Radiation-grafted cation-exchange membranes:an initial ex situ feasibility study into their potential use in reverse electrodialysis

A variety of radiation-grafted cation-exchange membranes (RG-CEM) were synthesised, using a high-dose rate electron-beam peroxidation method, for an initial evaluation of their applicability to reverse electrodialysis cells (RED, a type of salinity gradient “blue” energy). The RG-CEMs were adequately conductive (to Na+ cations) but without the incorporation of crosslinking co-monomers, the permselectivities were too low (≤80%). In contrast, when ETFE-based RG-CEMs were synthesised with incorporation of 10% mol bis(vinylphenyl)ethane (BVPE) crosslinking co-monomer into the styrene-containing grafting mixture, permselectivities of >90% were obtained without a significant decrease in conductivity. The use of BVPE in the grafting mixture also resulted in the RG-CEMs exhibiting enhanced ion-exchange capacities without any increase in water uptakes (cf. uncrosslinked variants). In contrast, the use of less flexible divinylbenzene crosslinker led to prohibitively large decreases in RG-CEM conductivity. This study highlights that the future development of both radiation-grafted cation-exchange and anion-exchange membranes for RED (and other electrodialysis applications) should utilise flexible crosslinkers (such as BVPE) to ensure adequate permselectivities

Raman Analysis of Meta-autunite

A sample of meta-autunite (Ca(UO2)2(PO4)2·6-8(H2O)) from a national reference collection was characterised by Raman spectroscopy as a representation of a potential spent nuclear fuel corrosion product. Raman spectra were collected at 457, 532, 633 and 785 nm; all exhibited some fluorescence effects, though to a lesser extent at 785 nm. The phosphate (v2(PO4)3−, v3(PO4)3−, v4(PO4)3−) and uranyl (v1(UO2)2+ and v2(UO2)2+) features could be unambiguously assigned in the resolved 785 nm spectrum. The position of the v3(UO2)2+ mode was predicted but not observed. The uranyl bond lengths and force constants were determined from the v1(UO2)2+ dominant and shoulder peak, as 1.78±0.01 and 1.79±0.01 Å and 5.69±0.08 and 5.29±0.08 millidynes Å−1, respectively

A Raman spectro-microscopic investigation of ETFE-based radiation-grafted anion-exchange membranes

This study used Raman spectro-microscopy to investigate the synthesis and degradation of radiation-grafted anion-exchange membranes (RG-AEM) made using 50 μm thick poly(ethylene-co-tetrafluoroethylene) (ETFE) films, vinylbenzyl chloride (VBC) monomer, and 1-methylpyrrolidine (MPY) amination agent. The data obtained confirmed the operation of the grafting-front mechanism. VBC grafting times of 1 and 4 h led to low degrees of grafting homogeneity, while 72 h led to extreme levels of grafting that resulted in mechanically weak RG-AEMs due to the excessive H2O contents. A grafting time of 16 h was optimal yielding a RG-AEM with an ion-exchange capacity (IEC) of 2.06 ± 0.02 mmol g-1 (n = 3). An excess of grafting was detected at the surface of this RG-AEM (at least within the first few μm of the surface). This RG-AEM was then degraded in O2-purged aqueous KOH (1.0 mol dm-3) for 14 d at 80 °C. Degradation was detected throughout the RG-AEM cross-section, where the Raman data was quantitatively consistent with the loss of IEC. A slight excess of degradation was detected at the surface of the RG-AEM. Degradation involved the loss of whole benzyl-1-methypyrrolidinium grafted units as well as the direct attack on the pendent (cationic) pyrrolidinium groups by the hydroxide anions

A Raman spectro-microscopic investigation of ETFE-based radiation-grafted anion-exchange membranes

This study used Raman spectro-microscopy to investigate the synthesis and degradation of radiation-grafted anion-exchange membranes (RG-AEM) made using 50 μm thick poly(ethylene-co-tetrafluoroethylene) (ETFE) films, vinylbenzyl chloride (VBC) monomer, and 1-methylpyrrolidine (MPY) amination agent. The data obtained confirmed the operation of the grafting-front mechanism. VBC grafting times of 1 and 4 h led to low degrees of grafting homogeneity, while 72 h led to extreme levels of grafting that resulted in mechanically weak RG-AEMs due to the excessive H2O contents. A grafting time of 16 h was optimal yielding a RG-AEM with an ion-exchange capacity (IEC) of 2.06 ± 0.02 mmol g-1 (n = 3). An excess of grafting was detected at the surface of this RG-AEM (at least within the first few μm of the surface). This RG-AEM was then degraded in O2-purged aqueous KOH (1.0 mol dm-3) for 14 d at 80 °C. Degradation was detected throughout the RG-AEM cross-section, where the Raman data was quantitatively consistent with the loss of IEC. A slight excess of degradation was detected at the surface of the RG-AEM. Degradation involved the loss of whole benzyl-1-methypyrrolidinium grafted units as well as the direct attack on the pendent (cationic) pyrrolidinium groups by the hydroxide anions

