A fast, efficient, and durable cathode is essential for electrocatalytic nitrate reduction (NO3RR) and nitrate removal in complex wastewaters. Herein, a self-supported CuNi3Co@NF cathode was fabricated by directly co-depositing Cu-Ni-Co ternary metallic microparticles onto three-dimensional (3D) nickel foam (NF). Morphological characterization confirms the uniform dispersion of Cu-Ni-Co microparticles across the NF skeleton. Compared with monometallic and bimetallic counterparts, CuNi3Co@NF exhibits markedly enhanced intrinsic NO3RR performance in Cl--free electrolyte, achieving near-complete NO3--N removal (99.99%) with high NH4+ selectivity (98%) as the dominant dissolved product. In chloride-containing wastewater, the system can be operated as a coupled electrochemical-chemical (EC-C) denitrification process, where the cathode efficiently reduces NO3- to reduced nitrogen species while anodically generated active chlorine species promotes further conversion toward gaseous nitrogen products, resulting in high NO3--N removal (up to 98%) and high TN removal. In addition, CuNi3Co@NF maintains stable performance over a broad range of initial nitrate concentrations (50-300 mg L-1 NO3--N) and solution pH values (3-12), and retains its activity over ten consecutive cycles, demonstrating strong durability under saline and pH-challenging conditions.

The potential of capacitive deionization (CDI) for sustainable desalination depends critically on breakthroughs in electrode materials. Defect-rich titanium (sub) oxides (anatase TiO2(A), Ti2O3, Ti3O5, Ti4O7) offer compelling advantages, including tunable capacity, low environmental impact, and robustness. This study provides a systematic comparison of their structural features, electrochemical responses, and desalination efficacy. Electrochemical characterization results show anatase TiO2(A) leads in specific capacitance (252.5 F g(-1) at 0.3 A g(-1)), while Ti3O5's highest oxygen vacancy minimizes charge transfer resistance and maximizes ion migration rates. In desalination trials, TiO2 delivers a maximum salt adsorption capacity of 37.1 mg g(-1) (500 mg L-1 NaCl, 1.2 V). All electrodes exhibit outstanding cycling stability (capacity retentions >83.5 %), affirming their practical potential. Correlation analysis discloses the oxygen vacancy-driven charge transfer mechanism inside these electrodes and establishes a structure-performance relationship. Overall, this work establishes fundamental structure-property relationships that underpin future electrode innovation via the oxygen vacancy-engineering strategy, which represents a promising pathway for advancing CDI performance boundaries.

To address the critical challenge of phosphorus pollution in surface waters, this study develops two chitosan-based magnetic biosorbents (denoted as Ce@mCS and Zr@mCS) for the efficient removal of phosphorus from wastewater. The biocomposites were engineered to provide a sustainable and high-performance solution, circumventing the limitations of existing phosphorus removal strategies. The successful fabrication of the biocomposites, including the incorporation of magnetic components (Fe3O4) and dispersion of Ce/Zr active centers (i.e., CeCO₃OH, ZrO₂) with the chitosan scaffolds, was rigorously confirmed through SEM, XRD, XPS, FTIR, and zeta potential analyses. Batch adsorption experiments were carried out to optimize key parameters, yielding removal efficiencies of 88.3% for Ce@mCS and 85.7% for Zr@mCS (C₀ = 25 mg L-1, dosage = 0.5 g L-1, T = 298 K, t = 8 h). The adsorption isotherm data were best described by the Langmuir model, indicating monolayer adsorption with maximum capacities of 62.23 mg g-1 for Ce@mCS and 45.07 mg g-1 for Zr@mCS, respectively. Recycling performance analysis confirms the excellent capacity retention of both biocomposites over five consecutive cycles, validating their high practical potential promise. Post-adsorption characterization reveals that the mechanism for P capture lies in ligand exchange, Coulombic attraction, and H-bonding. This work exemplifies chitosan-based magnetic biocomposites for phosphate removal and underscores the promise of tailored biosorbents, providing a viable path for sustainable wastewater remediation and management.

