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Harvesting water from the atmosphere is an important process to solve the extreme lack of water resources in arid regions. Adsorption-based atmospheric water harvesting (AWH) takes advantage of solar thermal energy to harvest water from air. This technique is particularly suitable for arid regions characterized by low humidity and an abundance of sunshine. Nonetheless, under low humidity conditions, AWH is highly dependent on water-adsorbing materials exhibiting excellent performance. In this work, a metal–organic framework (MOF), namely [Zn2(bpy) (btec)(H2O)2]·2H2O, also denoted as MWH-1, was investigated for application in water harvesting under low humidity conditions ( 200 cm3∙cm−3; RH = 10%, uptake: >250 cm3∙cm−3). This ensured effective water harvesting at high temperatures during the day. In situ powder X-ray diffraction and Fourier-transform infrared analyses confirmed the sensitive water adsorption process of MWH-1a. The X-ray single-crystal study further demonstrated that single-crystal structures could be completely restored following water harvesting. MWH-1 showed good structural stability and enabled water harvesting under low humidity and high temperature conditions. Thus, it has the potential for application in round-the-clock water harvesting in extremely arid regions.

Solid adsorbents that simultaneously have high selectivity and uptake capacity are highly promising as alternatives to conventional cryogenic distillation of propene/propane (C3H6/C3H8) separation. Coordinatively unsaturated metal sites (CUS) plays a vital role in selective adsorption of olefins over paraffins. Ultrathin poly (triazine imide) (PTI) nanosheets can reach rapid gas adsorption equilibrium, due to its large surface-to-volume ratio. In this work, combining the advantages of the CUS and the PTI nanosheets, Li CUSs were introduced into the PTI nanosheets for C3H6/C3H8 separation. Density functional theory (DFT) calculations demonstrated the thermodynamic feasibility of incorporating Li CUSs into the PTI nanosheets. These highly exposed Li CUSs were predicted to have a higher adsorption affinity toward C3H6 than C3H8. Using the DFT-derived force field parameters, we further performed grand canonical Monte Carlo (GCMC) simulations to investigate C3H6/C3H8 adsorption on the Li−PTI complexes slit pore model with different pore widths (H). We found that the Li−PTI complexes display considerable C3H6/C3H8 selectivity (4.2∼7.9) under relevant conditions. Moreover, the Li−PTI complexes slit pore have large C3H6 working capacities (1.5∼4.0 mmol g-1), superior to those calculated for the most of adsorbent materials that have been reported. The Li−PTI complexes with slit pore architecture show potential as C3H6/C3H8 separation materials.

In order to remove N2 from low quality natural gas, a mathematical model has been established by Aspen adsorption, using the CH4-selective sorbent silicalite-1 pellets. The dynamic adsorption isotherm was first simulated by breakthrough simulation of a CH4/N2 mixture at different adsorption pressures and feed flow rates based on breakthrough experiments. The resulting simulated CH4 dynamic adsorption amounts were very close to the experimental data at three different adsorption pressures (100, 200, and 300 kPa). Moreover, a single-bed, three-step pressure swing adsorption (PSA) experiment was performed, and the results were in good agreement with the simulated data, further corroborating the accuracy of the gas dynamic adsorption isotherm obtained by the simulation method. Finally, based on the simulated dynamic adsorption isotherm of CH4 and N2, a four-bed, eight-step PSA process has been designed, which enriched 75% (vol) CH4 and 80% (vol) CH4 to 95% (vol) and 99% (vol), and provided 99% (vol) recovery.

Direct separation of high purity ethylene (C2H4) from an ethane (C2H6)/ethylene mixture is a critical and challenging task owing to the very similar molecular size and physical properties of the two components. While some studies have attempted this separation, there is a lack of excellent porous materials with strong binding affinity for C2H6-selective adsorption via an energy-efficient adsorptive separation process. Herein, we report a titanium metal-organic framework with strong binding affinity and excellent stability for the highly efficient removal of C2H6 from C2H6/C2H4 mixtures. Single component adsorption isotherms demonstrated a larger amount of adsorbed ethane (1.16 mmol·g−1 under 1 kPa) and high C2H6/C2H4 selectivity (2.7) for equimolar C2H6/C2H4 mixtures, especially in the low-pressure range, which is further confirmed by the results of grand canonical Monte Carlo simulations for C2H6 adsorption in this framework. The experimental breakthrough curves showed that C2H4 with a high purity was collected directly from both 1:9 and 1:15 C2H6/C2H4 (volume ratio) mixtures at 298 K and 100 kPa. Moreover, the unchanged adsorption and separation performance after cycling experiments confirmed the promising applicability of this material in future.

The removal of trace propyne (C3H4) from propyne/propylene (C3H4/C3H6) mixtures is a technical and challenging task during the production of polymer-grade propylene in view of their very similar size and physical properties. While some progress has been made, it is still very challenging to use some highly stable and commercially available porous materials via an energy-efficient adsorptive separation process. Herein, we report the ultrafine tuning of the pore apertures in type-A zeolites for the highly efficient removal of trace amounts of C3H4 from C3H4/C3H6 mixtures. The resulting ion-exchanged zeolite 5A exhibits a large C3H4 adsorption capacity (2.3 mmol g−1 under 10−4 MPa) and high C3H4/C3H6 selectivity at room temperature, which were mainly attributed to the ultrafine-tuned pore size that selectively blocks C3H6 molecules, while maintaining the strong adsorption of C3H4 at low pressure region. High purity of C3H6 (>99.9999%) can be directly obtained on this material under ambient conditions, as demonstrated by the experimental breakthrough curves obtained for both 1/99 and 0.1/99.9 (V/V) C3H4/C3H6 mixtures.

