Electrochemically Switched Ion Exchange Research Articles

A self-driven Ni(OH)2/CB/PVDF film for highly efficient adsorption of tungsten via hydroxyl ligand exchange

A nickel hydroxide/carbon black/polyvinylidene fluoride (Ni(OH)2/CB/PVDF) film was coated on a graphite plate substrate and used for the selective and efficient extraction of W(VI) using self-driven film adsorption. The excellent self-driven adsorption performance of Ni(OH)2/CB/PVDF film for W(VI) was demonstrated by the comparison of the experimental performance of film adsorption and electrochemically switched ion exchange (ESIX) process. In the Ni(OH)2/CB/PVDF film, the adsorption of W(VI) by Ni(OH)2 was achieved through the ligand exchange reaction with W(VI) and abundant hydroxyl groups, which ensured the self-driven performance. The adsorption capacity of the self-driven Ni(OH)2/CB/PVDF film for W(VI) under neutral conditions could reach up to 37.53 mg·g−1 after 12 h. Moreover, the adsorption kinetics and adsorption thermodynamics showed that the adsorption of W(VI) on Ni(OH)2/CB/PVDF films was more in line with the pseudo-second-order kinetic model, and the adsorption was heat-absorbing and spontaneous. After seven cycles of adsorption/desorption, the adsorption capacity of W(VI) by Ni(OH)2/CB/PVDF film could reach 79.37 % of its initial value, which showed good adsorption/desorption cycle performance. Moreover, Ni(OH)2/CB/PVDF films showed high selectivity for W(VI) when WO42− coexisted with Cl−, NO3–, and SO42−, respectively. This study confirmed that the self-driven Ni(OH)2/CB/PVDF film had efficient and stable adsorption performance for W(VI), which can be regarded as a promising method for the selective adsorption of W(VI) from aqueous solution.

Selective lithium extraction with LiMn2O4: Impossible triangle and reconcile via in-situ growth on flexible 3D substrate

The electrochemically switched ion exchange (ESIX) with LiMn2O4, which can selectively extract lithium from salt-lake brines, has attracted intensive attention in recent years owing to the rapid development of the electric vehicle industry. However, the balancing of the membrane electrode’s impossible triangle, i.e., high load capacity, high porosity, and high conductivity, is something that has long puzzled scientists. In this study, one-step in-situ hydrothermal synthesis was utilized to prepare LiMn2O4 one-dimensional nano-rod (ODNR, 10 ∼ 40 nm and a length-diameter ratio of 18–220) on the flexible carbon cloth substrate (LiMn2O4@CC), thus reconciling the impossible triangle. The exchange capacity (37.73 mg/g), dissolution ratio (<0.05 %), kinetics (88 % capacity with 1.5 h), and specific energy consumption (5.04 Wh/mol·Li) of ODNR LiMn2O4@CC flexible electrode are significantly superior to the LiMn2O4 on rigid titanium electrode (LiMn2O4@RTE) ascribing to the 3 times higher conductivity, 2 to 4 orders of magnitude higher internal Li+ diffusion coefficient, and the intrinsic 3D porous nature of the flexible electrode. Electrochemical analyses verified the redox of ODNR LiMn2O4/λ-MnO2 is a one-electron transfer electrochemical reversible process with a fast electron transfer process, which may be induced by the in-situ growth ODNR and the 3D porous structure of the flexible substrate. The separation coefficients for Li+/Mg2+ and Li+/Na+ were 804.6 and 513.2, respectively. And the capacity retention ratio is > 92 % even after 50 cycles. This work sheds light on the reconciling of the impossible triangle for membrane electrode fabrication.