Struvite crystallization is a sustainable strategy for phosphorus (P) recovery, yet the presence of emerging contaminants (ECs) poses significant obstacles by disrupting struvite crystallization kinetics and compromising product purity and thus its potential agronomic safety. This study systematically investigates the impacts of tetracycline (TC), polyethylene terephthalate (PET), Cu2⁺, and humic acid (HA) on struvite formation using both batch reactors (BRs) and fluidized-bed reactors (FBRs). Batch experiments revealed that HA and Cu+TC act as potent inhibitors through a combination of surface-mediated interactions and Mg2⁺ complexation, reducing the apparent crystallization rate of struvite. Conversely, FBR results demonstrated that specific hydraulic conditions can mitigate the kinetic inhibition of Cu+TC, yielding larger pellets (∼ 1342 vs ∼ 1138 μm in diameter) with apparent Cu2⁺ incorporation into the pellet matrix. Trials with real swine wastewater verified that excessive dissolved organic matter and Ca2⁺ favor the formation of amorphous phases rather than crystalline struvite (84.9% vs 2.7% in the amorphous fraction). Density functional theory calculations indicated that the Mg2⁺ complexation is primarily governed by non-covalent ion-dipole (Mg-O) interactions between HA/TC with Mg2+. Besides, ternary complexes bridged by metal-O were identified as the most stable species (HA-Cu/Mg-TC) within these matrices, which may enhance the mobility or persistence of such ECs in aquatic environments. Consequently, robust P recovery requires integrated strategies-combining pre-treatment to remove strong inhibitors with specific FBR conditions (hydraulics and extended retention time) that leverage crystal growth and conglomeration. This work provides the kinetic and mechanistic insights necessary for developing such integrated solutions, advancing our understanding of EC-mediated crystallization of struvite and the viability of P recovery from increasingly complex waste streams.

The rapid growth of lithium (Li)-ion batteries particularly in electric vehicles (EVs) and large-scale energy storage facilities has catalyzed an ever-increasing demand for Li. Current Li mining from brines based on evaporation-precipitation is time-consuming and water-intensive. Here, we report three NiHCF/MnO2 composite electrodes based on core-shell construction strategies for Li+ extraction from brine on a rocking-chair capacitive deionization (RCDI) platform. We find that the MnO2 components varied with the composing condition from α-, δ- to λ-MnO2 and that the core-shell structured NiHCF@λ-MnO2 electrode showed the optimal ion migration rate, highest specific capacity, and the best cycling stability. Notably, we reveal that the NiHCF@λ-MnO2 electrode presented the optimum Li+ extraction performance with respect to adsorption capacity, adsorption rate, and energy consumption (e.g., achieving the highest Li+ capacity of 40.51 mg Li+ g−1 with a rate of 8.1 mg g−1 min−1, and at an energy cost of 0.86 Wh g−1 in 20 mM LiCl solution at 1.2 V). In addition, we demonstrate that the NiHCF@λ-MnO2 electrode maintained high cycling stability over 40 consecutive cycles of Li+ intercalation/deintercalation, with 78.4% capacity retention in 10 mM of LiCl solution. Importantly, the NiHCF@λ-MnO2 electrode also provided excellent Li+ selectivity in both the synthetic brine and the actual brine from the East Taijinaier salt lake, with exceptional separation factors as high as 68.7 and 21.0 for Li+ against Na+ and Mg2+ ions, respectively. Such unparalleled selectivity is believed to be attributed to the combination of structural and charge synergy of the NiHCF@λ-MnO2 composite. Our study highlights that a rational core-shell construction strategy can boost the optimal integration of NiHCF and MnO2, thus leveraging their potential to preferentially extract Li+ from brines.

