Porous organosilicon nanotubes in pebax-based mixed-matrix membranes for biogas purification

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.

Enhancement strategies of poly(ether-block-amide) copolymer membranes for CO2 separation: A review

Poly(ether-block-amide) (Pebax) membranes have become the preferred CO2 separation membrane because of their excellent CO2 affinity and robust mechanical resistance. Nevertheless, their development must be considered to overcome the typical obstacles in polymeric membranes, including the perm-selectivity trade-off, plasticization, and physical aging. This article discusses the recent enhancement strategies as a guideline for designing and developing Pebax membranes. Five strategies were developed in the past few years to improve Pebax gas transport properties, including crosslinking, mobile carrier attachment, polymer blending, filler incorporation, and the hybrid technique. Among them, filler incorporation and the hybrid technique were most favorable for boosting CO2/N2 and CO2/CH4 separation performance with a trade-off-free profile. On the other hand, modified Pebax membranes must deal with two latent issues, mechanical strength loss, and perm-selectivity off-balance. Therefore, exploring novel materials with unique structures and surface properties will be promising for further research. In addition, seeking eco-friendly additives has become worthwhile for establishing Pebax membrane sustainable development for gas separation.

Analysis of the Influence of Process Parameters on the Properties of Homogeneous and Heterogeneous Membranes for Gas Separation

Heterogeneous membranes, otherwise known as Mixed Matrix Membranes (MMMs), which are used in gas separation processes, are the subject of growing interest. This is due to their potential to improve the process properties of membranes compared to those of homogeneous membranes, i.e., those made of polymer only. Using such membranes in a process involves subjecting them to varying temperatures and pressures. This paper investigates the effects of temperature and feed pressure on the process properties of homogeneous and heterogeneous membranes. Membranes made of Pebax^®2533 copolymer and containing additional fillers such as SiO₂, ZIF-8, and POSS-Ph were investigated. Tests were performed over a temperature range of 25-55 °C and a pressure range of 2-8 bar for N₂, CH₄, and CO₂ gases. It was found that temperature positively influences the increase in permeability, while pressure influences permeability depending on the gas used, which is related to the effect of pressure on the solubility of the gas in the membrane.

A Review of the Recent Progress in the Development of Nanocomposites Based on Poly(ether-block-amide) Copolymers as Membranes for CO2 Separation

An inspiring challenge for membrane scientists is to exceed the current materials' performance while keeping the intrinsic processability of the polymers. Nanocomposites, as mixed-matrix membranes, represent a practicable response to this strongly felt need, since they combine the superior properties of inorganic fillers with the easy handling of the polymers. In the global strategy of containing the greenhouse effect by pursuing a model of sustainable growth, separations involving CO2 are some of the most pressing topics due to their implications in flue gas emission and natural gas upgrading. For this purpose, Pebax copolymers are being actively studied by virtue of a macromolecular structure that comprises specific groups that are capable of interacting with CO2, facilitating its transport with respect to other gas species. Interestingly, these copolymers show a high versatility in the incorporation of nanofillers, as proved by the large number of papers describing nanocomposite membranes based on Pebax for the separation of CO2. Since the field is advancing fast, this review will focus on the most recent progress (from the last 5 years), in order to provide the most up-to-date overview in this area. The most recent approaches for developing Pebax-based mixed-matrix membranes will be discussed, evidencing the most promising filler materials and analyzing the key-factors and the main aspects that are relevant in terms of achieving the best effectiveness of these multifaceted membranes for the development of innovative devices.

Exclusive and ultrasensitive detection of formaldehyde at room temperature using a flexible and monolithic chemiresistive sensor

Formaldehyde, a probable carcinogen, is a ubiquitous indoor pollutant, but its highly selective detection has been a long-standing challenge. Herein, a chemiresistive sensor that can detect ppb-level formaldehyde in an exclusive manner at room temperature is designed. The TiO₂ sensor exhibits under UV illumination highly selective detection of formaldehyde and ethanol with negligible cross-responses to other indoor pollutants. The coating of a mixed matrix membrane (MMM) composed of zeolitic imidazole framework (ZIF-7) nanoparticles and polymers on TiO₂ sensing films removed ethanol interference completely by molecular sieving, enabling an ultrahigh selectivity (response ratio > 50) and response (resistance ratio > 1,100) to 5 ppm formaldehyde at room temperature. Furthermore, a monolithic and flexible sensor is fabricated successfully using a TiO₂ film sandwiched between a flexible polyethylene terephthalate substrate and MMM overlayer. Our work provides a strategy to achieve exclusive selectivity and high response to formaldehyde, demonstrating the promising potential of flexible gas sensors for indoor air monitoring.

