on the AlO4(OH)2 centres of metal-organic framework MIL-53 (Al) by solid state NMR and structural analysis

The relationship between the adsorption of water on MIL-53 (Al) MOF, the structural phase of MIL-53 (Al), and the quadrupole coupling constant of ²⁷Al framework aluminium atom (QCC) of the MOF AlO₄(OH)₂ centres (Al-sites) has been investigated by combining solid-state ²⁷Al MAS NMR spectroscopy with XRD analysis and DFT calculations. It is established that ²⁷Al QCC is primarily sensitive to water adsorption to the Al-sites and by a minor extent to the framework contraction/expansion interconversions. We thus conclude that the ²⁷Al MAS NMR method is sensitive enough to differentiate the effects of pore contractions and water adsorption to Al-sites basing on the changes of the QCC value.

Solvent-Free and Phase-Selective Synthesis of Aluminum Trimesate Metal-Organic Frameworks

Aluminum-based metal-organic frameworks (Al-MOFs) have shown promise as commercially valuable materials due to the variety of applications, excellent thermal, hydrothermal, and chemical stabilities, and the abundance of aluminum. In this work, for the first time, we report the solvent-free synthesis of the aluminum trimesate (Al-BTC) MOFs (MIL-100(Al), MIL-96(Al), and MIL-110(Al)) with phase selectivity and high yield. These MOFs were traditionally prepared with HF, HNO₃, and bulk solvents, but these methods struggled to produce pure-phase isolations. The solvent-free strategy provides valuable insight into the future industrial scale-up production of the Al-MOFs and promotes the potential commercialization of such materials.

Synthesis, characterization, and CO2 adsorption properties of metal organic framework Fe-BDC

The iron-containing Metal-Organic Frameworks (MOFs) have attracted a great deal of attention in the areas of gas separation, catalytic conversion, and drug delivery, due to their high surface area and activity, as well as the non-toxicity of iron. In this study, Fe-based MOFs using BDC ligands, MIL-101(Fe), MIL-53(Fe) and Amino-MIL-101(Fe) are synthesized by a solvothermal method and characterized by conventional methods such as BET, SEM, and TGA. Afterwards, the synthesized MOFs are investigated from the point of view of the adsorbing capability of carbon dioxide at different pressures and temperatures, and also their resistance to water and solvent. The results showed that Amino-MIL-101(Fe) achieved more CO2 adsorption than MIL-101(Fe) and MIL-53(Fe), equal to 13 mmol g-1 at 4 MP. Although MIL-53(Fe) has the best temperature resistance, around 350 °C, Amino-MIL-101(Fe) is more stable against water and ethanol and its surface area is increased from 670 to 915 m2 g-1 after washing with ethanol. The adsorption study reveals that CO2 is adsorbed not only by a physical adsorption mechanism, but also by chemisorption of acidic carbon dioxide by basic NH2 agent in the structure of Amino-MIL-101(Fe).

Polymer-assisted modification of metal-organic framework MIL-96 (Al): influence of HPAM concentration on particle size, crystal morphology and removal of harmful environmental pollutant PFOA

A new synthesis method was developed to prepare an aluminum-based metal organic framework (MIL-96) with a larger particle size and different crystal habits. A low cost and water-soluble polymer, hydrolyzed polyacrylamide (HPAM), was added in varying quantities into the synthesis reaction to achieve >200% particle size enlargement with controlled crystal morphology. The modified adsorbent, MIL-96-RHPAM2, was systematically characterized by SEM, XRD, FTIR, BET and TGA-MS. Using activated carbon (AC) as a reference adsorbent, the effectiveness of MIL-96-RHPAM2 for perfluorooctanoic acid (PFOA) removal from water was examined. The study confirms stable morphology of hydrated MIL-96-RHPAM2 particles as well as a superior PFOA adsorption capacity (340 mg/g) despite its lower surface area, relative to standard MIL-96. MIL-96-RHPAM2 suffers from slow adsorption kinetics as the modification significantly blocks pore access. The strong adsorption of PFOA by MIL-96-RHPAM2 was associated with the formation of electrostatic bonds between the anionic carboxylate of PFOA and the amine functionality present in the HPAM backbone. Thus, the strongly held PFOA molecules in the pores of MIL-96-RHPAM2 were not easily desorbed even after eluted with a high ionic strength solvent (500 mM NaCl). Nevertheless, this simple HPAM addition strategy can still chart promising pathways to impart judicious control over adsorbent particle size and crystal shapes while the introduction of amine functionality onto the surface chemistry is simultaneously useful for enhanced PFOA removal from contaminated aqueous systems.

