Robust, readily scalable, high-flux graphene oxide (GO) mixed matrix composite membranes were developed for organic solvent nanofiltration. Hydroxylated polybenzimidazole was synthesized by N-benzylation of polybenzimidazole with 4-(chloromethyl)benzyl alcohol, which was confirmed by FTIR and NMR spectroscopy. Flat sheet composite membranes comprising of polybenzimidazoles and 1 or 2 wt% GO were fabricated via conventional blade coating and phase inversion. Subsequently, GO was covalently anchored to the hydroxyl groups of the polymer using a diisocyanate crosslinking agent. The even distribution of GO in the membranes was mapped by visible-light microscopy. Hydroxylation and incorporation of GO in the polymer matrix increased the permeance up to 45.2±1.6 L m–2 h–1 bar–1 in acetone, nearly 5 times higher than the unmodified benchmark membrane. The enhancement in permeance from the addition of GO did not compromise the solute rejection. The composite membranes were found to be tight in seven organic solvents, having molecular weight cut-offs (MWCO) as low as 140 g mol–1. Permeance increased with increasing solvent polarity, while rejection of a 420 g mol–1 pharmaceutical remained over 93%. The covalent anchoring resulted in robust composite membranes that maintained constant performance over 14 days in a continuous cross-flow configuration.

In order to address the increasing demand for fresh water due to accelerated social and economic growth in the world, water treatment technologies, such as desalination, have been rapidly developed in attempts to safeguard water security. Electromembrane desalination processes, such as electrodialysis and membrane capacitive deionization, belong to a category of desalination technologies, which involve the removal of ions from ionic solutions with the use of electrically charged membranes termed ion exchange membranes. The challenges associated with ion exchange membranes have drawn the attention of many researchers, who have investigated various approaches to enhance their properties. The incorporation of nanomaterials is one of the popular approaches employed. Much research on nanomaterials incorporated ion exchange membranes was conducted for the purpose of fuel cell applications rather than electromembrane desalination. This review reports on the advances in nanomaterials incorporated ion exchange membranes applicable to desalination. The nanomaterials employed in ion exchange membranes fabrication include carbon nanotubes, graphene-based nanomaterials, silica, titanium (IV) oxide, aluminum oxide, zeolite, iron (II, III) oxide, zinc oxide, and silver. The aims of this article are to provide a snap shot of the current status of nanomaterials incorporation in ion exchange membranes, to assess the status of nanomaterials-facilitated ion exchange membranes research for electromembrane desalination, and to stimulate progress in this area.

Mechanically robust and highly permselective anion exchange membranes (AEMs) were prepared based on a graphene oxide (GO) and polybenzimidazolium nanocomposite. GO was modified via diazonium chemistry for better dispersibility and used to fabricate unsupported, nanocomposite, dense, flat sheet AEMs with different GO loadings. A fabrication route using post-casting methylation was developed to avoid GO aggregation induced by the anion exchange polymer. The even GO distribution in the membranes was mapped by energy dispersive spectroscopy (EDS) and wavelength dispersive spectroscopy (WDS). Tensile testing and nanoindentation showed that the AEMs had great mechanical strength indicated by their high ultimate tensile strength and hardness. Furthermore, the AEMs exhibited high ion exchange capacity (1.7–2.1 mmol g⁻¹), good to exceptional permselectivity (up to 0.99) and relatively low area resistance (down to 2.9 Ω cm²). A trade-off between good selectivity and low resistance was investigated for membranes with low GO loadings (0.25–2.5%). The GO nanocomposite AEMs demonstrated excellent potential for electrodialysis.

In this work we introduce a sustainable membrane-based synthesis-separation platform for enantioselective organocatalysis. An azido derivatised cinchona squaramide bifunctional catalyst was synthesised, and subsequently grafted to the surface of a polybenzimidazole based nanofiltration membrane. The favourable effect of the covalent grafting — due to the change in geometry and increased secondary interactions — on the catalytic activity due to conformational changes was confirmed by quantum chemical calculations. Asymmetric Michael and aza-Michael reactions of 1,3-dicarbonyl and indole, pyrazole and triazole derivatives to β-nitrostyrene were performed with as high as 99% enantiomeric excess. This report on the enantioselective aza-Michael reaction of pyrazoles and triazoles opens new frontiers in the application of squaramide based cinchona catalysts. A catalytic membrane cascade reactor was developed for an integrated synthesis purification process allowing at least 98% product and substrate recovery, and quantitative in situ solvent recycling. The sustainability of the synthetic methodology was assessed through E-factor and carbon footprint.

Membrane technology is a dynamically developing field of separation science that is poised to result in new and efficient processes, energy and cost savings, and sustainability benefits. A key challenge in this field is the development of highly selective membranes, which can be addressed by the development of mixed-matrix membranes (MMMs) containing fillers such as metal–organic frameworks (MOFs). However, the lack of interfacial adhesion causes nanosized gaps between the filler and the polymer matrix. In this study, we aim to elucidate the intrinsic properties of MMMs and bridge the gap between their material constituents. A series of novel membranes comprising MOF nanoparticles with similar chemical and morphological properties but increasing pore size (UiO-66–68-NH₂) were prepared. The nanoparticles' surface was covalently grafted with poly(N-isopropylacrylamide) (PNIPAM) chains, which could then become entangled with the membranes' polymer matrix. Morphological characterization and organic solvent nanofiltration tests revealed that membranes with PNIPAM-grafted fillers do not suffer from the formation of pinholes at the filler–matrix interface that are detrimental to the filtration performance. For the first time, the experimental results showed an excellent match with a predictive model of nanofiltration built around the premise of liquid transport through the highly ordered pores of the MOF filler.

As a result of recent efforts in green solvent selection, methyl 5-(dimethylamino)-2-methyl-5-oxopentanoate, sold under the brand name Rhodiasolv PolarClean, has received considerable scientific and industrial attention as a possible non-toxic replacement for common polar aprotic solvents. However, the multicomponent nature and multi-step synthesis of this solvent remains an obstacle for its more widespread use and niche applications. In this work, a retrosynthetic approach was taken to identify novel shorter synthetic routes in alignment with green chemistry principles. High purity methyl 5-(dimethylamino)-2-methyl-5-oxopentanoate was obtained in novel single-step reactions via two different base-catalysed Michael additions from readily available building blocks. The more advanced synthetic route shows great potential owing to the swift (30 min), solvent-free reaction and catalytic amounts of base (<6.5 mol%). Green metrics analysis, including Atom Economy, Complete E factor, Carbon Intensity and hazard analysis found the new synthesis to be more sustainable than the patented routes. Application of this green solvent was demonstrated for the first time for O- and N-arylation in S_NAr reaction with solvent recovery with similar or superior yields compared to other green solvents. Moreover, broad opportunities for this green solvent in membrane science were identified, where the use of conventional, toxic polar aprotic solvents in large quantities is unavoidable. Important practical solvent properties and parameters such as dielectric constant, solubility parameters, solvent miscibility and NMR residual shifts have been determined to facilitate the uptake of methyl 5-(dimethylamino)-2-methyl-5-oxopentanoate as a green solvent.