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In this paper, a bimetallic Metal-Organic Framework (MOF) CoNiBTC was employed as a precursor for the fabrication of bimetallic nanoalloys CoNi@C evenly disseminated in carbon shells. These functional nanomaterials are characterized by powdered X-ray diffraction (PXRD), Fourier Transform Infra-Red spectroscopy (FTIR), surface area porosity analyzer, X-ray photoelectron spectroscopy (XPS), Field emission scanning electron microscopy (FESEM), Transmission electron microscopy (TEM), Hydrogen Temperature-Programmed Reduction (H2 TPR), CO2 Temperature-Programmed Desorption (CO2-TPD), and Inductively Coupled Plasma Mass Spectrometry (ICP-MS). This nanocatalyst was utilized in the synthesis of benzimidazole from o-phenylenediamine in the presence of CO2 and H2 in a good yield of 81%. The catalyst was also efficient in the manufacture of several substituted benzimidazoles with high yield. Due to the existence of a bimetallic nanoalloy of Co and Ni, this catalyst was also employed in the methanation of CO2 with high selectivity (99.7%).

Polymer inclusion membrane (PIM) has recently evolved as an alternative separation technique to conventional solvent extraction as it eliminates the use of toxic solvents, reduces separation cost, and simplifies the separation process. PIM is the new generation of a liquid membrane made by casting solution containing liquid phases (extractant and plasticizer/modifier) and base polymers. Despite its better performance and stability in comparison to the previous types of liquid membranes, PIM's robustness for applications on an industrial scale is still considered insufficient mainly due to its limited stability in the long-term separation process. In recent years, different approaches have been devoted to improving the stability of PIM while maintaining its performance. This review aims to summarize and evaluate the current literature on the improvement of the performance of PIMs with particular focus on the use of alternative base polymers, including non-conventional linear homopolymers, copolymers, or cross-linking polymers. Furthermore, more emphasis is given to the composition, fabrication process, and application of the PIMs. Finally, the performance of the PIMs with the alternative base polymers in terms of extraction rate and long-term stability is presented and compared to the PIMs fabricated using their corresponding common base polymers.

This study aims at comprehensively investigating the possibility of fabricating cross-linked polymer inclusion membranes (PIMs) using the most common base polymers (i.e., poly(vinyl chloride), cellulose triacetate and poly(vinylidene fluoride-co-hexafluoropropylene)), cross-linking polymers or monomers (i.e., poly(ethylene glycol) dimethylacrylate, poly(ethylene glycol) divinylether and N-ethylmaleimide) and photo-initiators (i.e., 2,2-dimethoxy-2-phenyl acetophenone, triarylsulfonium hexafluorophosphate and triphenylphosphine oxide). The suitability of the photo-initiators for the different cross-linking polymers/monomers in poly(vinyl chloride)-based membranes (without extractants) was assessed for the first time, which was followed by optimizing the cross-linking conditions (i.e., membrane composition and duration of UV-irradiation) for all three base polymers studied. The optimum concentrations of photo-initiator and UV-treatment times were different for the different base polymers used, thus highlighting the importance of this study. Aliquat 336 and di-(2-ethylhexyl)phosphoric acid, as the most frequently used PIM extractants, were added to the compositions of the homogeneous cross-linked membranes produced under optimal conditions and the extraction performance of the newly developed cross-linked PIMs was compared with that of their non-cross-linked counterparts in the extraction of SCN− and Zn2+, respectively. The results showed that all but one of the 13 homogeneous cross-linked PIMs obtained in this study could extract up to 45% more of the corresponding target species than their non-cross-linked counterparts and the remaining one performed similarly to the relevant non-cross-linked PIM. The initial fluxes for the cross-linked PIMs were up to 10 times higher than those of the relevant non-cross-linked membranes and in two cases the fluxes were similar in value. These results demonstrate the potential of cross-linking for enhancing the extraction performance of PIMs.

This study demonstrated the advantages of cross-linking of polymer inclusion membranes (PIMs) in terms of improved stability, rate of extraction and extractive capacity. These advantages were illustrated with the new cross-linked PIM for the selective extraction of Zn(II), developed as part of this study and containing bis-(2-ethylhexyl)phosphoric acid (D2EHPA) as the carrier (extractant). Three different base-polymers were tested, namely poly(vinyl chloride) (PVC), poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) and cellulose triacetate (CTA), using poly(ethylene glycol) dimethacrylate (PEG-DMA) as the cross-linking polymer and 2,2-dimethoxy-2-phenyl acetophenone (DMPA) as the initiator. Only PVDF-HFP- and CTA-based PIMs were found to be successful (i.e., homogenous, transparent and mechanically stable). CTA-based PIMs showed a higher extraction rate than the PVDF-HFP-based PIMs and non-cross-linked PIMs containing the same base-polymer, and thus CTA was chosen as the base-polymer for a more detailed study. The effect of the polymer ratio (CTA:PEG-DMA), concentration of D2EHPA, and concentration of plasticizer (i.e., 2-nitrophenyloctyl ether (NPOE)) on the membrane performance was studied. Best performance in terms of stability, rate of extraction and extractive capacity, which were superior to the corresponding non-cross-linked PIM, was achieved with the cross-linked PIM composed of 40 wt% D2EHPA, 10 wt% NPOE, polymers ratio of 6:4 (CTA:PEG-DMA), and 0.6 wt% DMPA. The PIM surface morphology, examined by atomic force microscopy (AFM), correlated well with the rate of Zn(II) extraction. It was also demonstrated that the cross-linked PIM could selectively extract Zn(II) from aqueous solutions at pH 3.0 in the presence of other common base metal ions such as Cd(II), Co(II), Cu(II), and Ni(II) in concentrations 5 times higher than that of Zn(II). Interference from Fe(III) was removed by precipitation with phosphate. The newly developed PIM transported practically all Zn(II) from a feed solution at pH 3 to a 1.0 M HCl receiving solution as a result of the simultaneous extraction and back-extraction of Zn(II) at the corresponding PIM/solution interfaces, and the facilitated transport of Zn(II) across the membrane.