A 3D Ba-MOF for selective adsorption of CO2/CH4 and CO2/N2

Autohomogenization of Polybenzimidazole Composites with Enhanced Mechanical Performance by Air Incorporation

Polybenzimidazoles are one of the most thermally and chemically stable polymers due to their rigid chemical structure with π-π stacking and conjugated bonding. Poly(2,5-benzimidazole) (ABPBI), the simplest structure of polybenzimidazole, was synthesized, but the cast film was not homogeneous and featured thick brown areas, which limited their further application. Silica nanospheres were adapted as porogen to generate nanopores in the ABPBI film by successive etching with hydrofluoric acid. As a result of air-composite formation, the ABPBI film became homogeneous and its surface roughness was reduced from 10.0 to 2.5 nm. The obtained air-composite ABPBI film had more favorable mechanical properties than the original film. An air-composite film prepared with 50 wt % silica content had a tensile strength of 128 MPa and an elongation at break of 23%, both of which values were approximately twice as high as the corresponding values of the original film.

A 2-fold interpenetrating 3D pillar-layered MOF for the gas separation and detection of metal ions

A 2-fold interpenetrating 3D pillar-layered MOF, which was assembled from a mixed-linker and paddle-wheel cluster, was successfully synthesized. It possesses good thermal and water stability as well as high selectivity for C2H6 over CH4 and CO2 over N2 under ambient conditions, which was further proved by breakthrough experiments. Moreover, this porous material exhibits good detection of Cu2+, [Co(NH3)6]3+ and Fe3+ in an aqueous solution.

The Reinforced Separation of Intractable Gas Mixtures by Using Porous Adsorbents

This review focuses on the mechanism and driving force in the intractable gas separation using porous adsorbents. A variety of intractable mixtures have been discussed, including air separation, carbon capture, and hydrocarbon purification. Moreover, the separation systems are categorized according to distinctly biased modes depending on the minor differences in the kinetic diameter, dipole/quadruple moment, and polarizability of the adsorbates, or sorted by the varied separation occasions (e.g., CO2 capture from flue gas or air) and driving forces (thermodynamic and kinetic separation, molecular sieving). Each section highlights the functionalization strategies for porous materials, like synthesis condition optimization and organic group modifications for porous carbon materials, cation exchange and heteroatom doping for zeolites, and metal node-organic ligand adjustments for MOFs. These functionalization strategies are subsequently associated with enhanced adsorption performances (capacity, selectivity, structural/thermal stability, moisture resistance, etc.) toward the analog gas mixtures. Finally, this review also discusses future challenges and prospects for using porous materials in intractable gas separation. Therein, the combination of theoretical calculation with the synthesis condition and adsorption parameters optimization of porous adsorbents may have great potential, given its fast targeting of candidate adsorbents and deeper insights into the adsorption forces in the confined pores and cages.

Multifunctional and Ultrastable Co-MOF Effectively Separates Various Different Component Gas Mixtures

Developing low-cost and multifunctional adsorbents for adsorption separation to obtain high-purity (>99.9%) gases is intriguing yet challenging. Notably, the ongoing trade-off between adsorption capacity and selectivity in separating multicomponent mixed gases still persists as a pressing scientific challenge requiring urgent attention. Herein, the ultrastable TJT-100 exhibits unique structural characteristics including uncoordinated carboxylate oxygen atoms, coordinated water molecules directed toward the pore surface, and sufficient Me2NH2+ cations in channels. TJT-100 exhibits a high adsorption capacity and exceptional separation performance, particularly notable for its high C2H2 capacity of 127.7 cm3/g and remarkable C2H2 selectivity over CO2 (5.4) and CH4 (19.8), which makes it a standout material for various separation applications. In a breakthrough experiment with a C2H2/CO2 mixture (v/v = 50/50), TJT-100 achieved a record-high C2H2 productivity of 69.33 L/kg with a purity of 99.9%. Additionally, TJT-100 demonstrates its effectiveness in separating CO2 from natural gas and flue gas. Its exceptional selectivity for CO2/CH4 (10.7) and CO2/N2 (11.9) results in a high CO2 productivity of 21.23 and 22.93 L/kg with 99.9% purity from CO2/CH4 (v/v = 50/50) and CO2/N2 (v/v = 15/85) mixtures, respectively.