Carbon quantum dots (CQDs) are promising cocatalysts in Fenton-like technologies, leveraging hydrogen peroxide and boosting Fe2 + generation and thereby expediting the advanced oxidation process. Although several studies have shown that the preparation affects the cocatalytic performance of the resulting CQDs, the precise correlation between the preparation and the cocatalytic efficiency is unclear. Here, we combine the batch experiments with the theoretical calculations to systematically explore how the parameters in electrochemical exfoliation preparation affect the cocatalytic performance of the as-prepared CQDs. The results show that adjusting parameters like voltage, electrolyte concentration, and electrolysis duration can precisely regulate the surface functional groups of CQDs, which in turn affects the cocatalytic performance. A linear positive correlation is identified between the surface carboxyl content and the pseudo-first-order rate constant (kobs) in Fenton-like reactions, with the highest carboxyl content (18.26 mmol/g) found in C@C3-30V-24H that induces the optimum catalytic performance to the C@C3-30V-24H-Fe3+/H2O2 system for phenol removal (97.75 % versus 21.17 % in Fe3+/H2O2 system at pH 3). DFT calculations reveal that phenolic compounds with electron-donating groups are more readily oxidized and that those with lower LUMO levels demonstrate higher kobs. This study underscores the crucial role of CQDs preparation on their cocatalytic performance in Fenton-like reactions.

The rapid growth of lithium (Li) ion batteries, particularly in electric vehicles (EVs) and large-scale energy storage facilities, has catalyzed an ever-increasing demand for Li. Current Li mining from brines based on evaporation-precipitation is time-consuming and water-intensive. Here, we report three NiHCF/MnO2 composite electrodes based on core-shell construction strategies for Li+ extraction from brine on a rocking-chair capacitive deionization (RCDI) platform. We find that the MnO2 components varied with the composing condition from alpha-, delta- to lambda-MnO2 and that the core-shell structured NiHCF@lambda-MnO2 electrode showed the optimal ion migration rate, highest specific capacity, and the best cycling stability. Notably, we reveal that the NiHCF@lambda-MnO2 electrode presented the optimum Li+ extraction performance with respect to adsorption capacity, adsorption rate, and energy consumption (e.g., achieving the highest Li+ capacity of 43.51 mg Li+ g-1 with a rate of 8.1 mg g-1 min-1, and at an energy cost of 0.86 Wh g-1 in 20 mM LiCl solution at 1.2 V). In addition, we demonstrate that the NiHCF@lambda-MnO2 electrode maintained high cycling stability over 40 consecutive cycles of Li+ intercalation/ deintercalation, with 78.4 % capacity retention in 10 mM of LiCl solution. Importantly, the NiHCF@lambda-MnO2 electrode also provided excellent Li+ selectivity in both the synthetic brine and the actual brine from the East Taijinaier Salt Lake, with exceptional separation factors as high as 68.7 and 21.0 for Li+ against Na+ and Mg2+ ions, respectively. Such unparalleled selectivity is believed to be attributed to the combination of structural and charge synergy of the NiHCF@lambda-MnO2 composite. Our study highlights that a rational core-shell construction strategy can boost the optimal integration of NiHCF and MnO2, thus leveraging their potential to preferentially extract Li+ from brines.

Struvite crystallization is a widely used technique for reclaiming nitrogen and phosphorus from waste streams. Kstruvite, an analogue of struvite ( NH+ ), has attracted ever-growing attention as its precipitation often occurs 4 under conditions similar to struvite (thereby, reactions can be implemented in existing facilities). However, Kstruvite formation is usually influenced by co-occurring impurities, particularly dissolved organic matters (DOMs). Here, we evaluated the roles of three typical DOMs (i.e., L-arginine, citric acid, and humic acid) in Kstruvite crystallization from a reaction kinetic perspective. It was found that K-struvite crystallization follows a well-defined first-order kinetics in the absence of any DOMs, regardless of the Mg/P molar ratio and supersaturation level. The presence of DOMs at varying levels (2-50 mg L-1) has been shown to have strong inhibition against K-struvite formation in batch reactors, with L-arginine acting as a phosphate binder, citric and humic acids as chelators of magnesium and potassium ions, and all DOMs as crystallization passivators via surface adsorption. Crystallographic and morphological analyses reveal that a lower supersaturation (0.47) level tends to yield amorphous precipitates with a small fraction of poorly crystallized K-struvite, failing to compensate for the inhibition from DOMs. While both the kinetic modeling and the structural examination indicate that the DOM inhibition was suppressed at a supersaturation as high as 2.57. In fluidized-bed reactors with a feed solution of a higher supersaturation (2.53), the natural DOMs appear to alter the phase composition and morphology significantly, with a majority of amorphous aggregates along with a few hexagonal K-struvite and shuttle-like vivianite crystals. Electrostatic potential mapping analysis of these DOMs reveals that the inhibition mechanisms varied with the type of DOMs, and future work would be necessary for molecular-level elucidation of the DOM-specific inhibition. This study offers a kinetic insight into K-struvite formation and underscores the necessity of strategies to tackle DOM-related issues in practical projects.

