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Xiangke Wang - One of the best experts on this subject based on the ideXlab platform.

  • direct synthesis of bacteria derived carbonaceous nanofibers as a highly efficient material for radionuclides elimination
    ACS Sustainable Chemistry & Engineering, 2016
    Co-Authors: Xiangxue Wang, Changlun Chen, Congcong Ding, Wencai Cheng, Tasawar Hayat, Ahmed Alsaedi, Jun Hu, Xiangke Wang
    Abstract:

    Bacteria-derived carbonaceous nanofibers (CNFs) can be directly synthesized by the pyrolysis of bacterial cellulose pellicles under N2 atmosphere. The batch adsorption experiments showed that the bacteria-derived CNFs displayed the excellent adsorption performance for radionuclides. The maximum adsorption capacities of the CNFs calculated from the Langmuir model at pH 4.5 and 293 K were 67.11 mg/g for Sr(II) and 57.47 mg/g for Cs(I). The adsorption of Cs(I) and Sr(II) on the CNFs decreased with increasing ionic strength at pH 6.0, indicating that the outer-sphere surface complexation dominated the radionuclide adsorption at pH 6.0. The further evidence of surface complexation modeling indicated that Sr(II) and Cs(I) adsorption on the CNFs can be satisfactorily fitted by a double Diffuse Layer model with an outer-sphere (SOHSr2+/SOHCs+) and an inner-sphere...

  • effect of humic acid fulvic acid ph ionic strength and temperature on 63ni ii sorption to mno2
    Radiochimica Acta, 2010
    Co-Authors: Guodong Sheng, Yixue Chen, Han Jing, Shitong Yang, Xuemei Ren, Xiangke Wang
    Abstract:

    The effects of pH, ionic strength, temperature, humic acid (HA) and fulvic acid (FA) on the sorption of radionuclide 63 Ni(II) to MnO 2 have been investigated by using batch techniques. The results indicated that the sorption of 63 Ni(II) on MnO 2 is obviously dependent on pH values but independent of ionic strength. The presence of HA/FA strongly enhances the sorption of 63 Ni(II) on MnO 2 at low pH values, whereas reduces 63 Ni(II) sorption at high pH values. The sorption of 63 Ni(II) on MnO 2 is attributed to inner-sphere surface complexation rather than outer-sphere surface complexation or ion exchange. The Diffuse Layer model (DLM) is used to simulate the experimental data well with the aid of FITEQL 3.2. The thermodynamic parameters (ΔH 0 , ΔS 0 , ΔG 0 ) are also calculated from the temperature dependent sorption isotherms, and the results suggest that the sorption of 63 Ni(II) on MnO 2 is a spontaneous and endothermic process.

  • adsorption of sr ii and eu iii on na rectorite effect of ph ionic strength concentration and modelling
    Radiochimica Acta, 2010
    Co-Authors: Changlun Chen, Guodong Sheng, Yixue Chen, Xiangke Wang
    Abstract:

    The surface charge characteristics of Na-rectorite (NaAl 4 [Si,bAl] 8 O 20 (OH) 4 ·nH 2 O) were studied by potentiometric acid-base titrations. Sr(II) and Eu(III) adsorptions on Na-rectorite as a function of pH, ionic strength, and Sr(II)/Eu(III) concentrations were carried out to investigate the surface interactions between Sr(II)/Eu(III) with Na-rectorite. The results indicated that the adsorptions of Sr(II) and Eu(III) on Na-rectorite increased with increasing pH and decreased with increasing ionic strength and initial Sr(II)/Eu(III) concentrations, and that the affinity of Na-rectorite for Eu(III) was much higher than for Sr(II). The experimental data of Sr(II)/Eu(III) adsorption were simulated by the Diffuse-Layer model (DLM) well with the aid of FTTEQL 3.2. Simultaneous adsorptions of Sr(II) and Eu(III) on Na-rectorite were also modeled using the DLM. The adsorption mechanisms of Sr(II) and Eu(III) on Na-rectorite may be dominated by ion exchange interaction at low pH or moderate pH, and by surface complexation interaction at high pH.

