In-situ growth of zeolitic imidazolate framework-67 nanoparticles on polysulfone/graphene oxide hollow fiber membranes enhance CO2/CH4 separation

Challenges and recent advances in MOF-based gas separation membranes

Membrane-based gas separation, characterized by a small footprint, low energy consumption and no pollution, has gained widespread attention as an environmentally friendly alternative to traditional gas separation. Metal-organic-frameworks (MOFs) are considered to be one of the most promising membrane-based gas separation materials because of their large specific surface area and high porosity. One of the hottest studies at the moment is how to utilize the characteristics of MOFs to prepare higher performance gas separation membranes. This paper provides a review of gas separation membranes used in recent years. Firstly, the synthesis methods of MOFs and MOF membranes are briefly introduced. Then, methods to improve the membrane properties of MOFs are described in detail, and include applications of lamellar MOFs, ionic liquid (IL) spin coating, functionalization of MOFs, defect engineering and mixed fillers. In addition, the challenges of MOF-based gas separation membranes are presented, including pore size, environmental disturbances, plasticization, interfacial compatibility, and so on. Finally, based on the current development status of the MOF membranes, the development prospects of MOF gas separation membranes are discussed. It is hoped to provide reliable and complete ideas for researchers to prepare high-performance gas separation membranes in the future.

Risk mitigation to healthcare workers against viral and bacterial bioaerosol load in laparoscopic surgical exhaust with a new flow mode in hollow fiber membranes-based filter

Laparoscopy of COVID-19-infected/suspected patients needs to be performed with the utmost care due to the chances of virus carryover through the pneumoperitoneum gas. In this study, polysulfone/polyvinyl-pyrrolidone hollow fiber membranes (HFMs) were fabricated by phase inversion process, and these HFMs were bundled into a module consisting of tortuous, circular-helical arrangement. Further, copper (Cu) and zinc (Zn) nanoparticles (NPs), known to have antimicrobial and antiviral properties, were flow-coated on the lumen side of the HFMs. To test functional efficiency, the modules were challenged with wet aerosol and bioaerosols. Wet aerosol removal efficiency was ∼98%. Bioaerosol-containing bacteria E. coli strain K-12, showed 2.6 log (∼99.8%), and 2.1 log (∼99.3%) removal efficiency for Cu NPs and Zn NPs coated HFMs modules, respectively, and 1.6 log (∼97%) removal for plain (uncoated) HFMs. Bioaerosols containing SARS-CoV-2 surrogate virus (MS2 bacteriophage) showed ∼5-7 log reduction of bacteriophage for plain HFMs, 3.9 log, and 2.3 log reduction for Cu and Zn coated HFMs, respectively. The flow of aerosols entirely through the HFM lumen helps in attaining a low ΔP of < 1 mm Hg, thus rendering its usefulness, particularly for exhausting pneumoperitoneum gases where high upstream pressures could lead to barotrauma. STATEMENT OF ENVIRONMENTAL IMPLICATION: Surgical smoke is generated during minimally invasive surgical (MIS) procedure such as laparoscopy when electrosurgical devices are used to cut any tissues. This smoke is a hazard as it contains toxic volatile compounds, mutagens, carcinogens, bacteria, and virus-laden aerosols. Infection to healthcare professionals through the bioaerosols containing smoke is well reported in literature. The limitation of using hypochlorite and pleated/HEPA filter, led us to design a low pressure drop bioaerosol filter, which can remove smoke, tissue fragments, and COVID-19 virus. It provides a much safer operation theatre environment during MIS procedures as well as in general for bioaerosol removal.

Alshgari R, Jamal M, Uz Zaman S, Umar M, Rafiq S, Muhammad N, Fawad JB, Shafiee SA. Deep Eutectic Solvent Coated Cerium Oxide Nanoparticles Based Polysulfone Membrane to Mitigate Environmental Toxicology

In this study, ceria nanoparticles (NPs) and deep eutectic solvent (DES) were synthesized, and the ceria-NP's surfaces were modified by DES to form DES-ceria NP filler to develop mixed matrix membranes (MMMs). For the sake of interface engineering, MMMs of 2%, 4%, 6% and 8% filler loadings were fabricated using solution casting technique. The characterizations of SEM, FTIR and TGA of synthesized membranes were performed. SEM represented the surface and cross-sectional morphology of membranes, which indicated that the filler is uniformly dispersed in the polysulfone. FTIR was used to analyze the interaction between the filler and support, which showed there was no reaction between the polymer and DES-ceria NPs as all the peaks were consistent, and TGA provided the variation in the membrane materials with respect to temperature, which categorized all of the membranes as very stable and showed that the trend of stability increases with respect to DES-ceria NPs filler loading. For the evaluation of efficiency of the MMMs, the gas permeation was tested. The permeability of CO2 was improved in comparison with the pristine Polysulfone (PSF) membrane and enhanced selectivities of 35.43 (αCO2/CH4) and 39.3 (αCO2/N2) were found. Hence, the DES-ceria NP-based MMMs proved useful in mitigating CO2 from a gaseous mixture.

