Adsorption Mechanism Of Ions Research Articles

Bioactive Ion‐Confined Ultracapacitive Memristors with Neuromorphic Functions

AbstractThe field of bioinspired iontronics, bridging electronic devices and ionic systems, has multiple biological applications. Carbon‐based ultracapacitive devices hold promise for controlling bioactive ions via electric double layers due to their high‐surface‐area and biocompatible porous carbon electrodes. However, the interplay between complex bioactive ions and porous carbons remains unclear due to the variety of structures of bioactive ions present in biological systems. Herein, we investigate the adsorption behavior of a series of bioactive ammonium‐based cations with varying alkyl chain lengths in nanoporous carbons. We find that strong physisorption results from the synergistic hydrophobic interaction and electrostatic attraction between porous carbons (with a negative zeta potential) and bioactive cations. Bioactive cations with varying alkyl chain lengths can be irreversibly physically adsorbed and confined within nanoporous carbons resulting in anion enrichment and depletion during electric polarization. This situation, in turn, results in a characteristic memristive behavior in all‐carbon capacitive ionic memristor devices. Our findings highlight the relationship between the resistance state of the memristor and ion adsorption mechanisms in all‐carbon capacitive devices, which hold potential for future transmitter delivery, biointerfacing, and neuromorphic devices.

Adsorption Studies of Ternary Metal Ions (Cs+, Sr2+, and Co2+) from Water Using Zeolite@Magnetic Nanoparticles (Z@Fe3O4 NPs)

The mixture of three metal ions (Cs+, Sr2+, and Co2+) is commonly found in radioactive waste, which induces several negative health effects. The removal of multiple metal ions is a true challenge for researchers due to the competitive adsorption of ions onto adsorbents. In this study, three metal ions, namely Cs+, Sr2+, and Co2+, have been successfully removed simultaneously from water using zeolite@magnetic nanoparticles (Z@Fe3O4 NPs). The optimized condition for the adsorption of ternary metal ions was obtained at an adsorbent weight of 0.2, pH of 6.0~7.0, and contact time of 60 min. The adsorption mechanism of ternary metal ions onto the surface of Z@Fe3O4 NPs was studied using the Pseudo-first-order, Pseudo-second-order, Elovich, and Intra-particle diffusion models. The Dubinin–Radushkevich Temkin, Freundlich, and Langmuir isotherm models were used to study the isotherm adsorption. The ternary metal ion adsorption (Cs+, Sr2+, and Co2+) on Z@Fe3O4 NPs was followed by the Pseudo-second-order model (PSO) with correlation coefficient (R2) range of 0.9826–0.9997. Meanwhile, the adsorption isotherms of ternary metal ions on Z@Fe3O4 NPs were in line with the Langmuir model with R2 values higher than 0.9206, suggesting monolayer chemisorption with maximum adsorption capacities of 48.31, 15.02, and 10.41 mg/g for Cs+, Sr2+, and Co2+, respectively. Thus, the selectivity trend in the ternary metal ions system towards the Z@Fe3O4 NPs is observed to be Cs+ > Sr2+ > Co2+, which indicates that the competitive effect of Cs+ is the strongest compared to Sr2+ and Co2+ions.

Adsorption effect for removing fluoride with species of nitrogen by using La-BDC-NH2/C3N4: Experiments and mechanism

Fluoride contamination has emerged as a significant global environmental concern, with prolonged consumption of fluoride-rich groundwater being a primary contributor to fluorosis. Nitrogen sites play an important role in the process of fluoride removal, but the influence of different nitrogen species on fluoride adsorption has not been clearly clarified. In this study, a lanthanide organic framework adsorbent La-MOF-NH2 was prepared by solvothermal method, and a new adsorbent La-MOF-NH2@g-C3N4 was synthesized by adding g-C3N4 rich in various nitrogen sources. The effects of adsorbent dosage, pH, temperature and co-existing anions on the adsorption of fluorine were systematically studied. Optimal conditions were identified at a dosage of 2 g/L and a pH of 3, achieving theoretical maximum adsorption capacities of 219.4406 mg/g and 63.1401 mg/g, respectively. The results of five regeneration experiments shown that La-MOF-NH2 and La-MOF-NH2@g-C3N4 have strong recovery capacity. According to the adsorption isotherm and kinetic model, the adsorption mechanism of fluoride ions is mainly hydrogen bonding and chemisorption. In addition, through the experimental characterization and mechanism study, it was proved that amino group > pyridinic nitrogen > graphitic nitrogen. It provides a good guide for designing adsorbents containing nitrogen sites.