The exploration of electrocatalysts with high oxygen evolution reaction (OER) activity is highly desirable and remains a significant challenge. Transition metal carbides (TMCs) have been investigated as remarkable hydrogen evolution reaction (HER) electrocatalysts but few used as oxygen evolution reaction (OER) electrocatalysts. Herein, a Co doped Ni3C/Ni uniformly dispersed in a graphitic carbon matrix was prepared by pyrolysis of a metal organic framework (Co/Ni-MOF) under a flow of Ar/H2 at 350 °C, and Ni3C/Ni@C was also prepared for comparison. The various characterization techniques confirmed the successful preparation of the heteroatom doped TMCs-based catalysts by pyrolysis of MOFs. Co doped Ni3C/Ni@C exhibited superior electrocatalytic properties for OER. For example, Co–Ni3C/Ni@C depicts a lower overpotential and smaller Tafel slope than Ni3C/Ni@C and IrO2 during the OER in 1 M KOH solution, additionally, it shows a higher active surface area than Ni3C/Ni@C. The outstanding electrocatalytic performance of Co-doped Ni3C/Ni@C in the OER was mainly ascribed to the synergistic effect of the Co and Ni3C/Ni active sites.

Samples of methane molecules grade diameter channel CHA-type molecular sieves (Chabazite-K, SAPO-34 and SSZ-13) were investigated using the adsorption separation of CH4/N2 mixtures. The isotherms recorded for CH4 and N2 follow a typical type-Ι behavior, which were fitted well with the Sips model (R2 > 0.999) and the selectivity was calculated using IAST theory. The results reveal that Chabazite-K has the highest selectivity (SCH4/N2 = 5.5). SSZ-13 has the largest capacity, which can adsorb up to a maximum of 30.957 cm3·g−1 (STP) of CH4, due to it having the largest pore volume and surface area, but the lowest selectivity (SCH4/N2 = 2.5). From the breakthrough test, we can conclude that SSZ-13 may be a suitable candidate for the recovery of CH4 from low concentration methane (CH4 50%) due to its higher selectivity.

Separating ethane (C2H6) from ethylene (C2H4) using ethane-selective adsorbents to replace energy-intensive cryogenic distillation technology is an important energy-saving method in the petrochemical industry to obtain high purity C2H4. Limited to the low separation efficiency in current commercial materials, it is very urgent and promising to fabricate such alkane selective adsorbents using cheap ligands and simple synthesis methods, which have characteristics such as stable structure, high C2H6 uptake, and adsorption selectivity. In this work, we have used one of the cheapest ligands (terephthalic acid, H2BDC) to prepare Cu(BDC)(DMF) via a simple and easy-to-scale up solvothermal method. The activated Cu(BDC) exposed diamond-shaped one-dimensional pores form a stronger affinity with C2H6 than C2H4 through the double function of C-H∙∙∙π interactions and C-H∙∙∙O hydrogen bonds. Benefiting from the difference in these interactions, Cu(BDC) exhibited a higher adsorption capacity of C2H6 (51.5 cm3/g) compared to C2H4 (45.1 cm3/g) at 1 bar and 298 K, which resulted in high adsorption selectivity (2.0) for the C2H6/C2H4 mixture (50/50, v/v). Breakthrough experiments indicated that Cu(BDC) successfully achieved the removal of C2H6 from C2H6/C2H4 (50/50 and 10/90, v/v) mixtures to obtain high purity C2H4 (> 99.99%) using a one-step separation process. When compared with the benchmark materials, Fe2(O2)(dobdc) and NIIC-20, Cu(BDC) had the advantages of much lower preparation cost and enhanced structural stability. These comprehensive properties indicated that Cu(BDC) with a commercially viable price and synthesis process, could be potentially used for the C2H6 removal step during the production of high purity C2H4.

It is notably challenging to fabricate controllable heteroatom-doped porous carbons for both highly effective mixed-gas separation and supercapacitor electrodes. In this work, novel algae-derived nitrogen-containing porous carbons were prepared as bifunctional materials. The pore structure of obtained carbons could be easily tailored by altering activation temperature or porogen/biomass ratio. The as-prepared porous carbon has a very high specific surface area of 1538.7 m2 g−1 and a large pore volume of 0.99 cm3 g−1 with a high N content of 2.77 wt%. As a solid-state adsorbent, the algae-derived carbon has an excellent CO2 adsorption capacity of 5.7 and 3.9 mmol g−1 at 273 and 298 K, respectively. The extraordinarily high CO2/N2, CO2/CH4, and CH4/N2 selectivity are demonstrated by the ideal adsorption solution theory (IAST) calculation and dynamic adsorption breakthrough experiments. As an electroactive material, the porous carbon exhibits outstanding capacitive performance in 6 M KOH aqueous electrolyte, with the specific capacitance of 287.7 and 190.0 F g−1 at 0.2 A g−1 in a three- and two-electrode system, respectively. Furthermore, the obtained carbon shows outstanding rate capability of 79.3% at 10 A g−1 and unprecedented cycling stability with 98% capacitance retention at 10 A g−1 after 8000 cycles as coin cell. This report introduces a biomass-derived and low-cost pathway to design porous carbon materials for efficient solid adsorbents and supercapacitive electrode materials.

