scholarly journals THERMODINAMIC PARAMETERS ON THE SORPTION OF PHOSPHATE IONS BY MONTMORILLONITE

2016 ◽  
Vol 4 (1) ◽  
Author(s):  
Ikhsan Jaslin ◽  
Wijayanti Endang ◽  
Sunarto Sunarto
Keyword(s):  
Active Sites ◽  
Surface Complexation ◽  
Outer Sphere ◽  
Hydroxyl Groups ◽  
Process Data ◽  
Surface Complexes ◽  
Surface Complexation Model ◽  
Surface Hydroxyl ◽  
Phosphate Ions ◽  
Sorbate Concentration

The sorption of phosphate by montmorillonite at 10, 30, and 50 oC were investigated aiming to mainly determine thermodynamic parameters for the formation of surface complexes in the adsorption of phosphate ions by montmorillonite. Data were collected by adsorption edge experiments investigating the effect of pH, adsorption isotherms enabling the effect of sorbate concentration, and acid-base titration calculating protons released or taken up by adsorption process. Data analysis was carried out using surface complexation model to fit the data collected in this study using the parameters obtained from previous study, as well as to calculate the values of ΔH and ΔS. Previous study reported that phosphate ions formed two outer-sphere surface complexes with active sites of montmorillonite through hydrogen bonding. In the first complex,  [(XH)0– H2L─]─, the phosphate was held to permanent-charge X─ sites on the tetrahedral siloxane faces, and the second complex, [[(SO─)(SOH)]– – [H2L]─] 2─ was formed through the interaction between the phosphate and variable charge surface hydroxyl groups at the edges of montmorillonite crystals and on the octahedral alumina faces. The values of ΔH for the first and second reactions are 39.756 and 3.765x10-7 kJ mol‒1 respectively. Since both reactions have positive enthalpy values, it can be concluded that the reactions are endothermic. Large energy for the first reaction is needed by X─  sites (permanent negatively charge sites of montmorillonite) to be partially desolvated, on which K+ or other surface cations are replaced by H+ ions in the surface protonated process, and are then ready to interact phosphate ions in the solution. Small values of ΔH for the second reactions indicates that hydrogen bonds formed by phosphate and SOH sites in the second reaction are easily broken out, and the phosphate can easily desorbed from the surface. The values of ΔS for the first and second reactions are 122.523 and 2.393 x10-2  J K‒1 mol‒1, which are greater than -10 kJ mol‒1 and indicates that the surface reactions occurs through dissociative mechanisms.Keywords:   montmorillonite, adsorption edge, extended constant capacitance, surface complexation model, enthalpy, reaction mechanisms

scholarly journals Nanocomposites SnO2/SiO2:SiO2 Impact on the Active Centers and Conductivity Mechanism

Materials ◽  
2019 ◽  
Vol 12 (21) ◽  
pp. 3618 ◽  
Author(s):  
Dayana Gulevich ◽  
Marina Rumyantseva ◽  
Artem Marikutsa ◽  
Tatyana Shatalova ◽  
Elizaveta Konstantinova ◽  
...  
Keyword(s):  
Active Sites ◽  
Nitrogen Adsorption ◽  
Hydroxyl Groups ◽  
Pure Sno2 ◽  
Active Centers ◽  
Paramagnetic Resonance ◽  
Surface Hydroxyl ◽  
Chemisorbed Oxygen ◽  
Temperature Dependences ◽  
Sio2 Nanocomposites

This paper is focused on the effect of the stabilizing component SiO2 on the type and concentration of active sites in SnO2/SiO2 nanocomposites compared with nanocrystalline SnO2. Previously, we found that SnO2/SiO2 nanocomposites show better sensor characteristics in CO detection (lower detection limit, higher sensor response, and shorter response time) compared to pure SnO2 in humid air conditions. Nanocomposites SnO2/SiO2 synthesized using the hydrothermal method were characterized by low temperature nitrogen adsorption, XRD, energy dispersive X-ray spectroscopy (EDX), thermo-programmed reduction with hydrogen (TPR-H2), IR-, and electron-paramagnetic resonance (EPR)-spectroscopy methods. The electrophysical properties of SnO2 and SnO2/SiO2 nanocomposites were studied depending on the oxygen partial pressure in the temperature range of 200–400 °C. The introduction of SiO2 results in an increase in the concentration of paramagnetic centers Sn3+ and the amount of surface hydroxyl groups and chemisorbed oxygen and leads to a decrease in the negative charge on chemisorbed oxygen species. The temperature dependences of the conductivity of SnO2 and SnO2/SiO2 nanocomposites are linearized in Mott coordinates, which may indicate the contribution of the hopping mechanism with a variable hopping distance over local states.

