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The zinc ion–imprinted 8-hydroxyquinoline/polypyrrole (8-HQ/PPy) composite film is successfully prepared by using the unipolar pulse electropolymerization (UPEP) method on the carbon cloth substrate. Based on the electrochemically switched ion exchange (ESIX) method, the ion-imprinted film is used to selectively separate zinc ions in the aqueous solution. The zinc ion adsorption kinetics is studied in a batch experiment due to the specific recognition of the ion-imprinted composite film toward zinc ion. The kinetics data of zinc ion adsorption by the imprinted composite film fits well with the pseudo-first-order kinetic model. As a result, when the adsorption potential and initial concentration are − 1.2 V and 25 ppm, respectively, the ion exchange capacity of the imprinted composite film for zinc ions reaches 145.6 mg g−1. In addition, the separation factor (α) are 2.6 and 2.3 of the imprinted composite film for Zn2+ compared with Co2+ and Ni2+, which is attributed to the specific recognition ability of the imprinted composite film for zinc ions. It is expected that the imprinted composite film prepared by the described method can be used for the separation target metal ions. [ABSTRACT FROM AUTHOR]

A three-dimensional (3D) polypyrrole (PPy)@graphene oxide (GO) composite membrane was developed for the continuous separation of dilute Pb 2+ from wastewater in a novel potential-controlled ion pump system based on an electrochemically switched ion permselectivity (ESIP) method. The 3D PPy@GO composite membrane was fabricated via a simple one-step electrochemical co-deposition way in an aqueous electrolyte solution using a stainless steel wire mesh (SSWM) as the conductive substrate. In this system, the directional uptake/release of Pb 2+ was realized by modulating the redox state of the PPy@GO membrane and coupling it with an external electric field. The coupling of the pulse potential and cell potential formed a novel potential-controlled ion pump system which controlled the transport of Pb 2+ . The permselectivity of the 3D PPy@GO membrane and the effects of the cell potential, pulse width, pulse potential and initial concentration on the Pb 2+ flux were investigated. The 3D PPy@GO composite coated electrodes showed excellent permselectivity of Pb 2+ with a flux of 4.7 g m −2 h −1 , a current efficiency of 51.9% and excellent cycling stability. The Pb 2+ concentration was reduced from 20 ppm in the source solution to 0.8 ppm with a removal percentage of 96%. This 3D PPy@GO membrane-based ESIP system could be used as a novel technique for wastewater treatment. [ABSTRACT FROM AUTHOR]

A BiOBr film electrode was prepared by electrodeposition method for verifying an electrochemically switched amphoteric ion exchange (ESAIX) mechanism. Physical and electrochemical characterization results reveal that the BiOBr can switch the valence of Bi between Bi3+ and Bi(3-x)+ to selectively insert Cs+ with simultaneously release Br− at a reduction potential, while it can selectively insert Br− with simultaneously release Cs+ at an oxidation potential. The separation factors of BiOBr film electrode for Cs+/K+, Cs+/Na+, Cs+/Li+, and Cs+/Rb+ cations were 3.71, 3.23, 4.94, and 7.46, respectively, and for Br−/F−, Br−/Cl− and Br−/NO 3 − anions were 2.11, 1.55 and 3.83, respectively, which showed relatively excellent selectivity for Br− and Cs+. Density functional theory (DFT) calculations reveal that the selectivity of BiOBr towards Br− and Cs+ comes from the lower ion migration energy barrier in the BiOBr lattice. Based on the ESAIX mechanism, a novel electrochemically switched amphoteric ion membrane coupling permselective (ESAIM-CP) system was further developed for the simultaneous separation and enrichment of Br− and Cs+, which successfully achieved the enriched CsBr with 2 folds of the original concentration from a mixed solution of Cs 2 SO 4 and KBr. [Display omitted] • A novel ESAIX mechanism and ESAIM-CP system were proposed for ion separation. • DFT calculations reveal that the selectivity source of BiOBr to Br− and Cs+. • The ESAIM-CP system enriched a CsBr solution with twice the initial concentration. [ABSTRACT FROM AUTHOR]

