Adsorption Mechanism Of Ions Research Articles

Changes in adsorption mechanisms of radioactive barium, cobalt, and strontium ions using spent coffee waste biochars via alkaline chemical activation: Enrichment effects of O-containing functional groups

The single adsorption of radioactive barium (Ba(II)), cobalt (Co(II)), and strontium (Sr(II)) ions using pristine (SCWB–P) and chemically activated spent coffee waste biochars with NaOH (SCWB-A) were thoroughly explored in order to provide deeper insights into the changes in their adsorption mechanisms through alkaline chemical activation. The greater removal efficiencies of SCWB-A (76.6–97.3%) than SCWB-P (45.6–75.2%) and the consistency between the adsorptive removal patterns (Ba(II) > Sr(II) > Co(II)) and oxygen bond dissociation enthalpies (BaO (562 kJ/mol) > SrO (426 kJ/mol) > CoO (397 kJ/mol)) of radioactive species supported the assumption that the adsorption removal of radioactive species with spent coffee waste biochars highly depended on the abundances of O-containing functional groups. The calculated R2 values of the pseudo-first-order (SCWB–P = 0.998–0.999; SCWB-A = 0.850–0.921) and pseudo-second-order kinetic models (SCWB–P = 0.988–0.998; SCWB-A = 0.935–0.966) are evident that the physisorption mainly controlled the adsorption of radioactive species toward SCWB-P and the chemisorption played a crucial role in their adsorptive removal with SCWB-A. From the calculated intra-particle diffusion, isotherm, thermodynamic parameters, it can be concluded that the intra-particle diffusion and monolayer adsorption primarily governed the adsorption of radioactive species using SCWB-P and SCWB-A, and their adsorption processes occurred spontaneously and endothermically. The dominant adsorption mechanism of spent coffee waste biochars was changed from physisorption (ΔH° of SCWB-P = 21.6–29.8 kJ/mol) to chemisorption (ΔH° of SCWB-A = 42.4–81.3 kJ/mol) through alkaline chemical activation. The distinctive M-OH peak in the O1s XPS spectra of SCWB-A directly corresponding to the decrease in the abundances of O-containing functional groups confirms again that the enrichment of O-containing functional groups markedly facilitated the adsorption removal of radioactive species by chemisorption occurred at the inner and outer surfaces of spent coffee waste biochars.

Effects of metal ions on the flotation separation of spodumene from feldspar and quartz

The effects of Ca(II), Mg(II), Cu(II), and Fe(III) on the flotation separation of spodumene from feldspar and quartz were investigated by single-mineral and artificial-mixed-ore flotation experiments using α-bromododecanoic acid (α-BDDA) as a collector. At pH≈7, Ca(II), Mg(II), and Cu(II) selectively improved the flotation of spodumene, which facilitated the separation of spodumene. Although Fe(III) exhibited strong activation ability, its selectivity toward spodumene was low, which impaired the separation of spodumene. Moreover, the sequence of addition of metal ions had an impact on the separation of spodumene. When Ca(II) and Mg(II) were used as activators in the artificial-mixed-ore flotation experiments, concentrates with recoveries of 75.6% and 76.3% and Li2O grades of 5.8% and 5.2% were obtained, respectively. Adsorption and activation mechanisms of metal ions were analyzed by adsorption amount measurements, Fourier transform infrared spectroscopy, species distribution calculation, and frontier orbital theory calculation. Results indicated that the amount of α-BDDA adsorbed on spodumene was higher than those adsorbed on feldspar and quartz when Ca(II), Mg(II), and Cu(II) were employed as activators, which led to a higher recovery of spodumene. When the pH was approximately 7, Ca(II), Mg(II), Fe(III), and Cu(II) were mainly present as Ca2+, Mg2+, Fe(OH)3 and Fe(OH)2+, and Cu(OH)2, Cu2+, and Cu(OH)+, respectively. The results of frontier orbital theory calculations demonstrated that α-BBBA, Ca2+, and Mg2+ easily adsorbed on spodumene than on feldspar and quartz. Therefore, Ca(II) and Mg(II) facilitated the separation of spodumene. However, Fe(OH)2+ preferentially reacted with spodumene, whereas Fe(OH)3 preferably reacted with feldspar and quartz, which caused low selectivity of Fe(III) toward spodumene. Similarly, Cu2+ and Cu(OH)+ easily adsorbed on spodumene, whereas Cu(OH)2 preferentially adsorbed on feldspar and quartz. Thus, the selectivity of Cu(II) toward spodumene was inferior compared to those of Ca(II) and Mg(II).

