Reaching the limiting current regime by linear sweep voltammetry in ion-exchange membrane systems

Enhancement of the Negative Capacitance Associated with the Dissolution of Silver by Salt Concentrations by Means of Anodic Stripping Voltammetry

The amount of anodically dissolved charge of silver by linear sweep stripping voltammetry has been observed to be smaller than that of the potentiostatically deposited charge. The imbalance in the charge is opposite to the participation in the double-layer capacitance. This can be explained in terms of the negative capacitive current, which is caused by dipoles of generated redox charge (Ag+) with counterions (NO3−). Lower concentrations of counterions may suppress the capacitance to retain the equality of the charge. This prediction is examined in this work by the oxidation of silver film at various concentrations of NO3− by anodic stripping voltammetry. The capacitance decreased with a decrease in the salt concentrations less than 0.05 mol dm−3. Low concentrations of salts prevent loss of the anodic charge in electroanalysis. This dependence was related with the lifespan of generated silver nitrate dipoles and is described theoretically.

Simultaneous Fractionation, Desalination, and Dye Removal of Dye/Salt Mixtures by Carbon Cloth-Modified Flow-electrode Capacitive Deionization

The critical challenges of using electromembrane processes [e.g., electrodialysis and flow-electrode capacitive deionization (FCDI)] to recycle resources (e.g., water, salts, and organic compounds) from wastewater are the fractionation of dissolved ionic matter, the removal/recovery of organic components during desalination, and membrane antifouling. This study realized the simultaneous fractionation, desalination, and dye removal/recovery (FDR) treatment of dye/salt mixtures through a simple but effective approach, that is, using a carbon cloth-modified FCDI (CC-FCDI) unit, in which the carbon cloth layer was attached to the surface of each ion-exchange membrane (IEM). The IEMs and carbon-based flow-electrodes were responsible for the fractionation and desalination of dye and salt ions, while the carbon cloth layers contributed to the active membrane antifouling and dye removal/recovery by the electrosorption mechanism. Attributed to such features, the CC-FCDI unit accomplished the effective FDR treatment of dye/salt mixtures with wide ranges of salt and dye concentrations (5-20 g L^-1 NaCl and 200-800 ppm methylene blue) and different dye components (cationic and anionic dyes) under various applied voltages (1.2-3.2 V). Moreover, the active membrane antifouling by virtue of the carbon cloth facilitated the excellent and sustainable FDR performance of CC-FCDI. The removal/recovery of dyes from the carbon cloth strongly depends on the characteristics of dye molecules, the surface properties of the carbon cloth, and the local pH at the IEM/CC interfaces. This study sheds light on the strategies of using multifunctional layer-modified FCDI units to reclaim resources from various high-salinity organic wastewater.