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Casein/starch composites are shown to act as potential candidates for binders of symmetric carbonaceous electrodes used in the capacitive deionization (CDI) of water. Casein and potato-starch biopolymers are cheap and environmentally friendly and may be implemented throughout a green process to obtain a carbonaceous CDI electrode using sole water as a solvent. It was found that among the different starch/casein mass ratios considered in this study (0 : 1, 1 : 1, 2 : 1, 1 : 2, 1 : 4 and 1 : 0), the ratio 1 : 2 resulted in an optimal CDI performance corresponding to 12.7 mg g−1, 50% and 1.01 W h g−1 for salt adsorption capacity, charge efficiency, and specific energy consumption, respectively. The outstanding performance observed is attributed to the formation of a binder with a hydrophilic mesoporous network carrying inherent positive and negative charges throughout the internal surface area, inducing both anion and cation-exchange membrane characteristics in the binder layer. For the optimal binder composition, the latter network possesses a dominant pore diameter of 4.65 nm, while the dominant pore diameter is less than 3.00 nm for the other samples, eventually enhancing ion species mass transfer through the polymer matrix. [ABSTRACT FROM AUTHOR]

As a promising continuous desalination technology, flow electrode capacitive deionization (FCDI) has received considerable attention. However, poor conductivity and dispersion of the traditional active carbon (AC) flow-electrode limit the properties of FCDI. In order to achieve excellent desalination performance, a flow electrode with good dispersion, low resistance, and high salt adsorption capacity is essential. In this study, nitrogen-doped porous carbon (NPC) was synthesized through one-step pyrolysis process of ethylenediamine tetraacetic acid tetrasodium (Na4EDTA). The prepared NPC material showed a high specific surface area (1168.4 m2 g−1), appropriate nitrogen and oxygen doping, excellent hydrophilicity and low resistance. At 1.2 V applied voltage, the desalting experiments showed that the FCDI system based on a NPC flow electrode exhibited a higher average salt removal rate of 0.0459 mg cm−2 min−1, and the salt adsorption capacity (148.93 mg g−1) based on the NPC flow electrode was about 2.3 times larger than that of AC. Furthermore, after continuous desalination cycling for long periods of time, the salt removal efficiency and average salt removal rate remained stable. The results of this study may be useful for the future exploration of high performance electrode materials for FCDI systems. [ABSTRACT FROM AUTHOR]

Cr(VI) in wastewater poses a serious threat to human health, so there is an urgent need to remove it using a cost-effective way. Herein, we report a composite electrode material of homemade paulownia biochar and MoS2 (PBC@MoS2) for the efficient and selective removal of Cr(VI) from wastewater. PBC@MoS2 has an excellent ability to selectively remove Cr(VI) by electrosorption under the coexistence of different anions and cations (385.74 mg g−1 at voltage = 1.2 V, spacing = 1 mm, and initial concentration = 60 mg L−1). It can achieve 98.75% desorption and regeneration of the electrode within 1 h, and after 5 cycles of adsorption/desorption, it still maintains 97.02% of the original adsorption capacity. The characterization analysis shows that the removal process of Cr(VI) has both electrosorption and reduction effects, which can reduce 85.4% of the highly toxic Cr(VI) to the less toxic Cr(III). This is facilitated by the large specific surface area and special two-dimensional sheet structure of PBC@MoS2 composites. The results of this work can provide data support for the design of high-performance CDI systems for the removal of Cr(VI) from wastewater. [ABSTRACT FROM AUTHOR]

Capacitive deionization (CDI) is an efficient new technology that can be used to remove charged pollutants. However, differences in the electrode selectivity for different ions limit its further application. Therefore, the electrosorption behavior and selectivity of four anions in a CDI system with activated carbon electrodes were investigated using mixed solutions. The results showed that the adsorption capacities and selectivities of the anions varied due to differences in their hydration energy and valence. The preferential electrosorption order was as follows: NO3− > Cl− > SO24− > phosphate (P). In addition, the competitive mechanism between different anions and P was studied. P competed with SO24− the most for electrosorption sites due to their spatial similarity. However, because the NO3− adsorption capacity was the highest, P had the lowest electrosorption selection coefficient when it coexisted with NO. Finally, the mechanism of the electrosorption selectivity was verified. The results indicated that the electrosorption selectivity of P was improved by decreasing the voltage to weaken the competition between P and other anions for sites and by adjusting the pH to optimize the hydration energy and electronegativity of P. This research may provide readers with a deeper understanding of electrosorption selectivity. [ABSTRACT FROM AUTHOR]