Highly selective extraction of lithium ions (Li+) from salt-lake brines is crucial to mitigate lithium supply shortages. In this work, a novel electrochemically switched lithium ion permselective membrane (ESLPM) was rationally designed through an ingenious tactic with an electroactive layer of lithium manganate (LiMn 2 O 4) as the active radical and a dense and positively charged polyamide (PA) on each side of polyethersulfone (PES) substrate for the rapid and selective separation of Li+ from salt-lake brines with high Mg/Li ratios. Here, the reversible uptake/release and enhancement electro-sorption selectivity of Li+ are controlled by changing the electrochemical potential of the membrane with an ion-pump effect coupling with the electric field to achieve the continuous recovery of Li+. As a result, the flux of Li+ in the optimum hierarchical ESLPM-240 of the electrochemically switched ion permselective (ESIP) membrane separation system reached 0.032 mol m−2 h−1 for the separation of Li+ from the salt lake brine with a high Mg/Li ratio (Mg2+/Li+ = 20), which is 25% higher than in electrodialysis (ED) system. Meanwhile, by constructing a hierarchical structure, the separation factor of Li+/Mg2+ was increased to 7.8 under the ESIP system, which is about 3.5 times higher that of PA layer, and about 2.2 times higher than that of the electroactive layer. In addition, theoretical calculation confirmed that electroactive LiMn 2 O 4 and positively charged PA layers are more favorable for Li+ transport when compared to Mg2+. Besides, the ESLPM-240 exhibited excellent long-term stability, indicating that the proposed strategy is promising for large-scale industrial applications in the Li+ extraction from salt lakes. Reversible electrochemical switched ion pump in hierarchical electroactive ion permselective membranes for the continuous separation of Li+. [Display omitted] • ESLPM-240 with electroactive layer and dense layer were prepared. • Transport mechanism of LiMn 2 O 4 -based ESIP membrane with ion pump effect was proposed. • ESLPM-240 exhibited excellent permselectivity and flux for Li+. • The energy consumption of the ESIP system for ESLPM-240 reached 0.39 kWh mol−1. [ABSTRACT FROM AUTHOR]

[Display omitted] • An electrochemically triggered TiO 2 /PANI ion exchange film was fabricated. • Adjusting layer spacing precisely fully expose ultra-affinity Pb2+ capture sites. • Conversion of Ti4+/Ti3+, M O H/M−O−Pb trigger the uptake/release of Pb2+. • Directional proton migration provided fast electron transport network. • TiO 2 /PANI shows ultrahigh uptake capacity (1499.99 mg·g−1) and selectivity. The slow accumulation of heavy metal in the sediment and aquatic food chain, leads to extremely bad health influence in human body. Most of the traditional adsorption materials have deficient adsorption capacity and selectivity. In this research, the TiO 2 /PANI composite material is synthesized successfully by intercalating 2HT (intercalating agent) and PANI into the interlayer of the TiO 2 nanosheet for the separation of Pb2+. During this synthesis process, the layer spacing of TiO 2 /PANI can be controlled precisely by adjusting the concentration of 2HT and PANI. The rapid Pb2+ uptake/ release process is triggered through turning the redox states of composite film which can leads to the conversion between Ti4+ and Ti3+ and the conversion between –OH and -O-Pb covalent bond for maintaining the electrical neutrality. In addition, the directional H+ proton migration, fast electronic transporting network and superfast Pb2+ ion transport path both are benefit for the transmission and uptake of Pb2+. As a result, this composite film illustrates ultrahigh uptake capacity (1499.99 mg∙g−1) and selectivity (K D = 15.2 L·g−1). It can even treat real wastewater to a level lower than WHO. Hence, this composite film with superior electrochemical performance is a promising material, which could be used for uptake/release of Pb2+. [ABSTRACT FROM AUTHOR]