Understanding the sorption behaviors of heavy metal ions in the interlayer and nanopore of montmorillonite: A molecular dynamics study

The molecular-scale adsorption mechanism of heavy metal ions in the interlayer and nanopore regions of montmorillonite (MMT) were investigated by molecular dynamics simulations. Three typical heavy metals (zinc, cadmium, and lead) were selected as the model ions, and two types of MMT (Arizona and Wyoming) were considered. The results showed that Cd2+ and Pb2+ can form both inner- and outer-sphere complexes on Wyoming MMT, while Zn2+ only formed outer-sphere complex due to the stronger hydration interaction of Zn2+ than Cd2+ and Pb2+. For Arizona MMT, all of the three ions only formed outer-sphere complexes on its interlayer and external basal surface in which the cations remained a fully hydrated state. The calculated diffusion coefficients of three cations in interlayer and nanopore indicated that their diffusion abilities were significantly impaired, implying that MMT adsorbents have a strong ability to fix and retard heavy metal ions. The derived results and mechanisms are instrumental to a profound understanding of the transport and retention of heavy metal elements in subsurface environments, and provide guidance for the management of heavy metal pollution.

What can S-shaped potential profiles tell us about the mechanism of membrane potential generation?

Membrane theory attributes the generation mechanism of the membrane potential to transmembrane ion transport, while Cheng's ISE (Ion selective electrode) mechanism attributes the ISE potential generation to ion adsorption on to the ISE surface. Although the membrane potential generation mechanism is different from the ISE potential generation mechanism, both the membrane potential and the ISE potential exhibit quite similar characteristics. For instance, both become indifferent to the variation of the ion concentration in both the high and the low ion concentration environment. Our experimental and theoretical investigations suggest that such a characteristic membrane potential behavior could be explained by the ion adsorption mechanism called Ling's adsorption theory (LA theory) instead of by membrane theory. If the membrane potential generation mechanism is explained by the LA theory, then the significant similarity between the membrane potential and the ISE potential is understandable, since both the LA theory and Cheng's ISE mechanism rely on the ion adsorption process. Although the LA theory is not acknowledged as the mechanism for the membrane potential generation in the mainstream physiology community, it does not have any serious defect in principleas a membrane potential generation mechanism. Hence, it is worth investigating if the current membrane potential generation mechanism needs reevaluation in light of evidence presented here. We conclude that the LA theory is a quite plausible membrane potential generation mechanism, suggesting that it may contribute to it.

Preparation and characterization of manganese‐containing biochars and their lead ion adsorption mechanism

AbstractHeavy metal pollution causes severely adverse impacts on human and ecosystem health. Adsorption is one of the most effective technologies used in the removal of heavy metal ions from contaminated water. However, its widespread applications are limited, owing to its high cost and low adsorbent selectivity. In this study, modified manganese‐containing biochars were synthesized to improve their Pb2+ adsorption ability. Fraxinus mandshurica sawdust samples were impregnated with pure water as well as KMnO4 and MnSO4 aqueous solutions (FM‐BC, FM‐M7BC, and FM‐M2BC, respectively) for 24 hours at 25°C and pyrolyzed at 400°C. The resulting biochars were characterized using x‐ray diffraction (XRD), scanning electron microscopy (SEM), energy‐dispersive x‐ray analyses (EDX), Fourier‐transform infrared spectroscopy (FTIR), N2 adsorption‐desorption isotherms, and Boehm titration. Batch adsorption experiments revealed the kinetics and magnitude of Pb2+ adsorption onto the biochars. The Pb2+ adsorption capacity of FM‐M7BC (156.25 mg · g−1) was significantly higher than those of FM‐M2BC (25.35 mg · g−1) and FM‐BC (11.99 mg · g−1), and based on FTIR and Boehm titration results before and after Pb2+ adsorption, an adsorption mechanism was proposed. FM‐M7BC showed the highest adsorption enhancement owing to the strong affinity of MnCO3 particles and O‐containing groups for Pb2+. Additionally, the influence of the different oxidation states of manganese (Mn(VII), and Mn(II)) in the manganese components on the Pb2+ adsorption performance of the biochars was extremely strong. FM‐M7BC was an effective adsorbent for removing Pb2+.