Modelling and optimization of Li+ extraction from brine with high Mg/Li ratio by electrochemically switched ion exchange considering thermodynamics and dynamics simultaneously

Electrochemically switched ion exchange (ESIX) technology has been proven to be an efficient and environmental-friendly method for extracting Li+ from brine lakes. To deeply understand and mathematically express the underlying physical process of Li+ extraction in ESIX, a model is developed to describe Li+ extraction from brine lakes with a high Mg/Li mass ratio (500:1) by ESIX with an electrode coated with λ-MnO2 film. The kinetics and thermodynamics of the Li+ extraction process is considered simultaneously by coupling the Frumkin-Bulter-Volmer theory modified by electroactive site concentration with a modified Gouy-Chapman-Stern model. The local sensitivity analysis indicates that the performance of ESIX in Li+ adsorption is greatly influenced by cell voltage, film mass, and Stern capacitance of carbon black film, whereas these parameters have little effect on Mg2+ adsorption. The individual parameter analysis elucidates that the mass and Stern capacitance of carbon black film can regulate the potential drop distributions in different regions of ESIX system, resulting in a maximum Li+ extraction efficiency of 90.22 % due to the increased driving force in the faradic reaction and reduced charge transfer resistance. The optimization of combined parameters indicates that the optimum operation can be achieved at the conditions with a cell voltage ranging between 1.0 and 1.2 V, a Stern layer capacitance with electric double layer volume for carbon black film of 5.4 × 107 F/L, and an initial Li+ content of the treatment solution: carbon black film: λ-MnO2 film mass ratio of 0.1 kg: 9 kg: 8 kg.

Recovery of metal ion resources from waste lithium batteries by in situ electro-leaching coupled with electrochemically switched ion exchange

A new green pathway of in situ electro-leaching coupled with electrochemically switched ion exchange (EL-ESIX) technology was developed for the separation and recovery of valuable metal ions from waste lithium batteries. By using the in situ electro-leaching, the leaching rates of Li+ and Co2+ from the prepared LiCoO2 film electrodes reached 100 % and 93.30 %, respectively, under the combined effect of the acidic microenvironment formed by the anodic electrolytic water and electrostatic repulsion. Subsequently, the Li+ in the electrolyte was further extracted by an electrochemically switched ion exchange (ESIX) process using LiMn2O4 as the film electrode, and Li+ was further enriched in the eluate by a cyclic adsorption and desorption process. The results indicate that the in situ electro-leaching has significant advantages over powder leaching, and for the recycling of waste lithium batteries, the final lithium recovery rate reached 94.51 % by using this in situ EL-ESIX technology.

(Invited) Electrochemically Driven Ion-Exchange Remediation of Water Containing High Fluoride Content

Remediation of water contaminated by anthropogenic activities is required to provide clean water for human consumption and prevent damage to the environment. The scale of the challenge is signaled by its inclusion in the UN 17 Sustainable Development Goals [1]. Major contributors to the problem are industrial activity and agriculture. The former commonly results in the release of metals; analysis and separation of such cationic species have received considerable attention [2]. In the latter instance, run-off of fertilizers used to enhance crop yields can result in unacceptable levels of nitrate or phosphate in natural waters. While monitoring of anionic species is widely undertaken using ion selective electrodes [3], the promise of electrochemical separation technologies [4] in this area is less well developed.For anthropogenic causes, remediation is the last resort following failure to prevent release of toxic materials into the environment. In contrast, there are instances where the “contaminant” is natural: fluoride is a prime example. The beneficial dental health effects of fluoride are widely appreciated, but excessive amounts are harmful to teeth, bones and various organs [5]. The World Health Organization (WHO) identifies the optimum fluoride level in drinking water to be 0.5-1.0 mg/L. In many regions, water is fluoridated to realize the health benefits. However, local geological conditions many countries can result in natural water fluoride levels significantly above the recommended upper limit of 1.5 mg/L.This presentation addresses the challenges associated with remediation of anions, with particular focus on fluoride. At the outset, it is recognized that for potable water the requirement is not full de-ionization but selective removal of contaminants: this is a separation challenge. The attributes, performance and potential for scale-up of a range of (electro)chemical remediation strategies will be discussed in general. We then focus on electrochemically switched ion-exchange (ESIX) [6], for which application to water softening [7] and perchlorate removal [8] has been demonstrated.We explore the facility of aniline-based (co-)polymer films to reversibly extract and eject fluoride ions as the charge (oxidation state) of the films are subject to electrochemical control. Homopolymer and copolymer films based on aniline, o-aminophenol and o-toluidine were deposited potentiodynamically. Film thickness was controlled via the number of potential cycles: the resultant electroactive site population was assayed coulometrically in monomer-free background electrolyte. Film mass was assayed gravimetrically using the EQCM. For relatively thin films, correlation of film mass and charge capacity revealed the solvent content. During deposition of thicker films, acoustic admittance data revealed the progressive evolution of viscoelastic effects. Co-monomer feedstock has a significant influence on film deposition rate, absolute solvent population and redox-driven solvent population change [9].The ion-exchange capacity of the films for redox-driven fluoride uptake was determined upon exposure to aqueous solutions of varying fluoride concentration, both in the absence and presence of chloride as a competing anion. EQCM mass and charge responses, respectively, provide overall “ion+solvent” and “solvent” population changes: correlation permits separation of fluoride and water uptake/release. Copolymer composition significantly influences the ease of fluoride uptake and release and reveals ion trapping. Complementary data on the dynamics of ion and solvent transfers are provided by shorter timescale experiments, involving voltammetry at faster scan rates and chronoamperometry. Correlation of gravimetric and coulometric data permits temporal separation of fluoride and solvent entry and exit.Practical exploitation of these promising fundamental observations will require scale-up and optimization of cycle life, film viscoelasticity and response time as functions of film thickness. We speculate that spatially variant film solvation will be a critical parameter. To this end, we consider the viability of neutron reflectivity measurements with isotopic substitution to determine the spatial distributions of fluoride and solvent in films of graded composition.

