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Gang Yang - One of the best experts on this subject based on the ideXlab platform.

  • Charge reversal and anion effects during Adsorption of Metal ions at clay surfaces: Mechanistic aspects and influence factors
    Chemical Physics, 2020
    Co-Authors: Xiaoxiao Huang, Gang Yang
    Abstract:

    Abstract Charge reversal occurs frequently during Adsorption of Metal ions at clay surfaces, and recent experimental studies manifest the strong anion specificities during Adsorption of Metal ions at clay surfaces. Herein, mechanisms and influence factors of charge reversal and anion specificities have been addressed by DFT calculations. Charge reversal is attributed to the intrinsic electrostatic interactions from clay surfaces, which become more depleted at higher surface charges due to existence of more counterions. The tendency of charge reversal is negatively correlated with the amount of surface charges. Charge reversal can be caused by all Metal ions while has a limited degree, even for high-valent Metal ions. Anions take effects by forming ionic bonds with charge-balancing Metal ions instead of forming direct interactions with clay surfaces, and the experimental observations are finely interpreted, such as anion specificities (Cl−

  • Adsorption of Metal ions at kaolinite surfaces: Ion-specific effects, and impacts of charge source and hydroxide formation
    Applied Clay Science, 2020
    Co-Authors: Xiaoxiao Huang, Qian Wang, Gang Yang
    Abstract:

    Abstract Adsorption of Metal ions at clay surfaces plays a critical role in a variety of geochemical, environmental and engineered processes, and p-DFT calculations with dispersion corrections were employed with aim to comprehensively understand the Adsorption of Metal ions at hydrated kaolinite surfaces, considering both (00 1 ¯ ) and (001) surfaces and different Metal ions (Mn+ = Li+, Na+, K+, Mg2+, Ca2+, Al3+, Fe3+). Ion-specific effects resulting from Adsorption also became the focus of this study. For Adsorption of alkali ions, inner-sphere complexes dominated for (00 1 ¯ ) surface while owing to hydroxide formation, outer-sphere complexes dominated for (001) surface. Both charge sources and surface structures can significantly alter Adsorption structures and their relative stabilities, and surface structures can further perturb ion-specific sequences. Hydroxide formation at (00 1 ¯ ) surface was favored for Metal ions (Mn+) of higher oxidation states: Non-existent for M+, geometrically stable but disfavored for M2+ while dominant for M3+. Al3+ Adsorption was likely to form AlOH2+, Al(OH)2+ and Al(OH)3 and released more H+ than base cations, which further caused soil acidification. Hydroxide formation affected significantly the extents of ion-specific effects and may further alter their sequences. Results were also helpful to rationalize and guide experimental studies.

  • Competitive Adsorption of Metal Ions at Smectite/Water Interfaces: Mechanistic Aspects, and Impacts of Co-Ions, Charge Densities, and Charge Locations
    The Journal of Physical Chemistry, 2019
    Co-Authors: Sen Yang, Xiantang Liu, Gang Yang
    Abstract:

    In natural environments, multiple Metal ions are concomitant, and their Adsorption at clay mineral/water interfaces is competitive and selective. In this study, the competitive mechanisms and impacts of co-ions for binary electrolyte solutions contacting smectite surfaces are probed by molecular dynamics simulations. Different binary Metal ions (Na⁺/Cs⁺, K⁺/Cs⁺ of 1:1 type, Na⁺/Pb²⁺ of 1:2 type, and Pb²⁺/Ca²⁺ of 2:2 type) are considered, and impacts of charge densities and locations that are critical to ion Adsorption are also subject to investigations. Impacts of charge densities and locations onto Adsorption of Metal ions are similar in single and binary systems, and increase of charge densities and shift of charge locations from octahedral to tetrahedral sheets may change the major surface complexes from the outer sphere to the inner sphere and greatly enhance the amounts and stabilities, with the enhancement degrees being Pb²⁺, Ca²⁺ > Na⁺ > K⁺ > Cs⁺. The major surface complexes of Metal ions can be changed by charge densities and locations and are more affected by co-ions than the minor surface complexes. Stronger competition and higher Adsorption selectivity occur (1) at higher charge densities; (2) for beidellite than montmorillonite; and (3) for the inner sphere than the outer sphere. As discussed, all binary systems show peculiarities regarding competition and Adsorption selectivity, and the competition capabilities and Adsorption selectivities may vary with charge densities and locations. These findings are consistent with experimental observations available and provide insights to unravel the complicated Adsorption mechanisms at clay mineral/water interfaces and to manage contaminated soil sites.

