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As nanofiltration applications increase in diversity, there is a need for new fabrication methods to prepare chemically and thermally stable membranes with high retention performance. In this work, thio-bromo “click” chemistry was adapted for the fabrication of a robust covalently attached and ultrathin nanofiltration membrane. The selective layer was formed on a pre-functionalized porous ceramic surface via a novel, liquid–vapor interfacial polymerization method. Compared to the most common conventional interfacial polymerization procedure, no harmful solvents and a minimal amount of reagents were used. The properties of the membrane selective layer and its free-standing equivalent were characterized by complementary physicochemical analysis. The stability of the thin selective layer was established in water, ethanol, non-polar solvents, and up to 150 °C. The potential as a nanofiltration membrane was confirmed through solvent permeability tests (water, ethanol, hexane, and toluene), PEG-in-water molecular weight cut-off measurements (≈700 g mol–1), and dye retention measurements.

Organic solvent nanofiltration (OSN) is gradually expanding from academic research to industrial implementation. The need for membranes with low and sharp molecular weight cutoffs that are able to operate under aggressive OSN conditions is increasing. However, the lack of comparable and uniform performance data frustrates the screening and membrane selection for processes. Here, a collaboration is presented between several academic and industrial partners analyzing the separation performance of 10 different membranes using three model process mixtures. Membrane materials range from classic polymeric and thin film composites (TFCs) to hybrid ceramic types. The model solutions were chosen to mimic cases relevant to today's industrial use: relatively low molar mass solutes (330–550 Da) in n-heptane, toluene, and anisole.

In this study we describe a novel and simple method to couple covalently poly (maleic anhydride-alt-1-alkenes) to γ-alumina nanofiltration membranes for the first time. The 1-alkenes varied from 1-hexene, 1-decene, 1-hexadecane to 1-octadecene. The grafting reaction was between the reactive anhydride moieties of the polymer and surface hydroxyl groups, resulting in highly stable bonds. The modified membranes were investigated for their permeation and rejection performance of Sudan Black (SB, Mw 457 Da) in either toluene or ethyl acetate (EA) solution, and very high rejections (> 90%) and high permeation flux were observed compared to unmodified membranes. Initially, the SB in toluene solution was found to bind strongly to the surface hydroxyl groups of the unmodified membranes, an effect not observed in EA solution.

PDMS-grafted alumina membranes have already demonstrated high organic solvent permeabilities; described and modeled in this paper are their retention capabilities. In contrast to pure PDMS polymeric membranes, higher retentions were found in nonpolar solvents than in polar solvents. This is attributed to a solvent-induced pore-constriction behavior: confined swelling of PDMS, grafted into the membrane pores, was found to increase retention. To test this hypothesis, pore sizes were obtained by integrating the Ferry, Verniory and steric hindrance pore (SHP) equations into the Spiegler Kedem Katchalsky (SKK) model in order to predict the retention of dyes. Ultimately, a diffusion pore size was introduced into the SKK model to reflect the ability of the solute to diffuse through the swollen PDMS graft. A better understanding of the transport mechanisms that impact performance was achieved by incorporating the unique pore structure of these ceramic-based hybrid membranes into the SKK model.

To the best of our knowledge, for the first time MIL-53(Al) and NH2-MIL-53(Al) modified α-alumina membranes are investigated for the adsorption of organic dyes from organic solvents. These new, modified membranes show excellent adsorption of high concentrations of Rose Bengal dye in methanol and isopropanol solutions.

To the best of our knowledge, for the first time MIL-53(Al) and NH 2 -MIL-53(Al) modified α-alumina membranes are investigated for the adsorption of organic dyes from organic solvents. These new, modified membranes show excellent adsorption of high concentrations of Rose Bengal dye in methanol and isopropanol solutions.

Here, we report the covalent coupling of poly (styrene-co-maleic anhydride) onto γ-alumina to develop high-performance organic solvent nanofiltration (OSN) membranes. A high molecular weight (M w ) alternating copolymer of maleic anhydride (MA) and styrene (St) was synthesized and directly grafted to the γ-alumina membrane, while commercially available low M w random copolymers of St and MA were also investigated. We show that solute rejection and membrane permeability strongly depend on the nature of the applied copolymer. In particular, the M w of the copolymer applied is potentially the key for improving the membrane performance. When a high M w copolymer was applied, the grafted layer covered the surface of the membrane. This results in membranes with significantly improved rejection, while maintaining a high permeability. In contrast, we observed pore grafting by applying low M w copolymers, which resulted in membranes with slightly higher rejection and dramatically lower permeability compared to unmodified membrane. The best results were obtained by grafting γ-alumina with a high M w alternating copolymer. These membranes showed a solute rejection of 98% for Sudan Black B (457 g mol −1 ) in toluene, while the permeability remained high at 2.9 L m −2 h −1 bar −1 .

The development of controlled polymerization techniques in the last decade has enabled polymer brushes to be grown from inorganic substrates with precision. Less studied are brushes grown from concave geometries of high curvature, such as mesopores, despite their application potential in the separation sciences. The method used here, surface-initiated, activators-regenerated-by-electron-transfer, atom-transfer radical polymerization (SI-ARGET-ATRP), is used to grow a polystyrene brush grown from aluminum oxide pores of 5 nm diameter, to-date the most confined geometry in which ATRP has been conducted. The brush is characterized by TGA, AFM, and FTIR, the latter two methods applied specifically to the external brush. Additionally, permporometry as well as permeability and retention measurements are used to characterize the graft within the mesopores. We show that the brush length is tunable, that the brush length is solvent-dependent, and we also demonstrate the application potential of this hybrid material as an organic solvent nanofiltration membrane. This new class of membranes shows excellent performance: a toluene permeability of 2.0 L m−2 h−1 bar−1 accompanied by a 90% rejection of diphenylanthracene (MW 330 g mol−1).

Uniquely suited to organic solvent nanofiltration (OSN) are hybrid, ceramic-based membranes. The stability of these membranes in the harsh solvents and conditions of industrial process streams is due to the sturdy and inert architecture of the ceramic, while the organic functionalization is responsible for surface and pore properties of the membrane, and hence its performance. Recently, this kind of inorganic-organic union has produced a plethora of stable and high-performance membranes in a variety of OSN conditions - the topic of this review. This work details and compares the surface modification methods used to fabricate these membranes and their resulting performance. Also, we discuss the capabilities and shortcomings of both the characterization tools and the transport models used to describe this class of membranes. Throughout we aim to provide insight into the challenges awaiting the researcher of hybrid, ceramic-based membranes for OSN.