Film electrode by incorporating polypyrrole/carbon black into cross-linked binders of chitosan/cationic polyacrylamide for selective chloride extraction in wastewater

Water-based binders are usually free of volatile organic compounds and hazardous reagents, which reduces the impact on the environment, and research and development of water-based binders has been progressing in recent years. In order to increase the adhesion and mechanical properties of the composite film electrode, lower the resistance to ion transfer, and improve the adsorption capacity of Cl−, a unique cross-linked aqueous binder composite film electrode was created. The film electrode for the electrochemically switched ion exchange (ESIX) system's Cl− adsorption and desorption was successfully prepared by incorporating polypyrrole (PPy-Cl)/carbon black (C) into chemically cross-linked chitosan (CS) and cationic polyacrylamide (CPAM) by glutaraldehyde (GA). The film electrode of formulated PPy-Cl/C/CS-c-CPAM had advantages over the film electrode of PPy-Cl/C/PVDF (polyvinylidene fluoride). The PPy-Cl/C/CS-c-CPAM film electrode had 33.56 mg g−1 adsorption capacity when operated at 0.8 V for the oxidation potential, high selectivity, short adsorption time, and excellent adhesions. CS-c-CPAM composite binders provide a new direction for realizing the superior performance of the film electrodes.

A potential-driven NiO/NiCo LDH film electrode for highly efficient extraction of Br- via electrochemical coordination and anion exchange

A potential-driven nickel oxide/NiCo layered double hydroxide (NiO/NiCo LDH) composite film was deposited within the stainless steel wire mesh, showing excellent Br− extraction in an electrochemically switched ion exchange (ESIX) system. In this composite film, NiO with a high specific surface area and porous structure served as the lower layer to improve the electrical conductivity and ion storage capacity of the film, while NiCo LDH served as the main selective separation layer to selectively adsorb the target Br−. The film electrode extracted Br− up to 159.25 mg·g−1 and the separation factors of Br−/Cl−, Br−/NO3−, and Br−/I− were 2.04, 8.89, and 5.45, respectively. The film electrode showed excellent adsorption–desorption cyclability and electrochemical stability since the NiO increased the binding force and electrical conductivity between NiCo LDH and substrate, and its porous structure accommodated Br−. The highly efficient extraction of Br− in neutral solution was attributed to the electrochemical coordination and interlayer anion exchange sites of NiO/NiCo LDH. This study provided a deep understanding of the ion selective extraction mechanism of LDH-based materials by ESIX technology and the novel electrochemical reaction design of electrodes, which could be used in other fields such as supercapacitors, sensors, and batteries.