Two types of ultra-high silica silicalite-1 (2000–4400 SiO2/Al2O3) were prepared using a seed crystal synthesis method; silicalite-1-M, which is microporous (0.5 nm) and silicalite-1-H, which is hierarchical porous (0.5 nm and 10–15 nm). From the experimental results, silicalite-1-H/M have almost the same adsorption isotherms for CO2, CH4, C2H6 and N2, surface area and equilibrium adsorption selectivity, however, silicalite-1-H has a shorter adsorption equilibrium time when compared with silicalite-1-M at a given pressure, which shows a mass transfer enhancement phenomenon due to its mesoporous structure. A mixed gas breakthrough test and simulation was carried out to verify the mass transfer upgrade theory to determine whether the material could be applied for adsorption separation. Interestingly, their performances on the breakthrough experiment were different; silicalite-1-H has a shorter breakthrough time for CO2, CH4, C2H6 and N2 when compared with silicalite-1-M. All the experiment data are consistent with the simulation results. A variety of flow rates were used to investigate and compare the breakthrough time and hold time, and the separation efficiency of CO2/CH4, CH4/N2 and CH4/C2H6 was improved based on the use of the hierarchical porous sorbent over a certain flow rate range.

Metal-organic frameworks (MOFs) have been rapidly developed in the fields of gas adsorption and storage, but are unsatisfactory in NH 3 adsorption due to their unstable structures. Considering NH 3 is both a toxic gas and the only carbon-free chemical energy carrier, MOFs exhibit great prospects for the adsorption and storage of NH 3 due to their advantages of structural diversity, modifiable structures and high surface area. In this work, we have researched, in detail, the structural characteristics, stability and NH 3 adsorption properties of MIL-53, NH 2 -MIL-53, MIL-100 and MIL-101. In addition, the NH 3 adsorption sites have been investigated using Grand canonical Monte Carlo simulations. The results showed that MIL-100 and MIL-101 have a large NH 3 uptake of 8 mmol/g and 10 mmol/g, respectively, and that the modified amino functional groups improve the NH 3 adsorption capacity in NH 2 -MIL-53. More importantly, the four MIL materials have reusable NH 3 uptake and excellent NH 3 (and NH 3 /H 2 O) stability, and are promising materials for NH 3 adsorption.

MIL-100(Cr), as a typical metal organic framework (MOF) possesses a great potential application for N2 removal from CH4 by physical adsorption, but the commonly used preparation process at present is time-consuming (96 h) and environmentally unfriendly (HF-needed). We developed a novel synthesis method which is able to prepare MIL-100(Cr) via steam-assisted conversion and avoids the usage of HF with a curtate reaction time (9 h) and excellent yield (96%), a higher selectivity of N2 from CH4. Obviously, this method is advantageous and suitable for green large-scale production of MIL-100 (Cr).

Natural gas purification by economic and low-energy adsorptive separation processes is important. However, as a difficult global problem, N2 removal from N2/CH4 mixtures is challenging because of their similar physical properties. In this study, the separation of N2/CH4 by Cr-metal–organic frameworks (MOFs) (MIL-100Cr, MIL-101Cr and TYUT-96Cr) with various open Cr site densities was studied. Gas sorption isotherms showed that TYUT-96Cr exhibited the highest N2/CH4 uptake ratio (13.67 at 0.01 bar and 298 K) of the selected Cr-MOFs, which was consistent with the highest density of Cr (III) sites. This material provided the highest CH4 productivity (0.716 mmol/cm3) per cycle for N2 removal from a 5:95 N2/CH4 mixture to produce 99.99% pure CH4, as shown by the breakthrough experiments. Pressure-swing adsorption simulations indicated that, by a two-bed six-step method, pristine 95% methane was enriched to 98.9% by TYUT-96Cr. The largest CH4 productivity, high breakthrough selectivity and thermal stability of TYUT-96Cr among the Cr-MOFs, made it a promising adsorbent in trace N2 removal for practical industrial application.

The Si/Al ratio in zeolite will be altered and the porous structure will be diluted by the traditional silica/aluminum-based binder in the granulation process. Here, a novel zeolite/activated carbon monolith (Z/AC) was prepared by adding coal-tar pitch in silicalite-1 (Si/Al greater than 400), where the pure silica characteristic is well maintained and the coal-tar pitch transforms to porous carbon with a uniform pore structure, in comparison, the aluminum-based bonded silicalite-1 pellet (ABSP) shows a much lower Si/Al ratio of 4.1. As a result, the Z/AC-600 monolith demonstrates a competitive CH4 adsorption capacity of 23.45 cm3/g, outperforming silicalite-1 powder and ABSP pellet, and the CH4/N2 selectivity is higher than 4.0 at 298 K and 1 bar. The gas-mixture breakthrough experiments demonstrated that Z/AC-600 can effectively separate the CH4/N2 mixtures (20/80 and 50/50; v/v) with dynamic selectivity of 4.2 and 3.9, respectively. Pressure swing adsorption (PSA) simulations further indicate that, by one step enrichment, pristine 50% methane can be enriched to 80% with a recovery of 85%.

The slight differences between ternary components of C2 hydrocarbons make the separation of C2H2/C2H6/C2H4 mixtures one of the most challenging tasks in the petrochemical industry. In this study, a family of saturated coordination titanium-based metal–organic frameworks with high stability is constructed for one-step C2H4 purification. Single component adsorption measurements along with dynamic breakthrough experiments illustrated that these MOFs clearly exhibited large adsorption for C2H2 and C2H6 compared to C2H4, and could efficiently extract low concentrations of C2H6 and C2H2 from ternary C2H2/C2H6/C2H4 mixtures simultaneously. Grand canonical Monte Carlo simulations revealed the stronger affinity of the MOFs toward C2H6 and C2H2 compared to C2H4. Furthermore, the mostly intact structure of these MOFs after various examinations revealed their distinctive stability. The reasonably high C2H6 and C2H2 adsorption capacity, ultrahigh structural stability, and excellent separation performance rendered these materials good candidates for C2H4 purification from C2H2/C2H6/C2H4 mixtures in industry.

