Capacitive Removal of Heavy Metal Ions from Wastewater via an Electro-Adsorption and Electro-Reaction Coupling Process

A coupled capacitive desalination (C-CDI) for enhanced desalination performance at ultralow voltage

A coupled capacitive desalination (CCDI) technique has been developed based on an innovative liquid-solid hybrid electrode design, wherein a thin layer of redox-active solution is confined near the surface of a porous carbon electrode. In this configuration, the desalination behavior is significantly enhanced through synergistically coupling of electrical double layer of the porous carbon and the redox reactions of the solution-phase redox species at the liquid-solid interface. To demonstrate the feasibility and superiority of this novel approach, the desalination behaviors of this liquid-solid hybrid have been investigated in a model system, where hierarchically porous hollow carbon spheres (HCS) are covered with a thin layer of ferrocene derivative (FcN2Br2) solution. The results reveal that the thickness of the redox electrolyte plays a critical role in determining the overall desalination performance. When confined within 500 µm, the thin layer of FcN2Br2 solution can effectively couple with the HCS electrode to achieve "overlay effects" in terms of both ion storage kinetics and capacity. Furthermore, the CCDI can achieve most of its desalination capacity with ultralow energy consumption, owing to the intense redox reaction of FcN2Br2 in a narrow potential range. Consequently, this setup attains a high desalination capacity of 52.2 mg g-1 and a rapid desalination rate of 6.6 mg g-1 min-1 at an ultralow voltage of 0.6 V, surpassing most reported benchmark devices. Overall, this pioneering work underscores the significant benefits of integrating liquid and solid electrodes, paving a groundbreaking and promising path for the future CDI evolution.

Recent Progress on Solar-Driven Interfacial Evaporation for Resource Recovery and Pollutant Removal

Solar-driven interfacial evaporation (SDIE) has emerged as a transformative technology for clean water generation by localizing solar-thermal energy conversion at the air-liquid interface. Beyond water production, recent advancements reveal its potential as a pivotal platform for addressing the challenges in resource reclamation and environmental sustainability. Drawing inspiration from plant transpiration mechanisms, particularly ion-selective absorption, long-distance transport, and bioactive enrichment, this review systematically examines bioinspired SDIE architectures that synergistically integrate membrane separation, adsorption, and photocatalytic processes. The recent progress is summarized across three tiers: 1) structural biomimetics replicating natural plants, 2) functional hybridization coupling complementary purification mechanisms, and 3) hierarchical integration of multi-process cascades. The review highlights the recent progress in material innovation and structure design to expand its function. Furthermore, implementation frameworks addressing interfacial engineering, process optimization, and system durability are proposed to bridge lab-scale prototypes with practical applications. The future prospects are also outlined for multifunctional SDIE technologies to address water-energy-resource interdependency, advancing their role in sustainable environmental management.

Highly Efficient Capacitive Removal of Heavy Metal Ions from Wastewater via In Situ π-π Stacking Covalent Organic Frameworks on Graphene Oxide Sheets

Capacitive deionization (CDI) is a promising technology for heavy metal wastewater purification but is limited by traditional carbon or Faradaic materials with low adsorption capacity, slow ion diffusion, poor selectivity, and inferior long-term cycling stability. Covalent organic frameworks (COFs) are recognized as highly anticipated porous materials, enable the construction of a stationary framework with superior structural properties, and provide numerous pores for ion transport in CDI applications. Herein, we synthesized a Schiff-based polymerized TOB-DAQ COF uniformly coated on graphene oxide (GO) sheets by a solvent-thermal in situ self-assembly strategy, leveraging π-π stacking interactions. These synthesized materials exhibit high efficiency and selectivity for heavy metal ion removal in complex and high-salinity solutions, enabled by their abundant active sites, rapid ion diffusion, and enhanced specific capacity. Crucially, conjoint material structural characterization and computational analysis of the electrostatic potential energy and adsorption energy barriers within the expanded framework elucidate the synergistic removal mechanism. This mechanism is attributed to central pore adsorption and carbonyl oxygen (-C═O) complexation. This study demonstrates the potential of COF materials to advance CDI-based wastewater treatment.

Sustainable Pb(II) Removal and Recovery from Wastewater Using a Bioinspired Metal-Phenolic Hybrid Membrane with Efficient Regeneration

High-performance adsorbents often require efficient selectivity in wastewater, recoverability, and ease of multiple regeneration cycles, but achieving this remains a significant challenge. We report a new strategy for the efficient removal of lead (Pb(II)) from contaminated water streams using an innovative tannic acid (TA)-Fe(III)-based metal-phenolic network (MPN) hybrid membrane (MPN-PAM). This novel membrane exploits the tunable pH-sensitive coordination structure of the MPN to achieve selective removal and recovery of Pb(II) while enabling efficient membrane regeneration by filtration. This membrane demonstrates superior selectivity for Pb(II) with a removal efficiency of up to 98 % and an adsorption capacity of approximately 117.58 mg/g, even in the presence of high salinity, as well as coexisting heavy metals. The membrane maintains high Pb(II) removal efficiency over 20 consecutive cycles and 95 % efficiency over 10 regeneration cycles. Under continuous operation, it treats approximately 85 L per m2 of membrane, reducing Pb(II) concentrations to trace levels (~40 μg/L), meeting electroplating wastewater standard (GB21900-2008). Additionally, even low concentrations of Pb(II) (<5 mg/L) are efficiently purified to below WHO drinking water standard (10 μg/L). The operational cost for treating Pb(II)-contaminated wastewater is about $0.13 per ton, highlighting the cost-effectiveness and potential for large-scale application in wastewater treatment.

Enhanced Removal of Cu2+ and Pb2+ Ions from Wastewater via a Hybrid Capacitive Deionization Platform with MnO2/N-Doped Mesoporous Carbon Nanocomposite Electrodes

Integrating MnO2 with carbon is a reliable strategy to improve capacitive deionization (CDI) performance by leveraging the unique properties of both components (i.e., MnO2 and carbon). However, the influences of preliminary functionalization of carbon (e.g., nitrogen doping, KOH activation) and pairing of cathodes and anodes on the CDI performance have yet to be systematically explored. Herein, we prepared a group of MnO2-decorated mesoporous carbon composites with nitrogen as a dopant (i.e., MK-NMCS, K-NMCS, NMCS, and CS), and systematically evaluated the desalination performance of various cathode//anode pairs in a hybrid capacitive deionization (HCDI) for capturing Na+, Cu2+, and Pb2+, respectively. Of all electrodes, the MK-NMCS//K-NMCS pair demonstrates the optimum desalination performance based on salt adsorption capacity (SAC) and cycling stability, offering a SAC of 25.4 mg g-1 and a SAC retention of 102.4% after 50 consecutive charge-discharge cycles at 1.2 V in 500 ppm of NaCl solution. In addition, the MK-NMCS//K-NMCS electrodes also show the maximum ion adsorption capacity (IAC) toward Cu2+ and Pb2+ ions compared to other cathode//anode pairs, attaining an IAC of 37.0 and 30.0 mg Cu2+ per gram electrode materials at 1.2 V in 500 and 200 ppm of Cu2+ solutions, respectively (cf. 32.2 mg of Pb2+ per gram of electrode materials in 200 ppm of Pb2+ solution). Besides, these electrodes exhibit excellent cycling stability when applied in removing each heavy metal ion separately, with IAC retentions of 90.0 and 98.5% after 50 cycles toward Cu2+ and Pb2+ ions, respectively. Mechanical analysis reveals that both heavy metals are likely to be sequestered via capacitive electrosorption by carbon, intercalation with MnO2, and surface complexation at the external surface of the [MnO6] octahedral layers. Our results demonstrated a great potential of the MnO2-decorated N-doped carbon//prefunctionalized carbon pairs, in particular, the MK-NMCS//K-NMCS electrode pair for capturing heavy metal ions via HCDI platforms. Such prefunctionalization and pairing strategies are very promising for screening high-performance composite electrodes for wastewater remediation.

