Search Results (190)

This study aims to address the issue of asphalt pavement performance deterioration caused by chloride salt erosion. Layered double hydroxides (CLDHs) calcined at different temperatures, including 400 °C, 500 °C, and 600 °C, were used for the modification of asphalt binder. The structural evolution and chloride ion adsorption characteristics of CLDHs were analyzed. The adsorption kinetic behavior of CLDHs for chloride ions was investigated by combining adsorption kinetic experiments and electrochemical titration experiments. Through characterizing the interfacial adhesion performance between CLDH-modified asphalt binder and aggregates, the chemical composition of asphalt–ash binder before and after salt corrosion, and the leaching stability of organic substances in an environment with abundant chloride ions, the influence of CLDHs on the salt corrosion resistance of asphalt–ash binder was quantified. The results indicate that chloride adsorption by CLDHs is predominantly chemisorption-driven. With increasing calcination temperature, the chloride adsorption capacity of CLDHs gradually improved. In chloride-rich environments, CLDHs significantly enhanced the interfacial adhesion between asphalt binder and aggregates, particularly for coarse aggregates with a particle size of 9.5–13.2 mm. Furthermore, CLDHs effectively suppressed the formation of carbonyl and sulfoxide groups during salt corrosion and substantially decreased the leaching of organic components from asphalt binder. In summary, CLDHs can specifically enhance the salt corrosion resistance of asphalt binder, with the 600 °C-CLDHs demonstrating the most significant improvement, followed by the 400 °C-CLDHs, while the 500 °C-CLDHs performed the least effectively. Full article

The development of electrode materials that combine high capacity with high anion selectivity is critical for chloride separation from complex aqueous matrices. Here, a NiFe LDH/BiOCl composite film electrode was fabricated on carbon paper via sequential electrodeposition and employed for electrically switched ion exchange (ESIX) of chloride. The composite delivers higher reversible chloride uptake than either NiFe LDH or BiOCl alone under identical electrochemical conditions, together with enhanced selectivity in mixed−anion solutions. Mechanistically, the synergy originates from the combination of (i) the high anion−exchange capacity and redox−tunable layer charge of NiFe LDH and (ii) halide−affinitive BiOCl domains that facilitate voltage−gated uptake/release; the heterointerface further improves charge/ion transport, enabling more effective electrochemical utilization. The electrode maintains stable cycling performance with high regeneration efficiency over repeated ESIX operation. Compared with representative LDH− or BiOX−based ESIX electrodes reported for halide capture, the proposed composite shows competitive chloride selectivity and reversible cycling, supporting its potential for electrochemical separations and water treatment. Full article

Heavy metals (arsenic, cadmium, and lead) remain one of the most common and complex environmental problems worldwide. Accordingly, there is a growing need for eco-friendly and affordable materials derived from agricultural waste for the removal of heavy metals from contaminated water. This study aims to demonstrate how biodegradable pineapple leaf cellulose (PLC) can be used effectively in the remediation of heavy metals. The PLC adsorbent was prepared by treating it with ethyl alcohol (EtOH, 99.5%), calcium chloride (CaCl₂), and 0.8 M sodium hydroxide. A scanning electron microscope equipped with energy-dispersive X-ray spectroscopy (SEM-EDS) and Fourier transform infrared spectroscopy (FT-IR) was used to investigate the surface of the adsorbent. Inductively coupled plasma mass spectrometry (ICP-MS) was employed to measure the concentration of metals before and after adsorption. Removal of metal ions (As⁵⁺, Cd²⁺, and Pb²⁺) by PLC was investigated under varying conditions, including pH, contact time, and adsorbent dosage. The analysis of cellulose composite revealed significant potential for adsorption of heavy metals such as As⁵⁺, Cd²⁺, and Pb²⁺. The highest removal efficiency of heavy metal ions was detected at a pH ranging from 3 to 7. The biosorption order of PLC at pH 6 was Pb²⁺ > Cd²⁺ > As⁵⁺ with 99.53% (63.45 mg/g), 98.44% (37.23 mg/g), and 42.40% (16.27 mg/g), respectively. After 120 min, the equilibrium of the adsorption process was reached for As⁵⁺, Cd²⁺, and Pb²⁺. FT-IR characterization discovered an increased abundance of functional groups on the adsorbent. The SEM-EDS analysis confirmed the occurrence of elements on the surface of PLC. The study revealed that the use of PLC is an innovative method for removing heavy metals from aquatic milieus, a potential resource for eco-friendly and affordable wastewater treatment. Full article