An Electroactive BiOBr/PVDF/CB Film Electrode for Electrochemical Extraction of Bromine Ions from Brines

An electroactive bismuth oxybromide/polyvinylidene difluoride/carbon black(BiOBr/PVDF/CB) composite film electrode was fabricated that had a bromide ion trap (Br–-trap) effect obtained by prereleasing of Br– under reduction potential. The Br–-trap BiOBr/PVDF/CB film electrode was used for the selective extraction of Br– from salt lake brine by electrochemically switched ion exchange (ESIX) technology. Moreover, an industrially scalable ESIX pilot system was designed and the effects of different process parameters were investigated. In the ESIX system, the obtained film electrode exhibited efficient adsorption quantity, and remarkable selectivity owing to its special ion trap effect. The extraction capacity of Br– reached 67.10 mg g–1 with the separation factors of 2.06 and 7.13 for Br–/Cl– and Br–/NO3–, respectively, and the desorption efficiency of the film electrode remained at 95.4% after seven repeated cycles. It manifested that the pilot system with the Br–-trap BiOBr/PVDF/CB film electrode is expected to provide a novel direction for practical industrial Br– extraction.

A novel CNTs/QCS/BiOBr composite membrane with electron–ion transfer channel for Br- recovery in ESIX process

Based on the superior selectivity of bismuth oxybromide (BiOBr) for Br-, the excellent electrical conductivity of carbon nanotubes (CNTs), and the ion exchange capacity of quaternized chitosan (QCS), a three-dimensional network composite membrane electrode CNTs/QCS/BiOBr was constructed, in which BiOBr served as the storage space for Br-, CNTs provided the electron transfer pathway, and QCS cross-linked by glutaraldehyde (GA) was used for ion transfer. The CNTs/QCS/BiOBr composite membrane exhibits superior conductivity after the introduction of the polymer electrolyte, which is seven orders of magnitude higher than that of conventional ion-exchange membranes. Furthermore, the addition of the electroactive material BiOBr improved the adsorption capacity for Br- by a factor of 2.7 in electrochemically switched ion exchange (ESIX) system. Meanwhile, the CNTs/QCS/BiOBr composite membrane displays excellent Br- selectivity in mixed solutions of Br-, Cl-, SO42- and NO3–. Therein, the covalent bond cross-linking within the CNTs/QCS/BiOBr composite membrane endows it great electrochemical stability. The synergistic adsorption mechanism of the CNTs/QCS/BiOBr composite membrane provides a new direction for achieving more efficient ion separation.

A potential-responsive ion-pump system based on nickel hexacyanoferrate film for selective extraction of cesium ions

A nickel hexacyanoferrate (NiHCF) film electrode was prepared with NiHCF, conductive carbon black, and polyvinylidene difluoride, which was coated on graphite plate substrate for selective extraction of Cs+ ions by using electrochemically switched ion exchange (ESIX) technology. A potential-responsive ion-pump system for efficient extraction of Cs+ ions was designed, and the effect of wet film thicknesses, charging modes, flow rates, and chamber widths on Cs+ ions extraction performance was investigated. In the system, the adsorption capacity and removal percentage of Cs+ ions on the NiHCF film electrode reached as high as 147.69 mg·g−1 and 92.47%, respectively. Furthermore, the NiHCF film electrode showed high selectivity for Cs+ ions and stability. After seven cycles of adsorption/desorption, the desorption percentage could reach about 100%. The excellent Cs+ extraction performance should be attributed to the strong driving force produced by the potential-responsive ion-pumping effect in the ESIX process, as well as the low ion transfer resistance of the film electrode which is caused by the special crystal structure of NiHCF. In addition, the NiHCF film electrode was implemented to work together with the bismuth oxybromide (BiOBr) film electrode to accomplish the simultaneous extraction of Cs+ and Br–. And the adsorption capacity and removal percentage of Br– ions on the BiOBr film electrode reached 69.53 mg·g−1 and 77.32%, correspondingly. It is expected that such a potential-responsive ion-pump system based on NiHCF and BiOBr film electrodes could be used for the selective extraction and concentration of Cs+ and Br– ions from salt lake brine..