Amino-functional biocarbon with CO2-responsive property for removing copper(II) ions from aqueous solutions

Amino-functional biocarbons (NH3-HTC, FA-HTC) were synthesized by one-pot hydrothermal carbonization of glucose (HTC) using ammonia (NH3) or ammonium formate (FA) additives. The as-prepared amino-functional biocarbons had specific surface areas of (5 to 8) m2/g, amino- content of (4 to 5) mmol/g, COOH content of (2 to 4) mmol/g and OH content of about 1 mmol/g. Experiments at 20 °C revealed that the as-prepared amino functional biocarbons NH3-HTC and FA-HTC, had copper (II) ion adsorption capacities of 182 mg/g and 265 mg/g over a 60 min period and approached 90 % saturation within 15 min. Adsorption isotherms of NH3-HTC could be described by the Freundlich model (R2> 0.95) and thermodynamic parameters of NH3-HTC showed that copper (II) adsorption was mainly physical adsorption. X-ray photo-electron spectroscopy (XPS) and Fourier transform infrared (FT-IR) spectroscopy of biocarbon adsorbents revealed that both amino groups and oxygen groups of the biocarbon adsorbent are involved in the copper (II) ion adsorption mechanism. Biocarbon adsorbents could be regenerated with 0.1 M nitric acid, 0.1 M organic acids (oxalic, citric), or CO2 bubbling. Amino-functional biocarbons are simple to prepare from biomass-derived compounds, they have high affinity for metal ions and they can be regenerated with environmentally-safe methods.

Adsorption of radioactive strontium by pristine and magnetic biochars derived from spent coffee grounds

This study rigorously investigated the adsorption behaviors and mechanisms of strontium ions (Sr2+) by the pristine and magnetic biochars prepared via the pyrolysis of pristine and FeCl3-pretreated spent coffee grounds (SCG). The FeCl3-pretreatment could magnetize successfully the pristine SCG biochars (magnetization value of pristine SCG biochars = 0.19 emu/g; magnetization value of magnetic SCG biochars = 8.99 emu/g) and improved substantially their specific surface area (pristine SCG biochars = 5.3 m2/g; magnetic SCG biochars = 431.7 m2/g) and total pore volume (pristine SCG biochars = 0.002 cm3/g; magnetic SCG biochars = 0.186 cm3/g). However, the removal efficiency of Sr2+ with the pristine SCG biochars (33.4–34.1%) was not significantly different from that with the magnetic SCG biochars (33.1–33.9%). The calculated kinetic parameters indicate that the adsorption of Sr2+ by the pristine and magnetic SCG biochars was governed by the chemisorption (R2 of the pseudo-first-order kinetic equation ≤ 0.602; R2 of the pseudo-second-order kinetic equation = 1.000). The higher R2 values of the Langmuir isotherm (R2 = 0.999) model compared to the Freundlich isotherm model (R2 ≤ 0.950) are evident that the monolayer adsorption mainly determined the adsorptive removal of Sr2+ with the pristine and magnetic SCG biochars. Moreover, the adsorption of Sr2+ using the pristine and magnetic SCG biochars was the spontaneous and endothermic process. These observations indicate that the FeCl3-pretreatment might offer a viable way to effectively recover the residual SCG biochars after the Sr2+ adsorption through the magnetic separation (recovery rate = 90%).

