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1. Structurally and chemically engineered graphene for capacitive deionization

   https://doi.org/10.1039/d0ta10087k  

   Chang, Liang; Fei, Yuhuan; Hu, Yun Hang (January 2021, Journal of Materials Chemistry A)

   null (Ed.)

   Highly efficient capacitive deionization (CDI) relies on unimpeded transport of salt ions to the electrode surface. Graphene is an ideal candidate to provide superb conditions for ion adsorption as it possesses high theoretical surface area and electrical conductivity. When ions are stored solely within the electric double layers (EDLs), a hydrophilic graphene surface with hierarchical pores can maximize the accessible surface area and promote the ion transport. In the case of synergistic ion storage via electrostatic adsorption and faradaic redox reaction, graphene can act as both the electron highway and the reciprocal spacer to provide surface-confined effects. Substantially, structural and chemical engineering towards graphene can enhance the ion removal capacity and rate, and improve the charge efficiency and ion selectivity. In this review, we keep pace with the in-depth studies of CDI technologies and recent progress on graphene-based materials for CDI. Major challenges in the rational assembly of the desired material functionalities in terms of surface area, pore structure, and hydrophilicity are addressed. As electrode materials develop, the ultimate goal is to achieve highly efficient, energy-saving, and environment-friendly CDI. 

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2. Seagrass deformation affects fluid instability and tracer exchange in canopy flow

   https://doi.org/10.1038/s41598-023-30401-9  

   Vieira, Guilherme S.; Allshouse, Michael R.; Mahadevan, Amala (December 2023, Scientific Reports)

   Abstract Monami is the synchronous waving of a submerged seagrass bed in response to unidirectional fluid flow. Here we develop a multiphase model for the dynamical instabilities and flow-driven collective motions of buoyant, deformable seagrass. We show that the impedance to flow due to the seagrass results in an unstable velocity shear layer at the canopy interface, leading to a periodic array of vortices that propagate downstream. Our simplified model, configured for unidirectional flow in a channel, provides a better understanding of the interaction between these vortices and the seagrass bed. Each passing vortex locally weakens the along-stream velocity at the canopy top, reducing the drag and allowing the deformed grass to straighten up just beneath it. This causes the grass to oscillate periodically even in the absence of water waves. Crucially, the maximal grass deflection is out of phase with the vortices. A phase diagram for the onset of instability shows its dependence on the fluid Reynolds number and an effective buoyancy parameter. Less buoyant grass is more easily deformed by the flow and forms a weaker shear layer, with smaller vortices and less material exchange across the canopy top. While higher Reynolds number leads to stronger vortices and larger waving amplitudes of the seagrass, waving amplitude is maximized at intermediate grass buoyancy. All together, our theory and computations develop an updated schematic of the instability mechanism consistent with experimental observations. 

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3. A Pore-Scale Model for Electrokinetic In situ Recovery of Copper: The Influence of Mineral Occurrence, Zeta Potential, and Electric Potential

   https://doi.org/10.1007/s11242-023-02023-2  

   Tang, Kunning; Li, Zhe; Da Wang, Ying; McClure, James; Su, Hongli; Mostaghimi, Peyman; Armstrong, Ryan T (December 2023, Transport in Porous Media)

   AbstractElectrokinetic in-situ recovery is an alternative to conventional mining, relying on the application of an electric potential to enhance the subsurface flow of ions. Understanding the pore-scale flow and ion transport under electric potential is essential for petrophysical properties estimation and flow behavior characterization. The governing physics of electrokinetic transport is electromigration and electroosmotic flow, which depend on the electric potential gradient, mineral occurrence, domain morphology (tortuosity and porosity, grain size and distribution, etc.), and electrolyte properties (local pH distribution and lixiviant type and concentration, etc.). Herein, mineral occurrence and its associated zeta potential are investigated for EK transport. The new Ek model which is designed to solve the EK flow in complex porous media in a highly parallelizable manner includes three coupled equations: (1) Poisson equation, (2) Nernst–Planck equation, and (3) Navier–Stokes equation. These equations were solved using the lattice Boltzmann method within X-ray computed microtomography images. The proposed model is validated against COMSOL multiphysics in a two-dimensional microchannel in terms of fluid flow behavior when the electrical double layer is both resolvable and unresolvable. A more complex chalcopyrite-silica system is then obtained by micro-CT scanning to evaluate the model performance. The effects of mineral occurrence, zeta potential, and electric potential on the three-dimensional chalcopyrite-silica system were evaluated. Although the positive zeta potential of chalcopyrite can induce a flow of ferric ion counter to the direction of electromigration, the net effect is dependent on the occurrence of chalcopyrite. However, the ion flux induced by electromigration was the dominant transport mechanism, whereas advection induced by electroosmosis made a lower contribution. Overall, a pore-scale EK model is proposed for direct simulation on pore-scale images. The proposed model can be coupled with other geochemical models for full physicochemical transport simulations. Meanwhile, electrokinetic transport shows promise as a human-controllable technique because the electromigration of ions and the applied electric potential can be easily controlled externally. Graphical abstract 

