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1. Phthalocyanines as a π–π Adsorption Strategy to Immobilize Catalyst on Carbon for Electrochemical Synthesis

   https://doi.org/10.1055/s-0037-1611792  

   Klunder, Kevin J.; Cass, Ashley C.; Anderson, Scott L.; Minteer, Shelley D. (May 2019, Synlett)

   In most electrochemical syntheses, reactions are happening at or near the electrode surface. For catalyzed reactions, ideally, the electrode surface would solely contain the catalyst, which then simplifies purification and lowers the amount of catalyst needed. Here, a new strategy involving phthalocyanines (Pc) to immobilize catalysts onto carbon electrode surfaces is presented. The large π structure of the Pc enables adsorption to the sp2-structure of graphitic carbon. TEMPO-modified Pc were chosen as a proof of concept to test the new immobilization strategy. It was found that the TEMPO-Pc derivatives functioned similarly or better than the widely used pyrene adsorption method. Interestingly, the new TEMPO-Pc catalyst appears to facilitate a cascade reaction involving both the anode and the cathode. The first step is the generation of an aryl aldehyde (anode) followed by the reduction of the aryl aldehyde in a pinacol-type coupling reaction at the cathode. The last step is the oxidation of a hydrobenzoin to create benzil. This work demonstrates the unique ability of electrochemistry and bifunctional catalysts to enable multistep chemical transformations, performing both reductive and oxidative transformations in one pot. 

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2. Promoting water-splitting in Janus bipolar ion-exchange resin wafers for electrodeionization

   https://doi.org/10.1039/C9ME00179D  

   Jordan, Matthew L.; Valentino, Lauren; Nazyrynbekova, Nargiza; Palakkal, Varada Menon; Kole, Subarna; Bhattacharya, Deepra; Lin, Yupo J.; Arges, Christopher G. (January 2020, Molecular Systems Design & Engineering)

   Electrochemical separation processes are undergoing a renaissance as the range of applications continues to expand because they offer opportunities for increased energy efficiency and sustainability in comparison to conventional separation technologies. Existing platforms such as electrodialysis and electrodeionization (EDI) are seeing significant improvement and are currently being deployed for treating a diverse set of liquid streams ( e.g. , water and wastewater treatment, organic acid separation, etc. ). In addition, the relatively low inherent electricity requirement for electrochemical separations could potentially be satisfied through integration with sustainable sources of renewable energy. In order to achieve a truly sustainable electrochemical separations process, it is paramount to improve the energy efficiency of electrochemical separations by minimizing all sources of resistances within these units. This work reports of a new class of symmetric and asymmetric Janus bipolar resin wafers (RWs) that augment the spacer channel ionic conductivity in EDI while having the additional functionality of splitting water into protons and hydroxide ions. The latter attribute is important in niche applications that require pH modulation such as silica and organic acid removal from liquid streams. The Janus bipolar RWs were devised from single ion-conducting RWs that were interfaced together to create an intimate polycation–polyanion junction. Interestingly, the conductivity of the single ion-conducting RWs at low salt concentrations was observed to be dependent on the ionic mobilities of the counterions that the RW was transferring. Using single ion-conducting RWs to construct Janus bipolar RWs enabled the incorporation of a water-splitting catalyst (aluminum hydroxide nanoparticles) into the porous ion-exchange resin bed. To the best of our knowledge, this is the first time a water dissociation catalyst has been implemented in the ion-exchange resin bed for EDI. The water dissociation catalyst in bipolar junctions pre-polarizes water making it easier to split into hydronium and hydroxide ion charge carriers under applied electric fields via the second Wien effect. The new molecularly layered Janus RWs demonstrate both satisfactory water-splitting and salt removal in bench scale EDI setups and these materials may improve, or even supplant, existing bipolar membrane electrodialysis units that currently necessitate large electrolyte feed concentrations. 

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3. Immobilized phosphate‐binding protein can effectively discriminate against arsenate during phosphate adsorption and recovery

   https://doi.org/10.1002/wer.1498  

   Venkiteshwaran, Kaushik; Wells, Erin; Mayer, Brooke K. (December 2020, Water Environment Research)