Bioactive Ion-Confined Ultracapacitive Memristors with Neuromorphic Functions.

The field of bioinspired iontronics, bridging electronic devices and ionic systems, has multiple biological applications. Carbon-based ultracapacitive devices hold promise for controlling bioactive ions via electric double layers due to their high-surface-area and biocompatible porous carbon electrodes. However, the interplay between complex bioactive ions and porous carbons remains unclear due to the variety of structures of bioactive ions present in biological systems. Herein, we investigate the adsorption behavior of a series of bioactive ammonium-based cations with varying alkyl chain lengths in nanoporous carbons. We find that strong physisorption results from the synergistic hydrophobic interaction and electrostatic attraction between porous carbons (with a negative zeta potential) and bioactive cations. Bioactive cations with varying alkyl chain lengths can be irreversibly physically adsorbed and confined within nanoporous carbons resulting in anion enrichment and depletion during electric polarization. This situation, in turn, results in a characteristic memristive behavior in all-carbon capacitive ionic memristor devices. Our findings highlight the relationship between the resistance state of the memristor and ion adsorption mechanisms in all-carbon capacitive devices, which hold potential for future transmitter delivery, biointerfacing, and neuromorphic devices.

Structure–Activity Mechanism of Sodium Ion Adsorption and Release Behaviors in Biochar

Structure–Activity Mechanism of Sodium Ion Adsorption and Release Behaviors in Biochar

Adsorption of fluoride ion on Al/La modified acidified attapulgite composite materials

This study developed a novel fluoride ion adsorbent material (Al/La-A) for efficient removal of fluoride ions in water. The crystal structure, elemental composition, surface morphology, specific surface area, thermal stability and surface electronegativity before and after modification were explored using FTIR, XRD, XPS, SEM-EDS, BET, TG-DSC, and zeta potential measurements. Results showed that the fluoride ion adsorption capacity of Al/La-A reached 130.42 mg/g, with the surface area increasing from 65.66 m2/g to 111.68 m2/g, respectively, compared to unmodified attapulgite. Al/La-A maintained excellent fluoride ion removal performance over a wide pH range, with the best adsorption at pH 2. Coexisting ion experiments indicated weak competitive adsorption effects of Cl-, SO42-, and HCO3–, with fluoride ion adsorption remaining above 100 mg/g in the presence of different concentrations of coexisting anions. After 5 adsorption–desorption cycles, Al/La-A exhibited strong adsorption capacity and reusability. The fitting of Langmuir adsorption model and pseudo-second-order kinetic model to the adsorption of fluoride ions on Al/La-A indicated that the adsorption of fluoride ions on Al/La-A was primarily monolayer chemical adsorption. The adsorption mechanism of fluoride ions involved electrostatic interactions, ion exchange, and coordination complexation. This study provides a new research approach for the optimal utilization of attapulgite-based adsorbent materials and the efficient removal of fluoride-containing wastewater.

