Capacitive deionization (CDI) is energetically favorable for desalinating low-salinity water. The bottlenecks of current carbon-based CDI materials are their limited desalination capacities and time-consuming cycles, caused by insufficient ion-accessible surfaces and retarded electron/ion transport. Here, we demonstrate porous carbon fibers (PCFs) derived from microphase-separated poly(methyl methacrylate)-block-polyacrylonitrile (PMMA-b-PAN) as an effective CDI material. PCF has abundant and uniform mesopores that are interconnected with micropores. This hierarchical porous structure renders PCF a large ion-accessible surface area and a high desalination capacity. In addition, the continuous carbon fibers and interconnected porous network enable fast electron/ion transport, and hence a high desalination rate. PCF shows desalination capacity of 30 mgNaCl g−1PCF and maximal time-average desalination rate of 38.0 mgNaCl g−1PCF min−1, which are about 3 and 40 times, respectively, those of typical porous carbons. Our work underlines the promise of block copolymer–based PCF for mutually high-capacity and high-rate CDI.
Nanorods of PCN-222, a large-pore, zirconiumbased porphyrinic metal−organic framework (MOF), have been prepared through coordination modulationcontrolled crystal growth through competing monodentate ligands known as modulatorsfor incorporation into reverse osmosis thin-film nanocomposite (TFN) membranes. Postsynthetic modification of the MOF node through binding of myristic acid (MA) altered channel dimensions and pore size distribution. The extent of MOF modification was characterized through Brunauer−Emmett−Teller gas sorption and 1 H NMR following digestion of the particles. TFN membranes containing PCN-222 nanoparticles modified with varying levels of MA were fabricated via dispersion in the aqueous phase during interfacial polymerization, and the resulting flux and rejection performance of each membrane were evaluated. Increased water flux was observed with increasing MA content in the PCN-222 nanorods. Up to 95% increase in water flux was observed for a TFN containing 0.01 wt % loading of PCN-222 nanorods with a 10:1 MA to linker ratio, while maintaining high salt rejection. The flux change was attributed to tunable water transport through the nanorod pore structure and also through rapid water transport pathways at the nanorod−polymer interface.
Block copolymer-based porous carbon fibers (PCFs) exhibit hierarchical porous structures, high surface areas, and exceptional electrochemical properties. However, the design of block copolymers for PCFs remains a challenge in advancing this type of fibrous material for energy storage applications. Herein, we have systematically synthesized a series of poly(methyl methacrylate-block-acrylonitrile) (PMMA-b-PAN) with well-controlled molecular weights and compositions to study the physical and electrochemical properties of PCFs. PCFs are synthesized via electrospinning, selfassembly, oxidation, and pyrolysis with no additives or chemical activation. By adjusting the molecular weights of polyacrylonitrile (PAN) and poly(methyl methacrylate) blocks, we have achieved tunable mesopore sizes ranging from 10.9 to 18.6 nm and specific capacitances varied from 144 to 345 F g −1 at 10 mV s −1 . Interestingly, regardless of the volume fraction of PAN, all the block copolymers produce hierarchical porous structures because of the self-assembly and cross-linking of PAN. Block copolymers with a PAN volume fraction of near 50% show the highest surface areas and gravimetric capacitances. The PCFs represent a new platform material with tunable specific surface areas, pore sizes, and electrochemical properties. This work has an immediate impact on designing block copolymers to create PCFs for applications in energy conversion and storage.
We present a method to modify carbon fiber microelectrodes (CFME) with porous carbon nanofibers (PCFs) to improve detection and to investigate the impact of porous geometry for dopamine detection with fast-scan cyclic voltammetry (FSCV). PCFs were fabricated by electrospinning, carbonizing, and pyrolyzing poly(acrylonitrile)-b-poly(methyl methacrylate) (PAN-b-PMMA) block copolymer nanofiber frameworks. Commonly, porous nanofibers are used for energy storage applications, but we present an application of these materials for biosensing, which has not been previously studied. This modification impacted the topology and enhanced redox cycling at the surface. PCF modifications increased the oxidative current for dopamine (2.0 ± 0.1)-fold (n = 33) with significant increases in detection sensitivity. PCFs are known to have more edge plane sites which we speculate lead to the 2-fold increase in electroactive surface area. Capacitive current changes were negligible, providing evidence that improvements in detection are due to faradaic processes at the electrode. The ΔE p for dopamine decreased significantly at modified CFMEs. Only a 2.2 ± 2.2% change in dopamine current was observed after repeated measurements and only 10.5 ± 2.8% after 4 h, demonstrating the stability of the modification over time. We show significant improvements in norepinephrine, ascorbic acid, adenosine, serotonin, and hydrogen peroxide detection. Lastly, we demonstrate that the modified electrodes can detect endogenous, unstimulated release of dopamine in living slices of rat striatum. Overall, we provide evidence that porous nanostructures significantly improve neurochemical detection with FSCV and echo the necessity for investigating the extent to which geometry impacts electrochemical detection.
The glass transition temperature, thermal degradation temperature, and complex viscosity of metal sulfonated polyetherimides decrease with an increase in metal cation size.
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