A composite adsorbent of ZnS nanoclusters grown in zeolite NaA synthesized from fly ash with a high mercury ion removal efficiency in solution

In this study, the nanocomposite adsorbent (ZnS-zeolite NaA) was prepared by a simple ion-exchange method, which modified the zeolite NaA synthesized from fly ash. The removal efficiency, adsorption mechanism of mercury ions by ZnS-zeolite NaA and release of zinc ion into aqueous solution during the adsorption process were determined. The results showed that ZnS nanoclusters were introduced the supercages of zeolite by ion exchange to synthesize the ZnS-zeolite NaA with high removal capacity for Hg2+ in the initial pH 2–7 of solution. Determination of the adsorption kinetics and thermodynamic parameters, in combination with X-ray diffraction, X-ray photoelectron spectroscopy and transmission electron microscopy analyses, revealed that the Hg2+ adsorption by ZnS-zeolite NaA was Hg2+ complexed and ion exchanged with ZnS in the ZnS-zeolite NaA to form stable HgS, and then, the released Zn2+ was adsorbed by the zeolite, preventing Zn2+ pollution. The Hg2+ removal rate was greater than 99.90% with the coexistence of either Zn2+ or Cu2+, Cd2+ and Pb2+. After five repetitions, the Hg2+ removal rate by the ZnS-zeolite NaA was only slightly decreased by 2%. Therefore, ZnS-zeolite NaA synthesized using fly ash has potential for broad application as a Hg2+ adsorbent.

Adsorption process and mechanism of heavy metal ions by different components of cells, using yeast (Pichia pastoris) and Cu2+ as biosorption models.

Microbial biomass has been recognized as an essential biosorbent to remove heavy metal ions, but the biosorption process and mechanism of different components of microbial cells have not been elucidated. In present study, Pichia pastoris X33 and Cu2+ was used as a biosorption model to reveal the biosorption process and mechanism of different components of microbial cells. For the biosorption of whole cells, the maximum removal efficiency was 41.1%, and the adsorption capacity was 6.2 mg g−1. TEM-EDX analysis proved the existence of Cu2+ on the cell surface and cytoplasm. The maximum Cu2+ removal efficiency of the cell wall, cell membrane and cytoplasm were 21.2%, 20.7% and 18.5%, respectively. The optimum pH of Cu2+ biosorption of the P. pastoris cell, cell wall, cell membrane and cytoplasm was 6. Moreover, the maximum adsorption capacity of the cell, cell wall, cell membrane and cytoplasm was 16.13, 11.53, 10.97 and 8.87 mg g−1, respectively. The maximum removal efficiencies of P. pastoris biomass treated with proteinase K and P. pastoris biomass treated with β-mannanase were 18.1% and 28.2%, respectively. The maximum removal efficiencies of mannan and glucan were 34% and 12%, respectively. The FTIR spectra showed that the amino group (N–H), hydroxyl (O–H), carbon oxygen bond (C–O), –CH, C–N and carbonyl group (C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> O) of a ketone or aldehyde may interact with Cu2+. Thus, our work provides guidance for further understanding the effect of different cell components on biosorption.

Qualitative and quantitative adsorption mechanisms of zinc ions from aqueous solutions onto dead carp derived biochar.