Confinement-induced Ni-based MOF formed on Ti3C2Tx MXene support for enhanced capacitive deionization of chromium(VI)

MXenes, as a novel two-dimensional lamellar material, has attracted much attention. However, MXenes lamellar are prone to collapse and stacking under hydrogen bonding and interlayer van der Waals forces, which affects their electrochemical and capacitive deionization performance. A three-dimensional Ni-1,3,5-benzenetricarboxylate/Ti3C2Tx (Ni-BTC/Ti3C2Tx) composite electrode material was developed to enhance the electrochemical and capacitive deionization performance. The uniformly decorated Ni-BTC can prevent MXenes from aggregation and provide a large specific surface area and rich pore structure. As a substrate supporting Ni-BTC, MXenes can effectively disperse the growth of Ni-BTC and enhance the ion transport rate. In addition, the unique three-dimensional structure of Ni-BTC/Ti3C2Tx provides horizontal charge transfer paths like two-dimensional nanosheets and has unique vertical charge transfer paths between nanosheets. Therefore, the Ni-BTC/Ti3C2Tx exhibits an exceptional chromium(VI) removal rate of 94.1%. The electrosorption capacity of the Ni-BTC/Ti3C2Tx for chromium(VI) is 124.5 mg g-1, much higher than that of the pure Ti3C2Tx (55.5 mg g-1). The superior CDI efficiency accomplished through the Ni-BTC/Ti3C2Tx electrode is due to the unique three-dimensional network structure and synergistic effect of the pseudocapacitance generated by the unique assembly of Ni-BTC and Ti3C2Tx. Ni-BTC/Ti3C2Tx is a promising CDI electrode material that can be used for capacitive deionization.

Bryophytes adapt to open-pit coal mine environments by changing their functional traits in response to heavy metal-induced soil environmental changes

Plants have unique adaptability to heavy metal pollution. However, the adaptation strategies of bryophytes are still unclear. In order to better understand the response of bryophytes to different heavy metal and the adaptation mechanisms of different species to heavy metal pollution, we studied soil physicochemical properties, distribution of heavy metal elements, ecological risk assessment and the community structure, functional characteristics of bryophytes in large open-pit coal mines in Inner Mongolia. The results indicate that: (1) The soil in three open-pit mining areas currently does not pose an ecological risk from the heavy metal pollution, but high concentrations of Zn and Hg are found in most parts of the study area; (2) The presence of a single heavy metal drives the distribution of specific taxa of bryophytes. Apart from Hg, Pb, and Zn, all the other heavy metals significantly impact the community structure of bryophytes; (3) With the exception of Pb and Hg, all the other heavy metals have an influence on the functional traits of bryophytes; 4) Different taxa of bryophytes will adapt to changes in soil environments caused by heavy metal pollution by altering their functional traits (blades, leaf cells, or plant size).

Advances in the Recovery of Critical Rare Dispersed Metals (Gallium, Germanium, Indium) from Urban Mineral Resources

Urban mineral resources, with their significant recycling potential, have increasingly accumulated worldwide and become an important source for extracting valuable metals, particularly critical rare dispersed metals (CRDMs) such as gallium, germanium, and indium. As the electronics industry continues to grow rapidly, the demand for CRDMs is rising. However, CRDMs in primary mineral resources are often found in small, dispersed concentrations, making extraction challenging. In contrast, urban mineral resources contain relatively higher concentrations of CRDMs, making their comprehensive exploitation more advantageous than that of primary minerals. This paper underscores the importance of metal recycling by examining the current state of e-waste recycling from urban mineral resources in China. It outlines the general process of e-waste recycling, briefly compares the advantages and disadvantages of common metal recycling methods, and summarizes the current status of CRDMs recycling from various electronic wastes. Finally, this paper discusses the development trends and future prospects of metal recycling technology in urban minerals.

Photo-induced protonation assisted nano primary battery for highly efficient immobilization of diverse heavy metal ions

Highly-stable heavy metal ions (HMIs) appear long-term damage, while the existing remediation strategies struggle to effectively remove a variety of oppositely charged HMIs without releasing toxic substances. Here we construct an iron-copper primary battery-based nanocomposite, with photo-induced protonation effect, for effectively consolidating broad-spectrum HMIs. In FCPBN, Fe/Cu cell acts as the reaction impetus, and functional graphene oxide modified by carboxyl and UV-induced protonated 2-nitrobenzaldehyde serves as an auxiliary platform. Due to the groups and built-in electric fields under UV stimuli, FCPBN exhibits excellent affinity for ions, with a maximum adsorption rate constant of 974.26 g∙mg-1∙min-1 and facilitated electrons transfer, assisting to reduce 9 HMIs including Cr2O72-, AsO2-, Cd2+ in water from 0.03 to 3.89 ppb. The cost-efficiency, stability and collectability of the FCPBN during remediation, and the beneficial effects on polluted soil and the beings further demonstrate the splendid remediation performance without secondary pollution. This work is expected to remove multi-HMIs thoroughly and sustainably, which tackles an environmental application challenge.

Mechanistic Insights into Micelle-Enhanced Nanofiltration for Heavy Metal Removal: Transformation of Ion Transport and Fouling Phenomena

Toxic heavy metals are widely present in typical scenarios, such as mines and electroplating wastewater, presenting significant risks to biological and environmental safety. Membrane processes encounter a challenge in effectively intercepting heavy metals due to their small hydration radius. This research showcases the high efficiency of micelle-enhanced nanofiltration (MENF) in removing heavy metals. At the critical micelle concentration, sodium dodecyl sulfate demonstrated a high removal of Cu2+, Ni2+, Zn2+, and Cd2+ while maintaining substantial potential for complexation of heavy metals. The formation of micelles and the bonding of heavy metals with surfactants bolstered the resistance of heavy metal ions to transmembrane transport. The presence of heavy metals in ionic form in wastewater facilitated their complexation with surfactants or micelles. Notably, the valence state and concentration of interfering ions in the environment could slightly influence the removal of heavy metals by MENF. Additionally, MENF displayed remarkable antifouling properties. The loose gel layer created by surfactant molecules and the micelle enhanced the membrane permeability and reduced the scaling tendency of heavy metals. This study contributes to an improved understanding of the mechanisms involved in heavy metal rejection by using MENF.