Methane Storage and Purification of Natural Gas in Metal-Organic Frameworks

Natural gas, primarily composed of methane (CH4), represent an excellent choice for a potentially sustainable renewable energy transition. However, the process of compressing and liquefying CH4 for transport and storage typically results in significant energy losses. In addition, in order to optimize its efficacy as a fuel, the CH4 content of natural gas needs to be increased to a level of at least 97 % to ensure its quality and efficiency in various applications. Metal-organic frameworks (MOFs) represent a novel category of porous materials that possess exceptional capability in modifying pore size and chemical environment, making them ideally suited for the storage of CH4 and the adsorption of propane (C3H8), ethane (C2H6), carbon dioxide (CO2), nitrogen (N2), and hydrogen sulfide (H2S) to facilitate the purification process of CH4 from natural gas. In this paper, we systematically summarize the mechanism by which MOF materials facilitate the storage of CH4 and the purification of CH4 from natural gas, leveraging the structural characteristics inherent to MOF materials. The focus of further research should also be directed towards the investigation of CH4 storage by flexible MOFs, the resolution of the trade-off dilemma, and the commercial application of MOFs.

Flexible Microporous Framework for One-Step Acquisition of Ethylene from Ternary C2 Hydrocarbons

One-step purification of ethylene (C2H4) from ternary C2 hydrocarbon mixtures is a crucial task and an enduring challenge because of their similar molecular size and physical properties. Owing to their intriguing structural dynamics, flexible MOFs have attracted more attention for gas adsorption and separation. Herein, we report a flexible MOF FJI-W-66 that exhibits rarely seen "breathing" behaviors for C2 hydrocarbons. Upon activation, the channels of guest-free FJI-W-66a significantly contract to a nearly closed-pore state. FJI-W-66a shows the stepwise adsorption isotherms for C2 hydrocarbons, which suggests the occurrence of structural transformation between less open and more open phases. Breakthrough experiments provide evidence that FJI-W-66a can selectively separate C2H4 from C2H2/C2H4/C2H6 mixtures with different ratios under ambient conditions, realizing the one-step acquisition of C2H4 from ternary C2 hydrocarbons.

Water-Stable Microporous Bipyrazole-Based Framework for Efficient Separation of MTO Products

Recently, methanol-to-olefins (MTO) technology has been widely used. The development of new adsorbents to separate MTO products and obtain high-purity ethylene (C2H4) and propylene (C3H6) has become an urgent task. Herein, an exceptionally highly water-stable metal-organic framework (MOF), [Cu3(OH)2(Me2BPZ)2]·(solvent)x (1) (H2Me2BPZ = 3,3'-dimethyl-1H,1'H-4,4'-bipyrazole) with hexagonal pores, has been elaborately designed and constructed. After being soaked in water for 7 days, it still maintains its structure, and the uptake of N2 at 77 K is unchanged. The adsorption capacity of C3H6 can reach 138 cm3 g-1, while the uptake of C2H4 is only 52 cm3 g-1 at 298 K and 1 bar. The dynamic breakthrough experiments show that the mixture of C3H6/C2H4 (50/50, v/v) can be efficiently separated in one step. High-purity C2H4 and C3H6 can be obtained through an adsorption and desorption cycle and the yields of C2H4 (purity ≥ 99.95%) and C3H6 (purity ≥ 99%) are 84 and 48 L kg-1, respectively. Surprisingly, when the flow rate is increased, the separation performance has no obvious change. Additionally, humidity has no effect on the separation performance. Finally, theoretical simulations indicate that there are stronger interactions between the C3H6 molecule and the framework, which are beneficial to capturing C3H6 over C2H4.