  • adsorption of eu iii onto tio2 effect of ph concentration ionic strength and soil fulvic acid
    Journal of Hazardous Materials, 2009
    Co-Authors: Xiangke Wang, Xiaoli Tan, Ming Fang
    Abstract:

    The effects of pH, initial Eu(III) concentration, ionic strength and fulvic acid (FA) on the adsorption of Eu(III) on TiO2 are investigated by using batch techniques. The results indicate that the presence of FA strongly enhances the adsorption of Eu(III) on TiO2 at low pH values. Besides, the adsorption of Eu(III) on TiO2 is significantly dependent on pH values and independent of ionic strength. The adsorption of Eu(III) on TiO2 is attributed to inner-sphere surface complexation. The Diffuse Layer model (DLM) is applied to simulate the adsorption data, and fits the experimental data well with the aid of FITEQL 3.2. X-ray photoelectron spectroscopy (XPS) is performed to study the species of Eu(III) adsorbed on the surfaces of TiO2/FA–TiO2 hybrids at a molecular level, which suggest that FA act as “bridge” between Eu(III) and TiO2 particles to enhance the ability to adsorb Eu(III) in solution.

  • modeling of radionickel sorption on mx 80 bentonite as a function of ph and ionic strength
    Science China-chemistry, 2009
    Co-Authors: Dadong Shao, Di Xu, Suowei Wang, Qiaohui Fang, Wangsuo Wu, Yunhui Dong, Xiangke Wang
    Abstract:

    MX-80 bentonite was detected using acid-based titration, XRD and FTIR in detail. The sorption behavior of 63Ni(II) from aqueous solution to MX-80 bentonite was investigated as a function of solid content, ionic strength and pH by using batch technique. The experimental data of 63Ni(II) sorption on MX-80 bentonite was obtained using the Diffuse Layer model (DLM) with the aid of FITEQL 3.1 program. The results indicated that the sorption of 63Ni(II) on MX-80 bentonite was mainly dominated by surface complexation, and cation exchange also contributed partly to 63Ni(II) sorption at low pH values. The sorption isotherms were simulated by Langmuir and Freundlich models, and the results indicated that Freundlich isotherm model fitted the sorption data better than the Langmuir isotherm model. The results are crucial to evaluate the sorption and migration of radionickel in MX-80 bentonite.

Michal Borkovec - One of the best experts on this subject based on the ideXlab platform.

  • Measuring Inner Layer Capacitance with the Colloidal Probe Technique
    MDPI AG, 2018
    Co-Authors: Alexander M. Smith, Michal Borkovec, Plinio Maroni, Gregor Trefalt
    Abstract:

    The colloidal probe technique was used to measure the inner Layer capacitance of an electrical double Layer. In particular, the forces were measured between silica surfaces and sulfate latex surfaces in solutions of monovalent salts of different alkali metals. The force profiles were interpreted with Poisson-Boltzmann theory with charge regulation, whereby the Diffuse Layer potential and the regulation properties of the interface were obtained. While the Diffuse Layer potential was measured in this fashion in the past, we are able to extract the regulation properties of the inner Layer, in particular, its capacitance. We find systematic trends with the type of alkali metal ion and the salt concentration. The observed trends could be caused by difference in ion hydration, variation of the binding capacitance, and changes of the effective dielectric constant within the Stern Layer. Our results are in agreement with recent experiments involving the water-silica interface based on a completely independent method using X-ray photoelectron spectroscopy in a liquid microjet. This agreement confirms the validity of our approach, which further provides a means to probe other types of interfaces than silica

  • charge regulation in the electrical double Layer ion adsorption and surface interactions
    Langmuir, 2016
    Co-Authors: Gregor Trefalt, Sven Holger Behrens, Michal Borkovec
    Abstract:

    Charge regulation in the electrical double Layer has important implications for ion adsorption, interparticle forces, colloidal stability, and deposition phenomena. Although charge regulation generally receives little attention, its consequences can be major, especially when considering interactions between unequally charged surfaces. The present article discusses common approaches to quantify such phenomena, especially within classical Poisson–Boltzmann theory, and pinpoints numerous situations where a consideration of charge regulation is essential. For the interpretation of interaction energy profiles, we advocate the use of the constant regulation approximation, which summarizes the surface properties in terms of two quantities, namely, the Diffuse Layer potential and the regulation parameter. This description also captures some pronounced regulation effects observed in the presence of multivalent ions.