Cross-linked PVDF-b-PAA composite binder enhanced LiMn2O4/C film based electrode for selective extraction of lithium from brine with a high Mg/Li ratio

A novel physically blended polyvinylidene fluoride (PVDF) and polyacrylic acid (PAA) composite binder enhanced LiMn2O4/C (carbon black) film based electrode was successfully fabricated, and applied in an electrochemically switched ion exchange (ESIX) process for selective extraction of Li+ from high Mg/Li ratio brine. The multifunctional composite binder system enabled the obtained LiMn2O4/C/PVDF-b-PAA film coated electrode to exhibit superior mechanical, hydrophilic and electrochemical properties compared with the LiMn2O4/C/PVDF film coated electrode. Based on the density functional theory (DFT) calculations, the ion exchange interaction between H+ of –COOH groups in PAA and Li+ facilitated the transport of Li+ at the electrode interface, which enhanced lithium extraction performance of the film coated electrode. For treating the simulated brine (Mg/Li: ∼500), the intercalation capacity of Li+ was about 15.1 mg g−1, and the total extraction efficiency of lithium reached up to 62.8% after two electrochemical intercalation tests. Moreover, the film coated electrode displayed excellent selectivity towards Li+ ions even in pre-treated actual brine (Mg/Li: ∼292.2). The Mg/Li mass ratio in the recovery solution could decrease to 0.46, and the calculated Li+/Mg2+ separation coefficient reached as high as 631.08. In particular, the highly stable and scalable electroactive film could be prepared effectively, thus increasing its applicability. It is expected that such a LiMn2O4/C/PVDF-b-PAA film coated electrode could be a promising candidate for the selective extraction of Li+ from high Mg/Li mass ratio brines.

Intrinsic facet-dependent electrochemical activities of BiOBr nanosheets for Br- exchange in electrochemically switched ion exchange process

Creating surface atomic arrangement and coordination of BiOBr with a special highly-exposed crystal facet could significantly alter its performance. Although many efforts have been made to explore the relationship between the exposed facet and photo-reactivity, little has been done to investigate Br- exchange activity on the specific facet during an electrochemically switched ion exchange (ESIX) process. In this study, BiOBr nanosheets with highly exposed (001) and (010) facets (named as BOB-001 and BOB-001, respectively) were synthesized, and the effect of exposed crystal facet on ESIX activity was investigated for the first time. The electrochemical investigation suggested that the BOB-010 had better ESIX performance for Br- recovery than the BOB-001. Due to the difference in the surface state as well as the property, the Bi-O bond of the exposed [Bi2O2] layer in the BOB-001 could be broken at a higher potential for the exchange of Br-. While for the BOB-010, Br- could easily pass through the open channel between the [Bi2O2] layers for ion exchange. Furthermore, the photo-assisted electrochemically switched ion exchange (P-ESIX) performances of BOB-001 and BOB-010 were investigated. It is found that the real photo-assisted performance of BOB-010 was remarkably higher than that of BOB-001 because of its better photo-response characteristics. This study gives a better insight into the facet-dependent electrochemical ion-exchange performance of BiOBr.

Manganese-based spinel adsorbents for lithium recovery from aqueous solutions by electrochemical technique

The manganese-based spinel adsorbent (HMO) refers to lithium-ion adsorbents derived from the spinel lithium manganese oxide (LMO). Two types of lithium ions extraction composite films composed of HMO (HMn2O4 and H1.6Mn1.6O4) are successfully prepared by the blade coating method. Based on the excellent Li+ selectivity of HMO and the outstanding conductivity of conductive carbon black (C), HMO/C films are carried out to extract lithium by electrochemically switched ion exchange (ESIX) technique. HMO has a certain adsorption capacity for Li+ when the Li+ concentration is close to the actual brine, and the adsorption capacity of HMn2O4 and H1.6Mn1.6O4 is 24.56 mg/g and 34.40 mg/g, respectively. HMO showed good selectivity for Li+ in multiple metal ions solution. The capacity of HMn2O4 and H1.6Mn1.6O4 keep 80% and 86% of the initial values after 5 cycles, respectively. The inherent different lithium occupied leads to the difference of electrical-adsorption abilities between HMn2O4 and H1.6Mn1.6O4. H1.6Mn1.6O4 has a broad application prospect in lithium extraction from salt lake brine due to its lower application voltage, large adsorption capacity and superior stability.