Selective Capacitive Recovery of Rare-Earth Ions from Wastewater over Phosphorus-Modified TiO2 Cathodes via an Electro-Adsorption Process

Large amounts of wastewater containing low-concentration (<10 ppm) rare-earth ions (REIs) are discharged annually in China's rare-earth mining and processing industry, resulting in severe environmental pollution and economic losses. Hence, achieving efficient selective recovery of low-concentration REIs from REIs-containing wastewater is essential for environmental protection and resource recovery. In this study, a pseudocapacitance system was designed for highly efficient capacitive selective recovery of REIs from wastewater using the titanium dioxide/P/C (TiO2/P/C) composite electrode, which exhibited over 99% recovery efficiency for REIs, such as Eu3+, Dy3+, Tb3+, and Lu3+ in mixed solution. This system maintained high efficiency and more than 90 times the enrichment concentration of REIs even after 100 cycles. Ti4+ of TiO2 was reduced to Ti3+ of Ti3O5 under forward voltage in the system, which trapped the electrons of phosphorus site and caused it to be oxidized to phosphate with a strong affinity for REIs, thus improving the selectivity of REIs. Under reverse voltage, Ti3O5 was oxidized to TiO2, which transferred electrons to phosphate and transformed to the phosphorus site, resulting in the desorption and enrichment of REIs and the regeneration of the electrode. This study provides a promising method for the efficient recovery of REIs from wastewater.

Engineering Faradaic Electrode Materials for High-Efficiency Water Desalination

Water desalination technologies play a key role in addressing the global water scarcity crisis and ensuring a sustainable supply of freshwater. In contrast to conventional capacitive deionization, which suffers from limitations such as low desalination capacity, carbon anode oxidation, and co-ion expulsion effects of carbon materials, the emerging faradaic electrochemical deionization (FDI) presents a promising avenue for enhancing water desalination performance. These electrode materials employed faradaic charge-transfer processes for ion removal, achieving higher desalination capacity and energy-efficient desalination for high salinity streams. The past decade has witnessed a surge in the advancement of faradaic electrode materials and considerable efforts have been made to explore optimization strategies for improving their desalination performance. This review summarizes the recent progress on the optimization strategies and underlying mechanisms of faradaic electrode materials in pursuit of high-efficiency water desalination, including phase, doping and vacancy engineering, nanocarbon incorporation, heterostructures construction, interlayer spacing engineering, and morphology engineering. The key points of each strategy in design principle, modification method, structural analysis, and optimization mechanism of faradaic materials are discussed in detail. Finally, this work highlights the remaining challenges of faradaic electrode materials and present perspectives for future research.

Luminescent carbon dots-rooted polysaccharide crosslinked hydrogel adsorbent for sensitive determination and efficient removal of Cu2

In this study, a novel luminescent carbon dot-rooted polysaccharide hydrogel (CDs@CCP hydrogel) was prepared by crosslinking cellulose, chitosan (CS), and polyvinyl alcohol (PVA) for simultaneous fluorescent sensing and adsorption of Cu2+. The crosslinking of these low-cost, polysaccharide polymers greatly enhance the mechanical strength of the composite hydrogel while making the polysaccharide-based adsorbent easy to reuse. This composite hydrogel exhibited an excellent adsorption capacity (124.7 mg∙g-1) for residual Cu2+ in water, as well as a sensitive and selective fluorescence response towards Cu2+ with a good linear relationship (R2 > 0.97) and a low detection limit (LOD) of 0.02 μM. The adsorption isotherms, adsorption kinetics, and thermodynamics studies were also conducted to investigate the adsorption mechanism. This composite hydrogel offers an efficient tool for simultaneous monitoring and treatment of Cu2+ from wastewater.

Application Prospect of Ion-Imprinted Polymers in Harmless Treatment of Heavy Metal Wastewater

With the rapid development of industry, the discharge of heavy metal-containing wastewater poses a significant threat to aquatic and terrestrial environments as well as human health. This paper provides a brief introduction to the basic principles of ion-imprinted polymer preparation and focuses on the interaction between template ions and functional monomers. We summarized the current research status on typical heavy metal ions, such as Cu(II), Ni(II), Cd(II), Hg(II), Pb(II), and Cr(VI), as well as metalloid metal ions of the As and Sb classes. Furthermore, it discusses recent advances in multi-ion-imprinted polymers. Finally, the paper addresses the challenges faced by ion-imprinted technology and explores its prospects for application.

Coordination Confined Silver-Organic Framework for High Performance Electrochemical Deionization

Silver (Ag) is deemed a promising anode material for capacitive deionization (CDI) due to its high theoretical capacity and efficient selectivity to Cl-. However, the strong volume change during the conversion reaction significantly undermines the cycling performance of the Ag electrode. Additionally, achieving well-dispersed Ag in the active matrix is challenging, as Ag electrodes prepared by conventional thermal reduction tend to agglomerate. Herein, the organic linker confinement strategy is proposed, applying metal-organic framework (MOF) chemistry between Ag nodes and organic ligands to construct Ag-based MOF. The uniform dispersion of Ag at the molecular level, confined in the organic matrix, efficiently enhances the utilization of active sites, and strengthens the interfacial stability of Ag. Consequently, the Ag-MOF for the CDI anode exhibits an excellent Cl- removal capacity of 121.52 mg g-1 at 20 mA g-1 in 500 mg L-1 NaCl solution, and a high Ag utilization rate of 60.54%. After 100 cycles, a capacity retention of 96.93% is achieved. Furthermore, the Cl- capture mechanism of Ag-MOF is elucidated through density functional theory (DFT) calculations, ex situ XRD, ex situ Raman and XPS. This ingenious electrode design can offer valuable insights for the development of high-performance conversion electrodes for CDI applications.

Na2MnSiO4/C as hybrid capacitive deionization electrode material to enhance desalination performance

The utilization of Na2MnSiO4 as a Faraday electrode in hybrid capacitive deionization (HCDI) is investigated to achieve efficient desalination. The Na2MnSiO4/C (NMSO) materials were fabricated via a simple sol-gel method, in which the synthesis process was modulated by adjusting the volume ratio of ethanol to water. When maintaining the volume ratio of water to ethanol at 3:1, the resultant NMSO-3/1 exhibited expected salt adsorption capacity of 31.06 mg g-1 and salt adsorption rate of 20.43 mg g-1 min-1. This distinguished desalination performance was mainly attributed to its inherent multiple redox pairs, as well as the integration of ethanol, which enhanced both specific capacitance and hydrophilicity of the material. This study opens a new perspective for the development of highly efficient materials in HCDI.