[Display omitted] • C C conjugated bonds can be activated via induced built-in electric field. • Ion capture with Bi-terminated dependence is realized by directional charge transfer. • Bi(3−x)+OBr 1−x with large lattice spacing can reserve Br− in the formation of BiOBr. • A practical criteria for screening promising electroactive materials is proposed. The further development of promising electrically switched ion exchange (ESIX) materials with considerable selectivity and large adsorption capacity have been generally concerned in ion removal filed. Herein, a hybrid film with core–shell structure and large lattice spacing, which integrated the virtues of highly adsorptive-selective BiOBr with conductive PPy was explored to be able to synergistically remove bromine ions (Br−) from an aqueous solution by combining density functional theory (DFT) calculations with experiments. The large-area and intimate contact between BiOBr and PPy generate a built-in electric field with quasi one-dimensional charge transfer from BiOBr to PPy, inducing the activation of C C conjugated bonds with the facilitating of the structure stability and electroactivity. Interestingly, the cooperation of PPy could significantly facilitate Br− migration on account of enhancing electroactivity without affecting the adsorption capacity of BiOBr. Meanwhile, BiOBr/PPy exhibits prominent selective capacity towards Br− in the presence of other competing ions, attributing to the shielding effect of PPy, particular electron transfer between Br and Bi, sucking stability and rapid ion kinetic diffusion accelerated by befitting adsorption capacity. Furthermore, the reversible redox process demonstrates that Bi(3−x)+OBr 1−x with a Bi-terminated dependent manner could store Br− in the formation of BiOBr through an ESIX procedure (Bi(3−x)+OBr 1−x + xBr−↔Bi3+OBr + xe−). It is expected that this study might propel the development of electroactive materials in the ion treatment field. [ABSTRACT FROM AUTHOR]

Contact with trace heavy metal contaminants will also lead to extremely bad health influence on human body and aquatic life. Although various adsorbents have been synthesized for the recovery of heavy metal ions, most of them shows deficient adsorption capacity, sluggish uptake rate and low selectivity. In this study, a montmorillonite/polypyrrole (MMT/PPy) film was successfully synthesized by intercalating polymers PPy into the interlayer of MMT nanosheets for selective and rapid capture of Pb2+. The electroactive film has ultrahigh uptake capacity (1373.29 mg⋅g−1), which is much higher than most conventional Pb2+ adsorbents. Meanwhile, it had an extreme selectivity towards Pb2+ due to the MMT/PPy film can accurately identified Pb2+. Through characterization testing and data analysis, the selective and rapid uptake/release of Pb2+ should be realized through three ways: (1) negatively-charged laminates of MMT can generate electrostatic attraction to Pb2+; (2) -OH on the surface of MMT laminates can accurately identified and bonded with Pb2+ (M-O-H↔ M-O-Pb); (3) PPy doped by PSSn- and protic acid can rapidly catch Pb2+ (PPy+·PSSn-+Pb2++e-→ PPy·PSSn-·Pb2+). Therefore, such a novel MMT/PPy nanocomposite film could has evident application prospect to remove Pb2+ from various water bodies. [Display omitted] • An electroactive film with sandwich-like structure was fabricated for Pb remove. • Adjusting layer spacing exposed ultra-affinity capture site and transport channel. • Doping PPy provided fast electron transport network. • The uptake capacity reached as high as 1373.29 mg/g for Pb ions. [ABSTRACT FROM AUTHOR]

[Display omitted] • Electroactive site concentration (ESC) is firstly introduced. • ESC is used to study pseudocapacitive ion adsorption in the ESIX process. • A dynamic ESIX model based on ESC is established and validated for ion adsorption. • The ion adsorption mechanism of ESIX is elucidated quantitatively by the model. • The operation parameters and film electrode parameters are assessed by the model. Electrochemically switched ion exchange (ESIX) technology has been proved as a promising valid method for separation of valued-added ions in diluted solutions. Herein, to promote industrial application of the ESIX technology, a general theoretical framework based on the electroactive site concentration (ESC) is proposed to describe the rigorous mechanism of ESIX process with electroactive ion exchange material (EIXM) coated electrodes. In particular, the pseudocapacitive ion adsorption process is modeled by modifying the electrochemical potential of the electroactive sites of EIXM. The proposed ESIX model reveals that the constant current density operation should be more suitable than the constant cell voltage operation for the ESIX process. It is found that the increasing of operating current density and the initial ion concentration can improve the average ion adsorption rate. For the ESIX process with the electroactive bismuth oxybromide (BiOBr) film coated electrode for bromine ions (Br−) separation, the simulation results are in good agreement with the dynamic experiment data. It is confirmed that the modeling of ESIX process based on the ESC provides an effective way to elucidate the ion separation mechanism in pseudocapacitive adsorption process and to predict the effect of various operating parameters on the ESIX process performance conveniently. [ABSTRACT FROM AUTHOR]