  • electric double Layer potentials and surface regulation properties measured by colloidal probe atomic force microscopy
    Physical Review E, 2014
    Co-Authors: Javier Montes F Ruizcabello, Plinio Maroni, Gregor Trefalt, Michal Borkovec
    Abstract:

    : We show how the colloidal-probe technique, which is based on force measurements made with the atomic force microscope, can be used to accurately determine the charging parameters of water-solid interfaces. Besides yielding accurate values of the double-Layer or Diffuse-Layer potential, the method also allows reliable determination of the charge regulation properties of the surfaces. The latter can be quantified with a regulation parameter, which is essential to properly describe forces between interfaces, especially in asymmetric situations when one of the interfaces is charged and the other one is close to neutral. The technique relies on a highly charged probe particle, for which the charging properties are accurately determined by interpreting the double-Layer contribution of the measured force profiles in the symmetric sphere-sphere geometry with Poisson-Boltzmann (PB) theory. Once the probe particle is calibrated, this particle is used to measure the force profile between an unknown substrate in the asymmetric sphere-sphere or sphere-plane geometry. From this profile, the Diffuse-Layer potential and regulation parameter of the substrate can be again determined with PB theory. The technique is highly versatile, as it can be used for a wide variety of substrates, including colloidal particles and planar substrates. The technique is also applicable in salt solutions containing multivalent ions. The current drawbacks of the technique are that it can only be applied up to moderately high salt levels, typically to 10 mM, and only for relatively large particles, typically down to about 1 μm in diameter. How the technique could be extended to higher salt levels and smaller particle size is also briefly discussed.

  • interaction between charged surfaces on the poisson boltzmann level the constant regulation approximation
    Journal of Physical Chemistry B, 2004
    Co-Authors: Ramon Pericetcamara, Sven Holger Behrens, Georg Papastavrou, Michal Borkovec
    Abstract:

    Interaction forces between ionizable surfaces across an electrolyte solution on the Poisson−Boltzmann level are discussed within the constant regulation approximation. The chemical response of each surface is expressed in terms of two parameters, namely, the Diffuse Layer potential and the regulation parameter p. Both parameters are easily available because they arise naturally within classical equilibrium models for a single noninteracting surface. This approximation, thus, eliminates the need to treat the more intricate problem of two chemical adsorption equilibria coupled to the overlapping double Layers between the surfaces. The ensuing simplicity makes this approach extremely versatile for the analysis of experimental data. The classical boundary condition of constant potential corresponds to p = 0, and that of constant charge corresponds to p = 1. While this approximation is rigorously correct at large separations, we find that it remains excellent down to contact in many realistic situations, such ...

  • interaction between charged surfaces on the poisson boltzmann level the constant regulation approximation
    Journal of Physical Chemistry B, 2004
    Co-Authors: Ramon Pericetcamara, Sven Holger Behrens, Georg Papastavrou, Michal Borkovec
    Abstract:

    Interaction forces between ionizable surfaces across an electrolyte solution on the Poisson-Boltzmann level are discussed within the constant regulation approximation. The chemical response of each surface is expressed in terms of two parameters, namely, the Diffuse Layer potential and the regulation parameter p. Both parameters are easily available because they arise naturally within classical equilibrium models for a single noninteracting surface. This approximation, thus, eliminates the need to treat the more intricate problem of two chemical adsorption equilibria coupled to the overlapping double Layers between the surfaces. The ensuing simplicity makes this approach extremely versatile for the analysis of experimental data. The classical boundary condition of constant potential corresponds to p = 0, and that of constant charge corresponds to p = 1. While this approximation is rigorously correct at large separations, we find that it remains excellent down to contact in many realistic situations, such as in symmetric or asymmetric systems involving metal oxides or silica described by the 1-pK basic Stern model.

Andre Revil - One of the best experts on this subject based on the ideXlab platform.