Radiation-grafted cation-exchange membranes: an initial ex situ feasibility study into their potential use in reverse electrodialysis

A variety of radiation-grafted cation-exchange membranes (RG-CEM) were synthesised, using a high-dose rate electron-beam peroxidation method, for an initial evaluation of their applicability to reverse electrodialysis cells (RED, a type of salinity gradient “blue” energy). The RG-CEMs were adequately conductive (to Na+ cations) but without the incorporation of crosslinking co-monomers, the permselectivities were too low (≤80%). In contrast, when ETFE-based RG-CEMs were synthesised with incorporation of 10% mol bis(vinylphenyl)ethane (BVPE) crosslinking co-monomer into the styrene-containing grafting mixture, permselectivities of >90% were obtained without a significant decrease in conductivity. The use of BVPE in the grafting mixture also resulted in the RG-CEMs exhibiting enhanced ion-exchange capacities without any increase in water uptakes (cf. uncrosslinked variants). In contrast, the use of less flexible divinylbenzene crosslinker led to prohibitively large decreases in RG-CEM conductivity. This study highlights that the future development of both radiation-grafted cation-exchange and anion-exchange membranes for RED (and other electrodialysis applications) should utilise flexible crosslinkers (such as BVPE) to ensure adequate permselectivities

An Asymmetric N-Rim Partially Substituted Calix[4]pyrrole: Its Affinity for Ag(I) and its Destruction by Hg(II)

A new partially substituted calix[4] pyrrole derivative obtained by the introduction of three thioamide functionalities in the N-rim has been synthesised and fully characterised by 1H,13C, HSQC, ROESY NMR and mass spectroscopy. Computer modelling suggested an alternate conformation which was confirmed through ROESY 1H NMR. The receptor interacts only with the silver cation as shown by 1H NMR. The strength of interaction is quantitatively assessed by titration calorimetry. N-rim modification eliminates the possibility of interaction with anions. Unlike calix[4] pyrrole derivatives obtained by the introduction of functionalities through the meso-position, addition of Hg(NO3)2 leads to the degeneration of the receptor as demonstrated by 1H NMR, FTIR and XPS analyses. This is for the first time reported. Molecular simulation studies show significant strain in the mercury bound ligand in bonds, angles, torsions leading to the destruction of the receptor. Given the negative environmental impact produced by the availability of silver ions in aquatic organisms, the fundamental studies indicate that this receptor offers potential applications for monitoring silver (ion selective electrode) or indeed as a decontaminating material for removing silver ions from water

The Alkali Degradation of LDPE-Based Radiation-Grafted Anion-Exchange Membranes Studied Using Different ex situ Methods

Radiation-grafted anion-exchange membranes (RG-AEM) in alkaline membrane fuel cells (AEMFC) exhibit promising performances (low in situ resistances, high power outputs and reasonably high alkali stabilities). Much research is focused on developing AEMs with enhanced chemical stabilities in the OH--forms at temperatures >60 °C. This study contributes towards this effort by providing a comparison of three different ex situ methods of screening alkali stabilities (where different laboratories conducted experiments on exactly the same batches of RG-AEM). Vinylbenzyl chloride monomer was radiation-grafted onto 25 µm thick low-density polyethylene (LDPE) precursor film in a single batch. This batch of grafted membrane was then split into three sub-batches, which were converted into RG-AEMs via amination with either: trimethylamine (TMA), N-methylpyrrolidine (MPY), or N-methylpiperidine (MPIP). Samples of each RG-AEM (L-AEM-TMA, L-AEM-MPY, and L-AEM-MPIP) were then distributed between the three collaborating institutes for evaluation using each institutes' test protocols. Out of the three head-group chemistries, the L-AEM-TMA generally exhibits the best balance of conductivity and ex situ alkali degradation, especially in lower humidity environments. The L-AEM-TMA also exhibited interestingly high Cl- ion conductivities (ca. 100 mS cm-1) when heated to 80 °C in a relative humidity RH = 95% atmosphere, a measurement frequently overlooked in favour of determining conductivities of RG-AEMs submerged in water (conductivities of submerged RG-AEMs can be suppressed due to excessive water contents and swelling)