   Abstract There is a strong impetus to establish a circular phosphorus economy by securing internally renewable phosphate (P_i) resources for use as agricultural fertilizers. Reversible P_iadsorption technologies such as ion exchange can remove and recover P_ifrom water/wastewater for reuse. However, existing reversible adsorbents cannot effectively discriminate against arsenate (As(V)) due to the similarity between As(V) and P_ichemical structure. If As(V) is co‐recovered with P_i, the value of the recovered products for agricultural reuse is low. The objective of this study was to construct an immobilized phosphate‐binding protein (PBP)‐based P_iremoval and recovery system and analyze its selectivity for P_iadsorption in the presence of As(V). A range of conditions was tested, including independent, sequential, and simultaneous exposure of the two oxyanions to immobilized PBP (PBP resin). The purity of the recovered P_iproduct was assessed after inducing controlled desorption of the adsorbed oxyanions at high pH (pH 12.5). P_iconstituted more than 97% of the adsorbed oxyanions in the recovered product, even when As(V) was initially present at twofold higher concentrations than P_i. Therefore, PBP resin has potential to selectively remove P_i, as well as release high‐purity P_ifree of As(V) contamination suitable for subsequent agricultural reuse. Practitioner pointsExisting reversible phosphate (P_i) adsorbents cannot effectively discriminate against arsenate (As(V)) due to the similarity in their chemical structure.Co‐recovery of As(V) with P_ican reduce the recovered product's reuse as a fertilizer.An immobilized phosphate‐binding protein (PBP)‐based system can be highly selective for P_ieven in the presence of As(V).P_iconstituted more than 97% of the recovered product, even when As(V) was present at 2‐fold higher concentrations than P_i.Immobilized PBP offers advantages over existing P_iadsorbents by providing high‐purity P_iproducts free of As(V) contamination for reuse. 

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4. Paired Flow Electrolyzers for Furanic Compounds Conversion to Valuable Chemicals

   https://doi.org/https://doi.org/10.1149/MA2021-01401300mtgabs  

   Liu, Hengzhou; Lee, Ting-Han; Cochran, Eric; Li, Wenzhen (May 2021, ECS Meeting Abstracts)

   null (Ed.)

   Paired electrolysis has been emerged as an electricity-powered platform for converting biorewable feedstock to higher-valued chemicals at both the cathode and anode. In this presentation, we explored paired electrolyzers of different architectures with remarkable performance and stability. We first designed three-electrode flow electrolyzers to pair electrocatalytic hydrogenation of 5-(hydroxymethyl)furfural (HMF) on oxide-derived silver electrode and TEMPO-mediated HMF oxidation on carbon cloth. The paired flow cell achieved a combined faradaic efficiency of 163% to desired 2,5-bis(hydroxymethyl)furan (BHMF) and 2,5-furandicarboxylic acid (FDCA) with a cell potential of ~1.7 V, at the constant current of 10 mA. When the anodic reaction was replaced by hydrogen oxidation, a minimized cell voltage of only ~0.9 V was achieved. We then assmbled a membrane electrode assembly (MEA)-based two-electrode flow cell, which realized a minimized cell potential of only ~1.5 V for a continuous 24 hours paired electrolysis of HMF. Finally, a pH asymmetric architecture was designed to match the optimum reaction conditions and to replace HMF oxidation on a NiFeOOH anode catalyst without a redox mediator. Our recent development of electrochemical-chemical combined reactors for furanic compounds conversion will also be briefly presented. 

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5. An isocyanide ligand for the rapid quenching and efficient removal of copper residues after Cu/TEMPO-catalyzed aerobic alcohol oxidation and atom transfer radical polymerization

   https://doi.org/10.1039/D0SC00623H  

   Szczepaniak, Grzegorz; Piątkowski, Jakub; Nogaś, Wojciech; Lorandi, Francesca; Yerneni, Saigopalakrishna S.; Fantin, Marco; Ruszczyńska, Anna; Enciso, Alan E.; Bulska, Ewa; Grela, Karol; et al (April 2020, Chemical Science)

   Transition metal catalysts play a prominent role in modern organic and polymer chemistry, enabling many transformations of academic and industrial significance. However, the use of organometallic catalysts often requires the removal of their residues from reaction products, which is particularly important in the pharmaceutical industry. Therefore, the development of efficient and economical methods for the removal of metal contamination is of critical importance. Herein, we demonstrate that commercially available 1,4-bis(3-isocyanopropyl)piperazine can be used as a highly efficient quenching agent ( QA ) and copper scavenger in Cu/TEMPO alcohol aerobic oxidation (Stahl oxidation) and atom transfer radical polymerization (ATRP). The addition of QA immediately terminates Cu-mediated reactions under various conditions, forming a copper complex that can be easily separated from both small molecules and macromolecules. The purification protocol for aldehydes is based on the addition of a small amount of silica gel followed by QA and filtration. The use of QA@SiO2 synthesized in situ results in products with Cu content usually below 5 ppm. Purification of polymers involves only the addition of QA in THF followed by filtration, leading to polymers with very low Cu content, even after ATRP with high catalyst loading. Furthermore, the addition of QA completely prevents oxidative alkyne–alkyne (Glaser) coupling. Although isocyanide QA shows moderate toxicity, it can be easily converted into a non-toxic compound by acid hydrolysis. 

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