[Display omitted] • An electroactive NiHCF/CTCM composite membrane was fabricated successfully. • Adjusting aperture can shorten ion transport path and accelerate mass transfer. • NiHCF/CTCM exhibited an ultrahigh removal efficiency (over 99.99%). • NiHCF/CTCM showed an excellent selectivity to Cs+ ions by affinity of NiHCF. Radioactive cesium (137Cs) ions exhibit high-energy gamma radiation and long half-life. When they enter water body, serious environmental problems and damage to the human body are always generated. Herein, an electroactive composite membrane was facilely prepared by uniformly deposition of nickel hexacyanoferrate (NiHCF) nanoparticles on the surface and inner wall of coal-based tubular carbon membrane (CTCM) for rapid and selective separation of Cs+ from wastewater. This NiHCF incorporated CTCM tube exhibited an extremely high removal rate (over 99.99%) over a long period. Meanwhile, it also demonstrated extreme Cs+ selectivities even in the solutions with high coexisting ion concentrations (e.g., Cs+:Na+ = 1:99, Cs+:K+ = 1:99). The rapid and selective Cs+ uptake/release should be attributed to the better dispersion of NiHCF nanoparticles with high selectivity to Cs+ in the CTCM tube, which reduced the mass transfer distance, increased fluid turbulence and accelerated mass transfer rate. It is expected that such a NiHCF incorporated CTCM tube could be a promising alternative of conventional materials for the separating of radioactive Cs+ ions. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel unipolar pulse potential oscillation (UPPO) system was proposed. • A novel HKUST-1(C)@CoAl LDH film was successfully prepared. • HKUST-1(C)@CoAl LDH film was successfully used for the separation of DS−. • HKUST-1(C)@CoAl LDH film exhibited a high DS− adsorption quantity of 733.84 mg g−1. • The selectivity factors for DS− to other anions varied between 11.67 and 13.28. A carbonized HKUST-1@CoAl layered double hydroxide (HKUST-1(C)@CoAl LDH) film with a three-dimensional (3D) porous structurewas successfully prepared on the copper mesh by using a two-step electrochemical deposition method, and applied in a novel unipolar pulse potential oscillation (UPPO) system for selective separation of dilute dodecyl sulfonate ions (DS−). In the HKUST-1(C)@CoAl LDH film, the CoAl LDH was served as a separating layer to improve the selectivity for DS− ions with the HKUST-1(C) as a storage layer to increase the adsorption amount of DS− ions. As a result, the 3D HKUST-1(C)@CoAl LDH film coated electrode showed excellent selectivity toward DS− ions with a high adsorption capacity of 733.84 mg g−1 and favorable electrochemical stability. More importantly, it is found that such a novel UPPO system can effectively reduce the influence of co-existing anions on the adsorption of DS− ions and accelerate the transport of DS− ions in the film by the periodic potential oscillation, which is expected to be used for the selective separation of DS− ions from practical wastewater. [ABSTRACT FROM AUTHOR]