Synthesis of ultra-high silica (SiO 2 /Al 2 O 3 > 1800) MFI type zeolite such as silicalite-1 is still considered to be luxury because of the long synthesis time (5–12 days). Here, this material with a highly uniform mesoporous (20 nm) structure was crystallized in a shorter time (20 h) using a crystal-seeds method when an appropriate amount of potassium fluoride was added. Characterization techniques including XRD, SEM, TEM and liquid nitrogen adsorption provided detailed information on the two kinds of porous structure silicalite-1. Due to the “smooth” adsorption surface of silicalite-1 containing few equilibrium ions, it is ideal for the separation of gas mixtures containing non-polar molecules with similar physical properties. Moreover, the CH 4 , N 2 , CO 2 and C 2 H 6 adsorption properties were also investigated. Microporous silicalite-1 has a high adsorption capacity for CH 4 , N 2 , CO 2 and C 2 H 6 and adsorption selectivity for CH 4 /N 2 , CO 2 /N 2 , CO 2 /CH 4 and C 2 H 6 /CH 4 . Although a lower adsorption capacity was observed for mesoporous silicalite-1, the pore size did not affect the outstanding adsorption selectivity, on the contrary, the selectivity of mesoporous silicalite-1 was improved.

Solvent-evaporated conversion (SEC) and steam-assisted conversion (SAC) have been developed to prepare the typical metal-organic frameworks (MOFs) Cu-BTC (HKUST-1) and ZIF-8 using a unique solvent recovery strategy using zeolite. As a green circulation medium, zeolite Na-4A loading and removal of solvent (H2O and EtOH) can transport solvent in the vapor phase and avoid solvent condensation, which was the defect in previous SAC syntheses of MOFs, and achieves efficient solvent recovery as well as being an economical and green synthetic process. Moreover, SEC and SAC processes exhibited different mechanisms during the multi-stage reaction and solid diffusion reaction, respectively and both can synthesize the desired products in 12 h. These two methods for MOFs preparation were characterized in detail using XRD, SEM and N2 adsorption during the different growing stages. According to polar molecules (H2O and EtOH) steam-assisted in those synthesis, polar destruction molecules (H2O, NH3) adsorption and stability of Cu-BTC and ZIF-8 was investigated.

The development of ethane (C2H6)-selective adsorbents displaying high uptake and selectivity to purify ethylene (C2H4) to obtain polymer-grade raw materials is a meaningful, but challenging process. Tailoring the pore chemistry of a metal-organic framework is an effective strategy used to construct high performance adsorbents. Herein, BUT-10 with a tailored pore environment for tuning the C2H6 adsorption ability has been synthesized via introducing functional sites into UiO-67. The single component gas adsorption capacity, adsorption heat and adsorption selectivity of BUT-10 have been proven to be effectively increased after modifying the pore environment. Computational studies have revealed that the stronger adsorption affinity for C2H6 was achieved via multiple adsorbate-framework interactions in the appropriate pore environment. Breakthrough experiments using BUT-10 as a C2H6-selective adsorbent have shown that polymer grade C2H4 was directly produced from C2H6/C2H4 (1/15 v/v) mixtures using a single separation process under ambient conditions.

The potential of metal–organic frameworks (MOFs) for application in gas separation processes has been widely recognized. Nonetheless, due to their structural instability and high cost, few MOFs have been utilized in the industry. Among them, UiO-66 is one of the most promising materials which displays good structural stability and its preparation is considered economical. Notably, it also provides a valuable platform for the construction of other robust MOFs for various applications. Herein, trifluoromethyl ligands were introduced into the UiO-66 framework to optimize pore environment also to improve its C2H2 recognition ability. Single component adsorption and the corresponding IAST calculation confirmed that compared to UiO-66, UiO-66-(CF3)2 exhibited 2 ~ 3 times higher selectivity for C2H2/C2H4 and C2H2/CO2 separation. Enhanced selectivity resulted in a significantly improved C2H4 separation productivity (56 compared to 36 cm3/cm3) and a reduction in the co-adsorption time. Importantly, the modified UiO-66 framework could be prepared using a simple method and inherited a highly stable structure and good cycling performance of the original material.

Ligand protected noble metal nanoclusters have unique physical and chemical properties and the effects of metal nanoclusters on photoluminescence and energy transfer process for fluorescence molecules are still unclear. In this work, we prepared silver nanoclusters (Ag NCs) with different emission wavelengths (blue, green and red emission) and investigated the energy transfer process between Ag NCs and fluorescein isothiocyanate (FITC). The photoluminescence of FITC can be regulated by the Ag NCs due to various electrons transfer and energy transfer processes between Ag NCs and FITC. The FITC can serve as electrons donor or acceptor which determines the electrons transfer direction between FITC and Ag NCs with different emissions. Astonishingly, the photobleaching of FITC can be effectively inhibited after interacting with Ag NCs, which will surely be of profound significance to the application of FITC.