Secondary Enrichment of REE in Weathered Granite, South Bangka, Indonesia

Rare earth elements (REEs) are essential materials for the manufacture of advanced technology. Secondary REE indications were found in alluvial and lateritic tin deposits within Southeast Asia Tin Belt. This study aims at the REE enrichment of weathering profiles underlain by Toboali Pluton of the main range S-type granite of this belt. Granite and weathering samples were collected and analyzed using XRF, ICP-MS/OES, XRD, SEM-EDX, and EPMA. The Chondrite-normalized REE patterns of granite in Toboali showed enrichment in REE with the highest value of 1,126 ppm. The Toboali Pluton is enriched in LREE and depleted in HREE. The enrichment of REE from the upper to lower horizon of weathering profiles was pointed out by the increase in REE values from a range of 156-188 ppm (horizon B) to 196-268 ppm (horizon C) in Toboali, and from a range of 230-330 ppm (horizon B) to 342-450 ppm (horizon C) in Air Gegas. These coincided with the presence of kaolinite with elevated REE and CeO2 in horizon C of weathering profile. Leaching test result proved that kaolinite plays a role in REE enrichment in the weathering profile through ion adsorption mechanisms in the Air Gegas. The weathering process of REE fluoro-carbonate (bastnäsite-(Ce)) and parisite-(Ce) in granite is believed to contribute in enrichment due to its high dissolution rate, which enhances kaolinite adsorption. In contrast, REE phosphates such as monazite-(Ce) and xenotime-(Y), because of their strong resistance and low solubility, are thought to be only slightly soluble, and most of these minerals remain in Toboali weathering products.

Experimental and computational study on the adsorption mechanism of silver ions on galena surface

With the increased use of silver in industry, a lot of wastewater containing silver is produced. If this wastewater is not treated, it will seriously impact both the ecological environment and human life. In order to effectively remove Ag+ from silver-containing wastewater, this study innovatively developed a natural mineral-based adsorption material (galena). The effects of reaction time, galena dosage, starting concentration, initial particle size, temperature, and solution pH on Ag+ removal were first studied using batch studies. The outcomes demonstrated that the initial Ag+ concentration of 50 mg/L reduced to 0.086 mg/L with the reaction duration of 15 min, the galena dose of 5 g/L, the initial particle size of −400 mesh (38 μm), the reaction temperature of 25 °C, and the pH of 5. The adsorption results show that the removal behavior of Ag+ by galena is consistent with the pseudo-second-order adsorption kinetic model and the Freundlich isothermal adsorption model, with the maximum adsorption amount of 18.78 mg/g. Solution chemical analysis shows that in the Ag+-NO32−-Pb2+-S2− system, Ag+ mainly reacts with S2− and forms a precipitate at pH = 5–6. SEM-EDS, FT-IR, and XPS analysis also showed that S2− and Ag+ are bound together as Ag2S in the galena surface. Orbital hybridization of the 4d orbitals of Ag+ with the S2− 3p orbitals occurs during the adsorption process according to density functional theory (DFT) calculations. During the adsorption process, Ag+ undergo charge transfer with S2− in the surface of galena.

Synthesis and performance of binder-free porous carbon electrodes in electrochemical capacitors.

Porous binder-free carbon electrodes were obtained by impregnating cellulose filter papers with phenolic resin through soft-salt template synthesis and thermal pyrolysis. These self-standing electrodes were used directly in a supercapacitor device. To understand the impacts of filter paper (FP) thickness on carbon filter paper (CFP) morphology, porosity, and surface functionalities, five different materials were examined. The CFP electrode thickness was adjusted linearly with the FP thickness to produce electrodes ranging from 100 to ∼800 μm. As the thickness of the CFP increased, there was an increase in the specific surface area and oxygen-based functionalities. Electrochemical testing in a 1 M KOH aqueous electrolyte demonstrated that electrode thickness played a key role in electrochemical capacitor (EC) performance, i.e., capacitance enhances linearly when the electrode becomes thinner. For low thicknesses (<280 μm), the capacitance and rate capability decreased slightly with increasing thickness; for high thicknesses, the performance drastically degraded despite the high specific surface area and oxygen surface functionalities. This effect was amplified at high regimes, indicating that high electrode thicknesses and fiber diameters limited electrolyte diffusion in the applied synthesis conditions. Thus, the high material porosity was inaccessible to ion adsorption. Consequently, thinner electrodes showed the highest capacitance (197 F g-1 at 0.1 A g-1) and rate capability (81%) values, exceeding those of their traditional binder-electrode counterparts prepared under similar conditions. Finally, for alkali metal hydroxide solutions, 1 M KOH exhibited a cation match with the salt template (KCl), while CsOH achieved additional capacitance retention (88% at 10 A g-1). Complex ion adsorption mechanisms were observed through a quartz crystal microbalance.