Asymmetric response of transition metal cationic orbitals to applied electric field

Understanding the quantum mechanical mechanisms underlying atomic/ionic interfacial processes and phenomena, particularly their dependence on the electronic orbital rearrangement of atoms/ions in an external electric field, remains a significant challenge. This study investigated the asymmetric response of transition metal (TM) cationic orbitals when subjected to an applied electric field. Quantum mechanical calculations were employed to quantify the newly formed hybrid orbitals and evaluate the corresponding orbital energies of the TM cations. Analysis of the quantitative contribution of asymmetric orbital hybridization to TM-surface interactions showed a significant change in orbital energy and increased effective charges of TM cations at the charged surface. This asymmetric response, induced by a negative external electric field generated from the structural charges of clay minerals (e.g., montmorillonite), repels electrons from the outer-shell orbital. This repulsion consequently increases the electron binding energy of the inner-shell orbitals, leading to new surface reactions, polarization-enhanced induction force, and polarization-induced covalent bonding between the TM cations and the charged surface. Our theoretical predictions regarding TM-clay mineral interactions are consistent with the experimental observations of TM cation adsorption. This finding has significant implications for the adsorptive removal of TM cations from wastewaters and for enhancing the catalytic efficiency of TM-surface catalysts. The unique physical and chemical characteristics exhibited by TMs at charged particle surfaces, resulting from their asymmetric response, can play pivotal roles in environmental and chemical engineering.

Innovative recovery of matrix layered double hydroxide from simulated acid mine wastewater for the removal of copper and cadmium from wastewater

This study innovatively added biochar to optimize regulation in the neutralization process of simulated acid mine drainage (AMD) and recovered a new type of matrix layered double hydroxides (MLDH), which can be used to remove copper (Cu(II)) and cadmium (Cd(II)) from wastewater. A series of batch experiments show that MLDH with strong selective removal ability of Cu(II) and Cd(II) can be successfully obtained by adding biochar (BC) at pH = 5 end in the neutralization process. Kinetic and isotherm modeling studies indicated that the removal of Cu(II) and Cd(II) by the MLDH was a chemical multilayer adsorption process. The removal mechanism of Cu(II) and Cd(II) was further analyzed through related characterization analysis with contribution rate calculation: the removal rates of Cu(II) and Cd(II) by ion exchange were 42.7% and 26%, while that by precipitation were 34.5% and 49.9%, respectively. This study can provide a theoretical reference and experimental basis for the recovery and utilization of valuable by-products in AMD and the treatment of heavy metal wastewater.

Study on the performance and mechanism of cobaltous ion removal from water by a high-efficiency strontium-doped hydroxyapatite adsorbent

In this study, a high-efficiency strontium-doped hydroxyapatite (Sr-HAP) adsorbent was synthesized by a sol-gel method for removing cobaltous ions (Co(II)) from water. The effects of adsorbent dose, initial solution pH, initial Co(II) concentration and temperature on the removal performance of Co(II) were investigated. Experimental results indicated that the optimum Sr-HAP dose was 0.30 g/50 mL solution, the Sr-HAP adsorbent could effectively remove Co(II) in a wide pH range of 3-8. Increasing temperature was conducive to the adsorption, and the maximum Co(II) adsorption capacity by Sr-HAP reached 48.467 mg/g at 45 °C. The adsorption of Co(II) followed the pseudo-second-order kinetic model, indicating that the Co(II) adsorption by Sr-HAP was attributed mainly to chemisorption. The isothermal adsorption results showed that at lower Co(II) equilibrium concentration, the Langmuir model fitted the data better than the Freundlich model but opposite at higher Co(II) equilibrium concentration. Therefore, the adsorption of Co(II) was a process from monolayer adsorption to multilayer adsorption with the increase of the Co(II) equilibrium concentration. The diffusion analysis of Co(II) to Sr-HAP indicated that the internal diffusion and surface adsorption were the rate-controlled steps of Co(II) adsorption. Thermodynamic study demonstrated that the Co(II) adsorption process was spontaneous and endothermic. The mechanism study revealed that in addition to chemisorption, Sr-HAP also removed Co(II) ions from water via ion exchange and surface complexation.

Insights into the Mechanism of Selective Removal of Heavy Metal Ions by the Pulsed/Direct Current Electrochemical Method

Heavy metal pollution treatment in industrial wastewater is crucial for protecting biological and environmental safety. However, the highly efficient and selective removal of heavy metal ions from multiple cations in wastewater is a significant challenge. This work proposed a pulse electrochemical method with a low-/high-voltage periodic appearance to selectively recover heavy metal ions from complex wastewater. It exhibited a higher recovery efficiency for heavy metal ions (100% for Pb2+ and Cd2+, >98% for Mn2+) than other alkali and alkaline earth metal ions (Na+, Ca2+, and Mg2+ were kept below 3.6, 1.3, and 2.6%, respectively) in the multicomponent solution. The energy consumption was only 34-77% of that of the direct current electrodeposition method. The results of characterization and experiment unveil the mechanism that the low-/high-voltage periodic appearance can significantly suppress the water-splitting reaction and break the mass-transfer limitation between heavy metal ions and electrodes. In addition, the plant study demonstrates the feasibility of treated wastewater for agricultural use, further proving the high sustainability of the method. Therefore, it provides new insights into the selective recovery of heavy metals from industrial wastewater.

Regulating Chemisorption and Electrosorption Activity for Efficient Uptake of Rare Earth Elements in Low Concentration on Oxygen-Doped Molybdenum Disulfide

Recovery of rare earth elements (REEs) with trace amount in environmental applications and nuclear energy is becoming an increasingly urgent issue due to their genotoxicity and important role in society. Here, highly efficient recovery of low-concentration REEs from aqueous solutions by an enhanced chemisorption and electrosorption process of oxygen-doped molybdenum disulfide (O-doped MoS2) electrodes is performed. All REEs could be extremely recovered through a chemisorption and electrosorption coupling (CEC) method, and sorption behaviors were related with their outer-shell electrons. Light, medium, and heavy ((La(III), Gd(III), and Y(III)) rare earth elements were chosen for further investigating the adsorption and recovery performances under low-concentration conditions. Recovery of REEs could approach 100% under a low initial concentration condition where different recovery behaviors occurred with variable chemisorption interactions between REEs and O-doped MoS2. Experimental and theoretical results proved that doping O in MoS2 not only reduced the transfer resistance and improved the electrical double layer thickness of ion storage but also enhanced the chemical interaction of REEs and MoS2. Various outer-shell electrons of REEs performed different surficial chemisorption interactions with exposed sulfur and oxygen atoms of O-doped MoS2. Effects of variants including environmental conditions and operating parameters, such as applied voltage, initial concentration, pH condition, and electrode distance on adsorption capacity and recovery of REEs were examined to optimize the recovery process in order to achieve an ideal selective recovery of REEs. The total desorption of REEs from the O-doped MoS2 electrode was realized within 120 min while the electrode demonstrated a good cycling performance. This work presented a prospective way in establishing a CEC process with a two-dimensional metal sulfide electrode through structure engineering for efficient recovery of REEs within a low concentration range.