Synergistic Adsorption and In Situ Catalytic Conversion of SO2 by Transformed Bimetal-Phenolic Functionalized Biomass

SO2 removal is critical to flue gas purification. However, based on performance and cost, materials under development are hardly adequate substitutes for active carbon-based materials. Here, we engineered biomass-derived nanostructured carbon nanofibers integrated with highly dispersed bimetallic Ti/CoOx nanoparticles through the thermal transition of metal-phenolic functionalized industrial leather wastes for synergistic SO2 adsorption and in situ catalytic conversion. The generation of surface-SO32- and peroxide species (O22-) by Ti/CoOx achieved catalytic conversion of adsorbed SO2 into value-added liquid H2SO4, which can be discharged from porous nanofibers. This approach can also avoid the accumulation of the adsorbed SO2, thereby achieving high desulfurization activity and a long operating life over 6000 min, preceding current state-of-the-art active carbon-based desulfurization materials. Combined with the techno-economic and carbon footprint analysis from 36 areas in China, we demonstrated an economically viable and scalable solution for real-world SO2 removal on the industrial scale.

Deep removal of trace C2H2 and CO2 from C2H4 by using customized potassium-exchange mordenite

Adsorptive separation using porous materials is a promising approach for separating alkynes/olefins due to its energy efficiency, while the deep removal of trace amounts of C2H2 and CO2 from C2H4 is still very challenging for a commercial adsorbent. Herein, we report a low-cost inorganic metal cation-mediated mordenite (MOR) zeolite with the specific location and distribution of K+ cations acting as a goalkeeper for accurately controlling diffusion channels, as evidence of the experimental and simulation results. Deep purification of C2H4 from ternary CO2/C2H2/C2H4 mixtures was first realized on K-MOR with exceptional results, achieving a remarkable polymer-grade C2H4 productivity of 1742 L kg-1 for the CO2/C2H2/C2H4 mixture. Our approach which only involves adjusting the equilibrium ions, is both promising and cost-effective, and opens up new possibilities for the use of zeolites in the industrial light hydrocarbon adsorption and purification process.

Recent advances in eco-friendly fabrics with special wettability for oil/water separation

Considering the serious damage to aquatic ecosystems and marine life caused by oil spills and oily wastewater discharge, efficient, environment-friendly and sustainable oil/water separation technology has become an inevitable trend for current development. Herein, fabrics are recognized as eco-friendly materials for water treatment due to their good degradability and low cost. Particularly, fabrics with rough structures and natural hydrophilicity/oleophilicity enable the construction of superwetting surfaces for the selective separation of oil/water mixtures and even complex emulsions. Therefore, superwetting fabrics for efficiently solving oil spills and purifying oily wastewater have received extensive attention. Especially, Janus and smart fabrics are highly anticipated to enable the on-demand and sustainable treatment of oil spills and oily wastewater due to their changeable wettability. Moreover, the fabrication of superwetting fabrics with multifunctional performances for oily wastewater purification can further promote their practical industrial applications, such as photocatalytic, self-cleaning, and self-healing characteristics. However, some potential challenges still exist, which urgently need to be systematically summarized to guide the future development of this research field. In this review, firstly, the fundamental theories of wettability and the separation mechanisms based on special wettability are discussed. Then, superwetting fabrics for efficient oil/water separation are systematically reviewed, such as superhydrophobic/superoleophilic (SHB/SOL), superhydrophilic/superoleophobic (SHL/SOB), SHL/underwater superoleophobic (SHL/UWSOB), and UWSOB/underoil superoleophobic (UWSOB/UOSHB) fabrics. Most importantly, we highlight Janus, smart, and multifunctional fabrics based on their superwetting property. Correspondingly, the advantages and disadvantages of each superwetting fabric are comprehensively analyzed. Besides, super-antiwetting fabrics with superhydrophobic/superoleophobic (SHB/SOB) property are also introduced. Finally, the challenges and future research directions are explained.