The performance of a zeolite is often related to its crystal morphology. In this work, the relationship between the crystal morphology of zeolite L and its gas separation performance was evaluated. Cylindrical-L (C-L: 3 × 2 μm), disk-shaped-L (D-L: 0.2 × 1.2 μm), and nanosized-L (N-L: 40 × 25 nm) were synthesized. Various characterization methods, including X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), and N2 adsorption–desorption isotherms at 77 K (BET), were employed to obtain complementary information. Due to its small crystal size, the BET specific surface area (427.2 m2/g) and total pore volume (0.382 cm3/g) of N-L are significantly higher than those of D-L (339.6 m2/g and 0.116 cm3/g) and C-L (279.8 m2/g and 0.098 cm3/g). The CO2 adsorption capacity on N-L (70.7 cm3/g) increases 20.9% than that on C-L (58.5 cm3/g). The shorter channel paths in N-L permit faster diffusion and mass transfer than in C-L or D-L, as confirmed by kinetic experiments. Furthermore, breakthrough experiments indicate that N-L has great application potential for separating and capturing CO2 from power-plant flue gas, biogas, or landfill gas.

Down-sizing zeolite crystals to achieve enhanced gas adsorption and separation performances is largely unexplored and underestimated. Nano-sized zeolite can expose more adsorption sites and shorten the diffusion path compared to micro-sized counterparts; however, the synthesis of Nano-sized zeolite is still very challenging. Herein, nano-sized ZK-5 is successfully prepared for the first time via the regulation effects of β-cyclodextrin. The crystal size of ZK-5 can be reduced from micron-size (3 μm) to nano-size (50–100 nm), thus the nano-ZK-5 exhibits a superior surface area (370 cm2 g−1) and pore volume (0.22 cm3 g−1) than the micron-sized sample (149 cm2 g−1 and 0.07 cm3 g−1), which may be due to the reduction in crystal size, which in turn leads to more micropores being detected. The CH4 adsorption capacity on nano-sized sample increased by 64% compared to that of micron-sized ZK-5. Notably, the record-high CH4 adsorption capacity of 1.34 mmol g−1 at 298 K is obtained on the nano-ZK-5 among the commercial zeolites. The equilibrium adsorption selectivity of CH4/N2 (20/80, v/v) mixed gas is as high as 4.2 (IAST method) at 1 bar and 298 K. The adsorption kinetics experiments have illustrated the boosted gas diffusion and mass transfer rate. Furthermore, the breakthrough experiments have confirmed the practical feasibility of separating various gas-mixtures, such as CH4/N2 (20/80, v/v).

Ethylene and acetylene are both important starting materials for the production of polyethylene, vinyl chloride, but-2-yne-1,4-diol, etc. To remove trace acetylene effectively from ethylene and the separation of acetylene from carbon dioxide are particularly challenging in the petrochemical industry. Although catalytic hydrogenation or cryogenic distillation for the separation of such light hydrocarbons is a very mature operation in the current petrochemical industry, it still requires huge capital and energy consumptions. Herein, a metal-organic framework (MOF), [Ni2(BTEC)(bipy)3] (H4BTEC = 1,2,4,5-benzene tetracarboxylic acid, bipy = 4,4′-bipyridine), has been developed for efficient adsorptive separation of C2H2 from C2H2/C2H4 or C2H2/CO2 mixtures. Ni2(BTEC)(bipy)3 exhibited extraordinary two-step adsorption for C2H2 with the adsorption capacity of 76.8 cm3/g at 298 K and 1 bar, significantly discriminating from C2H4 (7.9 cm3/g) and CO2 (13.0 cm3/g) in the same condition. The huge adsorption difference of Ni2(BTEC)(bipy)3 between C2H2 and C2H4/CO2 resulted in the record high uptake ratio for C2H2/C2H4 (9.7), C2H2/CO2 (5.9) and very high ideal adsorption solution selectivity (104, 33.5) in robust MOFs at 298 K and 1 atm. The excellent separation performance was verified by breakthrough experiments; this material could effectively separate C2H2/C2H4 or C2H2/CO2 mixtures directly to obtain high purity of C2H4 (>99.999%) and CO2 (>99.99%) in one separation cycle. Furthermore, this material could be easily scaled up to be synthesized at room temperature under mild conditions, indicating the great potential in actual industrial applications.

Two isomeric metal–organic frameworks (MOFs) with 2-dimensional (2D) and 3-dimensional (3D) topologies both comprised of Cu(II) and OTf (OTf = trifluoromethanesulfonate) ions were synthesized and characterized. The CO2, CH4 and N2 adsorption properties of the two isomeric MOFs were investigated from 263 K to 298 K at 0.1 MPa. The results showed that the 2D MOF exhibited a higher selectivity for CO2 from CO2/CH4 and CH4 from CH4/N2 compared to the 3D MOF, even though it possessed a lower surface area and pore volume. The higher adsorption heats of gases on the 2D MOF inferred the strong adsorption potential energy in the layered MOFs. Dynamic separation experiments using CO2/CH4 and CH4/N2 mixtures on the two MOFs proved that the 2D MOF had a longer elution time than the 3D MOF as well as better separation abilities.

With the conflicting problems of pollution due to ammonia emissions and the demand for ammonia, we propose M-2(INA) (M=Cu, Co, Ni, Cd) (INA=isonicotinic acid), a series of materials that exhibit flexible conversion in ammonia adsorption. They can capture both wet and dry ammonia for recycling. The materials were obtained by dehydration of coordination materials M(INA)2(H2O)4 (M=Cu, Co, Ni, Cd) (150°C) at atmospheric pressure for 2h. M-2(INA) could reversibly transform to the stable coordination compounds M(INA)2(H2O)2(NH3)2 by adsorbing ammonia in the presence of moisture. The capacity for pure ammonia could reach 12-13mmol/g. Importantly, these materials could stably retain NH3 at a maximum temperature of 80°C and could regenerate below 150°C with no performance loss.

