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Direct air capture of carbon dioxide is a viable option for the mitigation of CO 2 emissions and their impact on global climate change. Conventional processes for carbon capture from ambient air require 230 to 800 kJ thermal per mole of CO 2 , which accounts for most of the total cost of capture. Here, we demonstrate electrochemical direct air capture using neutral red as a redox-active material in an aqueous solution enabled by the inclusion of nicotinamide as a hydrotropic solubilizing agent. The electrochemical system demonstrates a high electron utilization of 0.71 in a continuous flow cell with an estimated minimum work of 35 kJ e per mole of CO 2 from 15% CO 2 . Further exploration using ambient air (410 ppm CO 2 in the presence of 20% oxygen) as a feed gas shows electron utilization of 0.38 in a continuous flow cell to provide an estimated minimum work of 65 kJ e per mole of CO 2 . Electrochemical direct air capture (DAC) of CO 2 requires air-stable redox-active materials. Here, the authors present an electrochemical DAC using air-stable redox couple of neutral red with a minimum energy requirement of 65 kJ e /mol CO2 .

Carbon capture is essential for mitigating carbon dioxide emissions. Compared to conventional chemical scrubbing, electrochemically mediated carbon capture utilizing redox-active sorbents such as quinones is emerging as a more versatile and economical alternative. However, the practicality of such systems is hindered by the requirement of toxic, flammable organic electrolytes or often costly ionic liquids. Herein, we demonstrate that rationally designed aqueous electrolytes with high salt concentration can effectively resolve the incompatibility between aqueous environments and quinone electrochemistry for carbon capture, eliminating the safety, toxicity, and at least partially the cost concerns in previous studies. Salt-concentrated aqueous media also offer distinct advantages including extended electrochemical window, high carbon dioxide activity, significantly reduced evaporative loss and material dissolution, and importantly, greatly suppressed competing reactions including under simulated flue gas. Correspondingly, we achieve continuous carbon capture-release operations with outstanding capacity, stability, efficiency and electrokinetics, advancing electrochemical carbon separation further towards practical applications. Redox-active organic compounds that reversibly bind and release CO 2 are promising candidates for carbon capture but are limited by the use of flammable, toxic aprotic electrolytes. Here the authors use salt-concentrated aqueous electrolytes in continuous CO 2 separation with good performance metrics.

The removal of highly toxic, ultra-dilute contaminants of concern has been a primary challenge for clean water technologies. Chromium and arsenic are among the most prevalent heavy metal pollutants in urban and agricultural waters, with current separation processes having severe limitations due to lack of molecular selectivity. Here, we report redox-active metallopolymer electrodes for the selective electrochemical removal of chromium and arsenic. An uptake greater than 100 mg Cr/g adsorbent can be achieved electrochemically, with a 99% reversible working capacity, with the bound chromium ions released in the less harmful trivalent form. Furthermore, we study the metallopolymer response during electrochemical modulation by in situ transmission electron microscopy. The underlying mechanisms for molecular selectivity are investigated through electronic structure calculations, indicating a strong charge transfer to the heavy metal oxyanions. Finally, chromium and arsenic are remediated efficiently at concentrations as low as 100 ppb, in the presence of over 200-fold excess competing salts. Chromium and arsenic are prevalent water pollutants, but their removal is currently limited by low selectivity. Here, the authors use redox-active metallopolymer electrodes based on poly(vinyl)ferrocene to selectively remove the two heavy metal oxyanions at concentrations as low as 100 ppb.