Modelling of pseudocapacitive ion adsorption of electrochemically switched ion exchange based on electroactive site concentration

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.

An electrochemically induced dual-site adsorption composite film of Ni-MOF derivative/NiCo LDH for selective bromide-ion extraction

An electrochemically induced electrode with bromide ion (Br-) dual adsorption sites was obtained by in-situ growing of Ni-MOF derivative/NiCo layered double hydroxide (Ni-MOF(D)/NiCo LDH) composite film on the stainless-steel wire mesh via an electrodeposition-assisted solvothermal method, which exhibited excellent Br- selectivity from ionic mixture solutions of Br-, NO3– and I- in an electrochemically switched ion exchange (ESIX) system. The Br- extraction capacity was as high as 126.30 mg·g−1 and the separation factors of Br-/NO3– and Br-/I- were 8.29 and 4.83 respectively. Combining the simulation and experimental results, it was confirmed that the highly efficient selective extraction of Br- in neutral solution should be derived from the dual-site (i.e., electrochemically induced laminate metal coordination sites and interlayer anion exchange sites of NiCo LDH) adsorption. Furthermore, the electrode demonstrated superior adsorption–desorption performance and electrochemical stability because of the in-situ growth strategy, which enhanced the binding force between NiCo LDH and substrate and improved the electrical conductivity of NiCo LDH, and provided a storage space for Br-. This study served deep understanding of ions selective extraction mechanism of LDH-based materials in the ESIX process, which could be a novel reaction concept for the design of those electrodes with specific recognition sites in the applications of them in other fields such as supercapacitors, sensors and batteries.

A novel photo-assisted electrochemically switched ion exchange technology for selective recovery of bromide ions

Effective recovery of high-value-added bromide ion (Br−) from aqueous solutions is significant because of its high application value. Electrochemically switched ion exchange (ESIX) has been proven as a valid method for the selective capture and recovery of target ions. As the photocatalysts are also used as the electroactive materials in the ESIX process, the light illumination could promote the excitation of electrons for the improvement of ion capture capacity. Herein, taking advantage of synergetic effect between photo and electric field we propose a novel photo-assisted electrochemically switched ion exchange (P-ESIX) strategy for the first time. As a try, Br−-vacancy BiOBr film is used as an ideal electrode material in P-ESIX system for the recovery of Br−, which not only possesses photo/electron bi-activity, but also exhibits high selectivity towards Br−. Compared with the traditional ESIX, this P-ESIX displays superior capture performances with a photo-assisted adsorption capacity growth rate of 23.09% with 1.23 times higher Br− adsorption capacity at 0.8 V applied potential. The capture capacity of Br− in P-ESIX reaches 106.80 mg g−1 with excellent stability. Meanwhile, P-ESIX working mechanism is deeply analyzed based on experiments and DFT calculations. This novel technology provides a new direction in separation field to achieve higher capture efficiency for the target ions.

Highly Efficient Defluoridation of Water through Reusable poly(aniline-co-o-aminophenol) Copolymer Modified Electrode Using Electrochemical Quartz Crystal Microbalance

Although the World Health Organization (WHO) recommends a limit of 1.5 mg l−1 fluoride ions in drinking water, this is not satisfied in many parts of the world. When this limit is exceeded, the electrochemically switched ion-exchange (ESIX) technique (mainly based on conductive polymers) has been identified as a promising method for removing the excess fluoride ions. The present study aimed to develop an efficient method based on the ESIX technique by using poly(aniline-co-o-aminophenol) copolymer to extract fluoride ions. Electrochemical quartz crystal microbalance (EQCM) and acoustic admittance data were utilized to assay the synthetic efficiency of copolymer deposition, and to evaluate the dependence of the defluoridation process on the proportions of the monomers in the copolymer matrix and on film thickness. The resulting films were characterised by Fourier transform infrared spectroscopy (FTIR) and scanning electrochemical microscopy (SEM) techniques. For optimized co-monomer ratio in the feedstock, poly(aniline-co-o-aminophenol) at an applied potential of 0.30 V showed excellent performance for fluoride removal from water at pH 6.6, to the extent of 20 (mg F−) (g polymer)−1. Comparison of the performance of ESIX using poly(aniline-co-o-aminophenol) with that of other techniques and materials reveal that it has significant potential for water defluoridation.