Formaldehyde, a probable carcinogen, is a ubiquitous indoor pollutant, but its ultraselective detection has been a long-standing challenge. Here, the authors develop a chemiresistive sensor that can detect ppb-level formaldehyde in an exclusive manner at room temperature.

Modelling the Molecular Permeation through Mixed-Matrix Membranes Incorporating Tubular Fillers

Membrane-based processes are considered a promising separation method for many chemical and environmental applications such as pervaporation and gas separation. Numerous polymeric membranes have been used for these processes due to their good transport properties, ease of fabrication, and relatively low fabrication cost per unit membrane area. However, these types of membranes are suffering from the trade-off between permeability and selectivity. Mixed-matrix membranes, comprising a filler phase embedded into a polymer matrix, have emerged in an attempt to partly overcome some of the limitations of conventional polymer and inorganic membranes. Among them, membranes incorporating tubular fillers are new nanomaterials having the potential to transcend Robeson's upper bound. Aligning nanotubes in the host polymer matrix in the permeation direction could lead to a significant improvement in membrane permeability. However, although much effort has been devoted to experimentally evaluating nanotube mixed-matrix membranes, their modelling is mostly based on early theories for mass transport in composite membranes. In this study, the effective permeability of mixed-matrix membranes with tubular fillers was estimated from the steady-state concentration profile within the membrane, calculated by solving the Fick diffusion equation numerically. Using this approach, the effects of various structural parameters, including the tubular filler volume fraction, orientation, length-to-diameter aspect ratio, and permeability ratio were assessed. Enhanced relative permeability was obtained with vertically aligned nanotubes. The relative permeability increased with the filler-polymer permeability ratio, filler volume fraction, and the length-to-diameter aspect ratio. For water-butanol separation, mixed-matrix membranes using polydimethylsiloxane with nanotubes did not lead to performance enhancement in terms of permeability and selectivity. The results were then compared with analytical prediction models such as the Maxwell, Hamilton-Crosser and Kang-Jones-Nair (KJN) models. Overall, this work presents a useful tool for understanding and designing mixed-matrix membranes with tubular fillers.

Fabrication, Properties, Performances, and Separation Application of Polymeric Pervaporation Membranes: A Review

Membrane separation technologies have attracted great attentions in chemical engineering, food science, analytical science, and environmental science. Compared to traditional membrane separation techniques like reverse osmosis (RO), ultrafiltration (UF), electrodialysis (ED) and others, pervaporation (PV)-based membrane separation shows not only mutual advantages such as small floor area, simplicity, and flexibility, but also unique characteristics including low cost as well as high energy and separation efficiency. Recently, different polymer, ceramic and composite membranes have shown promising separation applications through the PV-based techniques. To show the importance of PV for membrane separation applications, we present recent advances in the fabrication, properties and performances of polymeric membranes for PV separation of various chemicals in petrochemical, desalination, medicine, food, environmental protection, and other industrial fields. To promote the easy understanding of readers, the preparation methods and the PV separation mechanisms of various polymer membranes are introduced and discussed in detail. This work will be helpful for developing novel functional polymer-based membranes and facile techniques to promote the applications of PV techniques in different fields.

Preparation and Characterization of Polyphenylsulfone (PPSU) Membranes for Biogas Upgrading

Asymmetric polyphenylsulfone (PPSU) membranes were fabricated by a non-solvent induced phase inversion method. Glycerin and silica nanoparticles were added into the polymer solution to investigate their effects on the material properties and gas separation performance of prepared membranes. The morphology and structure of PPSU membranes were analyzed by scanning electron microscopy (SEM), the surface roughness of the selective layer was analyzed by atomic force microscopy (AFM), and the surface free energy was calculated based on the contact angle measurements by using various solvents. The gas separation performance of PPSU membranes was estimated by measuring the permeability of CO₂ and CH₄. The addition of glycerin as a nonsolvent into the polymer solution changed the cross-section structure from finger-like structure into sponge-like structure due to the delayed liquid-liquid demixing process, which was confirmed by SEM analysis. The incorporation of silica nanoparticles into PPSU membranes slightly increased the hydrophilicity, which was confirmed by water contact angle results. PPSU membrane fabricated from the polymer solution containing 10 wt.% glycerin showed the best CO₂/CH₄ selectivity of 3.86 and the CO₂ permeability of 1044.01 Barrer. Mixed matrix PPSU membrane containing 0.1 wt.% silica nanoparticles showed the CO₂/CH₄ selectivity of 3.16 and the CO₂ permeability of 1202.77 Barrer.