• An MMT/PANI electroactive film with a sandwich-like structure was fabricated. • Directional proton migration provided driving force for uptake/release of Pb2+ ions. • Atomically interlamellar ion transport paths accelerated Pb2+ ions transport. • Pb2+ ions were selectively captured by ultra-affinity ion capture sites on MMT layer. Although a variety of functional materials have been developed for the separation target ions, most of them suffer from sluggish uptake of ions and deficient selectivity. Herein, a nanocomposite electroactive film with a sandwich-like structure was facilely prepared by intercalating conductive polyaniline (PANI) into the interlayer of montmorillonite (MMT) with layered structure for rapid and selective separation of Pb2+ ions. This MMT/PANI nanocomposite film exhibited an extreme Pb2+ ion uptake rate (1422.67 μg∙(g∙s)−1), which exceeded those of conventional adsorbents by 2 to 4 orders of magnitude. Meanwhile, trace Pb2+ ions at ppb level in the wastewater were quantitatively detected by employing the MMT/PANI nanocomposite electroactive film based on its strong affinity towards Pb2+ ions. It was confirmed that the rapid and selective Pb2+ ion uptake/release by the MMT/PANI composite film was achieved via the directional proton migration powered by the electrochemical redox of the intercalated PANI, the superfast ion transport in atomically interlamellar ion transport path and the ultra-affinity ion recognition of ion capture sites on MMT layer. It is expected that such an MMT/PANI composite film could be a promising alternative of conventional materials for separating and detecting of Pb2+ ions in wastewater. [ABSTRACT FROM AUTHOR]

• A novel electrochemically triggered iodide-vacancy BiOI film was fabricated. • The I−-vacancy BiOI film exhibit superior selectivity to I− by vacancy trap effect. • The I− extraction capacity reached as high as 328 mg·g−1 within 1 h. • The I−-vacancy BiOI film can be completely and easily regenerated via ESIE process. The effective extraction and regeneration of radioactive iodide remains an urgent concern for safe nuclear energy utilization. Herein, we developed a novel electrochemically triggered iodide-vacancy BiOI film, which exhibited excellent I− ion extraction capacity of 328.3 mg·g−1. Especially, due to the ion vacancy trap effect, the film showed high selectivity towards I− ions in the existence of a large number of competitive anions. Additionally, the electrochemically switched ion extraction (ESIE) process with this iodide-vacancy BiOI film possessed fast extraction kinetics and high stability. More importantly, the trapped I− ions were easily desorbed from the film without the secondary pollution during the ESIE process and meanwhile, the iodide-vacancy BiOI film was able to be completely regenerated. It is expected that such an iodide-vacancy BiOI film with ESIE could become a promising process for the selective extraction of I− ions from the radioactive water. [ABSTRACT FROM AUTHOR]

• A hybrid film with molecular coupling synergistically-driven ability was fabricated. • Uptake/release of Ag+ ions were synergistically driven by electrostatic interaction. • Ag+ ions were selectively captured by carboxyl groups and disulfide bonds. • The regeneration rate of Ag+ ions was over 80% in each cycle. An electrically switched ion exchange film with molecular coupling synergistically-driven ability for the selective recovery of Ag+ ions is developed by coupling a conducting polypyrrole (PPy) with a 2, 2ʹ-dithiosalicylic acid (DTSA) at molecular scale. The rapid and selective uptake/release of Ag+ ions by this hybrid film was found to be realized by the electrochemical circulation of the PPy ↔ PPyn+ as well as the disulfide ↔ dithiolate and the recognition ability of the carboxyl groups and disulfide bonds of DTSA. As a result, the recovery of Ag+ ions can be handily achieved by adjusting the operating potential applied on the hybrid film coated electrode. The electrochemical quartz crystal microbalance measurements combined with the cyclic voltammetric technique, X-ray photoelectron spectroscopy and density functional theory computations were performed to identify the uptake/release mechanism of the hybrid film. Furthermore, the uptake capacity of the hybrid film maintained almost invariable after 10 consecutive uptake/release cycles, and the regeneration rate of Ag+ ions remained over 80% in each cycle. It is expected that such an electroactive hybrid film can be applied for the recovery of Ag+ ions from various industrial discharges. [ABSTRACT FROM AUTHOR]