A scalable three-dimensional porous λ-MnO2/rGO/Ca-alginate composite electroactive film with potential-responsive ion-pumping effect for selective recovery of lithium ions

A scalable three-dimensional (3D) porous composite electroactive film consisting of λ-MnO2, reduced graphene oxide (rGO) and calcium alginate (Ca-alg) was successfully fabricated and employed for the selective extraction of Li+ ions with low concentration via an electrochemically switched ion exchange (ESIX) technology. The Li+ ion adsorption capacity of the obtained λ-MnO2/rGO/Ca-alg composite electroactive film reached as high as 32.7 mg g−1 and more than 90% of its equilibrium adsorption capacity was achieved in 1 h. The λ-MnO2/rGO/Ca-alg composite electroactive film displayed evident selectivity towards Li+ ions. The separation factors for Li+/Na+ and Li+/Mg2+ reached 1040.57 and 358.96, respectively, while tested in simulated brine. The composite film also showed superior electrochemical stability, and the normalized ion exchange capacity retained at 98.3% of its initial value even after 100 successive cycles. The excellent Li+ ion recovery performance of the obtained composite film should be attributed to its low ion transfer resistance owing to the porous network structure and the potential-responsive ion-pumping effect in the ESIX process. In addition, a large-scale of such a composite electroactive film could be effectively fabricated by controlling the spreading area of the mixed solution consisting of λ-MnO2, rGO and alginate binder. It is expected that such a scalable 3D porous composite film could be a promising alternative for the recovery of lithium ions from salt lake brine.

A novel electrochemically switched ion exchange system for phenol recovery and regeneration of NaOH from sodium phenolate wastewater

An electrochemically switched ion exchange (ESIX) system was proposed as a novel electrochemical method for the treatment of high concentration phenolic sodium salty wastewater, in which a ferric ferricyanide (FeHCF) coated electrode with rigid open framework can control the insertion/extraction of sodium (Na+) ions by switching the redox state of FeHCF. It is found that this ESIX system can not only remove the phenol and desalinate the phenol-containing wastewater simultaneously, but also regenerate the FeHCF coated electrode and produce sodium hydroxide (NaOH). In the series operation, more than 79% of phenol could be removed with energy consumption of 9.677 × 10−3 kWh mol−1, and meanwhile NaOH solution with a pH of 12.84 was generated with energy consumption of 2.083 × 10−3 kWh mol−1 during the recovery process of Na+ ions. It is expected that such an ESIX system can be applied for the treatment of phenol-containing high salinity wastewater.

Electroactive polymers meet solid acid: A synergetic poly(acid yellow 9)/layered alpha tin phosphate (PAY/α-SnP) composite film for absorbing heavy metal ions

A potential-responsive ion exchange film composed of layered alpha tin phosphate (α-SnP) nanosheets and electroactive poly(acid yellow 9) (PAY) was developed for rapidly removing heavy metal ions. In this composite film, the PAY acts as the potential-sensitive function materials for capturing ions selectively during electrochemically switched ion exchange (ESIX) process, while α-SnP nanosheets work as solid acid materials to provide an acidic microenvironment for maintaining electroactivity of PAY and the interlayer space of α-SnP nanosheets play as the container of target ions. Experiment results reveal that the PAY/α-SnP composite film has excellent performance for removal of Pb2+ ions from wastewater rapidly and selectively. With applied potential of −0.3 V, composite film exhibits a saturated adsorption capacity of Pb2+ ions as high as 27.6 mg/g, and rapid ions uptake rate (uptake amount can reached 90.7% of saturated adsorption capacity during 15 min), which are 3 and 6 times higher as the spontaneous adsorption process. This excellent performance of composite films should be attributed to the synergistic effect of α-SnP and PAY components. This presented ESIX composite film should be valuable for removing Pb2+ions and/or other heavy metal ions from wastewater.