Metal-organic framework for the extraction and detection of pesticides from food commodities

Pesticide residues in food matrices, threatening the survival and development of humanity, is one of the critical challenges worldwide. Metal-organic frameworks (MOFs) possess excellent properties, which include excellent adsorption capacity, tailorable shape and size, hierarchical structure, numerous surface-active sites, high specific surface areas, high chemical stabilities, and ease of modification and functionalization. These promising properties render MOFs as advantageous porous materials for the extraction and detection of pesticides in food samples. This review is based on a brief introduction of MOFs and highlights recent advances in pesticide extraction and detection through MOFs. Furthermore, the challenges and prospects in this field are also described.

Towards complete elucidation of structural factors controlling thermal stability of IL/MOF composites: effects of ligand functionalization on MOFs

In this work, we incorporated an ionic liquid (IL), 1-n-butyl-3-methylimidazolium methyl sulfate ([BMIM][MeSO4]) into two different metal organic frameworks (MOFs), UiO-66, and its amino-functionalized counterpart, NH2-UiO-66, to investigate the effects of ligand-functionalization on the thermal stability limits of IL/MOF composites. The as-synthesized IL/MOF composites were characterized in detail by combining x-ray diffraction, scanning electron microscopy, Brunauer-Emmett-Teller analysis, x-ray fluorescence, infrared spectroscopies (FTIR), and their thermal stability limits were determined by thermogravimetric analysis (TGA). Characterization data confirmed the successful incorporation of the IL into each MOF and indicated the presence of direct interactions between them. A comparison of the interactions in [BMIM][MeSO4]-incorporated UiO-66 and NH2-UiO-66 with those in their 1-n-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6])-incorporated counterparts showed that the hydrophilic IL, [BMIM][MeSO4], interacts with the 1,4-benzenedicarboxylate (BDC) ligand of the UiO-66, while the hydrophobic IL, [BMIM][PF6], is interacting with the joints where zirconium metal cluster coordinates with BDC ligand. The TGA data demonstrated that the composite with the ligand-functionalized MOF, NH2-UiO-66, exhibited a lower percentage decrease in the maximum tolerable temperature compared to those of IL/UiO-66 composites. Moreover, it is discovered that when the IL is hydrophilic, its hydrogen bonding ability can be utilized to designate an interaction site on MOF's ligand structure, leads to a lower reduction in thermal stability limits. These results provide insights for the rational design of IL/MOF composites and contribute towards the complete elucidation of structural factors controlling the thermal stability.

Boosting CO2 adsorption and selectivity in metal–organic frameworks of MIL-96(Al) via second metal Ca coordination

Aluminum trimesate-based MOF (MIL-96-(Al)) has attracted intense attention due to its high chemical stability and strong CO₂ adsorption capacity. In this study, CO₂ capture and selectivity of MIL-96-Al was further improved by the coordination of the second metal Ca. To this end, a series of MIL-96(Al)–Ca were hydrothermally synthesised by a one-pot method, varying the molar ratio of Ca²⁺/Al³⁺. It is shown that the variation of Ca²⁺/Al³⁺ ratio results in significant changes in crystal shape and size. The shape varies from the hexagonal rods capped in the ends by a hexagonal pyramid in MIL-96(Al) without Ca to the thin hexagonal disks in MIL-96(Al)–Ca4 (the highest Ca content). Adsorption studies reveal that the CO₂ adsorption on MIL-96(Al)–Ca1 and MIL-96(Al)–Ca2 at pressures up to 950 kPa is vastly improved due to the enhanced pore volumes compared to MIL-96(Al). The CO₂ uptake on these materials measured in the above sequence is 10.22, 9.38 and 8.09 mmol g⁻¹, respectively. However, the CO₂ uptake reduces to 5.26 mmol g⁻¹ on MIL-96(Al)–Ca4. Compared with MIL-96(Al)–Ca1, the N₂ adsorption in MIL-96(Al)–Ca4 is significantly reduced by 90% at similar operational conditions. At 100 and 28.8 kPa, the selectivity of MIL-96(Al)–Ca4 to CO₂/N₂ reaches up to 67 and 841.42, respectively, which is equivalent to 5 and 26 times the selectivity of MIL-96(Al). The present findings highlight that MIL-96(Al) with second metal Ca coordination is a potential candidate as an alternative CO₂ adsorbent for practical applications.

MIL-96(Al)–Ca1 shows the highest CO₂ adsorption capacity; while MIL-96(Al)–Ca4 displays a distinguished morphology with the highest selectivity of CO₂/N₂.

Dynamics of isobutane is a sensitive probe for framework breathing in MIL-53 (Al) MOF

²H solid-state NMR shows that the dynamics of adsorbed isobutane is very sensitive to MIL-53 framework breathing detected by ²⁷Al MAS NMR.

