In this study, a novel electrical Mn-based film was developed for selective potassium (K+) separation, in which delaminated MnOx was obtained with the assistance of Ho3+ using a facile coprecipitation method and coated on carbon paper with poly(vinylidene fluoride) (PVDF) and graphitized carbon black. With the scanning electron microscope (SEM) and transmission electron microscope (TEM) observations, it was found that abundant multiphase interfaces and lattice dislocations appeared on the bulk of Ho-MnOx. Brunauer–Emmett–Teller (BET) analysis verified that the delamination assisted by Ho3+ increased the specific surface area from 110.3 m2/g (MnOx) to 166.8 m2/g (1% Ho-MnOx), which should be beneficial for the exposing of more electrochemical active areas and active sites for K+ adsorption and separation. Particularly, 1% Ho-MnOx had a high concentration of oxygen vacancies and showed a better K+ adsorption ability than MnOx. It was considered that the adsorption of K+ was mainly affected by the ion memory toward K+ for the 1% Ho-MnOx. In addition, the 1% Ho-MnOx film had good stable retention and regeneration capability for the separation of K+; after 10 cycles of adsorption and desorption, the film still retained 87.24% of the maximum adsorption capacity for K+. It is expected to provide an effective preparation method to obtain a high-performance K+ removal film electrode for the separation of K+ under a low concentration.
Abstract NiFe layered double hydroxide (LDH) films with different Ni/Fe molar ratios were successfully prepared on carbon paper (CP) by the potentiostatic method and were used for the removal of chloride ions (Cl − ) by electrically switched ion exchange (ESIX) technology. The results showed that the Ni/Fe ratios had a significant effect on the adsorption performance of LDH for Cl − . The prepared NiFe LDH film with Ni/Fe molar ratio of 1 : 1 showed the best Cl − ESIX performance and the maximum adsorption capacity could reach 43.8 mg ⋅ g −1 at 1.4 V (vs. SCE) in 20 ppm Cl − solution. The excellent adsorption performance of LDH for Cl − was mainly due to the coupling of the interlayer anion exchange mechanism and the electroactivity‐variable valence mechanism. In addition, the Cl − regeneration rate remained above 95 % during five repeated adsorption/desorption experiments, and the charging capacity was still about 96 % of the initial capacity even after 1000 CV cycles. Therefore, the NiFe LDH film could be a promising electroactive material for the removal of Cl − from aqueous solution.
A facile unipolar pulse electrodeposition combined with the thermal oxidation method was applied for fabrication of CuO/Co3O4 composites on carbon electrode for water electrolysis, and it was found that the sea anemone-like one with a 3D hierarchical structure formed at -0.8 V exhibited excellent performance for water electrolysis at a low overpotential with high stability.
Electroactive nickel hexacyanoferrate (NiHCF) thin films were synthesized by cathodic deposition and investigated as electrochemically switched ion exchange (ESIX) materials for the separation of Y3+ from aqueous solutions. In 0.1 mol·L-1 Y(NO3)3 solution, cyclic voltammetry (CV) combined with electrochemical quartz crystal microbalance (EQCM) technique was used to investigate the electroactivity, reversibility of the film electrodes and the mechanism of ion exchange. The electrochemical behavior of NiHCF film electrodes was also compared with that in Sr(NO3)2 solutions. The ion selectivity of the film was investigated in 0.1 mol·L-1 solutions containing [Y(NO3)3 + Sr(NO3)2]. The elementary composition of NiHCF films in reduced and oxidized forms were also characterized by X-ray photoelectron spectroscopy (XPS). Experimental results show that the electroactive NiHCF films have reversible electrochemical behavior in aqueous solutions containing Y3+ and Sr2+, respectively. The NiHCF film electrodes displayed a high Y3+ selectivity in Y3+/Sr2+ binary mixtures and the Y3+ ions could be separated effectively from aqueous solutions by ESIX processes.
The recovery of iodide ion (I–) from aqueous solutions is of great significance to economic development. Photoassisted electrochemically switched ion exchange (P-ESIX) takes advantage of the photo/electron bioactivity of EIXMs, which has been used for the recovery of bromide ion (Br–) to increase the adsorption capacity of Br–. To further expand the application of P-ESIX, we used iodide-vacancy bismuth oxyiodide (I–-vacancy BiOI) as the photoelectroactive ion exchange material (P-EIXM) for the recovery of I–. The results showed that an I–-vacancy BiOI film can effectively recover I– and improve the adsorption capacity because of its excellent selectivity and visible light adsorption ability. Compared with ESIX, the I– adsorption capacity increases by 1.38 times with a growth rate of 37.4% at 0.6 V (vs SCE). Also, the film electrode still retains 84.0% of the initial adsorption capacity after 10 cycles of use. The mechanism of P-ESIX system was further analyzed on the basis of the energy band structure theory. It is not only innovative and efficient technology for the recovery of I– but also shows that P-ESIX has potential as a new technology for a wide range of applications in the selective recovery of target ions.
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