Preparation of Polymeric Membranes and Microcapsules Using an Ionic Liquid as Morphology Control Additive

Emerging Trends in Porogens toward Material Fabrication: Recent Progresses and Challenges

Fabrication of tailor-made materials requires meticulous planning, use of technical equipments, major components and suitable additives that influence the end application. Most of the processes of separation/transport/adsorption have environmental applications that demands a material to be with measurable porous nature, stability (mechanical, thermal) and morphology. Researchers say that a vital role is played by porogens in this regard. Porogens (i.e., synthetic, natural, mixed) and their qualitative and quantitative influence on the substrate material (polymers (bio, synthetic), ceramic, metals, etc.) and their fabrication processes are summarized. In most cases, porogens critically influence the morphology, performance, surface and cross-section, which are directly linked to material efficiency, stability, reusability potential and its applications. However, currently there are no review articles exclusively focused on the porogen pores' role in material fabrication in general. Accordingly, this article comprises a review of the literature on various types of porogens, their efficiency in different host materials (organic, inorganic, etc.), pore size distribution (macro, micro and nano), their advantages and limitations, to a certain extent, and their critical applications. These include separation, transport of pollutants, stability improvement and much more. The progress made and the remaining challenges in porogens' role in the material fabrication process need to be summarized for researcher's attention.

Polymers and Solvents Used in Membrane Fabrication: A Review Focusing on Sustainable Membrane Development

(1) Different methods have been applied to fabricate polymeric membranes with non-solvent induced phase separation (NIPS) being one of the mostly widely used. In NIPS, a solvent or solvent blend is required to dissolve a polymer or polymer blend. N-methyl-2-pyrrolidone (NMP), dimethylacetamide (DMAc), dimethylformamide (DMF) and other petroleum-derived solvents are commonly used to dissolve some petroleum-based polymers. However, these components may have negative impacts on the environment and human health. Therefore, using greener and less toxic components is of great interest for increasing membrane fabrication sustainability. The chemical structure of membranes is not affected by the use of different solvents, polymers, or by the differences in fabrication scale. On the other hand, membrane pore structures and surface roughness can change due to differences in diffusion rates associated with different solvents/co-solvents diffusing into the non-solvent and with differences in evaporation time. (2) Therefore, in this review, solvents and polymers involved in the manufacturing process of membranes are proposed to be replaced by greener/less toxic alternatives. The methods and feasibility of scaling up green polymeric membrane manufacturing are also examined.

Fabrication of PES/PVP Water Filtration Membranes Using Cyrene®, a Safer Bio-Based Polar Aprotic Solvent

A more sustainable dialysis and water filtration membrane has been developed, by using the new, safer, bio-based solvent Cyrene® in place of N-methyl pyrrolidinone (NMP). The effects of solvent choice, solvent evaporation time, the temperature of casting gel, and coagulation bath together with the additive concentration on porosity and pore size distribution were studied. The results, combined with infrared spectra, SEM images, porosity results, water contact angle (WCA), and water permeation, confirm that Cyrene® is better media to produce polyethersulfone (PES) membranes. New methods, Mercury Intrusion Porosimetry (MIP) and NMR-based pore structure model, were applied to estimate the porosity and pore size distribution of the new membranes produced for the first time with Cyrene® and PVP as additive. Hansen Solubility Parameters in Practice (HSPiP) was used to predict polymer-solvent interactions. The use of Cyrene® resulted in reduced polyvinylpyrrolidone (PVP) loading than required when using NMP and gave materials with larger pores and overall porosity. Two different conditions of casting gel were applied in this study: a hot (70°C) and cold gel (17°C) were cast to obtain membranes with different morphologies and water filtration behaviours.

Hybrid Ionic Liquid Capsules for Rapid CO2 Capture

The CO₂ absorption by ionic liquids (ILs) were enhanced by the use of hybrid capsules composed of a core of IL and shell of polyurea and alkylated graphene oxide (GO). These composite structures were synthesized using a Pickering emulsion as a template and capsules of two different ILs were prepared. The contribution of the encapsulated IL on the CO₂ absorption of the capsules is consistent with agitated neat IL, but with improved kinetics of absorption across different pressures. This novel materials design allows for CO₂ to be absorbed significantly faster compared to bulk IL and provides insight into improved carbon capture technologies.

DMSO EVOL™ as novel non-toxic solvent for polyethersulfone membrane preparation

The possibility of replacing traditional toxic solvents normally employed during the preparation of polymeric membranes with greener alternatives represents a great challenge for safeguarding the human health and protecting the environment. In this work, an improved and pleasant-smelling version of dimethylsulfoxide (DMSO), i.e., DMSO EVOL™, was used as "greener solvent" for the preparation of polyethersulfone (PES) microfiltration (MF) membranes using a combination of non-solvent and vapor-induced (NIPS and VIPS, respectively) phase separation technique for the first time. The effect of two different additives polyvinylpyrrolidone (PVP) and poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) (Pluronic®) together with polyethylene glycol (PEG) on membrane properties and performances has been also evaluated. The membranes were characterized in terms of morphology, mechanical resistance, pore size, and water permeability. The obtained results show that DMSO EVOL™ is able to replace 1-methyl-2-pyrrolidone (NMP), which is a more toxic solvent normally used for the preparation of PES membranes. Furthermore, it was possible to tune the produced membranes in the range of MF (0.1-0.6 μm).

Pickering Emulsion-Templated Encapsulation of Ionic Liquids for Contaminant Removal

Ionic liquids (ILs) have received attention for a diverse range of applications, but their liquid nature can make them difficult to handle and process and their high viscosities can lead to suboptimal performance. As such, encapsulated ILs are attractive for their ease of handling and high surface area and have potential for improved performance in energy storage, gas uptake, extractions, and so forth. Herein, we report a facile method to encapsulate a variety of ILs using Pickering emulsions as templates, graphene oxide (GO)-based nanosheets as particle surfactants, and interfacial polymerization for stabilization. The capsules contain up to 80% IL in the core, and the capsule shells are composed of polyurea and GO. We illustrate that capsules can be prepared from IL-in-water or IL-in-oil emulsions and explore the impact of monomer and IL identity, thereby accessing different compositions. The spherical, discrete capsules are characterized by optical microscopy, scanning electron microscopy, infrared spectroscopy, Raman spectroscopy, thermogravimetric analysis, and ¹H NMR spectroscopy. We illustrate the application of these IL capsules as a column material to remove phenol from oil, demonstrating ≥98% phenol removal after passage of >170 column volumes. This simple method to prepare capsules of IL will find widespread use across diverse applications.

The synthesis of poly(phenylene sulfide sulfone) in ionic liquids at atmospheric pressure

High performance polymer poly(phenylene sulfide sulfone) was prepared under mild conditions based on 4,4-difluorodiphenylsulfone and Na₂S in i-pmim PF₆ (IL)/MImBS (ZI) at atmospheric pressure and compared with conventional methods.