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.

Integrating Faradaic (charge transfer) materials with carbon has been proven extensively to be a valid strategy to prepare highly efficient electrodes for electrochemical desalination or removal of heavy metal ions from wastewater via a capacitive deionization (CDI) platform. However, the influences of preliminary functionalization of the carbon component (e.g., nitrogen doping, hydroxyl grafting) and pairing of cathodes and anodes on the desalination performance have yet to be thoughtfully 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 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 Cu2+ solutions, respectively (cf. 32.2 mg Pb2+ per gram electrode materials in 200 ppm Pb2+ solution). Besides, these electrodes exhibit excellent cycling stability when applied in removing each heavy metal ion separately, with an IAC retention 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 the MnO2, and surface complexation at the external surface of the [MnO6] octahedral layers. These findings underscore the pivotal roles of pre-functionalization of the original carbon and pairing of cathodes and anodes in the configuration of HCDI cells with improved performance and provide valuable insight into the optimization of Faradaic/carbon composite electrodes for remediation of wastewater with heavy metals via CDI platforms.

Capacitive deionization (CDI) is a promising water desalination technology known for its energy efficiency and low environmental impact. Charge-transfer materials (e.g., Prussian blue analogues, PBAs) have gained much attention as electrodes for CDI due to their much higher salt adsorption capacities (SACs) beyond conventional carbon-based electrodes, though they face challenges such as conductivity, stability, and ion transfer kinetics. Integrating these charge-transfer materials with carbon offers a promising strategy to enhance CDI performance and address these limitations. Herein, using a stepwise "ship-in-the-boat" approach, we incorporated a typical PBA, i.e., NiHCF, with hollow mesoporous carbon spheres (HMCS) to yield hierarchical composite materials (i.e., PBA@HMCS). This composite combines the protective and conductive roles of carbon materials with the high ion storage capacity of PBAs. The resulting PBA@HMCS electrodes demonstrated exceptional CDI performance, with a maximum salt adsorption capacity of 80.5 mg g- 1 in 500 mg L- 1 NaCl solution at 1.2 V. Notably, the PBA@HMCS-1 electrode exhibited enhanced cycling stability, while the unwrapped PBA micropellets showed reduced performance. Furthermore, our investigation revealed the high affinity of PBA@HMCS electrodes for Na+ over other ions in synthetic brine, and particularly, the yolk-shell PBA@HMCS-3 electrode demonstrated high repulsion to K+, highlighting its potential for selectively extracting specific ions from dicationic brines with K+ ions. This study highlights the potential of hierarchical yolk-shell PBA@HMCS as a promising CDI electrode and underscores the need for continued exploration into the hierarchically structural design of composite materials for high-performance CDI platforms.

Capacitive deionization (CDI) is a highly efficient approach for sustainable water desalination and ion-selective separation from complex brines. Layered metatitanic acid (H₂TiO₃, HTO) is a promising platform for electrochemical separation of monovalent ions due to its unique structural properties, but it faces lower conductivity when applied solely to CDI. Coupling HTO with carbon offers a valid strategy to address its charge transfer limitation and thereby enhance the CDI performance. Herein, we report a yolk-shell structured HTO/carbon electrode (denoted as ys-HTO@C) based on a stepwise nanoscale architectonic strategy that demonstrates superior charge transfer and storage properties and, therefore, better CDI performance relative to its core-shell structured and bulk counterparts (denoted as cs-HTO@C and HTO, respectively). Electrochemical desalination reveals that ys-HTO@C electrode has a Na⁺ adsorption capacity of 53.1 mg g-1 in 500 mg L-1 of NaCl solution at 1.2 V, a charge efficiency of 0.68, and moderate cycling stability (70.5 % of capacity retention over 40 cycles) due to its unique void space inside. Structural analyses indicate that capacity fading during cycling is primarily attributed to carbon oxidation and HTO degradation over time. Additionally, lithium extractions in synthetic and actual brines show that the HTO/carbon electrodes exhibit preferential capture of Li⁺ over Na⁺, Ca²⁺, Mg²⁺, and Pb²⁺ ions, with a separation factor of Li⁺/Na⁺ up to 60.7 for the ys-HTO@C electrodes in natural brine from East Taijinaier Salt Lake. It was observed that Li⁺ selectivity is concentration-dependent and likely driven by both the HTO's intrinsic Li⁺ preference and the ion's properties. The findings underscore the potential of the yolk-shell construction strategy for preparing novel and highly efficient electrodes for electrochemical desalination and selective Li⁺ extraction from complex brines.