Capacitive removal of Pb ions via electrosorption on novel willow biochar-manganese dioxide composites

Biochar derived from lignocellulosic biomass has been used as a low-cost adsorbent in wastewater treatment applications. Due to its rich porous structure and good electrical conductivity, biochar can be used as a cost-effective electrode material for capacitive deionization of water. In this work, willow biochar was prepared through carbonization of shrub willow chips, activated with potassium hydroxide, and loaded with manganese dioxide (WBC-K-MnO2 nanocomposite). The prepared materials were used to electrochemically adsorb Pb2+ from aqueous solutions. Under the applied potential of 1.0 V, the WBC-K-MnO2 electrode exhibited a high Pb2+ specific electrosorption capacity (23.3 mg/g) as compared to raw willow biochar (4.0 mg/g) and activated willow biochar (9.2 mg/g). KOH activation followed by MnO2 loading on the surface of raw biochar enhanced its BET surface area (178.7 m2/g) and mesoporous volume ratio (42.1%). Moreover, the WBC-K-MnO2 nanocomposite exhibited the highest specific capacitance value of 234.3 F/g at a scan rate of 5 mV/s. The electrosorption isotherms and kinetic data were well explained by the Freundlich and pseudo-second order models, respectively. The WBC-K-MnO2 electrode demonstrated excellent reusability with a Pb2+ electrosorption efficiency of 76.3% after 15 cycles. Thus, the WBC-K-MnO2 nanocomposite can serve as a promising candidate for capacitive deionization of heavy metal contaminated water.

Robust and highly reactive membranes for continuous disposal of chemical warfare agents: Effects of nanostructure and functionality in MOF and nanochitin aerogel composites

Developing appropriate disposal of stockpiles of chemical warfare agents (CWAs) has gained significant attention as their lethal toxicity seriously harms humanity. In this study, a novel green-fabrication method with UiO-66 catalysts and amine-functionalized chitin nanofibers (ChNFs) was suggested to prepare durable and highly reactive membranes for decomposing chemical warfare agents (CWAs) in the continuous flow system. The strong interaction between ChNFs and the UiO-66 led to stable loading of the UiO-66 on the continuous nano-porous channel of the ChNF reactive membrane even with high loading of UiO-66 (70 wt% of UiO-66 in the ChNF substrate). In addition, the Brønsted base functionalities (-NH2 and -NHCOCH3) of the ChNF enhanced the catalytic activity and recyclability of the UiO-66. The resulting 70-ChNF composites can effectively decompose a nerve agent simulant (methyl paraoxon) even after 7 repeatable cycles, which has been not obtained in the previous UiO-66 catalyst. The ChNF/UiO-66 reactive membranes with 1 m2 of the area decomposed 130 g of CWAs within an hour in a continuous flow system. We believe these robust and highly reactive membranes can provide a sustainable and efficient solution for the massive CWA disposal and also contribute to the advancement of functional membrane material science.

An Amiable Design of Cobalt Single Atoms as the Active Sites for Oxygen Evolution Reaction in Desalinated Seawater

Green fuel from water splitting is hardcore for future generations, and the limited source of fresh water (<1%) is a bottleneck. Seawater cannot be used directly as a feedstock in current electrolyzer techniques. Until now single atom catalysts were reported by many synthetic strategies using notorious chemicals and harsh conditions. A cobalt single-atom (CoSA) intruding cobalt oxide ultrasmall nanoparticle (Co3 O4 USNP)-intercalated porous carbon (PC) (CoSA-Co3 O4 @PC) electrocatalyst was synthesized from the waste orange peel as a single feedstock (solvent/template). The extended X-ray absorption fine structure spectroscopy (EXAFS) and theoretical fitting reveal a clear picture of the coordination environment of the CoSA sites (CoSA-Co3 O4 and CoSA-N4 in PC). To impede the direct seawater corrosion and chlorine evolution the seawater has been desalinated (Dseawater) with minimal cost and the obtained PC is used as an adsorbent in this process. CoSA-Co3 O4 @PC shows high oxygen evolution reaction (OER) activity in transitional metal impurity-free (TMIF) 1 M KOH and alkaline Dseawater. CoSA-Co3 O4 @PC exhibits mass activity that is 15 times higher than the commercial RuO2 . Theoretical interpretations suggest that the optimized CoSA sites in Co3 O4 USNPs reduce the energy barrier for alkaline water dissociation and simultaneously trigger an excellent OER followed by an adsorbate evolution mechanism (AEM).

Capacitive deionization system with ultra-high salt adsorption performance: from lab design to agricultural applications

Capacitive deionization is an emerging water desalination technology for industrial applications. Recent advancements in electrode design and system development have led to the reporting of ultra-high salt adsorption performance, benefiting its potential application in agricultural water treatment at a potentially low cost. In this study, we provide a comprehensive summary of the porous electrode design strategy to achieve ultra-high ion adsorption performance, considering factors such as experimental parameters, chemically tuned material properties, redox chemistry and smart nanoarchitecture for future electrode design. Furthermore, we endeavor to establish a correlation between capacitive deionization (CDI) technology and its applicability in the agricultural sector, specifically concentrating on water treatment with an emphasis on undesirable ions associated with salinity, hardness, and heavy metals, to achieve harmless irrigation. Additionally, to ensure the efficient and cost-effective application of CDI systems in agriculture, a thorough overview of the literature on CDI cost analysis is presented. By addressing these aspects, we anticipate that ultra-high salt adsorption CDI systems hold great promise in future agricultural applications.

Selective Removal of Organic Pollutants in Groundwater and Surface Water by Persulfate-Assisted Advanced Oxidation: The Role of Electron-Donating Capacity

The efficiency of persulfate-assisted advanced oxidation processes (PS-AOPs) in degrading organic pollutants is affected by the electron-donating capability of organic substances present in the water source. In this study, we systematically investigate the electron-donating capacity (EDC) difference between groundwater and surface water and demonstrate the dependence of removal efficiency on the EDC of target water by PS-AOPs with carbon nanotubes (CNTs) as a catalyst. Laboratory analyses and field experiments reveal that the CNT/PS system exhibits higher performance in organic pollutant removal in groundwater with a high concentration of phenols, compared to surface water, which is rich in quinones. We attribute this disparity to the selective electron transfer pathway induced by potential difference between PS-CNT and organic substance-CNT intermediates, which preferentially degrade organic substances with stronger electron-donating capability. This study provides valuable insights into the inherent selective removal mechanism and application scenarios of electron transfer process-dominated PS-AOPs for water treatment based on the electron-donating capacity of organic pollutants.