Radiation-grafted anion-exchange membranes for reverse electrodialysis: a comparison of N,N,N′,N′-tetramethylhexane-1,6-diamine crosslinking (amination stage) and divinylbenzene crosslinking (grafting stage)

Radiation-grafted anion-exchange membranes (RG-AEM) are being developed to evaluate a range of chemistries that have relevance to a variety of electrochemical applications including reverse electrodialysis (RED) salinity gradient power. RG-AEMs are typically fabricated using an electron-beam activated (peroxidated) polymer substrate film. These activated films are first grafted with a monomer, such as vinylbenzyl chloride (VBC) and then reacted with a variety of tertiary amines to yield the desired RG-AEMs. The amination process forms covalently bound quaternary ammonium (QA) head-groups that allow the RG-AEMs to conduct anions such as Cl−. RG-AEMs are of interest as they exhibit high conductivities (100 mS cm−1 at elevated temperatures when containing Cl− anions). However, the current generation of RG-AEMs have two main Achilles' heels: (1) they exhibit low permselectivities; and (2) they exhibit a high degree of swelling in water. Introducing covalent crosslinking into ion-exchange membranes is a well-known strategy to overcome these issues but it often comes with a price – a significantly lowered conductivity (raised in situ resistance). Therefore, the level of crosslinking must be carefully optimised. RG-AEMs can be primarily crosslinked using two methods: (1) introduction of a divinyl monomer into the monomer mixture used during grafting; or (2) introduction of a diamine agent into the amination process. This study looks into both methods where either divinylbenzene (DVB) is added into the grafting mixture or N,N,N′,N′-tetramethylhexane-1,6-diamine (TMHDA) is added into the amination mixture. We show that on the balance of two application-relevant properties (resistances in aqueous NaCl (0.5 mol dm−3) solution and permselectivity), the diamine crosslinking method is the most effective for RG-AEMs being used in RED cells

ETFE-based anion-exchange membrane ionomer powders for alkaline membrane fuel cells: a first performance comparison of head-group chemistry

In the last few years, the development of radiation-grafted powder-form anion-exchange ionomers (AEI), used in combination with anion-exchange membranes (AEM), have led to the assembly of AEM-based fuel cells (AEMFC) that routinely yield power densities ranging between 1 – 2 W cm-2 (with a variety of catalysts). However, to date, only benzyltrimethyammonium-type powder AEIs have been evaluated in AEMFCs. This study presents an initial evaluation of the relative AEMFC power outputs when using a combination of ETFE-based radiation-grafted AEMs and AEIs containing three different head-group chemistries: benzyltrimethylammonium (TMA), benzyl-N-methylpyrrolidinium (MPY), and benzyl-N-methylpiperidinum (MPRD). The results from this study strongly suggest that future research should focus on the development and operando long-term durability testing of AEMs and AEIs containing the MPRD head-group chemistry

ETFE-based anion-exchange membrane ionomer powders for alkaline membrane fuel cells: A first performance comparison of head-group chemistry

In the last few years, the development of radiation-grafted powder-form anion-exchange ionomers (AEI), used in combination with anion-exchange membranes (AEM), has led to the assembly of AEM-based fuel cells (AEMFC) that routinely yield power densities ranging between 1-2 W cm-2 (with a variety of catalysts). However, to date, only benzyltrimethylammonium-type powder AEIs have been evaluated in AEMFCs. This study presents an initial evaluation of the relative AEMFC power outputs when using a combination of ETFE-based radiation-grafted AEMs and AEIs containing three different head-group chemistries: benzyltrimethylammonium (TMA), benzyl-N-methylpyrrolidinium (MPY), and benzyl-N-methylpiperidinium (MPRD). The results from this study strongly suggest that future research should focus on the development and operando long-term durability testing of AEMs and AEIs containing the MPRD head-group chemistryThe research was funded by the Engineering and Physical Sciences Research Council (EPSRC grants EP/M014371/1, EP/M022749/1, and EP/M005933/1). ALGB's exchange was funded by FAPESP grants 2016/13277-9 and 2015/09210-3, while EIS' exchange was funded by FAPESP grants 2015/23621-6, 2014/09087-4 and 2014/50279-4. DH's student-exchange was funded by a PDIF Short Stay Scholarship of the Autonomous University of Madrid. GS' 2015 exchange was funded by the ERASMUS+work placement schem