Understanding the role of substrates on thin film composite membranes: A green solvent approach with TamiSolve® NxG

Using the Assembly Time as a Tool to Control the Surface Morphology and Separation Performance of Membranes with a Tannic Acid-Fe3+ Selective Layer

Thin-film composite (TFC) membranes containing a metal-polyphenol network (MPN)-based selective layer were fabricated on a porous polyacrylonitrile support. The MPN layer was formed through coordination-based self-assembly between plant-based tannic acid (TA) and an Fe3+ ion. For the first time, we demonstrate that TFC membranes containing TA-Fe3+ selective layers can separate small organic solutes in aqueous media from equimolar mixtures of solutes. The effect of the assembly time on the characteristics and performance of the fabricated selective layer was investigated. An increase in the assembly time led to the formation of selective layers with smaller effective pore sizes. The tannic acid-Fe3+ selective layer exhibited a low rejection towards neutral solutes riboflavin and poly(ethylene glycol) while high rejections were observed for anionic dyes of orange II and naphthol green B. Permeation selectivities in the range of 2-27 were achieved between neutral and charged dyes in both single- and mixed-solute experiments, indicating the significant role of Donnan exclusion and the charge-selective nature of the membranes. The rejection efficiency improved with an increasing assembly time. Overall, this study demonstrates that the assembly time is a vital casting parameter for controlling the permeance, rejection and selectivity of thin-film composite membranes with a tannic acid-Fe3+ selective layer.

Green Synthesis of Cation Exchange Membranes: A Review

Cation exchange membranes (CEMs) play a significant role in the transition to a more sustainable/green society. They are important components for applications such as water electrolysis, artificial photosynthesis, electrodialysis and fuel cells. Their synthesis, however, is far from being sustainable, affecting safety, health and the environment. This review discusses and evaluates the possibilities of synthesizing CEMs that are more sustainable and green. First, the concepts of green and sustainable chemistry are discussed. Subsequently, this review discusses the fabrication of conventional perfluorinated CEMs and how they violate the green/sustainability principles, eventually leading to environmental and health incidents. Furthermore, the synthesis of green CEMs is presented by dividing the synthesis into three parts: sulfonation, material selection and solvent selection. Innovations in using gaseous SO3 or gas-liquid interfacial plasma technology can make the sulfonation process more sustainable. Regarding the selection of polymers, chitosan, cellulose, polylactic acid, alginate, carrageenan and cellulose are promising alternatives to fossil fuel-based polymers. Finally, water is the most sustainable solvent and many biopolymers are soluble in it. For other polymers, there are a limited number of studies using green solvents. Promising solvents are found back in other membrane, such as dimethyl sulfoxide, Cyrene™, Rhodiasolv® PolarClean, TamiSolve NxG and γ-valerolactone.

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.

Solvent-Resistant UV-Cured Polysulfone Support Membranes Using a Green Solvent

Solvent-resistant UV-cured supports consisting of a semi-interpenetrating network of polysulfone (PSf) and cross-linked poly-acrylate were successfully synthesized for the first time using an alternative, non-reprotoxic, and biodegradable solvent. Tamisolve^® NxG is a high-boiling, dipolar aprotic solvent with solubility parameters similar to those of dimethylformamide (DMF) and N-methyl-2-pyrrolidone (NMP), making it an eco-friendly alternative. The support membranes, prepared via UV-curing followed by non-solvent-induced phase inversion, can serve as a universal solvent-resistant support for the synthesis of a broad set of membranes, for which the selective layer can be deposited from any solvent. Parameters such as UV irradiation time and intensity, as well as the concentrations of PSf, penta-acrylate, and photo-initiator in the casting solution were varied to obtain such supports. The characteristics of the resulting supports were investigated in terms of separation performance, hydrophobicity, porosity, degree of acrylate conversion, and pure water flux. The resulting membranes showed improved chemical resistance in solvents such as ethyl acetate, NMP, tetrahydrofuran (THF), and toluene. Solvent-resistant supports with different pore sizes were synthesized and used for the preparation of thin film composite (TFC) membranes to demonstrate their potential. Promising separation performances with Rose Bengal (RB) rejections up to 98% and water permeances up to 1.5 L m^-2 h^-1 bar^-1 were reached with these TFC-membranes carrying a polyamide top layer synthesized via interfacial polymerization.