An electroactive ion exchange hybrid film of polypyrrole/reduced graphene oxide/NiCo-layered double hydroxide (PPy/rGO/NiCo-LDH) with three-dimensional (3D) "sand rose" flower-like structure was fabricated by a two-step electrodeposition method. NiCo-LDH nanosheets were electrodeposited on the surface of polypyrrole/graphene oxide (PPy/GO) conducting substrate for the removal of dodecyl sulfonate ions (DS− ions) with low concentrations. Herein, the electroreduction of GO to rGO enhanced the electron conductivity and the unique structure of hybrid PPy/rGO/NiCo-LDH film ensured the fast diffusion of electrons as well as ions. The electrochemical performance of hybrid film was characterized by cyclic voltammetry (CV) and electrochemical impedance spectrum (EIS), and the effects of the applied electrode potential, initial concentration of DS− ions and pH of the simulated wastewater on the uptake kinetics of DS− ions were investigated. As a result, the coexisting anions had no obvious effect on the adsorption of DS− ions and the removal percentage of DS− ions reached 92.31% in a 10 mg L−1 DS− solution with 0.8 V electrode potential. Especially, in the pH ranging from 5.0 to 9.0, the DS− ions were efficiently removed. In addition, the double-driven ion exchange mechanism coupling electric double-layer (EDL) effect of rGO and pseudo capacitance effect of PPy to remove DS− ions was proposed based on the X-ray photoelectron spectroscopy (XPS) and CV analyses. It is expected that such a novel PPy/rGO/NiCo-LDH hybrid electroactive ion-exchange film separation technology based on the double-driven mechanism could be a potential technique for wastewater treatment. Image 1 • A double-driven electroactive ion exchange hybrid film was fabricated. • The charge capacity of the film retained 88.8% after 1000 successive cycles. • The coexisting anions had a slight impact on the uptake of DS− ions. • The removal of dilute DS− ions was achieved using the film in ESIX process. [ABSTRACT FROM AUTHOR]

• An I− trapping polypyrrole film was fabricated for the ESIE process. • The PPy/I− film demonstrated superior selectivity towards I−. • The I− extraction capacity reached as high as 287 mg/g in 5 ppm I− solution. • The PPy/I− film was electrochemically regenerated completely for several times. Effective extraction of iodide ions (I−) from low-concentration brine or radioactive wastewater remains a great challenge. In this study, an electroactive I− trapping polypyrrole film (PPy/I− film) was fabricated via a facile one-step electrodeposition method and used in a novel and effective electrochemically switched ion extraction (ESIE) system for capture of I− from dilute aqueous solutions. Herein, the PPy/I− film displayed superior performance owing to the special I− trapping efficiency. The extraction capacity as high as 287 mg/g was achieved in 5 ppm KI solution, and the separation factors for I−/Cl−, I−/Br−, I−/SO 4 2−, I−/PO 4 3− were 6.93, 22.16, 15.92, 7.92, respectively. Moreover, the desorption efficiency of I− from the PPy/I− film extracted with I− was approximately 100% even after several repeated cycles. It manifested that the present ESIE system with the PPy/I− film had efficient extraction capacity, remarkable selectivity and excellent recyclability, which could be applied in the extraction of I− from the dilute industrial solutions. [ABSTRACT FROM AUTHOR]

• A 2D model of electrochemically switched ion permselectivity was developed. • Model was validated in a wide range of conditions with experimental data. • The effectiveness of operating parameters was evaluated. • The optimum conditions for maximum current efficiency was computered. Electrochemically switched ion permselective (ESIP) is an emerging technology which requires very little energy for trace concentration ionic separation and has markedly high selectivity. Fully understanding transport process of ions through ESIP membranes is of importance for ESIP. In this work, a two-dimensional, steady-state, simple mathematical model was established, based on Nernst–Planck theory for the ions transport in ESIP system. The model is used to evaluate and analyze the effects of inlet concentration, volume flow, and cell voltage on the separation flux. Furthermore, the current efficiency model was established, paving the way for future energy calculations and cost estimation. It is critical to minimize its operating costs and energy consumption. The simulation results are in good agreement with dynamic experiments using laboratory reactors results, which verifies the reliability and practicability of the model. [ABSTRACT FROM AUTHOR]