The objective of this study is to investigate the qualitative mechanisms of Zn2+ adsorption on carp biochars (CMBx) produced from dead carp at different temperatures (450–650 °C) and their quantitative contribution. The pseudo second order kinetic model and the Langmuir model could fit the kinetic and isothermal adsorption data well, respectively. The intra-particle diffusion was the main rate-limiting step but not the only rate-limiting step. The maximum adsorption capacity obtained from the Langmuir model for CMB650 was 87.7 mg g−1 which was greater than those of other biochars. Precipitation with minerals, ion exchange, and complexation with functional groups (OFGs) were the main adsorption mechanisms. Quantum chemistry calculations confirmed that the functional groups (e.g., hydroxyl, carboxyl and C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> C) tended to bind with Zn2+ more strongly than with Ca2+ and Mg2+, because the structure of the complex formed by the former was more stable. The contribution of different adsorption mechanisms varied with the pyrolysis temperature to prepare biochar. With increasing pyrolysis temperature, the contribution of the interaction between Zn2+ and the minerals increased from 46.4% to 84.7%, while that of complexation with OFGs decreased from 41.7% to 4.7%. Overall, the mechanism of Zn2+ adsorption on CMB450 was dominated by complexation with OFGs and exchange with cations (accounting for 73.2%), while the mechanisms on CMB650 were dominated by the interaction with minerals. In view of the total adsorption capacity, 650 °C was the optimized pyrolysis temperature for CMBx preparation and adsorption treatment of Zn-contaminated water. These results are useful for screening effective biochars as engineered sorbents to treat Zn-containing wastewater.

Mechanism of Chloride Ion Adsorption in Cement Hydrates as per Time-Dependent Behavior

Mechanism of Chloride Ion Adsorption in Cement Hydrates as per Time-Dependent Behavior

Improved Adsorption and Migration of Divalent Ions Over C4N Nanosheets: Potential Anode for Divalent Batteries

Divalent ion batteries are potential substitutes to existing rechargeable batteries because of the high-energy density, safety, and low cost. However, the applications of divalent batteries are strongly dependent on the availability of efficient electrode materials. We herein report the adsorption and migration mechanism of divalent ions like Mg+2 and Ca+2, on two-dimensional carbon nitride monolayer (C4N). The adsorption of both Mg and Ca ions are much stronegr on C4N saturated with functional groups like hydrogen (-H), hydroxyl (-OH), and carboxylic (-COOH) as compared to the pristine monolayers, which implies the improvement in metal storage caused by the functional groups. On functionalized C4N, the first Mg binds within the binding energy range of 1.5-2.2 eV having migration barrier, at the saturated sites, of around 0.5 eV, which indicates desirable binding and robust diffuse. However, the functional groups tend to act as the trapping sites for Ca ions and the diffusion might get hindered as compared to Mg ions. In addition to binding and diffusion mechanism, charge transfer, electronic structures and open circuit volatges have also been calculated for both Mg and Ca on pristine and functionalized C4N monolayers. We find that -H, -OH, and -COOH play important role for the cyclic performance of C4N as the prospective anode material for divalent ion batteries.

Synthesis of novel Mg–Al–Fe-type hydrotalcite with various Mg/Al/Fe ratios and its selective adsorption of As(V) from water

Arsenic is present both in groundwater and wastewater, and arsenic-contaminated water causes environmental pollution and serious health disorders, even at exposure to very low concentrations. Therefore, adsorption methods are attracting interest owing to their simple operation and low cost. It is crucial to develop inexpensive and effective adsorption technologies for removing As(V) from aqueous solutions. In this study, we synthesized novel Mg/Al/Fe (MAF) hydrotalcites at various ratios and evaluated the characteristics of MAF and As(V) ion adsorption capability. Physicochemical properties of MAF were characterized using X-ray diffraction, scanning electron microscopy, or fluoride ion adsorption method, whereas surface binding energy of MAF was measured using an XPS (spectroscopy system by X-ray photoelectron). Adsorption capabilities of MAF were evaluated by examining the effects of various metal adsorbate solution, multiple mixed adsorbate solution, solution pH, and treatment time, and assaying the Langmuir-adsorption and kinetics. MAF had high As(V) adsorption capacity; the amount of As(V) adsorption on MAF-2 was greater than other adsorbents, with selective As(V) adsorption capacity in multiple component solutions. Adsorption isotherm data were fitted using Freundlich and Langmuir models and adsorption dynamics were described by a pseudo-second-order model. A positive linear relationship was observed between the chloride ion eluted from MAF-2 and amount of As(V) ion adsorbed using MAF-2 (r ≥ 0.96). This indicates that the As(V) ion adsorption mechanism involves electrostatic attraction, surface inner-sphere complex formation, and ion exchange between As(V) and hydroxide ions, suggesting that in multiple metal ion mixed liquid phase, MAF-2 is useful for selective and effective adsorption of As(V) ion from arsenic polluted waters.