Correction: Selective Adsorption Mechanism of Zinc Ions on the Surfaces of Galena and Sphalerite in the Flotation Separation of Pb-Zn

Correction: Selective Adsorption Mechanism of Zinc Ions on the Surfaces of Galena and Sphalerite in the Flotation Separation of Pb-Zn

Cadmium Removal from Synthetic Aqueous Solutions by Adsorption on Peanut Shells: Kinetic and Thermodynamic Studies

Peanut shells were used in this study as an adsorbent carrier in the treatment of wastewater containing a trace metal element (TME), namely cadmium, a pollutant with adverse effects on health and the environment. The influences of contact time between adsorbent and adsorbate, initial cadmium concentration, adsorbent mass, reaction medium temperature and solution pH were evaluated. To determine the optimum parameters, pseudo-first-order and pseudo-second-order kinetic models were applied to the experimental results of the contact time study. Similarly, experimental results relating to the influence of concentration and temperature were modeled. Modeling of the data from the adsorbate-adsorbent contact time study showed that the kinetics of the cadmium adsorption reaction are well described by the pseudo-second-order kinetic model. The isotherm of the adsorption mechanism of cadmium ions (Cd2+) by peanut shells is perfectly described by the Freundlich equation. Thermodynamic studies using temperature variation have shown that adsorption is spontaneous and endothermic. This study led to a low entropy during cadmium adsorption. The best adsorption capacity was obtained at low pH = 5, i.e. favorable adsorption in acidic media.

Dynamic self-balanced electrochemical model for non-uniform corrosion of steel reinforcement in concrete under combined effects of heat-moisture-chlorine-oxygen

In this study, we developed a dynamic self-balanced electrochemical model to explore the intricate interplay between coupled heat-moisture transmission and the corrosion process of steel reinforcement in concrete structures. The model accounts for the diffusion, convection, and adsorption mechanisms of chloride ions in both the cement paste and interfacial transition zone (ITZ) phases. Additionally, it incorporates the balance between gaseous and dissolved oxygen, along with oxygen consumption during cathodic reactions. This framework allows for the dynamic self-balancing of macrocell and microcell, thus offering a comprehensive understanding of the non-uniform corrosion process under various environmental factors including temperature, humidity, chloride ions, and oxygen. To validate the model, we employed comprehensive monitoring approaches, coupled with artificial climate-accelerated corrosion experiments. These were designed to record variables such as temperature, humidity, oxygen concentration, and corrosion current density under time-varying environmental conditions. Our results indicate that while temperature within the concrete remains relatively uniform, humidity exhibits a non-uniform distribution. This non-uniformity in humidity is particularly noticeable at concrete cover surface, leading to convection and accumulation effects of chloride ions. Moreover, we observe a strong correlation between oxygen concentration and relative humidity. Corrosion current density for steel rebar is found to be higher at edge regions compared to central regions, owing to varying distances from the external soaking solution. The insights gained from this research offer valuable theoretical guidance for the design, construction, and maintenance of reinforced concrete structures, particularly those exposed to marine environments.

Robust functionalized cellulose-based porous composite for efficient capture and ultra-fast desorption of aqueous heavy metal pollution

The heavy metal pollution control industry requires convenient and cost-effective solutions to address complex aqueous environment. Adsorption method can be an effective strategy to realize these goals. Considering the importance of environmental and sustainable development strategies, there is an urgent need to develop efficient, green and non-toxic heavy metal adsorbents. In this work, a robust aminated cellulose-based porous adsorbent (PGPW) was developed from delignified wood and amino-rich polymer using a solvent-free, mild, simple and efficient preparation method. Such adsorbent exhibited excellent adsorption capacity (188.68 mg g−1) for Cu(II), and its adsorption behavior was consistent with pseudo-second order kinetic and Langmuir isotherm models. Notably, PGPW with superior compressibility could be squeezed to achieve rapid desorption and reach equilibrium within 5 min, while still retaining 87 % adsorption efficiency after 50 cycles. In addition, PGPW showed remarkable selectivity towards various coexisting ionic systems and demonstrated a considerable adsorption capacity in natural water applications. The adsorption mechanism of heavy metal ions on porous adsorption material was elucidated. This approach provides a simple, gentle and sustainable strategy for preparing functionalized wood-based composites with efficient adsorption and ultra-fast desorption of heavy metal ions.