Enhanced Pseudo-Capacitance Process in Nanoarchitectural Layered Double Hydroxide Nanoarrays Hollow Nanocages for Improved Capacitive Deionization Performance

Layered double hydroxides (LDHs) are perceived as a hopeful capacitive deionization (CDI) faradic electrode for Cl^- insertion due to its tunable composition, excellent anion exchange capacity, and fast redox activity. Nevertheless, the self-stacking and inferior electrical conductivity of the two-dimensional structure of LDH lead to unsatisfactory CDI performance. Herein, the three-dimensional (3D) hollow nanocage structure of CoNi-layered double hydroxide/carbon composites is well designed as a CDI anode by cation etching of the pre-carbonized ZIF-67 template. C/CoNi-LDH has a unique 3D hollow nanocage structure and abundant pore features, which can effectively suppress the self-stacking of LDH sheets and facilitate the transport of ions. Moreover, the introduced amorphous carbon layer can act as a conductive network. When employed as the CDI anode, C/CoNi-LDH exhibited a high Cl^- removal capacity of 60.88 mg g^-1 and a fast Cl^- removal rate of 18.09 mg g^-1 min^-1 at 1.4 V in 1000 mg L^-1 NaCl solution. The mechanism of the Cl^- intercalation pseudo-capacitance reaction of C/CoNi-LDH is revealed by electrochemical kinetic analysis and ex situ characterization. This study provides vital guidance for the design of high-performance electrodes for CDI.

Nanoscale Adsorption, Assembly, and Deionization Dynamics Recorded by Optical Fiber Sensors

Capacitive deionization in environmental decontamination has been widely studied and now requires intensive development to support large-scale deployment. Porous nanomaterials have been demonstrated to play pivotal roles in determining decontamination efficiency and manipulating nanomaterials to form functional architecture has been one of the most exciting challenges. Such nanostructure engineering and environmental applications highlight the importance of observing, recording, and studying basically electrical-assisted charge/ion/particle adsorption and assembly behaviors localized at charged interfaces. In addition, it is generally desirable to increase the sorption capacity and reduce the energy cost, which increase the requirement for recording collective dynamic and performance properties that stem from nanoscale deionization dynamics. Herein, we show how a single optical fiber can serve as an in situ and multifunctional opto-electrochemical platform for addressing these issues. The surface plasmon resonance signals allow the in situ spectral observation of nanoscale dynamic behaviors at the electrode-electrolyte interface. The parallel and complementary optical-electrical sensing signals enable the single probe but multifunctional recording of electrokinetic phenomena and electrosorption processes. As a proof of concept, we experimentally decipher the interfacial adsorption and assembly behaviors of anisotropic metal-organic framework nanoparticles at a charged surface and decouple the interfacial capacitive deionization within an assembled metal-organic framework nanocoating by visualizing its dynamic and energy consumption properties, including the adsorptive capacity, removal efficiency, kinetic properties, charge, specific energy consumption, and charge efficiency. This simple "all-in-fiber" opto-electrochemical platform offers intriguing opportunities to provide in situ and multidimensional insights into interfacial adsorption, assembly, and deionization dynamics information, which may contribute to understanding the underlying assembly rules and the exploring structure-deionization performance correlations for the development of tailor-made nanohybrid electrode coatings for deionization applications.

Controlled fabrication of nitrogen-doped porous carbon foam with refined hierarchical architectures for desalination via capacitive deionization

Porous carbon materials have been regarded as a promising alternative to activated carbon for desalination via capacitive deionization (CDI) due to refined architectures and functionalities. However, it is still challenging to obtain a controlled hierarchical pore structure and considerable nitrogen-doped content by convenient method. Herein, nitrogen-doped hierarchical porous carbon foams (NHCFs) with different microstructural features, nitrogen contents and nitrogen species were successfully fabricated via a stepwise pyrolysis carbonization strategy using easily available melamine foam. Due to the synergistic effect of hierarchical porous structure and doped nitrogen, the optimized NHCF sample carbonized at 800℃ (NHCF-800) exhibited a maximum desalination capacity of 30.1 mg g^-1 at the optimal operating parameters (500 mg/L NaCl solution, 1.2 V) and an excellent regeneration performance after 50 continuous adsorption-desorption cycles. Furthermore, density functional theory (DFT) was also conducted to elaborate the disparity of sodium adsorption energy among the nitrogen species for in-depth understanding, and it mainly benefits from the ascendency of the pyrrolic-N and pyridinic-N over the graphitic-N dopant. This work paves the way of rational regulation of nitrogen-doped process and hierarchical porous structure carbon as CDI electrode materials for desalination.

"Blockchain-Like" MIL-101(Cr)/Carbon Black Electrodes for Unprecedented Defluorination by Capacitive Deionization

Metal-organic frameworks (MOF) have attracted extensive attention due to their ultra-high specific surface area and tunable structure, the mechanism of direct utilization for capacitive deionization (CDI) defluorination remains undefined. Here, MIL-101(Cr) with ultra-high specific surface area, high water stability, and open metal sites (OMSs) is prepared by a hydrothermal method for defluorination of CDI. Carbon black is used as a "chain" to connect F-stored in the holes of MIL-101(Cr) (Cr-MOF)as "blocks" to enhance the conductivity and ion storage capacity of MIL-101(Cr)/carbon black electrodes (Cr-MOF electrodes). This simple construction method avoids the process complexity of in situ synthesis and performs better. These easily constructed "blockchain-like" Cr-MOF electrodes exhibit excellent defluorination capacity (39.84 mg_NaF g_electrodes ^-1 ), low energy consumption (1.2 kWh kg_NaF ^-1 ), and good stability. The coupling of the electrochemical redox reaction of Cr³⁺ /Cr⁴⁺ with confined water is investigated using in situ and ex situ analysis methods combined with density functional theory (DFT), resulting in an unprecedented defluorination mechanism for Cr-MOF electrodes. This study opens up new ideas for the application of MOF in CDI, clarifies the removal mechanism of MOF, and lays a foundation for further promoting the application of raw materials with poor conductivity in the field of CDI.

Uranium capture by a layered 2D/2D niobium phosphate/holey graphene architecture via an electro-adsorption and electrocatalytic reduction coupling process

As an energy-efficient and eco-friendly technique, capacitive deionization (CDI) has shown great potential for uranium (U(VI)) capture recently. However, extracting U(VI) with high kinetics, capacity and selectivity remains a major challenge due to the current surface active sites-based material and co-existing ions in aqueous solution. Here we rationally designed a layered 2D/2D niobium phosphate/holey graphene (HGNbP) electrode material, and originally demonstrated its efficient U(VI) capture ability via an electro-adsorption and electrocatalytic reduction coupling process. The less-accumulative loose layered architecture, open polycrystalline construction of niobium phosphate with active phosphate sites, and rich in-plane nano-pores on conductive graphene nanosheets endowed HGNbP with fast charge/ion transport, high electroconductivity and superior pseudocapacitance, which enabled U(VI) ions first to be electro-adsorbed, then physico-chemical adsorbed, and finally electrocatalysis reduced/deposited onto electrode surface without the limitation of active sites under a low potential of 1.2 V. Based on these virtues, the HGNbP exhibited a fast adsorption kinetics, with a high removal rate of 99.9% within 30 min in 50 mg L^-1 U(VI) solution, and a high adsorption capacity up to 1340 mg g^-1 in 1000 mg L^-1 U(VI) solution. Furthermore, the good recyclability and selectivity towards U(VI) were also realized.