  • connecting complex conductivity spectra to mercury porosimetry of sedimentary rocks
    Geophysics, 2016
    Co-Authors: Qifei Niu, Andre Revil
    Abstract:

    ABSTRACTThe measured spectral-induced polarization (SIP) response of highly porous granular materials can be modeled by upscaling the Nernst-Planck equation for a single grain and performing a convolution product with the particle size distribution. The distribution of relaxation times associated with the polarization of consolidated porous media seems, intuitively, to be controlled by the pore size distribution because of the radius of curvature of the interface between the solid and the pore water. We have explored a mechanistic model connecting the SIP response of consolidated media to mercury injection capillary porosimetry (MICP) data. First, we developed a mechanistic electric double Layer (EDL) polarization model for porous media, which considered the polarization of the Stern Layer, which was possibly enhanced by the polarization of the Diffuse Layer and the effect of the pore size distribution. The new model revealed that the relaxation time of porous media such as sandstones could be overestimat...

  • spectral induced polarization of shaly sands influence of the electrical double Layer
    Water Resources Research, 2012
    Co-Authors: Andre Revil
    Abstract:

    [1] I developed a new model named POLARIS describing the complex conductivity of (pyrite-free) shaly poorly sorted sands. This model is based on the solution given by the effective medium theory for grains coated by an electrical double Layer and immersed in a background electrolyte. The electrical double Layer comprises the Stern Layer and the Diffuse Layer. Both Layers play very distinct roles in the in-phase and quadrature conductivities. The polarization of the shaly sands is mainly controlled by the polarization of the Stern Layer (except at very high salinities) with a very small mobility of the counterions contained in this Layer. The in-phase component of the conductivity is controlled by the conductivity of the pore water with a contribution associated with the Diffuse Layer (the contribution of the Stern Layer seems negligible). The fraction of counterions in the Stern Layer is computed from a simple sorption isotherm and is used to infer the quadrature conductivity. The quadrature conductivity is assumed to be frequency independent, which is a reasonable approximation in clayey sands and sandstones, in agreement with observations. The polarization model is also based on the assumption that the Stern Layer is discontinuous between grains, an assumption that is consistent with recent models of ionic transport in clayey sands. POLARIS explains the dependence of the quadrature conductivity on the salinity, cation exchange capacity, specific surface area (or specific surface per unit pore volume), and temperature. It can be used to predict the saturation and the permeability (inside 1 order of magnitude).

  • The pH dependence of spectral induced polarization of silica sands: Experiment and modeling
    Geophysical Research Letters, 2011
    Co-Authors: Magnus Skold, Andre Revil, P. Vaudelet
    Abstract:

    In electrolyte-saturated sands, the storage of electrical charges under an alternating electrical field (called "induced polarization") is responsible for a phase lag between the applied current and the resulting electrical field. Because a variety of polarization mechanisms exists in porous materials, the underlying physics of induced polarization is somehow unclear and the field data difficult to interpret quantitatively. Measurements at various pHs and salinities can be used to discriminate between different competing mechanisms at low frequencies (1 mHz-1 kHz) in porous media in the absence of electronic conductors. New experimental data point out that, in addition to the polarization of the Stern Layer (the inner part of the electrical double Layer coating the surface of the silica grains), there is another polarization mechanism possibly associated with a hopping process of the protons on the silica surface. We propose that such a process could follow a Grotthuss cooperation mechanism (as in ice) involving the bound water of the silica surface. Our data also rule out a mechanism based on the Diffuse Layer. The new polarization mechanism may be applied to quantifying induced-polarization data collected over acidic contaminant plumes.

  • a mechanistic model for the spectral induced polarization of clay materials
    Journal of Geophysical Research, 2009
    Co-Authors: Philippe Leroy, Andre Revil
    Abstract:

    Water-saturated clay-rich media exhibit low-frequency (1 Hz to 1 MHz) effective conductivity and effective permittivity dispersions that are the consequence of both the polarization of the mineral/water interface coating the surface of the grains and the Maxwell-Wagner polarization. These low-frequency properties are modeled by combining (1) a complexation model of the surface properties of clay minerals (kaolinite, illite, and smectite), (2) a polarization model of the Stern Layer (the inner portion of the electrical double Layer coating the surface of the minerals), and (3) a macroscopic model comprising the electrochemical polarization of the grains and the contribution of the Maxwell-Wagner effect. The macroscopic model is based on the differential effective medium theory. It includes a convolution product with the grain size distribution. For kaolinite, the Diffuse Layer occupies a small fraction of the pore space and is considered as part of the surface of the grains. This is due to the low specific surface area of kaolinite. In the case of illite and smectite, the situation is different. Because of the high specific surface areas of these minerals, the Diffuse Layer occupies a large fraction of the pore space and is considered as part of the pore space and is described using a Donnan equilibrium model. We obtain excellent comparisons between various experimental data reported in the literature and our model. Then, we considered low-porosity (compacted or cemented) clay rocks and shales. Here too, we obtained a good agreement between the data and the predictions of a model based on a volume-averaging approach. We also note that at very low frequencies (<1 Hz), another polarization mechanism exists that is not reproduced by our model. We believe that this polarization corresponds to a nonlinear membrane polarization contribution.