Sorption of Pb2+, Zn2+, Cu2+ and Ni2+ Ions on Na-enriched Natural Zeolite for Wastewater Treatment Process: A Kinetic Approach

Low-cost and easily available natural zeolite is a promising adsorbent for metal ions removal in wastewater treatment. The possibility of using zeolitic tuff from Serbia in the form of Na-enriched natural zeolite (Na-Z) for the adsorption of Pb2+, Zn2+, Cu2+, and Ni2+ ions from wastewater was investigated in the presented paper. The research included Na-Z characterization and determination of adsorption kinetics in individual ion adsorption tests using non-linear pseudo-first-order (PFO), pseudo-second-order (PSO) and mixed-order (MO) kinetic models. The results indicate that the adsorption processes of metal ions on Na-Z are complex processes dominated by multiple rate-limiting mechanisms and best defined by the MO model. The mechanisms of ion diffusion and adsorption to active sites are equally represented in the Pb2+ ions adsorption process. The mechanism of ion diffusion is more pronounced in the Zn2+ ions adsorption process, while in the case of the adsorption of Cu2+ and Ni2+ ions adsorption on the active sites is the main kinetic mechanism. Within the MO model, the PFO rate (external/internal diffusion) and the PSO rate (adsorption on the active sites) were calculated and results were applied to a multicomponent wastewater sample in order to determine and explain the adsorption efficiency in wastewater treatment. The results show that the rate of adsorption of individual metal ions and the efficiency of ion removal from a multicomponent wastewater sample are influenced by several factors including the radius of the hydrated ion and the free energy of hydration. The achieved removal of metal ions by Na-Z is Pb2+ (89%) &gt; Cu2+ (72%) &gt; Zn2+ (61%) &gt; Ni2+ (58%) and defines Na-enriched natural zeolite as an effective adsorbent in wastewater treatment.

Selective Adsorption Mechanism of Zinc Ions on the Surfaces of Galena and Sphalerite in the Flotation Separation of Pb-Zn

Selective Adsorption Mechanism of Zinc Ions on the Surfaces of Galena and Sphalerite in the Flotation Separation of Pb-Zn

Facet-dependent adsorption of heavy metal ions on Janus clay nanosheets

Understanding the facet-dependent adsorption behavior and mechanism of heavy metal ions (HMs) on two-dimensional (2D) Janus nanoclays has important implications for the environment and ecosystem but still remains elusive. Herein, ultrathin Janus serpentene (2D serpentine) nanosheets were fabricated via a facile, nontoxic, and residue-free exfoliation strategy. Fabricated serpentene nanosheets exhibited promising Cd(II) and Pb(II) adsorption capacities due to their high surface areas and abundant active sites, approximately four times higher than those of bulk serpentine powders. Interestingly, Cd(II) and Pb(II) adsorption on serpentene nanosheets exhibited a facet-dependent feature, with the adsorption amount on the Mg–OH plane considerably higher than that on the Si–O plane. This facet-dependent adsorption behavior was mainly attributed to the difference in the interaction mechanisms of HMs with the Mg–OH (monodentate inner-sphere complexation) and Si–O (outer-sphere complexation) planes, which was further confirmed via density functional theory calculations. The Cd(II) adsorption on serpentene nanosheets was limited by strong kinetic restrictions (e.g., stronger electrostatic repulsion and higher dehydration energy barrier than that for Pb(II) adsorption). This study provides insights into the facet-dependent adsorption mechanisms of HMs on Janus serpentene nanosheets, which can be extended to other nanoclays used in wastewater treatment and many environmental processes.