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4. Probe the Localized Electrochemical Environment Effects and Electrode Reaction Dynamics for Metal Batteries using In Situ 3D Microscopy

   https://doi.org/10.1002/aenm.202103484  

   Feng, Guangxia; Guo, Jiaming; Tian, Huajun; Li, Zhao; Shi, Yaping; Li, Xiaoliang; Yang, Xu; Mayerich, David; Yang, Yang; Shan, Xiaonan (December 2021, Advanced Energy Materials)

   Abstract Uncontrollable dendrite growth is closely related to non‐uniform reaction environments. However, there is a lack of understanding and analysis methods to probe the localized electrochemical environment (LEE). Here the effects of the LEE are investigated, including localized ion concentrations, current density, and electric potential, on metal plating/stripping dynamics and dendrite minimization. A novel in situ 3D microscopy technique is developed to image the morphology dynamics and deposition rate of Zn plating/stripping processes on 3D Zn–Mn anodes. Using the in situ 3D microscope, the electrode morphology changes during the reactions are directly imaged and Zn deposition rate maps at different time points are obtained. It is found that reaction kinetics are highly correlated to LEE and electrode morphology. To further quantify the LEE effects, the digital twin technique is employed that allows the accurate calculation of the electrochemical environments, such as localized ion concentrations, current density, and electric potential, which cannot be directly measured from experiments. It is found that the curvature of the 3D electrode surface determines the LEE and significantly influences reaction kinetics. This provides a new strategy to minimize the dendrite formation by designing and optimizing the 3D geometry of the electrode to control the LEE. 

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5. A High-Throughput Microfluidic Cell Sorter Using a Three-Dimensional Coupled Hydrodynamic-Dielectrophoretic Pre-Focusing Module

   https://doi.org/10.3390/mi14101813  

   Aghaamoo, Mohammad; Cardenas-Benitez, Braulio; Lee, Abraham P. (October 2023, Micromachines)

   Beskok, A. (Ed.)

   Dielectrophoresis (DEP) is a powerful tool for label-free sorting of cells, even those with subtle differences in morphological and dielectric properties. Nevertheless, a major limitation is that most existing DEP techniques can efficiently sort cells only at low throughputs (<1 mL h−1). Here, we demonstrate that the integration of a three-dimensional (3D) coupled hydrodynamic-DEP cell pre-focusing module upstream of the main DEP sorting region enables cell sorting with a 10-fold increase in throughput compared to conventional DEP approaches. To better understand the key principles and requirements for high-throughput cell separation, we present a comprehensive theoretical model to study the scaling of hydrodynamic and electrostatic forces on cells at high flow rate regimes. Based on the model, we show that the critical cell-to-electrode distance needs to be ≤10 µm for efficient cell sorting in our proposed microfluidic platform, especially at flow rates ≥ 1 mL h−1. Based on those findings, a computational fluid dynamics model and particle tracking analysis were developed to find optimum operation parameters (e.g., flow rate ratios and electric fields) of the coupled hydrodynamic-DEP 3D focusing module. Using these optimum parameters, we experimentally demonstrate live/dead K562 cell sorting at rates as high as 10 mL h−1 (>150,000 cells min−1) with 90% separation purity, 85% cell recovery, and no negative impact on cell viability. 

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