Efficient separation of the CH4/N2 mixture is of great significance for coalbed methane purification. It is an effective strategy to separate this mixture by tuning the van der Waals interaction due to the nonpolar properties of CH4 and N2 molecules. Herein, we prepared several isoreticular Al-based metal–organic frameworks (MOFs) with different ligand sizes and polarities because of their high structural stability and low cost/toxicity feature of Al metal. Adsorption experiments indicated that the CH4 uptake, Q st of CH4, and CH4/N2 selectivity are in the order of Al-FUM-Me (27.19 cm3(STP) g–1, 24.06 kJ mol–1 and 8.6) > Al-FUM (20.44 cm3(STP) g–1, 20.60 kJ mol–1 and 5.1) > Al-BDC (15.98 cm3(STP) g–1, 18.81 kJ mol–1 and 3.4) > Al-NDC (10.86 cm3(STP) g–1, 14.89 kJ mol–1 and 3.1) > Al-BPDC (5.90 cm3(STP) g–1, 11.75 kJ mol–1 and 2.2), confirming the synergetic effects of pore sizes and pore surface polarities. Exhilaratingly, the ideal adsorbed solution theory selectivity of Al-FUM-Me is higher than those of all zeolites, carbon materials, and most water-stable MOF materials (except Al-CDC and Co3(C4O4)2(OH)2), which is comparable to MIL-160. Breakthrough results demonstrate its excellent separation performance for the CH4/N2 mixture with good regenerability. The separation mechanism of Al-FUM-Me for the CH4/N2 mixture was elucidated by theoretical calculations, showing that the stronger affinity of CH4 can be attributed to its relatively shorter interaction distance with adsorption binding sites. Therefore, this work not only offers a promising candidate for CH4/N2 separation but also provides valuable guidance for the design of high-performance adsorbents.

Selectively separating CH 4 from N 2 in natural gas purification is extremely important, but challenging. Herein, a copper-based metal-organic framework (MOF) NKMOF-8-Me with inert pore environment was reported for efficient CH 4 /N 2 separation.Adsorption results show that this material owns the highest CH 4 uptake (1.76 mmol/g) and initial adsorption heat (Q st 0 ) of CH 4 (28.0 kJ/mol) as well as difference in Q st 0 (9.1 kJ/mol) among all materials with good water stability. Breakthrough experiments confirm that this MOF can completely separate the CH 4 /N 2 mixture with the highest CH 4 /N 2 breakthrough selectivity (7.8) reported so far. Theoretical calculations reveal the separation mechanism is the short average distance between CH 4 and pore wall, resulting in a stronger adsorption affinity for CH 4 . In addition, this MOF exhibits highly structural stability and regeneration. These results guarantee this MOF as a promising adsorbent for the recovery of CH 4 from coalbed methane.

Pursuing best-performing porous adsorbents to realize an effective SF6 recovery from SF6/N2 blends is of pronounced industrial worth. To tackle this key obstacle, we propose a single-molecule SF6 trap, which is based upon a splint-like pore in a highly stable metal–organic framework Ni­(adc)­(dabco)0.5 through multipoint F···π affinity. The pore walls are decorated with oppositely parallel anthracene rings, and the overlapping region of anthracene rings forms a giant overlap of potential fields. This very strong SF6 trap presents a record initial isosteric heat of adsorption (47.6 kJ mol–1), Henry constant (285.0 mmol g–1 bar–1), and uptake (2.23 mmol g–1) for SF6, making it a new benchmark with an unexampled ideal selectivity (919.4) toward SF6 capture. The SF6 adsorption mechanism within the Ni­(adc)­(dabco)0.5-based single-molecule trap is identified via in situ powder X-ray diffraction and Fourier transform infrared reflection spectroscopy in conjunction with theoretical studies. The highest selectivity (948.2), SF6 breakthrough uptake (2.1 mmol g–1), and dimensionless time (481.6) with the breakthrough effect of complete separation further consolidated that this MOF-based single-molecule SF6 trap is a novel state-of-the-art candidate toward SF6/N2 separation.

Chemical recycling of polyethylene terephthalate (PET) attracts increasing attention worldwide since it is a sustainable way to tackle the escalating plastic waste problem and create a circular plastic economy. Herein, defect-rich CeO 2 nanoparticles (NPs) with tunable sizes and shapes were conveniently synthesized by one-step precipitation with KH550 modification and first used as novel catalysts for the glycolysis of PET. Among the obtained CeO 2 catalysts, CeO 2 −2.7 nm NPs possessed the best performance for depolymerization at 196 °C, completing the reaction in 15 min with a PET conversion of 98.6% and a monomer yield of 90.3%. The glycolysis mechanism study reveals the relationship between defect engineering and catalytic activity. An ultrasmall size of 2.7 nm minimizes oxygen defect formation energy of CeO 2 NPs and increases the dispersity in ethylene glycol (EG). Rich oxygen defects on CeO 2 nanoparticles accelerate the glycolysis reaction evidently via inducing the generation of Ce 3+ and providing sites for the adsorption and activation. This work provides the application prospect of defective heterogeneous catalysts in the depolymerization reaction under low energy consumption.

Polyethylene terephthalate (PET), as one of the most indispensable synthetic organic compounds with high strength and transparency properties, can be widely used for textile and food packaging. With the increasing demand for PET production, the recycling of discarded PET has attracted great interest. In this work, we first proposed ethylene glycol (EG) dispersions of highly dispersed Fe3O4 nanoparticles, which were prepared through a co-precipitation route, as efficient and recoverable nanocatalysts for a PET chemical depolymerization achieved by a glycolysis reaction. The as-prepared Fe3O4 nanoparticles have an average size of 11 nm and can be stably dispersed in EG for up to 6 months. This glycolysis process was optimized in terms of catalyst concentrations, EG dosages, degradation temperature, and reaction time. Furthermore, the possible reaction mechanism of PET glycolysis using Fe3O4 as a catalyst was presented. More importantly, 100% PET conversion was achieved, and the bis(2-hydroxyethyl) terephthalate (BHET) yield reached more than 93% under optimal conditions (Fe3O4/PET = 2%, EG/PET = 13, 210 °C 30 min) even after three cycles. The Fe3O4 nanocatalysts are relatively stable during recycling and have great application prospects in chemocatalysis for future research.