The separation of propane (C3H8) from propylene (C3H6) to obtain high purity C3H6 as a petrochemical raw material is an important, but challenging process. In the traditional industrial process, the separation mainly relies on energy-intensive cryogenic distillation. One alternative process that is currently becoming more attractive in the separation of C3H6 is adsorptive separation technology. Using porous materials, especially C3H8 selective adsorbents, high purity C3H6 can be directly obtained and thus, significantly simplifies the process. Herein, a series of functionalized ligands were introduced into UiO-type materials to finely regulate the C3H8 separation performance. Single-component adsorption isotherms reveal that BUT-10 has a distinct binding affinity for C3H8 over C3H6 over a wide range of temperature from 298 to 338 K and thus, achieved by far the highest C3H8 capture capacity (105 cm3 g−1 at 0.1 bar and 298 K) reported among the C3H8-selective materials reported to date. A combination of Grand Canonical Monte Carlo and density-function theory simulations demonstrate that the favorable pore environment provided by the multiple host-guest interactions toward C3H8 result in the higher C3H8 binding affinity observed in the separation process. Breakthrough experiments indicate that BUT-10 can selectively separate C3H8 from C3H8/C3H6 (1/1 and 1/15, v/v) mixtures and thus, directly produces high purity C3H6 (>99.99%) under ambient conditions.

N2O and CO2 are two linear molecules, which have almost the same molecular size and similar physical properties (polarizability and quadrupole moment). Therefore, the separation of CO2 and N2O is extremely challenging. Flexible metal organic frameworks exhibit a gate-opening phenomenon for one type of gas molecule, but not for another, thus enabling excellent selectivity for twin-like molecules. In this study, the separation of CO2/N2O by flexible metal organic frameworks with different structures was studied systematically using a combination of adsorption and breakthrough tests. The results show that the gate-opening pressure of CO2 is lower than that of N2O on Cu(bpy)2(BF4)2 (ELM-11) and Cu(bpy)2(OTf)2 (ELM-12), which are two-dimensional layered flexible MOFs, whereas N2O has a lower gate-opening pressure than CO2 on MIL-53Al, a three-dimensional breathing structure with an adsorption capacity of up to 8 mmol/g was observed at 298 K and ~5 bar, indicating its good separation properties for N2O from CO2 under high pressure. Breakthrough experiments for N2O/CO2 mixtures confirmed that MIL-53Al is capable of separating N2O and CO2 under the optimized conditions (8 bar), making it a promising material for industrial application.

In this work, we have studied high-silica (Si/Al = 200) zeolite silicalite-1 pellets sorbent for the separation of methane and nitrogen in a pressure swing adsorption (PSA) process. The pellet samples have well maintained similar adsorption and separation performances of the zeolite powder samples. The adsorption kinetic parameters were determined by actual breakthrough experiments on the pellet samples. The effects of feed flow and cycle time on methane product purity and recovery have been investigated. The accuracy of the numerical simulation method has been verified by the experiment data. In order to optimize the coalbed methane enrichment performance, the two-bed six-step PSA cycle was applied in the simulation. The simulation results revealed that 45% and 57% methane concentration could be achieved from 20% and 30% methane feedings with a recovery above 80%.

The separation of low concentration ethane (C2H6) from ethylene (C2H4) is of great importance in petrochemical processes; however, it is widely considered to be a challenging task. Nonetheless, utilizing suitable C2H6 selective adsorbents, adsorptive separation technology approaches can be employed to obtain high purity ethylene with high energy efficiency. Herein, we report a series of MOF materials, namely M-PNMI (M = Mn, Zn, Cd), which were synthesized using N,N′-di(4-pyridyl)-1,4,5,8-naphthalenetetracarboxdiimide. Cooperative single component adsorption analysis, as well as Ideal Adsorbed Solution Theory (IAST) calculation, and Grand Canonical Monte Carlo (GCMC) simulation revealed that these MOF materials exhibit distinctly higher adsorption capacity and preferential binding affinity for C2H6 over C2H4. These observations are due to the presence of favorable pore environments in the MOFs, which result in strong C2H6 adsorption potential. The specific C2H6 binding sites were clearly determined by density functional theory (DFT) calculations. Thus, the described M-PNMI materials can efficiently remove C2H6 from C2H6/C2H4 (1/9 and 1/15, v/v) mixtures to directly produce high purity C2H4 (>99.99%) under ambient conditions.