Adsorption Mechanism and Structure-Performance Relationship of Chromium Ions by Biochar

In order to further explore the adsorption mechanism of chromium ion by biochar, organic components (OCs) and inorganic components (ICs) of biochar (RC) were prepared, and adsorption experiments of chromium ions by these types of carbon (RC, OC, IC) were performed. The three types of carbon were characterized before and after adsorption of chromium ions, using Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), Boehm titration, and zero charge (pHpzc). Results showed that the adsorption efficiency of IC on trivalent chromium (Cr3+) was the strongest, ion exchange of Cr3+ with metal cations present on IC being the main adsorption mechanism, accounting for 61% of the total adsorption capacity. Among the metal ions, K+ accounted for about 51%. The REDOX between Cr3+ and carboxyl accounted for 20% of the total adsorption capacity. Other adsorption mechanisms, such as chelation between Cr3+ and carboxyl, and co-precipitation between Cr3+ and carbonate, occupied a small proportion. OC showed the largest adsorption capacity to hexavalent chromium (Cr6+). The adsorption mechanism of OC to Cr6+ was the result of combined actions, such as electrostatic attraction, and REDOX between Cr6+ with the aromatic π-conjugated system and reductive functional groups like hydroxyl. Among them, the REDOX accounted for 53% of the total adsorption of Cr6+ by OC.

Rapid removal of uranium(Ⅵ) using functionalized luffa rattan biochar from aqueous solution

Due to its reliable performance and low manufacturing cost, biochar has gradually attracted attention in the treatment of uranium-containing wastewater. Herein, Luffa rattan (LR), a biowaste material, was used to synthesize functional biochar (F-LRBC) to adsorb U(VI) from aqueous solutions for the first time. The effect of solution pH, contact time and initial concentration of uranyl ions on uranium(Ⅵ) adsorption by F-LRBC was evaluated. FT-IR and SEM analysis confirmed that there are abundant oxygen-containing functional groups and pores on the surface of F-LRBC. Experiments demonstrated that the adsorption behavior of uranium(Ⅵ) by F-LRBC is spontaneous and efficient. The maximum adsorption capacity of F-LRBC for uranyl ions predicted by the Langmuir model was higher than that of most biochar adsorbent. The adsorption mechanism of uranyl ions on F-LRBC is complicated, including electrostatic interaction, complexation and physical adsorption.

Graphene oxide aerogel assembled by dimethylaminopropylamine /N-isopropylethylenediamine for the removal of copper ions

Graphene Oxide Monolith composites (GOMs) were prepared using dimethylaminopropylamine (DMPDA) and N-isopropylethylenediamine (IPEDA) with one-step method in water medium, respectively. Fourier transform-infrared (FTIR), X-Ray Diffraction (XRD) tests proved the formation of new structure and credible interactions between crosslinkers and GO. Scanning electron microscopy (SEM) showed distinct change of morphology after complexing. Bath adsorption tests suggested that the fast adsorption of copper ions (II) was strongly affected by pH, ionic strength, temperature, and concentration, etc.. Isothermal Langmuir and Freundlich kinetic model showed the different degree of fitting conformity according to different conditions. SEM and XRD further provided a supporter of adsorption of copper ions onto GOMs, and Density functional theory (DFT) was used to analyze the crosslinking details of DMPDA and GO and the adsorption mechanism of copper ions. The theoretical calculation results clarified an efficacious and quantitative understanding for the crosslinking and adsorption mechanism.