Selective Adsorption Mechanism of Ferric Ions on the Surfaces of Chalcopyrite and Pyrite in Flotation

Selective Adsorption Mechanism of Ferric Ions on the Surfaces of Chalcopyrite and Pyrite in Flotation

Polystyrene Coating on APTES-Primed Hydroxylated AA2024-T3: Characterization and Failure Mechanism of Corrosion

Polystyrene has limited adhesivity to inorganic materials such as metals. However, the inorganic surface can be treated to enhance bonding to energetically stable polystyrene. This concept is verified in this paper with organosilane aminopropyltriethoxysilane (APTES) as the coupling agent primed on hydroxylated aluminum alloy AA2024-T3. We characterize the structural integrity and electrical impedance of the polystyrene coating on APTES-primed surfaces with different cured conditions after exposure to 3.5 wt.% NaCl solution for seven days. The results show that top-coated polystyrene on APTES is more structurally intact and less electrically conductive than the polystyrene coating alone. The coating layer made of top-coating polystyrene on a curing APTES film has the largest water uptake rate in the early stage of immersion in the corrosion solution. In the later stage, all coating layers tested regained their impedance while losing structural integrity. The charge transfer in the double layer of coated specimens for all types of coatings tested is predominantly through capacitance-based charging/discharging, presumably governed by the adsorption mechanism of ions at the coating/substrate interface.

Computational Insights into the Adsorption Mechanism of Zn Ion on the Surface (110) of Sphalerite from the Perspective of Hydration

Zn ions are widely reported to possess a depression effect on sphalerite in flotation. The effective adsorption of Zn ions on a sphalerite surface is critical to realize the inhibition effect. At the same time, zinc ions are easily hydrated in a slurry solution. Therefore, based on the first principle DFT calculation, the molecular mechanism of Zn ion adsorption on the surface of Sphalerite is further studied from the perspective of hydration. [Zn(H2O)5]2+, [Zn(OH)(H2O)3]+ and [Zn(OH)2(H2O)2] are found to be the effective components of Zn ions adsorbed on a sphalerite (110) surface in the neutral condition. Furthermore, the adsorption mechanism of [Zn(H2O)5]2+ on a sphalerite (110) surface is mainly via the hybridization of Zn 3d orbital in the structure of [Zn(H2O)5]2+ with surface S 3p orbitals. Additionally, the adsorption mechanism of [Zn(OH)(H2O)3]+ and [Zn(OH)2(H2O)2] on a sphalerite (110) surface is primarily ascribed to the hybridization of surface Zn 3d orbital with O atom of hydroxyl ligand 2p orbitals. In addition, the H 1s orbits in the water molecules have a weaker interaction with the sphalerite surface S 3p orbits. This work sheds new light on the adsorption and inhibition mechanism of zinc ions on a sphalerite surface in a neutral aqueous solution.

Ion adsorption on nanofiltration membrane surface and its effect on rejection of charged solutes: A zeta potential approach

The net charge on nanofiltration (NF) membrane surface, which differs from the inherent fixed charges due to the adsorption of ions from the feed water, has a great effect on the rejection selectivity of the membrane. In this study, by taking advantage of the electric double layer theory, streaming zeta potentials of the membrane varying with solution composition and concentration were utilized to investigate the characteristics and mechanisms of ion adsorption on the typical negatively charged NF membrane surface, which were then utilized to interpret the (selective) rejection behaviors for different solutes. Results showed that the cation adsorption all followed the Langmuir isotherm, indicative of monolayer adsorption mechanism. Both Langmuir adsorption fitting results and Gibbs free energy calculation showed that the cation adsorption is primarily of Coulomb force origin, rather than the chemical complexation. In addition, Ca2+ and Mg2+ could occupy the membrane surface much more facilely than Na+, with the adsorption of divalent cations reaching near saturation at relatively low concentrations in the magnitude of 1 mmol L−1. Contrary to the original presumption, no remarkable difference was observed between the adsorptions of Ca2+ and Mg2+, as was also the case between -COOH and -SO3H, the two common types of acidic functional groups on membrane surface for cation adsorption. These mechanisms of ion adsorption, when incorporated with the existing NF theory, could well interpret the seemingly “strange” rejection behaviors including the counter-ion competition effect. This study evidenced that zeta potential measurements could act as a useful approach for the study of ion adsorption on NF membrane surface and selective rejection mechanisms of NF membranes as well.