  • Electric fields within clay materials: How to affect the Adsorption of Metal ions
    Journal of colloid and interface science, 2017
    Co-Authors: Gang Yang
    Abstract:

    Abstract Electric fields exist ubiquitously in chemical and biological systems while how to affect the interfacial Adsorption processes remain elusive. Here, molecular dynamics simulations are used to understand at a molecular level the Adsorption of Metal ions at the interface of aqueous solutions and clay materials that are generally endowed with strong electric fields. In absence of electric fields, even Cs+, one of the strongest adsorbed Metal ions, is facile to detach from solvated clay surfaces. Electric fields are critical to construct stable inner-sphere complexes and enhance pronouncedly the Adsorption strengths of both inner- and outer-sphere complexes. Heavy Metal ions such as Pb2+ that are exclusively outer-sphere adsorbed are driven inner-sphere by electric fields, causing the Adsorption strengths to surpass Cs+ and explaining partially the serious pollution to clay systems. Adsorption quantities of inner-sphere alkali ions increase with electric fields and in the case of Pb2+, are closely correlated with the intensities of electric fields. Previous models fail to account for Hofmeister effects occurring at solvated clay surfaces, and forceful supports are given to polarization effects that correctly interpret Hofmeister series (Cs+ > Na+) and respond towards the change of electric fields.

  • Promoting the Adsorption of Metal Ions on Kaolinite by Defect Sites: A Molecular Dynamics Study
    Scientific reports, 2015
    Co-Authors: Gang Yang
    Abstract:

    Defect sites exist abundantly in minerals and play a crucial role for a variety of important processes. Here molecular dynamics simulations are used to comprehensively investigate the Adsorption behaviors, stabilities and mechanisms of Metal ions on defective minerals, considering different ionic concentrations, defect sizes and contents. Outer-sphere adsorbed Pb(2+) ions predominate for all models (regular and defective), while inner-sphere Na(+) ions, which exist sporadically only at concentrated solutions for regular models, govern the Adsorption for all defective models. Adsorption quantities and stabilities of Metal ions on kaolinite are fundamentally promoted by defect sites, thus explaining the experimental observations. Defect sites improve the stabilities of both inner- and outer-sphere Adsorption, and (quasi) inner-sphere Pb(2+) ions emerge only at defect sites that reinforce the interactions. Adsorption configurations are greatly altered by defect sites but respond weakly by changing defect sizes or contents. Both Adsorption quantities and stabilities are enhanced by increasing defect sizes or contents, while ionic concentrations mainly affect Adsorption quantities. We also find that Adsorption of Metal ions and anions can be promoted by each other and proceeds in a collaborative mechanism. Results thus obtained are beneficial to comprehend related processes for all types of minerals.

Tae Yoon Eom - One of the best experts on this subject based on the ideXlab platform.

  • Hydrophobic Effects of o-Phenanthroline and 2,2′-Bipyridine on Adsorption of Metal(II) Ions onto Silica Gel Surface
    Journal of Colloid and Interface Science, 1993
    Co-Authors: Yeong Jae Park, Kyung-hoon Jung, Kyoung Kyun Park, Tae Yoon Eom
    Abstract:

    Abstract The effects of o-phenanthroline and 2,2′-bipyridine on the Adsorption of Metal(II) (Fe, Co, Ni and Cu) ions onto silica gel surface have been studied. The Adsorption is expressed in terms of the measured concentrations of both Metal and ligand at equilibrium. Each Adsorption of the four Metal ions is increased with the presence of the ligands. In addition, Adsorption increases slowly with pH at low pH values and then increases rapidly up to near the pKa value of silica gel (≈6.5). The Adsorption of each Metal ion at low pH is increased with increased ligand concentration. However, at high pH the Adsorptions of Fe(II) and Cu(II) are decreased with increased ligand concentration whereas the Adsorptions of Co(II) and Ni(II) are always increased. At low pH values the ligand to Metal ratio adsorbed on the silica gel surface is ca. 3:1 while at high pH values it is 1:1, 2:1, and 3:1, corresponding to the initial ligand to Metal ion concentration ratio. The addition of ethanol to the phenanthroline-SiO2 solution results in a decrease in the Adsorption of phenanthroline. The effect of ethanol is also observed in the Fe(II)-phenanthroline-SiO2 system. The behavior of the Adsorption is interpreted qualitatively by hydrophobic expulsion, the formation of surface complexes, and electrostatic interaction. It is concluded that hydrophobic expulsion plays an important role in the Adsorption of Metal ions in the presence of hydrophobic ligands on silica gel surface.

