A thin-film (700 nm) DDR zeolite disc membrane was evaluated for separating a 1/1 CO2/CH4 mixture in a wide temperature range (−35 to 180 °C). The highest selectivity of 2325 paired with a high CO2 permeance of 34 × 10−7 mol/(m2·s·Pa) was observed at −30 °C and a feed pressure of 3 bar. At the same feed pressure, the highest CO2 permanence was recorded at + 10 °C reaching 44 × 10−7 mol/(m2·s·Pa), while selectivity remained remarkably high at 1118. High permeance and selectivity were also observed at higher feed pressures. These results surpass all previously published data on CO2/CH4 separation using DDR zeolite membranes and indicate that the membranes have strong potential for upgrading natural gas and biogas. A model describing mass transfer while considering adsorption, surface barrier, and surface diffusion was fitted to experimental single gas permeation data and showed that it can accurately describe the mass transfer in the zeolite pores while indicating that the limiting step was the surface barrier. These findings highlight the potential of DDR membranes for industrial gas purification across a broad range of temperatures and feed pressures.

The development of high-performance adsorbents for azo-dye removal from wastewater is crucial for environmental remediation. This study reports the synthesis of a novel metal-phenolic networks-functionalized MOFs-derived core-shell porous carbon materials, showcasing enhanced adsorption capabilities. Through an optimized carbonization process, these materials realized an adsorption capacity of 5221 mg/g for Congo red (CR) with an initial CR concentration of 500 mg/L, exceeding unmodified MOFs-derived carbons. The adsorption kinetics, adhering to pseudo-second-order and Langmuir models, indicate chemisorption and monolayer adsorption. The materials' reusability was demonstrated with over 89% retention after five cycles. This study's novelty stems from the strategic integration of MPNs with MOFs-derived carbons, capitalizing on MOFs' high surface area and tunable pores to augment adsorption. Moreover, DFT simulations and experimental results pinpointed π-π interactions, hydrogen bonding, and electrostatic forces as pivotal adsorption mechanisms. This approach marks a significant leap in adsorbent design, offering a sustainable solution to dye pollution and contributing to the fields of green chemistry and environmental protection.

Ultra-thin (450 nm) CHA zeolite membranes were assessed for upgrading a synthetic natural gas mixture with a composition representative of the natural gas after a Joule Thomson process. At a feed pressure of 30 bar(a), the membranes provided high fluxes and excellent selectivity for CO2/CxHy, CO2/N2, and N2/CxHy separations. The most favourable conditions for CO2 removal were observed near 25 °C, yielding a CO2 flux of 1.2 (mol/m2·s) and a permeance of 13 × 10−7 (mol/m2·s·Pa) (3900 GPU). At this temperature, selectivities for CO2/CH4, CO2/C2H6, and CO2/C3H8 were 68, 101, and 190, respectively. For N2 separation, the optimal temperature was ∼35 °C, where a N2 flux of 2.5 × 10−3 (mol/m2·s) and a permeance of 1 × 10−7 (mol/m2·s·Pa) (300 GPU) were achieved, along with selectivities of 5 (N2/CH4), 9 (N2/C2H6), and 15 (N2/C3H8). A process simulation based on these separation properties indicated that only 11.3 m2 of membrane area is required to upgrade 1000 Nm3/h of natural gas to pipeline quality at 30 bar(a). These results demonstrate the strong promise of ultra-thin CHA membranes for efficient natural gas upgrading.

The adsorption equilibrium isotherms of the common components of natural gas and biogas, CO2, CH4, N2, and He were experimentally measured over wide temperature ranges on all-silica MFI, CHA, and DDR zeolite crystals. First, large zeolite crystals, suitable for adsorption measurements, were synthesized and characterized by XRD and SEM. In the next step, gas adsorption data was recorded and the Toth equation was fitted to the measured adsorption data, and the adsorption capacity at saturation (Csat), affinity constant (b), and Toth heterogeneity parameter (t) were estimated. Finally, the van't Hoff equation was used to calculate the isosteric enthalpy of adsorption and adsorption entropy for all gases on each zeolite. The results reveal that the Toth equation can accurately predict the adsorption of gases on the studied microporous zeolite crystals in the investigated temperature range. To the best of our knowledge, the saturation adsorption capacity and adsorption enthalpy for helium on CHA and DDR zeolites have been determined experimentally for the first time in the present work. The estimated adsorption parameters presented in this work are accurate, primarily due to the large crystals used for the adsorption measurements and the recording of low-temperature adsorption equilibrium isotherms over broad temperature ranges. These factors are crucial for the reliability of our results, which are invaluable for understanding adsorption and mass transfer in zeolite materials, as well as for advancing the development of zeolite materials for gas separation.

Urea-formaldehyde (UF) resin microspheres prepared by polymerization of urea and formaldehyde have broad applications because of their unique properties. In this paper, we present the preparation of UF microspheres with particle sizes of several microns at 100–180 °C and 1.5 MPa in 6–24 s in a simple microchannel reactor. A urea aqueous solution and formaldehyde solution containing formic acid as the catalyst were used as raw materials. Porous and flower-like UF microspheres as well as dense ones can be readily produced, with the former obtained mainly at lower temperatures, shorter residence times, and lower reactant concentrations. The porous microspheres can further grow to dense ones by prolonging the residence time, increasing the reaction temperature, or using reactants with higher concentrations. Compared with the present mainly used batch process to prepare UF microspheres using the same raw materials which need 3 h at 50 °C, this preparation method is swift and versatile in adjusting the particle size and structure. Moreover, flower-like UF microspheres could be produced and the pore size could be adjusted without additives. The results indicate a more environmentally friendly and economical synthesis method we developed. A possible formation mechanism of UF microspheres with various structures was proposed.