This study presents an approach to synthesizing LTA-type zeolite from spodumene residue generated during a lithium extraction process. A residue was obtained after leaching β-spodumene with 2 mol/L phosphoric acid. After solid–liquid separation, the delithiated residue was first treated with 2 mol/L sodium hydroxide and then subjected to hydrothermal synthesis using sodium aluminate as an additional aluminum source. The resulting material was characterized by XRD, SEM-EDS, XPS, and FTIR, which collectively confirmed the formation of a crystalline material exhibiting the structural features, elemental composition, and morphological characteristics consistent with LTA-type zeolite. Additional analyses, including BET surface area, particle size distribution, and zeta potential measurements, were performed to further evaluate the physicochemical properties of the synthesized zeolite. The spodumene leach residue (SLR)-derived zeolite was further tested for its adsorption performance in heavy metal ions removal from a mixed ion solution containing Pb²⁺, Cu²⁺, Zn²⁺, and Ni²⁺ ions. The zeolite demonstrated a high selectivity for Pb²⁺, followed by moderate uptake of Cu²⁺, while Zn²⁺ and Ni²⁺ adsorption was minimal. These findings demonstrate that spodumene residue, a waste by-product of lithium processing, can be effectively upcycled into LTA zeolite suitable for heavy metal remediation in water treatment applications. Full article

This work reports the electrochemical behavior of a nickel hydroxide electrode, electrodeposited in a deep eutectic solvent (DES), in alkaline solutions of varying composition, aiming to elucidate the influence of the cation (Na⁺ vs. K⁺), urea, and carbonate ions on the mechanism and kinetics of anodic processes. Cyclic voltammetry and electrochemical impedance spectroscopy were employed to analyze the electrochemical responses of electrode processes in alkaline water electrolysis systems. For the urea oxidation reaction (UOR), the frequency-dependent characteristics were thoroughly characterized, and the impedance response was simulated according to the Armstrong–Henderson equivalent circuit. It was found that the addition of urea significantly transforms the impedance structure, sharply reducing the polarization resistance and increasing the pseudo-capacitive component of the constant phase element at low frequencies, indicating activation of the slow steps of urea oxidation via a direct mechanism and the formation of an extended adsorptive surface. It was demonstrated that, unlike conventional alkaline electrolysis where KOH-based systems are generally more effective, urea-assisted systems exhibit superior performance in NaOH-based electrolytes, which provides more favorable kinetics for the electrocatalytic urea oxidation process. Furthermore, the accumulation of carbonate ions was shown to negatively affect UOR kinetics by increasing polarization resistance and partially blocking surface sites, highlighting the necessity of controlling electrolyte composition in practical systems. These findings open new opportunities for the rational design of efficient urea-assisted electrolyzers for green hydrogen generation. Full article

Perfluorooctanoic acid (PFOA) contamination poses serious environmental risks due to its persistence and mobility. Conventional ex situ method using preformed layered double hydroxides (LDHs) shows limited performance, particularly under complex leachate conditions. This study developed an effective in situ Zn/Al LDH strategy for enhanced PFOA removal. Batch experiments, solid-phase characterization, and theoretical simulations were conducted to elucidate the adsorption mechanism and the effect of fluoride ion (F⁻). The results demonstrated that the in situ method exhibited superior performance in the presence of fluoride, achieving a PFOA adsorption density of up to 54.93 mmol/mol-Al, which is significantly higher than that of the ex situ method (26.76 mmol/mol-Al). Unlike the competitive adsorption observed in the ex situ method, the in situ process relies on synergistic mechanisms: F⁻ participates in LDH formation as an interlayer anion and coordinates with Zn²⁺ and Al³⁺ to regulate LDH growth, thereby optimizing the surface chemical environment for PFOA capture. Molecular dynamics (MDs) and density functional theory (DFT) further showed that preferentially adsorbed F⁻ affects hydrogen-bond networks and stabilizes PFOA through inner and outer sphere complexation. Overall, these findings clarify the fluoride-regulated adsorption mechanism and demonstrate the potential of in situ LDH coprecipitation for PFAS remediation in leachates. Full article

