A mechanically enhanced metal-organic framework/PDMS membrane for CO2/N2 separation

Preparation of PDMS and PDMS-UiO-66 oxygen-rich membranes and modules for membrane-aerated biofilm reactors

A membrane-aerated biofilm reactor (MABR) combines membrane technology with biofilm processes and has unique advantages in the treatment of organic wastewater and volatile wastewater. The common membranes for MABR systems usually have relatively uneven pore structures and low bubble point pressure, resulting in unsatisfactory O2 utilization and wastewater treatment efficiency. In this work, polydimethylsiloxane (PDMS) and UiO-66 (a Zr-based metal organic framework) were coated on the surface of a commercial polypropylene (PP) hollow fiber membrane to prepare oxygen-rich MABR membranes and modules, which showed an attractive O2 utilization rate and wastewater treatment efficiency. The bubble points of the PDMS and PDMS-UiO-66 membranes were significantly higher than those of the PP membranes, and the PDMS-UiO-66 membranes had better oxygen enrichment capacity and biological affinity. The optimal PDMS-UiO-66 membrane modules had an O2 permeance of 31.65 GPU (1 GPU = 3.35 × 10-10 mol m-2 s-1 Pa-1), with O2/N2 selectivity of 2.21. The membrane hanging effect and processing capacity for domestic sewage were greatly improved. This study may provide insights and guidelines to fabricate porous mixed matrix membranes and modules in the industry for MABR. The developed products are expected to be applied in the actual separation process.

Investigation of the effect of Ni and Cu variant MOF-74 in the Polydimethylsiloxane (PDMS)-based Mixed Matrix Membranes (MMMs) for efficient gas separation applications

Mixed matrix membranes (MMMs) containing metal-organic frameworks (MOFs) have been an emerging and promising membrane technology to contribute to different gas separation applications including carbon dioxide (CO2) and oxygen (O2) separation, because of their large surface areas and distinctive gas adsorption features. In this work, the fabrication process of Polydimethylsiloxane (PDMS)-based MMMs was reported, in which 0.5 to 2 wt.% of each type of (Cu, Ni)-based MOF-74 variants were incorporated into a PDMS matrix in order to achieve high CO2/N2, O2/N2, and CO2/O2 separation efficiency. These MMMs and their nanofillers (MOF-74) were extensively characterized using scanning electron microscopy (SEM) along with Energy Dispersive X-Ray (EDX) mapping, X-ray Diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), a single gas permeation testing system, and an ultimate tensile strength testing (UTS) unit in order to gain insight into their properties in relation to their gas separation performance. The 1 wt.% of both (Cu and Ni)-MOF-74@PDMS were selected as the most optimum MMMs due to their uniform morphology and enhanced tensile strength, which exhibited high CO2 permeabilities of 4432 Barrer (37.9% increase) and 4288 Barrer (33.5% increase), respectively. Furthermore, in the case of 1 wt.% Ni-MOF-74@PDMS, the CO2/N2, O2/N2, and CO2/O2 selectivities were also enhanced to 36.2 (141.6% increase), 3.2 (21.9% increase), and 11.25 (98.1% increase), respectively. While, in the case of 1 wt.% Cu-MOF-74@PDMS the CO2/N2 and O2/N2 selectivities showed an increment up-to 94.7 (531.5% increase) and 6.47 (145% increase), respectively, Whereas, at 0.5 wt.%, Cu-MOF-74@PDMS showed the best CO2/O2 selectivity of 25.26 (344.7% increase).

Polydimethylsiloxane/Magnesium Oxide Nanosheet Mixed Matrix Membrane for CO2 Separation Application

Carbon dioxide (CO₂) concentration is now 50% higher than in the preindustrial period and efforts to reduce CO₂ emission through carbon capture and utilization (CCU) are blooming. Membranes are one of the attractive alternatives for such application. In this study, a rubbery polymer polydimethylsiloxane (PDMS) membrane is incorporated with magnesium oxide (MgO) with a hierarchically two-dimensional (2D) nanosheet shape for CO₂ separation. The average thickness of the synthesized MgO nanosheet in this study is 35.3 ± 1.5 nm. Based on the pure gas separation performance, the optimal loading obtained is at 1 wt.% where there is no observable significant agglomeration. CO₂ permeability was reduced from 2382 Barrer to 1929 Barrer while CO₂/N₂ selectivity increased from only 11.4 to 12.7, and CO₂/CH₄ remained relatively constant when the MMM was operated at 2 bar and 25 °C. Sedimentation of the filler was observed when the loading was further increased to 5 wt.%, forming interfacial defects on the bottom side of the membrane and causing increased CO₂ gas permeability from 1929 Barrer to 2104 Barrer as compared to filler loading at 1 wt.%, whereas the CO₂/N₂ ideal selectivity increased from 12.1 to 15.0. Additionally, this study shows that there was no significant impact of pressure on separation performance. There was a linear decline of CO₂ permeability with increasing upstream pressure while there were no changes to the CO₂/N₂ and CO₂/CH₄ selectivity.

Metal-Organic Frameworks (MOFs)-Based Mixed Matrix Membranes (MMMs) for Gas Separation: A Review on Advanced Materials in Harsh Environmental Applications

The booming of global environmental awareness has driven the scientific community to search for alternative sustainable approaches. This is accentuated in the 13th sustainable development goal (SDG13), climate action, where urgent efforts are salient in combating the drastic effects of climate change. Membrane separation is one of the indispensable gas purification technologies that effectively reduces the carbon footprint and is energy-efficient for large-scale integration. Metal-organic frameworks (MOFs) are recognized as promising fillers embedded in mixed matrix membranes (MMMs) to enhance gas separation performance. Tremendous research studies on MOFs-based MMMs have been conducted. Herein, this review offers a critical summary of the MOFs-based MMMs developed in the past 3 years. The basic models to estimate gas transport, preparation methods, and challenges in developing MMMs are discussed. Subsequently, the application and separation performance of a variety of MOFs-based MMMs including those of advanced MOFs materials are summarized. To accommodate industrial needs and resolve commercialization hurdles, the latest exploration of MOF materials for a harsh operating condition is emphasized. Along with the contemplation on the outlook, future perspective, and opportunities of MMMs, it is anticipated that this review will serve as a stepping stone for the coming MMMs research on sustainable and benign environmental application.

Polydimethylsiloxane Membranes Incorporating Metal-Organic Frameworks for the Sustained Release of Antibacterial Agents

Cyclodextrin metal-organic frameworks (CD-MOFs) possess great potential in environmental applications due to their high specific surface area and good biocompatibility properties. However, the hydrophilicity of the CD-MOF hinders its ability to maintain a sustained release in water as a carrier. In this study, we prepared a CD-MOF that has codelivery ability for both phytochemicals [caffeic acid (CA)] and silver nanoparticles (Ag NPs) and further incorporated this material (CA@Ag@CD-MOF) into the polydimethylsiloxane (PDMS) matrix to construct a hybrid membrane. This hybrid membrane could effectively maintain the release capacity of the CD-MOF in water, while endowing PDMS with swelling ability in water. The hybrid membrane can achieve a sustained release for up to 48 h in water. In addition, the elastic modulus of the hybrid membrane increases by nearly 100%, and the swelling degree of the hybrid membrane in water increases by 42% compared with that of the pure PDMS membrane, indicating better mechanical properties. The hybrid membrane exhibits excellent antibacterial effects on Escherichia coli O157:H7 (E. coli O157:H7) and Staphylococcus aureus (S. aureus). We expect that this work will be beneficial to the delivery research of the CD-MOF in more environmental scenarios, especially in water treatment.