The usage of recycled alloys in the high pressure die casting (HPDC) applications for automobiles is gaining rapid interest. Even though the skin microstructure, which is typically induced on the casting surface during the HPDC process, is believed to improve the properties of the HPDC castings, it may not always form continuously throughout on the casting surface, and thereby can influence the mechanical properties. Thus, the current study evaluated and compared the effects of inhomogeneously formed surface skin with that of other defects on the ductility exhibited by the HPDC castings of a recycled secondary AlSi10MnMg(Fe) alloy. The formation of inhomogeneous skin in the current study was attributed to a phenomenon related to the “waves and lakes” type of defects created by the HPDC process. Such skin structure limited the ductility of the HPDC castings, irrespective of the tested strain rates in the current case, by undergoing abrupt fracture due to its poor bonding with the adjoining matrix resulting from the aforementioned inhomogeneity. Even if the investigated AlSi10MnMg(Fe) alloy contained an abundance of porosity, cold flakes and intermetallics, which are usually considered the driving factors behind the fracture of HPDC processed alloys, the effect from the inhomogeneous skin layer dominated all other factors in the current case. The order of detrimental effect on the ductility of HPDC processed AlSi10MnMg(Fe) alloy followed a sequence of inhomogeneous skin, cold flakes and pores, with the inhomogeneity in skin turning out to be the most harmful one.

We explore the separation of H₂ from CH₄ using ultrathin DDR membranes across various temperatures and feed pressures. Using a membrane that featured a zeolite film around 700 nm thick, we measured an H₂ permeance of 7.2 × 10^–7 mol/(m2·s·Pa), equivalent to 2.2 × 10³ GPU, for a 1/1 H₂/CH₄ gas mixture at 3 bar(a) under ambient temperature. This permeance exceeds previously reported values for DDR membranes by more than 10-fold and is comparable to the permeance reported for the best palladium membranes. Under the same conditions, H₂/CH₄ separation selectivity reached 207, well above values earlier reported for DDR membranes. These membranes also demonstrate outstanding performance under high pressures and temperatures of up to 180 °C, and high feed pressure is needed for achieving high H₂/CH₄ selectivities at elevated temperatures. Interestingly, the experimental data fit a mass-transfer model that incorporates surface diffusion and surface barriers, indicating that the selective surface barrier governs the overall selective transport; meanwhile, the important parameters related to the mass transfer of H₂ and CH₄ in DDR zeolite are explored.

The current study investigated the microstructure evolution, mechanical properties, and fracture behavior of a high pressure die cast (HPDC) novel secondary alloy. The as-cast microstructure comprised (i) Primary α-Al, (ii) α-Al15(FeMn)3Si2 intermetallics, and (iii) Al–Si eutectics. The microstructure starting from the surface through the depth of the HPDC casting consisted of (i) fine-grained skin at surface, (ii) increased Al–Si eutectics at intermediate location, and (iii) coarse α-Al dendrites at center. Accordingly, the hardness increased from skin to the intermediate section and then decreased toward the center of the casting. The formation of skin layer was highly discontinuous, which was attributed to the complicated fluid flow pattern inside the die cavity. The skin layer indicated to slightly improve the strength of the HPDC alloy; however, it restricted the ductility of the material with a large variation. Such ductility behavior resulted from a fracture mechanism triggered by the inhomogeneous skin because of its poor bonding with the adjacent matrix. Even though the secondary alloy contained casting defects and α-Al15(FeMn)3Si2 intermetallics that are known to be driving factors for the fracture in such materials, the effects from the inhomogeneous skin turned out to be predominant in the current study. 

The increasing presence of pharmaceutical active compounds (PhACs) in the environment has become a significant ecological and health concern, necessitating the development of efficient and cost-effective removal strategies. This study presents a novel composite, MIL-53(Al)@TA-Fe(Ⅲ) MPNs, integrating metal-phenolic networks (MPNs) with metal–organic frameworks (MOFs) for efficient tetracycline removal from aqueous solutions. The composite was synthesized through an environmentally benign process, involving surface modification of MIL-53(Al) with tannic acid (TA) and Fe(Ⅲ). Comprehensive characterization revealed that the optimal composite, achieved at a MIL-53(Al) to TA mass ratio of 1:1.2 and a TA to Fe(Ⅲ) molar ratio of 1:5, exhibited a large specific surface area and pore volume, contributing to its high adsorption capacity of 532 mg/g for tetracycline. Adsorption isotherm, kinetics, and thermodynamic analyses indicated that the process was spontaneous, endothermic, and chemically driven. Mechanistic studies highlighted the roles of electrostatic and π-π interactions between the composite and tetracycline molecules. The composite also demonstrated excellent reusability, retaining over 92 % of its initial adsorption capacity after five cycles. This work not only provides a green and efficient strategy for tetracycline remediation but also offers valuable insights for the development of advanced adsorbents using MPNs-modified MOFs, holding significant potential for broader environmental applications in the future.