Crystallization of a liquid usually starts at a solid surface — for instance, that of impurities or of a container's walls — and surface roughness is known to enhance crystal nucleation rates. It is now shown with polymer films patterned with spherical nanopores 15–120 nm in size that the shape of the pores can either enhance or hinder crystal nucleation. Crystallization of a molecular liquid from solution often initiates at solid–liquid interfaces 1 , 2 , 3 , and nucleation rates are generally believed to be enhanced by surface roughness 4 , 5 . Here we show that, on a rough surface, the shape of surface nanopores can also alter nucleation kinetics. Using lithographic methods, we patterned polymer films with nanopores of various shapes and found that spherical nanopores 15–120 nm in diameter hindered nucleation of aspirin crystals, whereas angular nanopores of the same size promoted it. We also show that favourable surface–solute interactions are required for angular nanopores to promote nucleation, and propose that pore shape affects nucleation kinetics through the alteration of the orientational order of the crystallizing molecule near the angles of the pores. Our findings have clear technological implications, for instance in the control of pharmaceutical polymorphism and in the design of ‘seed’ particles for the regulation of crystallization of fine chemicals.

Driven by the potential applications of ionic liquids (ILs) in many emerging electrochemical technologies, recent research efforts have been directed at understanding the complex ion ordering in these systems, to uncover novel energy storage mechanisms at IL–electrode interfaces. Here, we discover that surface-active ILs (SAILs), which contain amphiphilic structures inducing self-assembly, exhibit enhanced charge storage performance at electrified surfaces. Unlike conventional non-amphiphilic ILs, for which ion distribution is dominated by Coulombic interactions, SAILs exhibit significant and competing van der Waals interactions owing to the non-polar surfactant tails, leading to unusual interfacial ion distributions. We reveal that, at an intermediate degree of electrode polarization, SAILs display optimum performance, because the low-charge-density alkyl tails are effectively excluded from the electrode surfaces, whereas the formation of non-polar domains along the surface suppresses undesired overscreening effects. This work represents a crucial step towards understanding the unique interfacial behaviour and electrochemical properties of amphiphilic liquid systems showing long-range ordering, and offers insights into the design principles for high-energy-density electrolytes based on spontaneous self-assembly behaviour.

Precisely shaped polymeric particles and structures are widely used for applications in photonic materials 1 , MEMS 2 , biomaterials 3 and self-assembly 4 . Current approaches for particle synthesis are either batch processes 5 , 6 , 7 , 8 , 9 , 10 or flow-through microfluidic schemes 11 , 12 , 13 , 14 , 15 , 16 that are based on two-phase systems, limiting the throughput, shape and functionality of the particles. We report a one-phase method that combines the advantages of microscope projection photolithography 7 and microfluidics to continuously form morphologically complex or multifunctional particles down to the colloidal length scale. Exploiting the inhibition of free-radical polymerization near PDMS surfaces, we are able to repeatedly pattern and flow rows of particles in less than 0.1 s, affording a throughput of near 100 particles per second using the simplest of device designs. Polymerization was also carried out across laminar, co-flowing streams to generate Janus particles containing different chemistries, whose relative proportions could be easily tuned. This new high-throughput technique offers unprecedented control over particle size, shape and anisotropy.

Electrochemical carbon-capture technologies, with renewable electricity as the energy input, are promising for carbon management but still suffer from low capture rates, oxygen sensitivity or system complexity 1 – 6 . Here we demonstrate a continuous electrochemical carbon-capture design by coupling oxygen/water (O 2 /H 2 O) redox couple with a modular solid-electrolyte reactor 7 . By performing oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) redox electrolysis, our device can efficiently absorb dilute carbon dioxide (CO 2 ) molecules at the high-alkaline cathode–membrane interface to form carbonate ions, followed by a neutralization process through the proton flux from the anode to continuously output a high-purity (>99%) CO 2 stream from the middle solid-electrolyte layer. No chemical inputs were needed nor side products generated during the whole carbon absorption/release process. High carbon-capture rates (440 mA cm −2 , 0.137 mmol CO2  min −1  cm −2 or 86.7 kg CO2  day −1  m −2 ), high Faradaic efficiencies (>90% based on carbonate), high carbon-removal efficiency (>98%) in simulated flue gas and low energy consumption (starting from about 150 kJ per mol CO2 ) were demonstrated in our carbon-capture solid-electrolyte reactor, suggesting promising practical applications. By combining O 2 /H 2 O redox electrolysis with a modular solid-electrolyte reactor, a design for continuous electrochemical carbon capture showing high capture rates, high Faradaic efficiencies and low energy consumption is demonstrated.