Clas Persson - One of the best experts on this subject based on the ideXlab platform.

  • Adsorption of Metal adatoms on single layer phosphorene
    Physical Chemistry Chemical Physics, 2015
    Co-Authors: Vadym V Kulish, Oleksandr I Malyi, Clas Persson
    Abstract:

    Single- or few-layer phosphorene is a novel two-dimensional direct-bandgap nanomaterial. Based on first-principles calculations, we present a systematic study on the binding energy, geometry, magnetic moment and electronic structure of 20 different adatoms adsorbed on phosphorene. The adatoms cover a wide range of valences, including s and p valence Metals, 3d transition Metals, noble Metals, semiconductors, hydrogen and oxygen. We find that adsorbed adatoms produce a rich diversity of structural, electronic and magnetic properties. Our work demonstrates that phosphorene forms strong bonds with all studied adatoms while still preserving its structural integrity. The Adsorption energies of adatoms on phosphorene are more than twice higher than on graphene, while the largest distortions of phosphorene are only ∼0.1–0.2 A. The charge carrier type in phosphorene can be widely tuned by adatom Adsorption. The unique combination of high reactivity with good structural stability is very promising for potential applications of phosphorene.

Hiroyuki Yoshida - One of the best experts on this subject based on the ideXlab platform.

  • Adsorption of Metal ions on polyaminated highly porous chitosan chelating resin
    Industrial & Engineering Chemistry Research, 1993
    Co-Authors: Yoshihide Kawamura, Masaki Mitsuhashi, Hiroaki Tanibe, Hiroyuki Yoshida
    Abstract:

    Highly porous chelating resin was fabricated from the natural polysaccharide chitosan. The Adsorption capacity was increased by polyamination with poly(ethylene imine) (MW = 10,000). The capacity was about 1-2 times larger than that of commercial chelate resins. The selectivity for Adsorption of Metal ions on the resin, which was determined for a single solute at pH [approx equal] 7, was Hg(II) > UO[sub 2](II) > Cd(II) > Zn(II) > Cu(II) > Ni(II). Mg(II), Ca(II), Ga(III), As(III), and Sr(II) were not adsorbed on the resin at all. The selectivity depended on the pH of each Metal solution. The equilibrium isotherms for Adsorption of HgCl[sub 2] were correlated by the Langmuir equation. The saturation capacities were close to the concentration of amino group fixed on the resin. When HCl or NaCl coexisted in HgCl[sub 2] solution and their concentrations were lower than 100 mol/m[sup 3], the saturation capacity of HgCl[sub 2] was little affected by them. When 500 mol/m[sup 3] H[sub 2]SO[sub 4] coexisted in HgCl[sub 2] solution, extremely low pH inhibited the Adsorption of Hg(II) at all.

Alzira Maria Serpa Lucho - One of the best experts on this subject based on the ideXlab platform.

  • Diethylenetriamine ion-imprinted silica gel for copper determination in tap water
    Journal of Applied Electrochemistry, 2018
    Co-Authors: Paulo Cesar Mendes Villis, Yoshitaka Gushikem, José Costa Sampaio Filho, Wolia Costa Gomes, Rita De Cassia Mendonça Miranda, Gilvanda Silva Nunes, Fábio Luiz Pissetti, Alzira Maria Serpa Lucho
    Abstract:

    This paper proposes the preparation of a hybrid adsorbent material organically modified with N 1-[3-(trimethoxysilyl)propyl]diethylenetriamine and imprinted ionically with Cu(II) ions. The structure of functionalized silica matrix with an organic group containing electron-donating nitrogen atoms allows several applications such as Adsorption of Metal ions, electrocatalytic studies, and development of electrochemical sensors. The electrochemical behavior of the hybrid material was investigated using a carbon paste electrode in different electrochemical techniques: cyclic voltammetry, differential pulse voltammetry, differential pulse anodic stripping voltammetry, and chronoamperometry. DPASV yielded the best results and linear response to Cu(II) in the concentration range of 6.0 × 10^−4 to 5.4 × 10^−3 mmol L^−1 ( R ^2 = 0.999; n  = 9) using a pre-concentration time ( t _pc) of 1800 s at a reduction potential ( E _red) of − 0.51 V versus SCE and a scan rate of 20 mV s^−1, with a detection limit estimated at 1.82 × 10^−7 mmol L^−1. The samples were evaluated using the proposed sensor and a good recovery of Cu(II) was obtained in the range from 92.88 to 110.89%. The proposed method for DPASV was used for Cu(II) determination in samples of tap water, and the results from literature and that of flame atomic absorption spectrometry. Graphical Abstract