Small-pore zeolites have been a research hotspot in the field of gas adsorption and separation. Despite the high adsorption levels of these zeolites, the slow adsorption and desorption rate as well as desorption hysteresis are detrimental to the industrial applications. In this work, nano/micro-scale (~500 nm) K-KFI zeolite crystals were synthesized via hydrothermal and ultrasound-assisted (US) methods. The US-K-KFI zeolites obtained were characterized by means of X-ray diffraction, scanning electron microscopy, and nitrogen adsorption-desorption isotherms at 77 K. The effect of the ultrasonic treatment time on zeolite formation was investigated. The results revealed that the ultrasonic time had a significant effect on the morphology of the K-KFI zeolite, and the particle size was reduced from 1.5 μm to 500 nm. Furthermore, the sample ultrasonically treated for 3 h and crystallized for 1 day (US-K-KFI-3h/1d) exhibited the same high level of crystallinity as the sample hydrothermally crystallized for 3 days without ultrasonic treatment (HT-K-KFI-0h/3d). Compared with large-crystal (3 μm) zeolite (HT-K-KFI-0h/3d) at a given pressure, nano/micro-scale (500 nm) zeolite (US-K-KFI-10h/1d) was characterized by a shorter adsorption equilibrium time and exhibited enhanced mass transfer due to its shorter diffusion path. Moreover, compared with that of HT-K-KFI-0h/3d, the adsorption capacity of US-K-KFI-10h/1d for CO2, CH4, N2, and O2 was 31%, 24%, 18%, and 26% higher, respectively, at room temperature (298 K) and 1 bar. The results of this work showed that the ultrasound-assisted method represents a rapid and controllable means of synthesizing nano/micro-scale zeolites.

To date, separating CO2 and N2O mixtures is still a great challenge due to their identical molecular masses and sizes. It is noteworthy that CO2 is acid gas, while N2O is not, we infered that they can be separated through acid-base coordination. Herein, we report the use of an ethylenediamine–functionalized metal organic framework ED-MIL-100Cr-0.2/0.4/0.6 towards the construction of a new alkaline adsorption site for the CO2 binding. The experimental results show that ED-MIL-100Cr-0.4 with the highest adsorption heat of CO2 up to ~80 KJ/mol and N2O being 25 KJ/mol, and it has the highest equilibrium adsorption selectivity (28.0, IAST method) of CO2 v N2O reported to date. It was also confirmed that ED-MIL-100Cr-0.4 had the best performance in the separation of CO2 and N2O mixtures by the breakthrough test. Finally, the cycling experiments revealed its good renderability, making its potentially useful in industrial CO2/N2O separation.

Metal-organic frameworks with open metal site are potential sorbents for the separation of gas mixtures; however, low valence metal will bind to oxygen in the open air causing a decrease in adsorption ability. We now report open-metal sites V(III) on both MIL-100V(III/IV) and MIL-101V(III/IV) that can be protected with water molecules, and which associated CO2/CH4/N2/O2 adsorption properties on these two mesoporous V-MOFs were investigated. The protective properties of water were investigated and evaluated using density functional theory simulations. The binding energy of single O2 on open-metal V(III) site was 93.278 kJ/mol, which decreased to 26.5 kJ/mol when H2O occupies the site. When the water coating is removed, the X-ray photoelectron spectroscopy pattern of V2p showed that the V-MOF changes to MIL-100V(IV) and MIL-101V(IV) at 298 K because of the action of O2. Under these conditions, O2 binds strongly on the open V site significantly reducing the BET (Brunauer-Emmett-Teller) surface and CH4 adsorption volume of the V-MOFs. From the ideal adsorbed solution theory calculated, the adsorption selectivity of CH4/N2 is higher before than after binding of O2 (with V(III) site). In contrast, the adsorption selectivity of CO2/CH4 is higher after than before O2 binding (with no more V(III) sites).

Three metal–organic frameworks (MOFs), [Cu(INA) 2 ], [Cu(INA) 2 I 2 ] and [Cu(INA) 2 (H 2 O) 2 (NH 3 ) 2 ], were synthesized with 3D, 2D, and 0D structures, respectively. Reversible flexible structural changes of these MOFs were reported. Through high temperature (60–100 °C) stimulation of I 2 or ambient temperature stimulation of NH 3 , [Cu(INA) 2 ] (3D) converted to [Cu(INA) 2 I 2 ] (2D) and [Cu(INA) 2 (H 2 O) 2 (NH 3 ) 2 ] (0D); as the temperature increased to 150 °C, the MOFs changed back to their original form. In this way, this 3D MOF has potential application in the capture of I 2 and NH 3 from polluted water and air. XRD, TGA, SEM, NH 3 -TPD, and the measurement of gas adsorption were used to describe the changes in processes regarding the structure, morphology, and properties.

Methane enrichment from nitrogen is a necessary means for low-quality unconventional natural gas (coal mine methane) extraction, where adsorption-separation technology has become a research hotspot due to its low energy consumption and cost-effectiveness. In this work, three SOD-type ZIFs (ZIF-8, ZIF-90 and SIM-1, the latter also known as ZIF-94) are taken as methane sorbents for CH4/N2 separation. The experimental results show that SIM-1 (ZIF-94) has the highest CH4 adsorption capacity (1.5 mmol/g, 298 K and 1 bar) and adsorption heat (23.9 kJ/mol), although its surface area is the lowest (597 m2/g). No other known ZIF material has a higher CH4 adsorption capacity than SIM-1(ZIF-94), although some rare MOF and other porous materials can achieve such a high value. By comparing its CH4 adsorption capacity and BET surface with ZIF-93 (RHO type), which has the same units as Zn-almeIm, SIM-1(ZIF-94) has a high adsorption capacity of CH4 due to its suitable SOD cage size (0.84 nm) acting as a strong adsorption potential. Indeed, excellent enrichment–separation of the CH4/N2 mixture (30:70 and 50:50, v/v) with a high adsorption selectivity of 7.0 (IAST) rarely occurs for sorbents at room temperature and ambient pressure. Both the experimental and simulated data of the gas mixtures indicate that SIM-1 (ZIF-94) has excellent capability for enriching and removing nitrogen from methane, and it shows extraordinary industrial value.