Investigation on the Removal Performances of Heavy Metal Copper (II) Ions from Aqueous Solutions Using Hydrate-Based Method

Since heavy metal ion-contaminated water pollutionis becoming a serious threat to human and aquatic lives, new methods for highly efficient removal of heavy metal ions from wastewater are important to tackle environmental problems and sustainable development. In this work, we investigate the removal performances of heavy metal copper (II) ions from aqueous solutions using a gas hydrate-based method. Efficient removal of heavy metal copper (II) ions from wastewater via a methane hydrate process was demonstrated. The influence of the temperature, hydration time, copper (II) ions concentration, and stirring rate on the removal of heavy metal copper (II) ions were evaluated. The results suggested that a maximum of 75.8% copper (II) ions were removed from aqueous solution and obtained melted water with 70.6% yield with a temperature of -2 °C, stirring speed 800 r/min, and hydration time of 4 h with aninitial copper concentration of 100 mg/L. The initial concentration of copper (II) ions in the aqueous solution could be increased to between 100 and 500 mg/L. Meanwhile, our study also indicated that 65.6% copper (II) ions were removed from aqueous solution and the yield of melted water with 56.7%, even with the initial copper concentration of 500 mg/L. This research work demonstrates great potential for general applicability to heavy metal ion-contaminated wastewater treatment and provides a reference for the application of the gas hydrate method in separation.

Ion Exchange Conversion of Na-Birnessite to Mg-Buserite for Enhanced and Preferential Cu2+ Removal via Hybrid Capacitive Deionization

Layered manganese oxides (LMOs) have recently been demonstrated to be one of the most promising redox-active material platforms for electrochemical removal of heavy metal ions from solution via capacitive deionization (CDI). However, the impact of interlayer spacing of LMOs on the deionization performance of electrodes in a hybrid capacitive deionization (HCDI) system with an LMO cathode and a carbon anode (i.e., LMO/C electrodes), and their phase transformation behaviors, particularly during the desalination operations, have yet to be extensively evaluated. In this study, we thoroughly evaluate Mg-buserite obtained by ion exchange of fresh Na-birnessite and Na- and K-birnessite as HCDI electrodes to remove copper ions (Cu²⁺) from saline solutions. Among the three LMO/C electrodes, the Mg-buserite/C (MgB/C) electrodes demonstrate the best deionization performance in terms of salt adsorption capacity (SAC), electrosorption rate, and cycling stability, followed by K-birnessite/C (KB/C) and Na-birnessite/C (NaB/C). More importantly, MgB/C exhibits the highest Cu²⁺ ion adsorption capacity (IAC) of 89.3 mg Cu²⁺ per gram electrode materials at a cell voltage of 1.2 V in 500 mg L^-1 CuCl₂ solution, with an IAC retention as high as 96.3% after 60 charge/discharge cycles. Given that electrosorption of Cu²⁺ ions is often competed by alkali and alkaline earth metal ions, our data reveal that the MgB/C electrodes demonstrate selectivities of 4.7, 7.7, and 8.1 for Cu²⁺ over Na⁺, Ca²⁺, and Mg²⁺, respectively. Moreover, X-ray diffraction and spectroscopic analyses show that the enhanced deionization performance and preference for Cu²⁺ are mainly attributed to the expanded interlayer spacing of LMO minerals. This study provides a promising strategy for tailoring LMO minerals for improving their electrosorption capacity and preference for copper ions from a multivalent-ion solution via an HCDI platform.

High-performance pseudocapacitive removal of cadmium via synergistic valence conversion in perovskite-type FeMnO3

Cadmium pollution is a serious threat for the global drink water and natural environment. Herein, a poly-pyrrole coated dual-metal perovskite-type oxide FeMnO₃ (PFMO@PPy) was developed firstly as pseudocapacitive cathode for the reversible capture and release of cadmium ions by asymmetry pseudocapacitive deionization (APCDI) technology, extending the library of CDI electrodes. Our work highlighted several points: (i) PFMO@PPy achieved a maximum Cd-removal capacity of 144.6 mg g^-1, and maintained the retention rate of 93.4% after 15-cycle CDI process for up to 150 h, far beyond other previous work. (ii) PFMO@PPy showed the superior removal ratio (~90%) under different real water environments such as tap water, lake water and the groundwater. (iii) The superior Cd(II) electrosorption and desorption behavior is ascribed to the reversible synergistic valence conversion (Fe³⁺/Fe⁰ and Mn³⁺/Mn²⁺), which is confirmed by ex-situ XPS measurement and electrochemical tests. (iv) DFT calculations confirmed the synergistic effect from Mn and Fe elements in perovskite-type bimetallic oxide FeMnO₃. This study paves a new way for promising future applications of perovskite-type oxides containing dual Faradic redox-activity for wastewater treatment and environmental remediation.

Magnetic relaxation switching assay based on three-dimensional assembly of Fe3O4@ZIF-8 for detection of cadmium ions

The design and construction of a novel magnetic resonance switch (MRS) sensor for cadmium ion (Cd2+) detection is described. Fe3O4@ZIF-8 was synthesized through seed-mediated growth of dimercaptosuccinic acid-coated Fe3O4. Fe3O4@ZIF-8 with high relaxation value (163.086 mM-1 s-1) and large negative zeta potential (-20.69 mV) exhibited good magnetic relaxation performance and water solubility. The successfully synthesized Fe3O4@ZIF-8 was used to develop an immune recognition-based MOFs-MRS sensor for highly sensitive detection of Cd2+. The proposed MRS detected a wide linear range of Cd2+ concentration from 2 to 200 ng mL-1 with a low limit of detection of 0.65 ng mL-1 (S/N = 3), and displayed high selectivity towards matrix interference. The robust sensing system was effective even in a complex sample matrix, enabling the quantitative analysis of Cd2+ content in rice samples and drinking water samples with good reliability. Recoveries of Cd2+ ranged from 91.50 to 112.05% for spiked drinking water and from 95.86 to 110.45% for spiked rice samples. The versatility of Fe3O4@ZIF-8 with customized relaxation responses could allow the adaptation of magnetic resonance platforms for food safety purposes.