  • nature of surface electrical conductivity in natural sands sandstones and clays
    Geophysical Research Letters, 1998
    Co-Authors: Andre Revil, Paul W J Glover
    Abstract:

    The electrical conductivity of rocks results from conduction through the bulk solution occupying the pores and from surface conduction occurring at the fluid/grain interface. The nature of the surface electrical conductivity of shaly and clean sands and sandstones is examined. Surface conduction is characterized by the specific surface conductance which is the sum of three contributions: (i) Conduction within the electrical Diffuse Layer, which makes a negligible contribution to the total specific surface conductance, (ii) Conduction in the Stern Layer, which is shown to vary significantly with the salinity of the pore fluid at low salinities (10−6 to 10−3 mol 1−1), but becomes independent of salinity at higher salinities, (iii) A mechanism operating directly on the mineral surface, independent of salinity, and perhaps associated with proton transfer. At salinities higher than 10−3 mol 1−1 and at 25°C, the specific surface conductance of quartz and clays is equal to 8.9×10−9 S and 2.5×10−9 S respectively. Equations describing the influence of surface conductivity and microstructure upon the macroscopic electrical conductivity of sands, sandstones, and shales are also developed.

Xiaoli Tan - One of the best experts on this subject based on the ideXlab platform.

  • adsorption of eu iii onto tio2 effect of ph concentration ionic strength and soil fulvic acid
    Journal of Hazardous Materials, 2009
    Co-Authors: Xiangke Wang, Xiaoli Tan, Ming Fang
    Abstract:

    The effects of pH, initial Eu(III) concentration, ionic strength and fulvic acid (FA) on the adsorption of Eu(III) on TiO2 are investigated by using batch techniques. The results indicate that the presence of FA strongly enhances the adsorption of Eu(III) on TiO2 at low pH values. Besides, the adsorption of Eu(III) on TiO2 is significantly dependent on pH values and independent of ionic strength. The adsorption of Eu(III) on TiO2 is attributed to inner-sphere surface complexation. The Diffuse Layer model (DLM) is applied to simulate the adsorption data, and fits the experimental data well with the aid of FITEQL 3.2. X-ray photoelectron spectroscopy (XPS) is performed to study the species of Eu(III) adsorbed on the surfaces of TiO2/FA–TiO2 hybrids at a molecular level, which suggest that FA act as “bridge” between Eu(III) and TiO2 particles to enhance the ability to adsorb Eu(III) in solution.

  • surface complexation modeling of sr ii and eu iii adsorption onto oxidized multiwall carbon nanotubes
    Journal of Colloid and Interface Science, 2008
    Co-Authors: Changlun Chen, Xiaoli Tan, Yuedong Meng, Xiangke Wang
    Abstract:

    Acid-base titrations of oxidized multiwall carbon nanotubes (MWCNTs), Sr(II) and Eu(III) adsorptions onto oxidized MWCNTs were conducted to investigate the surface charge characteristics of oxidized MWCNTs and the surface complexation interactions between Sr(II)/Eu(III) and oxidized MWCNTs. The results suggested that Sr(II) and Eu(III) adsorptions onto oxidized MWCNTs increased with increasing pH, and decreased with increasing ionic strength, and the affinity of oxidized MWCNTs for Eu(III) was much higher than that for Sr(II). The Diffuse Layer model (DLM) fitted the experimental data of Sr(II) and Eu(III) adsorptions well with the aid of FITEQL 3.2.

C. W. Outhwaite - One of the best experts on this subject based on the ideXlab platform.