We demonstrate a microfluidic continuous-flow protein separation process in which silica-coated superparamagnetic nanoparticles interact preferentially with hemoglobin in a mixture with bovine serum albumin, and the resulting hemoglobin-nanoparticle aggregates are recovered online using magnetophoresis. We present detailed modeling and analysis of this process yielding quantitative estimates of the recovery of both proteins, validated by experiments. While several previous studies utilize an average particle size in modeling magnetophoretic particle trajectories or process design, in this study we emphasize the importance of accounting for particle size distributions in calculating particle recovery, and therefore in estimating separation efficiency. We combine experimentally measured size distributions of protein-nanoparticle aggregates with simulations of particle trajectories and provide a simple analytical method to calculate the efficiency of separation at various flow speeds, which fully accounts for heterogeneity in particle sizes. Our method can potentially be used for affinity based biomolecular separations at both analytical and preparative scales by exploiting well-established techniques to functionalize nanoparticle surfaces with selective ligands. Further, the modeling methodology presented here may be applied to provide better estimates of particle recovery in a broad range of magnetophoretic separation processes involving heterogeneity in particle sizes.

We report the use of a simple yet highly effective magnetite-waste tea composite to remove lead(II) (Pb(2+)) ions from water. Magnetite-waste tea composites were dispersed in four different types of water-deionized (DI), artificial rainwater, artificial groundwater and artificial freshwater-that mimic actual environmental conditions. The water samples had varying initial concentrations (0.16-5.55 ppm) of Pb(2+) ions and were mixed with the magnetite-waste tea composite for at least 24 hours to allow adsorption of the Pb(2+) ions to reach equilibrium. The magnetite-waste tea composites were stable in all the water samples for at least 3 months and could be easily removed from the aqueous media via the use of permanent magnets. We detected no significant leaching of iron (Fe) ions into the water from the magnetite-waste tea composites. The percentage of Pb adsorbed onto the magnetite-waste tea composite ranged from ∼70% to 100%; the composites were as effective as activated carbon (AC) in removing the Pb(2+) ions from water, depending on the initial Pb concentration. Our prepared magnetite-waste tea composites show promise as a green, inexpensive and highly effective sorbent for removal of Pb in water under environmentally realistic conditions.

Aerosol filtration using electrospun cellulose acetate filters with different mean fiber diameters is reported, and the results are compared with those for two conventional filter media, a glass fiber filter and a cellulose acetate microfiber filter. The performance of these filters was studied using two aerosols, one solid (NaCl) and one liquid (diethyl hexyl sebacate), under conditions of relatively high face velocity (45 cm/s). The experimental observations are compared to theoretical predictions based on single fiber filtration efficiency. Our results indicate that the mechanisms for single fiber filtration efficiency provide reasonable predictions of the most penetrating particle size (MPPS), in the range of 40–270 nm, percentage penetration from 0.03 to 70 %, and fiber diameter in the range from 0.1 to 24 µm. Using an analysis based on blocking filtration laws, we conclude that filtration by cake formation dominated in the case of NaCl aerosols on electrospun filter media, whereas filters with larger fiber diameter showed a transition in mechanisms, from an initial regime characterized by pore blocking to a later regime characterized by cake formation. The liquid aerosol did not exhibit cake formation, even for the smallest fiber diameters, and also had much smaller influence on pressure drop than did the solid aerosol. The electrospun filters demonstrated slightly better quality factors compared to the commercial glass fiber filter, at a much lower thickness. In general, this study demonstrates control of the properties of electrospun cellulose acetate fibers for air filtration application.