Removing miscellaneous heavy metals by all-in-one ion exchange-nanofiltration membrane

The composition of wastewater containing heavy metal mixtures is often complex and poses a serious threat to human and environmental health. Effective removal of a variety of heavy metal ions with a single technology is challenging, and the conventional split integrated technologies require multi-step processing and a massive footprint. For the first time, we achieve hierarchically integrating ion exchange and nanofiltration into all-in-one "iNF" membranes. The iNF membrane has a hierarchical structure with an interfacial polymerization layer and an ion exchange layer, which can achieve highly efficient indiscriminate heavy metal ion removal, overcoming the defect that traditional nanofiltration membranes can only remove single metal cations or oxyanions. The ion exchange layer can remove heavy metal ions through sulfonic acid groups and quaternary amine groups. In addition, the ion exchange layer can be regenerated by electro-deionization, which is meaningful for sustainable membrane usage. This facile, scalable, and compact integrated process shows outstanding potential and universal applicability in complex wastewater treatment.

Removal of Zn(II) by magnetic composite adsorbent: synthesis, performance, and mechanism

In this study, L-methionine and nano-Fe₃O₄ were encapsulated and cured on sodium alginate by the ionic cross-linking method to form magnetic composite gel spheres (SML) as an adsorbent for the removal of Zn(II) from water. The influence of adsorbent dosages, pH, reaction time, and initial ion concentration on the ability of the gel spheres to adsorb Zn(II) was investigated, and the adsorption mechanism was identified. The experimental results showed that under the optimum conditions (pH = 5, t = 60 min, dosage of SML is 0.7 g·L^-1), the maximum amount of Zn(II) adsorbed by the adsorbent gel spheres reached 86.84 mgˑg^-1. The reaction process of this adsorbent fits well with the Langmuir and pseudo-second-order kinetic models and is a heat absorption reaction. The adsorbent would preferentially adsorb Pb(II), and the adsorption efficiency of Zn(II) decreased when the concentration of interfering ions increased in the coexistence system. Further mechanistic research showed that this magnetic composite adsorbent is a mesoporous material with superior adsorption performance, and the amino and carboxyl groups on it react with Zn(II) via ligand chelation; the ion exchange effect of Ca(II) also plays a role. The adsorption amount of Zn(II) was maintained at a higher level after 5 cycles, and the loss of Fe was approximately 0.2%. In summary, SML, which is environmentally friendly, efficient, and recyclable, is an ideal adsorbent for Zn(II) removal.

Recent advances of carbon-based nanomaterials (CBNMs) for wastewater treatment: Synthesis and application

Carbon-based nanomaterials (CBNMs) have attracted significant alert due to the affluent science underpinning their implementations associated with a novel mixture of high aspect proportions, greater thermal and electrical performance, outstanding optical features, and high exterior area. CBNMs not only bear assurance in a broad range of implementations in medication, nano and microelectronics, and ecological remedies but may also be utilized in practical laboratory determinations. More specifically, CBNMs perform as an outstanding adsorbent in terminating heavy metal ions (HMI) from wastewater. There is presently a deficiency of powerful threat inspection instruments owing to their complex detection and related deficit in the health risk database. Therefore, our present review concentrates on spreading CBNMs to release pollutants from wastewater. The article wraps the effect of these contaminants and photocatalytic strategies towards treating these mixtures in wastewater, along with their restrictions and challenges, convincing resolutions, and possibilities of these approaches.

Constructing titanium carbide MXene/reduced graphene oxide superlattice heterostructure via electrostatic self-assembly for high-performance capacitive deionization

Capacitive deionization has attracted wide concern on accountof its high energy efficiency, low manufacturing cost and environmental friendliness. Nevertheless, the development of capacitive deionization is still impeded because of the scarcity of suitable electrode materials with superior performance. Herein, we successfully prepared the two-dimensional (2D) titanium carbide (Ti₃C₂T_x) MXene/ reduced graphene oxide (rGO) superlattice heterostructure by a facile electrostatic self-assembly strategy and systematically investigated its performance as capacitive deionized electrode materials. The unique 2D/2D superlattice heterostructure not only effectively alleviates the self-stacking problem of Ti₃C₂T_x MXene nanosheets, but also endows the heterostructure with superior conductivity and fast ion diffusion rate. As a result, the MXene/rGO superlattice heterostructure exhibits an outstanding salt (Na⁺) adsorption capacity (48 mg g^-1) at 1.2 V significantly superior to pristine Ti₃C₂T_x MXene nanosheets, along with outstanding long-term cycling performance. Furthermore, the mechanism involved was elucidated through comprehensive characterizations. Therefore, this study offers a new pathway for designing high-performance electrode materials for capacitive deionization.

Carbon Nanoarchitectonics with Bi Nanoparticle Encapsulation for Improved Electrochemical Deionization Performance

Electrochemical deionization (EDI) is hopefully the next generation of water treatment technology. Bismuth (Bi) is a promising anode material for EDI, due to its high capacity and selectivity toward Cl^-, but the large volume expansion and severe pulverization aggressively attenuated the EDI cycling performance of Bi electrodes. Herein, carbon-layer-encapsulated nano-Bi composites (Bi@C) were prepared by a simple pyrolysis method using a Bi-based metal-organic framework as a precursor. Bi nanoparticles are uniformly coated within the carbon layer, in which the Bi-O-C bond enhances the interaction between Bi and C. Such a structure effectively relieves the stress caused by volume expansion by the encapsulation effect of the carbon layer. Moreover, the introduction of a carbon skeleton provides a conductive network. As a consequence, the Bi@C composite delivered excellent electrochemical performance with a capacity of 537.6 F g^-1 at 1 mV s^-1. The Cl^- removal capacity was up to 133.5 mg g^-1 at 20 mA g^-1 in 500 mg L^-1 NaCl solution. After 100 cycles, the Bi@C electrode still maintains 71.8% of its initial capacity, which is much higher than the 26.3% of the pure Bi electrode. This study provides a promising strategy for improving EDI electrode materials.

Electrosorption of cadmium ions in aqueous solutions using a copper-gallate metal-organic framework

Recently, there is a recognized need for green technologies for the effective decontamination of toxic heavy metal ions in wastewater. This study demonstrates the electrochemically assisted uptake and release of cadmium ions (Cd²⁺) using a redox-active Cu-based metal-organic framework (MOF) electrode. Copper gallate (CuGA), which was synthesized in an aqueous solution, is a water-stable and cost-effective MOF adsorbent in which naturally abundant gallic acid is used as a linker. This work utilized copper within the CuGA structure as a redox center to attract Cd²⁺ by means of Cu²⁺/Cu⁺ reduction, exhibiting rapid uptake kinetics and a much higher capacity (>60 mg g^-1) compared to the case without electrochemical assistance (~15 mg g^-1). In addition, by applying an opposite overpotential to induce the re-oxidation of copper, the facile recovery of Cd²⁺ and the regeneration of the electrode were possible without regenerants. Physicochemical characterizations including XPS were conducted to investigate the chemical oxidation states and stability of the electrode after the effective electrosorption-regeneration process. This work presents the feasibility of a Cu-based MOF electrode as a reusable platform for the efficient removal of Cd²⁺, supporting the continued discovery and development of new Faradaic electrodes for electrochemical wastewater treatments.