In this work, the ablation characteristic, surface structure, and wetting property of the femtosecond laser-processed copper (Cu) surface are systematically studied. With the increase of laser pulse number, the area of the ablation crater increases and then tends to be stable, the period (0.62λ ∼ λ) of the generated ripple structures decreases, and the area of the periodic ripple structures in the Cu ablation crater first increases and then decreases. With the increase in laser fluence, the area of the ablation crater slightly increases, the period of the generated ripple structures varies oscillatively, and the area of the periodic ripple structures in the Cu ablation craters increases. Different columnar structures on the Cu surface are obtained through femtosecond laser cross-scanning processing. The height of columnar structures basically increases with the increase in laser power, laser scanning times, and laser scanning spacing. The wetting properties of the Cu columnar structure surfaces are also investigated. It reveals that the droplet contact angle obviously decreases with the increase in laser power and laser scanning times, and increases with the increase in laser scanning spacing. The variation of droplet contact angle on the laser-processed Cu surface is attributed to the different columnar structures and their different heights. It also reveals that the Cu surface changes from original hydrophobic to superhydrophilic with a contact angle of 8.9°. This work indicates the ability of femtosecond laser processing in regulating micro/nanostructure and wetting property of the Cu surface, which can be applicable to the surface treatment and performance control of other metallic materials.

Struvite crystallization, a promising technology for nutrient recovery from wastewater, is ever more encountering challenges due to the presence of emerging contaminants such as microplastics, which are ubiquitous in wastewater. In this study, we investigate the roles of microplastics and humic acid in struvite crystallization in batch and fluidized bed reactors, with emphasis on crystallization kinetics and physicochemical properties of struvite crystals. Batch crystallization kinetic experiments were conducted with synthetic wastewater with varying concentrations of microplastics and humic acid. The results showed that microplastics expedited the nucleation and growth rates of struvite (e.g., 1.43 times the blank suspension in the presence of 30 mg L−1 of zinc loaded polyethylene terephthalate particulates), while humic acid hindered the formation of struvite. Besides, X-ray diffraction analysis and the Rietveld refinement revealed that the presence of microplastics and/or humic acid can result in quite many changes in phase compositions of the reclaimed precipitates in batch and fluidized bed reactors. The characterization analysis demonstrated that microplastics act as seeds of struvite nucleation, spurring the formation of well-defined struvite, while humic acid favors the formation of newberyite rather than struvite in both the batch and the fluidized bed reactors. These findings highlight the need for a more comprehensive understanding of the interactions between emerging contaminants and struvite crystallization processes to optimize nutrient recovery strategies for mitigating their adverse impact on the quality and yield of struvite-based fertilizers.

Microplastics (MPs) have aroused growing environmental concerns due to their biotoxicity and vital roles in accelerating the spread of toxic elements. Illuminating the interactions between MPs and heavy metals (HMs) is crucial for understanding the transport and fate of HM-loaded MPs in specific environmentally relevant scenarios. Herein, the adsorption of copper (Cu2+) and zinc (Zn2+) ions over polyethylene (PE) and polyethylene terephthalate (PET) particulates before and after heat persulfate oxidation (HPO) treatment was comprehensively evaluated in simulated and real swine wastewaters. The effects of intrinsic properties (i.e., degree of weathering, size, type) of MPs and environmental factors (i.e., pH, ionic strength, and co-occurring species) on adsorption were investigated thoroughly. It was observed that HPO treatment expedites the fragmentation of pristine MPs, and renders MPs with a variety of oxygen-rich functional groups, which are likely to act as new active sites for binding both HMs. The adsorption of both HMs is pH- and ionic strength-dependent at a pH of 4-6. Co-occurring species such as humic acid (HA) and tetracycline (TC) appear to enhance the affinity of both aged MPs for Cu2+ and Zn2+ ions via bridging complexation. However, co-occurring nutrient species (e.g., phosphate and ammonia) demonstrate different impacts on the adsorption, improving uptake of Cu2+ by precipitation while lowering affinity for Zn2+ owing to the formation of soluble zinc-ammonia complex. Spectroscopic analysis indicates that the dominant adsorption mechanism mainly involves electrostatic interactions and surface complexation. These findings provided fundamental insights into the interactions between aged MPs and HMs in swine wastewaters and might be extended to other nutrient-rich wastewaters.