The transition toward a circular economy requires innovative strategies for valorizing industrial by-products. This study investigates the potential of steelmaking furnace slag (SFS) as a low-cost adsorbent for the removal and recovery of nickel and copper ions from aqueous systems. The slag was characterized using XRF, XRD, SEM, FTIR, and thermal analyses, confirming the presence of reactive phases such as lime, periclase, and calcium silicates. Batch adsorption experiments revealed high sorption capacities (up to 147 mg·g⁻¹) and were best described by the Langmuir isotherm and pseudo-second-order kinetic model, indicating chemisorption as the rate-limiting step. FTIR and SEM analyses demonstrated the formation of nickel and copper hydroxide/oxide phases, confirming surface precipitation mechanisms. Subsequent thermal treatment produced NiO- and CuO-enriched oxide systems with photocatalytic and antibacterial potential, while hydrometallurgical recovery using ammonia solutions achieved desorption efficiencies of 90–97%. The results highlight the dual role of SFS as an efficient sorbent for wastewater pre-treatment and as a secondary source of valuable metals, contributing to sustainable materials management and circular economy goals. Full article

The enrichment of cadmium (Cd) in farmland soil poses serious risks to agricultural safety and remains challenging to remediate. This study evaluated CaAl-layered double hydroxide (CaAl-LDH) as a highly efficient and stable passivator for Cd-contaminated soil. Laboratory adsorption tests demonstrated that Cd²⁺ adsorption on CaAl-LDH followed pseudo-second-order kinetics and the Langmuir model, indicating monolayer chemisorption, with a maximum capacity of 469.48 mg·g⁻¹ at pH 6. The adsorption mechanisms include surface complexation, interlayer anion exchange, dissolution–precipitation, and isomorphic substitution. A three-year field trial in Yongkang City, China showed that CaAl-LDH promoted the transformation of Cd in rhizosphere soil from the ion exchange state (F2) to the residual state (F7) and Fe–Mn oxidized state (F5), reducing the exchangeable Cd content by 26.71%. Consequently, Cd content in rice grains decreased by 68.42% in the first year and remained over 37% lower in the second year, consistently below the national food safety limit. Future research should focus on the optimization of material’s stability and application protocol. The results demonstrate that CaAl-LDH provides a cost-effective and sustainable strategy for the in situ passivation remediation of Cd-contaminated farmland, contributing to food safety and sustainable agriculture. Full article

In this work, the removal of Cu(II) ions from an aqueous effluent was studied using an Mg/Fe layered double hydroxide (LDH) as the adsorbent. The material was synthesized and characterized before and after the adsorption process to identify structural and morphological changes induced by copper uptake. Techniques such as X-ray diffraction (XRD), scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS), ultraviolet-visible spectroscopy (UV-Vis), Raman spectroscopy, and nitrogen physisorption (BET) were employed to confirm the interaction between the metal ions and the LDH surface. The LDH-Mg/Fe exhibited a high maximum adsorption capacity of 526 mg/g, and the adsorption kinetics followed a pseudo-second-order model, achieving over 90% removal of Cu(II) within 2.5 h. The Cu(II)-loaded material was subsequently evaluated as a sustainable catalyst in two applications: (i) an organic synthesis via “click” chemistry, reaching yields of up to 85%, and (ii) the decoloration of Congo Red via a Fenton-like process, achieving a decoloration efficiency of at least 84%. These dual uses demonstrate the potential of Cu(II)-loaded LDH as a cost-effective and environmentally friendly approach to simultaneous pollutant removal and catalytic valorization. Full article