In this report we studied the gas adsorption and breakthrough characteristics of M/DOBDC (M = Mg, Co, or Ni) metal–organic frameworks, with honeycomb-like structures and high concentrations of coordinatively unsaturated sites. We studied these characteristics by using M/DOBDC to separate CO2/CH4 and CH4/N2 mixtures and compared those results to separation using MIL-100(Cr) and activated carbon, particularly focusing on the adsorption capacities and equilibrium times. We show that the presence of coordinatively unsaturated sites greatly influences gas adsorption, separation, and regeneration. Mg/DOBDC displayed excellent separation efficiency for CO2/CH4 and simple regeneration under dynamic conditions, while Ni/DOBDC had superior CH4/N2 adsorption selectivity and CH4/N2 separation and exhibited strong interactions between CH4 molecules and its coordinatively unsaturated Ni atoms. Overall, the M/DOBDC frameworks demonstrated extremely high capacity, high selectivity, and easy regeneration for CO2 and CH4 separation under dynamic conditions, making them suitable for gas separation.

In this paper we used MOF-5 and Cu3(BTC)2 to separate CO2/CH4 and CH4/N2 mixtures under dynamic conditions. Both materials were synthesized and pelletized, thus allowing for a meaningful characterization in view of process scale-up. The materials were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). By performing breakthrough experiments, we found that Cu3(BTC)2 separated CO2/CH4 slightly better than MOF-5. Because the crystal structure of Cu3(BTC)2 includes unsaturated accessible metal sites formed via dehydration, it predominantly interacted with CO2 molecules and more easily captured them. Conversely, MOF-5 with a suitable pore size separated CH4/N2 more efficiently in our breakthrough test.

We describe the successful synthesis of Fe2(dobdc) (dobdc4−=2, 5-dioxido-1, 4-benzenedicarboxylate), which has an open metal coordination site Fe(II), and investigate the adsorption properties of three important molecules CO2, CH4 and N2 on Fe2(dobdc) and an oxidized analog, Fe2(O2)(dobdc). We found that CO2 adsorption isotherm of Fe2(dobdc) at 10 bar was very different from Fe2(O2)(dobdc), with the capacities of 144.5 cm3 g−1 and 98.1 cm3 g−1, respectively. The adsorption capacities for CH4 were 75.8 cm3 g−1 and 36.8 cm3 g−1, respectively, at 10 bar in these materials. Using ideal adsorbed solution theory (IAST), we obtain the adsorption selectivity for CO2 using equimolar mixtures of CO2/CH4 and CO2/N2 with Fe2(dobdc) and Fe2(O2)(dobdc) as a function of pressure. Fe2(dobdc) has a higher, more stable separation factor.

A microporous zirconium phosphate material with the chemical composition |(C4H12N+)6(H3O+)2(H2O)2|[Zr32P48O176F8(OH)16] (ZrPOF-DEA) has been synthesized ionothermally using diethylammonium chloride and oxalic acid to form the deep eutectic solvent. It is closely related to the analagous ethylammonium material ZrPOF-EA, which has already been shown to discriminate very well between CO2 and CH4. The framework structures, with two different 8-ring channels running parallel to the x-axis, one of which intersects a 7-ring channel running parallel to the z-axis, proved to be identical. Only the positions of the non-framework cations and water molecules differ. The structure of ZrPOF-DEA (Pbam, a = 20.03757(1) A, b = 37.19099(1) A, c = 6.62488(1) A) was solved from synchrotron powder diffraction data using the charge-flipping algorithm in Superflip. Difference Fourier analyses were then used to locate the non-framework species in the channels. Rietveld refinement of the final structure converged with RF = 0.037 and Rwp = 0.138. Although this material, like ZrPOF-EA, is stable up to 410 °C, it does not discriminate as well between CO2 and CH4. Thermogravimetric analysis shows that not all of the organic species have been removed at 410 °C, and this is presumably the reason for the poorer adsorption results.

Adsorption of CO 2 , CH 4 and N 2 was measured in two differently spaced flexible layer metal–organic frameworks (MOFs), [Cu(dhbc) 2 (bpy)] (Kitagawa S, 2003) and [Cu(BF 4 ) 2 (bpy) 2 ] (ELM-11, Kaneko K, 2002), using a gravimetric method at temperatures of 77–298 K with a high pressure 20 bar. It was found that the gate-opening pressure was much lower at reduced temperatures in the flexible layer MOFs. Gas molecules were easily adsorbed into the widely spaced layers, but the organic ligands which play a supportive role in the layers prevent the spread of more molecules, because more of the space between the layers was occupied. The experimental results also showed the gate phenomenon and implied that these materials would be applicable for gases separated, especially the adsorption ratio of CH 4 /N 2 in [Cu(dhbc) 2 (bpy)] was up to 42 at normal pressure when the temperature decreased to 195 K.

High pure metal–organic framework chromium terephthalate (MIL-101) was synthesized from TMAOH-Cr(NO 3 ) 3 -H 2 BDC-H 2 O for the first time. Typical synthesized samples were characterized by X-ray diffraction, scanning electron microscopy, thermal gravimetric analysis, and volumetric nitrogen adsorption. Hydrogen adsorption isotherms of the material were studied at 77 K. The results showed that H 2 adsorption was up to 4.01 wt% at 1 MPa which approached the documented value (4.1 wt% at 1 MPa and 77 K). It was confirmed that alkaline medium played an important role in this study, on the one hand, it promoted dissolution of the raw material H 2 BDC in water in the system and the pure sample was obtained easily, on the other hand, the pure sample which was more beneficial was used as the hydrogen storage material.