Graphene in Polymeric Nanocomposite Membranes—Current State and Progress

One important application of polymer/graphene nanocomposites is in membrane technology. In this context, promising polymer/graphene nanocomposites have been developed and applied in the production of high-performance membranes. This review basically highlights the designs, properties, and use of polymer/graphene nanocomposite membranes in the field of gas separation and purification. Various polymer matrices (polysulfone, poly(dimethylsiloxane), poly(methyl methacrylate), polyimide, etc.), have been reinforced with graphene to develop nanocomposite membranes. Various facile strategies, such as solution casting, phase separation, infiltration, self-assembly, etc., have been employed in the design of gas separation polymer/graphene nanocomposite membranes. The inclusion of graphene in polymeric membranes affects their morphology, physical properties, gas permeability, selectivity, and separation processes. Furthermore, the final membrane properties are affected by the nanofiller content, modification, dispersion, and processing conditions. Moreover, the development of polymer/graphene nanofibrous membranes has introduced novelty in the field of gas separation membranes. These high-performance membranes have the potential to overcome challenges arising from gas separation conditions. Hence, this overview provides up-to-date coverage of advances in polymer/graphene nanocomposite membranes, especially for gas separation applications. The separation processes of polymer/graphene nanocomposite membranes (in parting gases) are dependent upon variations in the structural design and processing techniques used. Current challenges and future opportunities related to polymer/graphene nanocomposite membranes are also discussed.

A comprehensive review on zeolite-based mixed matrix membranes for CO2/CH4 separation

Biogas consisting of carbon dioxide/methane (CO₂/CH₄) gas mixtures has emerged as an alternative renewable fuel to natural gas. The presence of CO₂ can decrease the calorific value and generate greenhouse gas. Hence, separating CO₂ from CH₄ is a vital step in enhancing the use of biogas. Zeolite and zeolite-based mixed matrix membrane (MMM) is considered an auspicious candidate for CO₂/CH₄ separation due to thermal and chemical stability. This review initially addresses the development of zeolite and zeolite-based MMM for the CO₂/CH₄ separation. The highest performance in terms of CO₂ permeance and CO₂/CH₄ selectivity was achieved using zeolite and zeolite-based MMM, which exhibited CO₂ permeance in the range of 2.0 × 10^{- 7}-7.0 × 10^{- 6} mol m^{- 2} s^{- 1} Pa^{- 1} with CO₂/CH₄ selectivity ranging from 3 to 300. Current trends directed toward improving CO₂/CH₄ selectivity via modification methods including post-treatment, ion-exchanged, amino silane-grafted, and ionic liquid encapsulated of zeolite-based MMM. Those modification methods improved the defect-free and interfacial adhesions between zeolite particulates and polymer matrices and subsequently enhanced the CO₂/CH₄ selectivity. The modifications via ionic liquid and silane methods more influenced the CO₂/CH₄ selectivity with 90 and 660, respectively. This review also focuses on the possible applications of zeolite-based MMM, which include the purification and treatment of water as well as biomedical applications. Lastly, future advances and opportunities for gas separation applications are also briefly discussed. This review aims to share knowledge regarding zeolite-based MMM and inspire new industrial applications.

Status and future trends of hollow fiber biogas separation membrane fabrication and modification techniques

With the increasing global demand for energy, renewable and sustainable biogas has attracted considerable attention. However, the presence of various gases such as methane, carbon dioxide (CO₂), nitrogen, and hydrogen sulfide in biogas, and the potential emission of acid gases, which may adversely influence the environment, limits the efficient application of biogas in many fields. Consequently, researchers have focused on the upgrade and purification of biogas to eliminate impurities and obtain high-quality and high-purity biomethane with an increased combustion efficiency. In this context, the removal of CO₂ gas, which is the most abundant contaminant in biogas, is of significance. Compared to conventional biogas purification processes such as water scrubbing, chemical absorption, pressure swing adsorption, and cryogenic separation, advanced membrane separation technologies are simpler to implement, easier to scale, and incur lower costs. Notably, hollow fiber membranes enhance the gas separation efficiency and decrease costs because their large specific surface area provides a greater range of gas transport. Several reviews have described biogas upgrading technologies and gas separation membranes composed of different materials. In this review, five commonly used commercial biogas upgrading technologies, as well as biological microalgae-based techniques are compared, the advantages and limitations of polymeric and mixed matrix hollow fiber membranes are highlighted, and methods to fabricate and modify hollow fiber membranes are described. This will provide more ideas and methods for future low-cost, large-scale industrial biogas upgrading using membrane technology.

Efficient Separation of Acetylene-Containing Mixtures Using ZIF-8 Membranes

Metal-organic framework (MOF) membranes show great potential in the separation of acetylene mixtures. In this work, we have prepared ZIF-8 membranes on polyamide (PA) substrates for the highly selective separation of acetylene/methane and acetylene/carbon dioxide mixtures. The C₂H₂/CH₄ and C₂H₂/CO₂ mixtures can be successfully separated using the ZIF-8 membranes, with separation factors of 12.1 and 1.8, respectively. Based on the results of the cross-permeation tests of C₂H₂/CH₄, CO₂/CH₄, and C₂H₂/CO₂, the separation mechanism of C₂H₂/CH₄ in our ZIF-8 membrane can be attributed to a higher affinity for acetylene and molecular sieving effect, while C₂H₂/CO₂ separation is related to thermodynamic factors. It is worth noting that this is the first example of MOF membranes to successfully separate C₂H₂ from CH₄ and CO₂.