Electrokinetic (EK) remediation is a promising approach for the removal of heavy metals from fine-grained soils; however, its efficiency is often hindered by electrode polarization, pH imbalance, and ion accumulation. In this study, we developed a novel hydrogel-based electrode (NH electrode), composed of sodium alginate and multilayer graphene oxide (GO), to enhance the electrokinetic removal of Cu²⁺ and Pb²⁺ from loess. The electrode was systematically characterized by atomic force microscopy (AFM), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS), confirming its structural integrity, electrochemical activity, and interfacial conductivity. The NH electrode exhibited a smooth layered graphene structure with abundant oxygen-containing functional groups (AFM), negligible electrochemical polarization (CV), and low internal resistance with high conductivity (EIS), enabling efficient ion transport and adsorption. Electrokinetic tests revealed that the NH electrode outperformed conventional graphene (Gr) and electrokinetic graphite (EKG) electrodes. Single regulation strategies, including focusing position adjustment and electrode exchange, improved local removal efficiency by mitigating ion accumulation in targeted regions. The combined regulation strategy, integrating both measures, achieved the most uniform Cu²⁺ and Pb²⁺ removal, significantly suppressing hydroxide precipitation in cathodic zones and enhancing ion migration in the mid-section. Compared with literature-reported systems under similar or even more favorable conditions, the NH electrode and combined regulation approach achieved superior performance, with Cu²⁺ and Pb²⁺ removal efficiencies reaching 47.25% and 16.93%, respectively. These findings demonstrate that coupling electrode material innovation with spatial–temporal pH/flow field regulation can overcome key bottlenecks in EK remediation of heavy-metal-contaminated loess. Full article

Phosphates pollution, primarily from agricultural runoff and wastewater discharge, is a major contributor to water eutrophication, adversely affecting aquatic ecosystems. This study reports the synthesis, characterization, and phosphates adsorption performance of a MgAlFe-layered double hydroxide (MgAlFe-LDH) with a 2:1:1 cationic ratio. The material was prepared via co-precipitation and characterized using digital microscopy, XRD, BET, XPS, and FTIR. Adsorption experiments were conducted at pH 3 and 9 to investigate equilibrium, kinetics, and reusability. The MgAlFe-LDH exhibited a high maximum adsorption capacity (q_max ≈ 215 mg/g) largely independent of pH, with adsorption well described by the Langmuir model. Kinetic studies revealed a pseudo-first-order mechanism, indicating that adsorption is dominated by surface diffusion and electrostatic interactions. Phosphate removal occurs through a dual mechanism involving rapid electrostatic attraction at protonated surface sites and slower ion exchange in the LDH interlayers. The material retained over 75% of its adsorption capacity after five consecutive adsorption–desorption cycles, highlighting its potential for sustainable phosphate recovery. Overall, the MgAlFe-LDH represents a promising, reusable adsorbent for phosphorus removal from wastewater, supporting circular economy strategies. Full article

Addressing the challenge of sulfonated lignite (SL) removal from oilfield wastewater, this study introduces a novel hierarchical MgFe-layered double hydroxide (LDH) adsorbent. The material was fabricated via in situ co-precipitation, utilizing a template formed by the NaCl-induced co-assembly of oleylaminopropyl betaine (OAPB) and sodium dodecyl sulfate (SLS) into zwitterionic, anionic, shear-responsive viscoelastic gels. This gel-templating approach yielded an LDH structure featuring a hierarchical pore network spanning 1–80 nm and a notably high specific surface area of 199.82 m²/g, as characterized by SEM and BET. The resulting MgFe-LDH demonstrated exceptional efficacy, achieving a SL removal efficiency exceeding 96% and a maximum adsorption capacity of 90.68 mg/g at neutral pH. Adsorption kinetics were best described by a pseudo-second-order model (R² > 0.99), with intra-particle diffusion identified as the rate-determining step. Equilibrium adsorption data conformed to the Langmuir isotherm, signifying monolayer uptake. Thermodynamic analysis confirmed the process was spontaneous (ΔG < 0) and exothermic (ΔH = −20.09 kJ/mol), driven primarily by electrostatic interactions and ion exchange. The adsorbent exhibited robust recyclability, maintaining over 79% of its initial capacity after three adsorption–desorption cycles. This gel-directed synthesis presents a sustainable pathway for developing high-performance adsorbents targeting complex contaminants in oilfield effluents. Full article