Comparison of Pb(II) and Cd(II) micro-interfacial adsorption on fine sediment in the Pearl River Basin, China

The complex micro-interfacial interaction theories of heavy metal ions such as Pb(II) and Cd(II) adsorption on fine sediment in aqueous solution were not systematically investigated. The aim of this work was to reflect the micro-interfacial adsorption characteristics. Sediment samples were collected from an estuary. The Isothermal and kinetics adsorption experiment were done to acquire the data. Isothermal, kinetics, film diffusion and intraparticle diffusion models were adopted to fit the adsorption experimental data. The results indicated that the Langmuir, Freundlich and Temkin models were suitable for analyzing the isothermal experimental data. The maximum adsorption capacities of Pb(II) and Cd(II) on the sediment were 1.1377 and 0.9821 mg·g−1, respectively. The qm and KL of the Langmuir model, Kf and nF of the Freundlich model, and b and A of the Temkin model all exhibited a power function relationship with the initial adsorbate concentration. The pseudo-second-order model provided a better fit for the experimental kinetics data compared with the fit of the pseudo-first-order and Elovich models. The pseudo-second-order parameters k2 and qe of Pb(II) and qe of Cd(II) both had a power function relationship with adsorption time, additionally, the k2 of Cd(II) had an exponential function relationship with adsorption time. The liquid-film diffusion parameters kfd of Pb(II) and Cd(II) were 0.0569 and 0.1806 min−1, respectively. The intraparticle diffusion parameter kid values of Pb(II) and Cd(II) were 0.0055 mg·g−1·min1/2 and 0.0049 mg·g−1·min1/2, respectively. The physical significance of the model parameters showed that Pb(II) adsorption on sediment was stronger than Cd(II). The results of this study provided a theoretical reference for the micro-interfacial mechanism of heavy metal ion adsorption on sediment.

Adsorption mechanism of toxic heavy metal ions on oxygen-passivated nanopores in graphene nanoflakes

In this work, using density functional theory, we investigate the adsorption process of toxic metal ions (Hg2+, Cd2+, and Pb2+) on graphene nanoflakes (GNF) comprised of various sized oxygen-passivated nanopores to gain molecular insights into the ability of such surfaces in effectively removing the metal ions from contaminated environments. Thermodynamically, the adsorption of these ions on the oxygen-passivated nanopores is shown to be more energetically favorable than that on the pristine surface. The dispersion corrected adsorption energy calculations indicate Hg2+ ion to have the highest and Pb2+ ion the lowest affinities for interaction with such surfaces (Hg2+ > Cd2+ > Pb2+). The highest adsorption of Hg2+ and Cd2+ ions on the surfaces is seen in the 12-crown-3…Hg2+ (− 382.9 kcal/mol) and 12-crown-3…Cd2+ (− 314.7 kcal/mol) complexes, while Pb2+ ion shows the highest adsorption energy for the 18-crown-6 surface (− 195.0 kcal/mol). Noncovalent interaction plots, Hirshfeld charge analysis and energy decomposition analysis conclude that the role of charge transfer in formation of surface…ion complexes is more important than noncovalent interactions and therefore plays a key role in the adsorption of these ions on the surfaces. The magnitude of charge transfer in the complexes follows the order: surface…Hg2+ > surface…Cd2+ > surface…Pb2+, which is consistent with the adsorption energetic order of these metal ions on the surfaces. We also found that Pb2+ ion is mainly adsorbed on the surfaces via electrostatic interactions, while Hg2+ and Cd2+ ions are adsorbed through van der Waals (vdW) interactions. This could be attributed to the presence of vacant p orbitals on Pb2+ ion, which interact with the π bonds on the GNF and oxygen atoms in the nanopores through electrostatic interactions. No such vacant orbitals are available for Hg2+ and Cd2+ ions thus resulting in such ions adsorbing via vdW interactions. The contribution of ΔEorb, induction energy component of total energy, for the surface…Hg2+ complexes is more than that for the surface…Cd2+ and surface…Pb2+ complexes, following the order: surface…Hg2+ > surface…Cd2+ > surface…Pb2+ again, consistent with the calculated adsorption energy order suggesting that charge transfer indeed plays a major role in formation of such surface…ion complexes. Finally, time-dependent density functional theory calculations show that the absorption spectra of the surfaces undergo significant changes, including peak shifts, peak quenching and appearance of new peaks, upon interaction with Hg2+, Cd2+, and Pb2+ ions, such changes being consistent with binding energetics rank order of ions on these surfaces. These complexes would have potential applications in near-infra-red photonics in addition to their service of effectively remediating of toxic heavy elements from contaminated environments.