Exfoliated Ni-Al LDH 2D nanosheets for intermediate temperature CO2 capture

CO₂ capture is projected as one of the pragmatic approaches to deal with the global warming phenomenon. Adsorption-based CO₂ capture is considered an economically attractive option to reduce CO₂ emission. The success of the adsorption-based capture primarily relies on adsorbents and thus a variety of adsorbents have been investigated in the literature. We here report a high surface area (210.2 m²/g) exfoliated Ni-Al LDH nanoplatelet as a promising candidate for CO₂ capture at an intermediate temperature of 200 °C applicable to integrated gasification combined cycle (IGCC) and sorption enhanced water gas shift (SEWGS) reactions. The materials were well characterized by PXRD, TGA, FTIR, TEM, ICP-OES, and N₂ adsorption surface area, and pore size distribution techniques. A unique nanoflower morphology comprising of exfoliated LDH platelets of ca. 5 layer thickness was obtained. The CO₂ capture capacity (0.66 mmol/g) of the exfoliated Ni-Al LDH nanoplatelet is comparable to that of the widely reported Mg-Al LDH-derived mixed oxides and MgO-based adsorbents. Provided that Ni-Al and other transition metal LDH materials are known to exhibit superior catalytic properties for CO₂ methanation, this work could pave the way for development of dual-functional materials for CO₂ capture and conversion.

Modification of multi-walled carbon nanotubes by 1,3-diaminopropane to increase CO2 adsorption capacity

Greenhouse gas emissions have increased dramatically over the past years and had a significant impact on global warming. This study investigates the modification of multi-walled carbon nanotubes (MWCNTs) with diamine precursor to improve the carbon dioxide adsorption capacity. To achieve this goal, pristine multi-walled CNTs were functionalized in a two-step process. In the first step, multi-walled carbon nanotubes were functionalized with a mixture of diluted sulfuric and nitric acid (5 M HNO₃/5 M H₂SO₄ with a volume ratio of 1:3) to sequestrate catalytic metal particles and oxidation of MWCNTs. In the second step, oxidized carbon nanotubes were functionalized with 1,3-diaminopropane (DAP) solution to improve the performance of multi-walled CNT in the carbon dioxide adsorption process. Specifications and characteristics of raw and modified carbon nanotubes were determined using FTIR, SEM, TGA, XRD, and N₂ adsorption-desorption isotherms at 77 K. The CO₂ adsorption capacity was measured at 303-323 K and pressures up to 17.3 bar using volumetric method. At 303 K and pressure of 17.3 bar, 92.71 mg g^-1 of CO₂ was adsorbed on MWCNT/DAP, while the CO₂ uptake of raw MWCNT in similar conditions was just 48.49 mg g^-1. The results revealed that amine groups attached to the carbonaceous surfaces during the functionalization process cause the formation of carbon dioxide-adsorption sites on multi-walled CNTs which increased the adsorption capacity of MWCNTs. Experimental data was modeled with Langmuir and Freundlich adsorption isotherms and concluded that the Freundlich model has more fitness with the experimental data.

Recent advances on porous organic frameworks for the adsorptive removal of hazardous materials

Environmental pollution is one of the most serious problems facing mankind today, and has attracted widespread attention worldwide. The burgeoning class of crystalline porous organic framework materials, metal-organic frameworks and covalent organic frameworks present promising application potential in areas related to pollution control due to their interesting surface properties. In this review, the literature of the past five years on the adsorptive removal of various hazardous materials, mainly including heavy metal ions, harmful gases, organic dyes, pharmaceutical and personal care products, and radionuclides from the environment by using COFs and MOFs, is summarized. The adsorption mechanisms are also discussed to help understand their adsorption performance and selectivity. Additionally, some insightful suggestions are given to enhance the performance of MOFs and COFs in the adsorptive removal of various hazardous materials.

A review on modified carbon materials as promising agents for hydrogen storage

Carbon materials have been regarded as promising agents for hydrogen storage because of properties such as their light weight, acceptable affinity of carbon for hydrogen and high specific surface area. We can identify many different carbon materials which have been studied extensively such as activated carbons (AC) graphene sheets (GS), carbon nanotubes (CNTs) and other derivative carbon materials derived from theoretical and experimental methods such as g-C3N4, graphyne and carbon nanolayer. These materials can be modified by additional ingredients like free metals, metal oxides, and alloys to improve their hydrogen storage capacity. In this short review article, we attempt to introduce new, reliable, complete and categorised data for researchers concentrating on articles from the last five years (2013-2017) relating to hydrogen storage.