Lead-zinc mine tailing waste can have significant environmental impacts due to its potential for releasing toxic elements into the surroundings and contaminating local soil and water. This paper focuses on the valorization of lead-zinc mine tailing waste through geopolymerization, a sustainable process that can transform waste into useful building materials. Geopolymer matrixes with various mixtures of mine tailing (0-100 wt%), fly ash (0-100 wt%), and flue gas desulfurization (FGD) gypsum (0, 5, and 10 wt%) were synthesized using different activators such as sodium hydroxide (NaOH, 5, 10 M) and sodium silicate (waterglass, 0, 12.5 wt%). Visual inspection, unconfined compressive strength (UCS) testing, and microstructural analysis (e.g., X-ray diffractions, Fourier transforms infrared, and scanning electron microscopy) were employed for the physicochemical characterization of these geopolymers. The highest UCS value of 24.1 MPa was observed in a geopolymer specimen with 100 wt% fly ash and activated by 10 M NaOH and cured for 28 days. The blending of mine tailings would result in strength recession, e.g., the integrating of 25 wt% tailings showed a UCS of 12.3 MPa. The addition of 5 wt% gypsums can improve early strength development, particularly for matrixes with 50-75 wt% fly ash. But adding 10 wt% gypsums would lead to strength retrogression of the resulting geopolymers. The introduction of waterglass can also facilitate geopolymerization and improve strength development. However, the cointegrating of gypsum and waterglass can induce an antagonistic effect and lead to the collapse of the geopolymer specimens. The findings revealed that the strength and microstructural properties of geopolymer are determined by the matrix compositions, alkaline activators, etc. Effective regulation of these factors can produce geopolymer matrixes with high dimensional stability and UCS that well meet construction material standards. Overall, the study indicates that geopolymerization represents a viable and eco-friendly solution for valorizing lead-zinc mine tailing waste and gaining alternative building materials.

Capacitive deionization (CDI) is a promising technology for seawater desalination, offering a green, low-cost, and low-energy alternative to traditional methods. However, its widespread adoption relies on the development of high-performance electrode materials. Prussian blue analogs (PBAs), such as NiHCF, are attractive candidates due to their high theoretical ion storage capacity but often suffer from poor conductivity and structural integrity. To address these limitations, we designed a group of hierarchical composite materials (i.e., PBA@HMCS) by integrating NiHCF with hollow mesoporous carbon spheres (HMCS) using a stepwise "ship-in-the-boat" approach. This composite combines the protective and conductive roles of carbon materials with the high ion storage capacity of PBAs. The resulting PBA@HMCS electrodes demonstrated exceptional CDI performance, with a maximum salt adsorption capacity of 80.5 mg g−1 in 500 mg L−1 NaCl solution at 1.2 V. Notably, the core-shell PBA@HMCS-1 electrode exhibited enhanced cycling stability, while the unwrapped PBA micropellets showed reduced performance. Furthermore, our investigation revealed the high affinity of PBA@HMCS electrodes for Na+ over other ions in synthetic brine, and particularly, the yolk-shell PBA@HMCS-3 electrode demonstrated high repulsion to K+, highlighting its potential for selectively extracting specific ions from dicationic brines with K+ ions. This study highlights the vast potential of hierarchical yolk-shell PBA@HMCS as a promising CDI electrode design and underscores the need for continued exploration into hierarchical structured PBA-based materials with tunable features to further enhance their CDI performance.