Sorption and mechanism studies of Cu2+, Sr2+ and Pb2+ ions on mesoporous aluminosilicates/zeolite composite sorbents.

The research aimed to develop a novel mesoporous aluminosilicate/zeolite composite by the template co-precipitation method. The effect of aluminosilicate (AlSi) and zeolite (NaY) on the basic properties and adsorption capacity of the resultant composite was conducted at different mass ratios of AlSi/NaY (i.e., 5/90, 10/80, 15/85, 20/80, and 50/50). The adsorption characteristics of such composite and its feedstock materials (i.e., aluminosilicates and zeolite) towards radioactive Sr2+ ions and toxic metals (Cu2+ and Pb2+ ions) in aqueous solutions were investigated. Results indicated that BET surface area (SBET), total pore volume (VTotal), and mesopore volume (VMeso) of prepared materials followed the decreasing order: aluminosilicate (890 m2/g, 0.680 cm3/g, and 0.644 cm3/g) > zeolite (623 m2/g, 0.352 cm3/g, and 0.111 cm3/g) > AlSi/NaY (20/80) composite (370 m2/g, 0.254 cm3/g, and 0.154 cm3/g, respectively). The Langmuir maximum adsorption capacity (Qm) of metal ions (Sr2+, Cu2+, and Pb2+) in single-component solution was 260 mg/g, 220 mg/g, and 161 mg/g (for zeolite), 153 mg/g, 37.9 mg/g, and 66.5 mg/g (for aluminosilicate), and 186 mg/g, 140 mg/g, and 77.8 mg/g for (AlSi/NaY (20/80) composite), respectively. Ion exchange was regarded as a domain adsorption mechanism of metal ions in solution by zeolite; meanwhile, inner-surface complexation was domain one for aluminosilicate. Ion exchange and inner-surface complexation might be mainly responsible for adsorbing metal ions onto the AlSi/NaY composite. Pore-filling mechanism was a less important contributor during the adsorption process. The results of competitive adsorption under binary-components (Cu2+ and Sr2+) and ternary-components (Cu2+, Pb2+, and Sr2) demonstrated that the removal efficacy of target metals by the aluminosilicate, zeolite, and their composite remarkably decreased. The synthesized AlSi/NaY composite might serve as a promising adsorbent for real water treatment.

Removal of fluoride using magnesium and iron complex hydroxides

Abstract In this study, metal complex hydroxide materials containing magnesium to iron in molar ratios of 3:1 and 5:1, referred to in this study as Mg-Fe-CH3.0 and Mg-Fe-CH5.0, respectively, were prepared, and their adsorption capability with respect to fluoride ions was investigated. The physicochemical characteristics of adsorbents were determined using scanning electron microscopy and X-ray diffraction, and specific surface area and the number of hydroxyl groups were calculated. The adsorption behaviors and mechanism of fluoride ions were assessed. The adsorption capability of fluoride ions using Mg-Fe-CH3.0 was greater than that using Mg-Fe-CH5.0. In addition, the amount adsorbed depended on the adsorption temperatures; the adsorption was comparatively less at 5 °C than at 25 °C. Adsorption mechanism of fluoride ions was evaluated by elemental distribution analysis and binding energy. The binding energy of fluorine onto Mg-Fe-CH3.0 and Mg-Fe-CH5.0 could be detected after adsorption. Additionally, it was clear that one of the adsorption mechanisms was related to the ion exchange between fluoride ions and chloride ions in the interlayer space of the Mg-Fe-CH3.0 and Mg-Fe-CH5.0 (correlation coefficient 0.923–0.965). This study illustrates that both Mg-Fe-CH3.0 and Mg-Fe-CH5.0 have a high potential for fluoride ion adsorption from the aqueous phase.