Iron, an essential element for virtually all known organisms, serves not only as a micronutrient but also as an energy source for bacteria. Iron-oxidizing microorganisms mediate Fe(II) oxidation under diverse redox conditions, yielding amorphous iron (hydr)oxides or crystalline iron minerals. This globally significant biogeochemical process drives modern iron cycling across terrestrial and aquatic ecosystems. The resulting biomineralization not only produces secondary minerals but also effectively immobilizes heavy metals, offering a sustainable strategy for environmental remediation. This review systematically examines (1) the biogeochemical mechanisms and mineralogical signatures of Fe(II) oxidation by four distinct iron oxidizers: acidophilic aerobes (e.g., Acidithiobacillus), neutrophilic microaerophiles (e.g., Gallionella), nitrate-reducing anaerobes (e.g., Acidovorax), and anoxygenic phototrophs (e.g., Rhodobacter); (2) research advances in heavy metal immobilization by biogenic iron minerals: adsorption, coprecipitation, and structural incorporation; and (3) the impact of pH, temperature, organic matter, and coexisting ions on Fe(II) oxidation efficiency and iron mineral formation by iron-oxidizing bacteria. By characterizing iron-oxidizing bacterial species and their functional processes under varying pH and redox conditions, this study provides critical insights into microbial behaviors driving the evolution of acid mine drainage (AMD). Full article

Tungsten and tungsten alloys are widely used in important industrial fields due to their high density, hardness, melting point, and corrosion resistance. However, machining often leaves processing marks on their surface, significantly affecting the surface quality of precision components in industrial applications. Electrolytic polishing offers high efficiency, low workpiece wear, and simple processing. In this study, an electrolytic polishing method is adopted and a novel trisodium phosphate–sodium hydroxide electrolytic polishing electrolyte is developed to study the effects of temperature, voltage, polishing time, and solution composition on the surface roughness of a tungsten–nickel–iron alloy. The optimal voltage, temperature, and polishing time are determined to be 15 V, 55 °C, and 35 s, respectively, when the concentrations of trisodium phosphate and sodium hydroxide are 100 g·L⁻¹ and 6 g·L⁻¹. In addition, glycerol is introduced into the electrolyte as an additive. The calculated LUMO value of glycerol is −5.90 eV and the HOMO value is 0.40 eV. Moreover, electron enrichment in the hydroxyl region of glycerol can form an adsorption layer on the surface of the tungsten alloy, inhibit the formation of micro-pits, balance ion diffusion, and thus promote the formation of a smooth surface. At 100 mL·L⁻¹ of glycerol, the roughness of the tungsten–nickel–iron alloy decreases significantly from 1.134 μm to 0.582 μm. The electrochemical polishing mechanism of the tungsten alloy in a trisodium phosphate electrolyte is further investigated and explained according to viscous film theory. This study demonstrates that the trisodium phosphate–sodium hydroxide–glycerol electrolyte is suitable for electropolishing tungsten–nickel–iron alloys. Overall, the results support the application of tungsten–nickel–iron alloy in the electronics, medical, and atomic energy industries. Full article

This study presents a sustainable approach for synthesizing high-performance activated carbon from Spirulina Alga through hydrothermal carbonization followed by chemical activation using potassium hydroxide. The resulting activated carbon exhibited a high Brunauer–Emmett–Teller (BET) surface area of 1747 m²/g and a total pore volume of 1.147 cm³/g, with micropore volume accounting for 0.4 cm³/g. Characterization using Scanning Electron Microscopy-Energy Dispersive X-ray Spectroscopy (SEM-EDS), X-ray Photoelectron Spectroscopy (XPS), and gas adsorption analyses confirmed the presence of hierarchical micro- and mesoporosity as well as favorable surface functional groups. The synthesized carbon was used to fabricate electrodes for membrane capacitive deionization (MCDI) along with cation and anion-selective membranes, which were then tested with saline water (500–5000 ppm) and synthetic hard water (898 ppm of total salts). The salt adsorption capacity (SAC) reached 25 (batch) to 40 (continuous) mg/g, while rapid adsorption rates with average salt adsorption rates (ASARs) values exceeding 10 (batch) to 30 (continuous) mg·g⁻¹·min⁻¹ during early stages were obtained. Batch MCDI experiments demonstrated a higher SAC compared to continuous operation, with non-monotonic trends in SAC observed as a function of feed concentration. Ion adsorption kinetics were influenced by ion valency, membrane selectivity, and pore structure. The specific energy consumption (SEC) was calculated as 8–21 kJ/mol for batch and 0.1–0.5 kJ/mol for continuous process. These performance metrics are on par with or surpass those reported in the recent literature for similar single-electrode CDI configurations. The results demonstrate the viability of using Alga-derived carbon as an efficient and eco-friendly electrode material for water desalination technologies. Full article