Cation selectivity of activated carbon and nickel hexacyanoferrate electrode materials in capacitive deionization: A comparison study.

In this study, the electrosorption selectivity of porous activated carbon (AC) and nickel hexacyanoferrate (NiHCF), which represent two working mechanisms of capacitive electrosorption and redox intercalation, was investigated to separate cations in capacitive deionization (CDI). The cyclic voltammetry diagrams of AC showed the rectangular shape of double-layer charging, while that of NiHCF showed separated peaks associated with redox reactions. The specific capacitance of NiHCF was 143.6 F/g in 1 M NaCl, which was almost two times higher than that of AC. Cation selectivity experiments were conducted in single-pass CDI for a multi-cation solution. The electrosorption preference of the AC cathode was determined by a counterbalance between the ionic charge and hydrated size, reflecting the selectivity coefficient of different cations over Na+ in the range of 0.86-2.63. For the NiHCF cathode, the cation selectivity was mainly dominated by the hydrated radius and redox activity. Notably, high selectivities of K+/Na+ ≈ 3.57, Na+/Ca2+ ≈ 9.97, and Na+/Mg2+ ≈ 18.92 were obtained. A significant improvement in the electrosorption capacity and monovalent ion selectivity can be achieved by utilizing the NiHCF electrode. The study demonstrates the fundamental aspects and promising opportunities of CDI in regard to ion selectivity.

Transformation of theranostic alginate-based microbubbles from raspberry-like to core-shell-like microbubbles and in vitro studies.

In this study alginate-based microbubbles with a raspberry-like or core-shell-like morphology and with an average particle size of 553.6 ± 69.6 µm were synthesized; this was done through a novel procedure of transforming the structure with a 40 kHz ultrasonication which also stimulated the release of the components inside. Through the use of the electrospray technique in conjunction with agitation processes, components such as shikonin (SHK) and indocyanine green (ICG) were simultaneously encapsulated in alginate microbubbles to produce SHK-ICG alginate microbubbles; these microbubbles had half-maximal inhibitory concentrations of approximately 2.08 and 4.43 µM toward CP70 and SKOV3 ovarian cancer-cell lines, respectively, in an in vitro cell model. Moreover, these SHK-ICG alginate microbubbles enhanced brightness by 2.5 fold in ultrasound imaging relative to CaCl2 medium only. In conclusion, SHK-ICG alginate microbubbles have promise for use in theranostics.

The effect of redox potential on the removal characteristic of divalent cations during activated carbon-based capacitive deionization.

The main objective of the study is to explore the removal characteristics of Cu2+ and Zn2+ ions in activated carbon-based capacitive deionization (CDI). In this work, CDI experiments were performed to remove divalent ions (e.g., Cu2+, Zn2+, and Ca2+) from single- and multicomponent aqueous solutions. As evidenced, divalent heavy metals could be successfully removed by charging the CDI cell at 1.2 V. Notably, the preferential removal of Cu2+ ions over Zn2+ and Ca2+ ions was observed in the charging step. The removal capacities for Cu2+, Zn2+, and Ca2+ ions in a competitive environment were 29.6, 19.6, and 13.8 µmol/g, respectively. In contrast, the regeneration efficiencies for the removal of Cu2+ and Zn2+ were much lower than that of Ca2+, suggesting the occurrence of irreversible Faradaic reactions on the cathode. X-ray photoelectron spectroscopy analysis demonstrated that Cu2+ ions were reduced to Cu(I) and Zn2+ ions were transformed to ZnO/Zn(OH)2 on the cathode. Therefore, there were two major mechanisms for the removal of divalent heavy metal ions: capacitive electrosorption and cathodic electrodeposition. Specifically, the reduction potential played a crucial role in determining the removal characteristics. When regarding divalent cations with similar hydrated sizes, the divalent cation with a higher reduction potential tended to be separated by cathodic electrodeposition rather than double-layer charging, indicating the high removal selectivity of activated carbon-based CDI. This paper constitutes a significant contribution to promoting the application of CDI for contaminant sequestration.

Diatom-assisted biomicroreactor targeting the complete removal of perfluorinated compounds.

Persistent perfluorinated compounds (PFCs) have been recognized as a global environmental issue. Developing methods without leading to additional burden in nature will be essential for PFCs removal. Herein, we functionalized iron nanoparticles on living diatom (Dt) to efficiently enable the Fenton reaction and reactive oxygen species (ROS) production. Iron nanoparticles at the surface of living diatom act as promising catalytic agents to trigger OH radical generation from H2O2. Dt plays dual roles: i) as solid support for effective adsorption, and ii) it supplies oxygen and inherently produces ROS under stress conditions, which improves removal efficiency of PFCs. We also demonstrated its reusability by simple magnetic separation and 85% of decomposition efficiency could still be achieved. This newly developed diatom-assisted bioremediation strategy enables green and efficient PFC decomposition and shall be readily applicable to other persistent pollutants.