Uranyl Sorption Onto Alumina

1996 ◽  
Vol 465 ◽  
Author(s):  
Anna-Maria M. Jacobsson ◽  
Robert S. Rundberg
Keyword(s):  
Metal Ion ◽  
Dissociation Constants ◽  
Surface Complexation ◽  
Uranyl Complex ◽  
Acid Dissociation ◽  
Oxide Surface ◽  
Acid Dissociation Constants ◽  
Surface Complexation Model ◽  
Surface Hydroxyl ◽  
Free Environment

ABSTRACTThe mechanism for the adsorption of uranyl onto alumina from aqueous solution was studied experimentally and the data were modeled using a triple layer surface complexation model. The experiments were carried out at low uranium concentrations (9×10-11 - 5×10-8M) in a CO2 free environment at varying electrolyte concentrations (0.01 – 1 M) and pH (4.5 – 12). The first and second acid dissociation constants, pKal and pKa2, of the alumina surface were determined from potentiometric titrations to be 7.2 ± 0.6 and 11.2 ± 0.4, respectively. The adsorption of uranium was found to be independent of the electrolyte concentration. We therefore conclude that the uranium binds as an inner sphere complex. The results were modeled using the code FITEQL. Two reactions of uranium with the surface were needed to fit the data, one forming a uranyl complex with a single surface hydroxyl and the other forming a bridged or bidentate complex reacting with two surface hydroxyls of the alumina. There was no evidence from these experiments of site heterogeneity. The constants used for the reactions were based in part on predictions made utilizing the Hard Soft Acid Base, HSAB, theory, relating the surface complexation constants to the hydrolysis of the sorbing metal ion and the acid dissociation constants of the mineral oxide surface.

Approaches to modelling uranium(VI) adsorption on natural mineral assemblages

2000 ◽  
Vol 88 (9-11) ◽  
Author(s):  
T.D. Waite ◽  
James A. Davis ◽  
B.R. Fenton ◽  
Timothy E. Payne
Keyword(s):  
Performance Assessment ◽  
Goodness Of Fit ◽  
Surface Complexation ◽  
Acid Base ◽  
Surface Complexes ◽  
Natural Mineral ◽  
Surface Complexation Model ◽  
Surface Sites ◽  
Stepwise Manner ◽  
Mineral Assemblages

Component additivity (CA) and generalised composite (GC) approaches to deriving a suitable surface complexation model for description of U(VI) adsorption to natural mineral assemblages are pursued in this paper with good success. A single, ferrihydrite-like component is found to reasonably describe uranyl uptake to a number of kaolinitic iron-rich natural substrates at pH > 4 in the CA approach with previously published information on nature of surface complexes, acid-base properties of surface sites and electrostatic effects used in the model. The GC approach, in which little pre-knowledge about generic surface sites is assumed, gives even better fits and would appear to be a method of particular strength for application in areas such as performance assessment provided the model is developed in a careful, stepwise manner with simplicity and goodness of fit as the major criteria for acceptance.

scholarly journals Zr(OH)4/GO Nanocomposite for the Degradation of Nerve Agent Soman (GD) in High-Humidity Environments

Materials ◽  
2020 ◽  
Vol 13 (13) ◽  
pp. 2954 ◽  
Author(s):  
Seongon Jang ◽  
Dongwon Ka ◽  
Hyunsook Jung ◽  
Min-Kun Kim ◽  
Heesoo Jung ◽  
...  
Keyword(s):  
Active Sites ◽  
Adsorbed Water ◽  
Interaction Force ◽  
Nerve Agents ◽  
Nerve Agent ◽  
Zirconium Hydroxide ◽  
Hydroxyl Groups ◽  
High Humidity ◽  
Surface Hydroxyl ◽  
Diffuse Reflectance Infrared

Zirconium hydroxide, Zr(OH)4 is known to be highly effective for the degradation of chemical nerve agents. Due to the strong interaction force between Zr(OH)4 and the adsorbed water, however, Zr(OH)4 rapidly loses its activity for nerve agents under high-humidity environments, limiting real-world applications. Here, we report a nanocomposite material of Zr(OH)4 and graphene oxide (GO) which showed enhanced stability in humid environments. Zr(OH)4/GO nanocomposite was prepared via a dropwise method, resulting in a well-dispersed and embedded GO in Zr(OH)4 nanocomposite. The nitrogen (N2) isotherm analysis showed that the pore structure of Zr(OH)4/GO nanocomposite is heterogeneous, and its meso-porosity increased from 0.050 to 0.251 cm3/g, compared with pristine Zr(OH)4 prepared. Notably, the composite material showed a better performance for nerve agent soman (GD) degradation hydrolysis under high-humidity air conditions (80% relative humidity) and even in aqueous solution. The soman (GD) degradation by the nanocomposite follows the catalytic reaction with a first-order half-life of 60 min. Water adsorption isotherm analysis and diffuse reflectance infrared Fourier transform (DRIFT) spectra provide direct evidence that the interaction between Zr(OH)4 and the adsorbed water is reduced in Zr(OH)4/GO nanocomposite, indicating that the active sites of Zr(OH)4 for the soman (GD) degradation, such as surface hydroxyl groups are almost available even in high-humidity environments.

Modeling of Neptunium(V) Sorption Behavior onto Iron-Containing Minerals

1994 ◽  
Vol 353 ◽  
Author(s):  
T. Fujita ◽  
M. Tsukamoto ◽  
T. Ohe ◽  
S. Nakayama ◽  
Y. Sakamoto
Keyword(s):  
Dominant Role ◽  
Ph Dependence ◽  
Surface Complexation ◽  
Hydroxyl Group ◽  
Bulk Solution ◽  
Sorption Behavior ◽  
Solution Ph ◽  
Surface Complexation Model ◽  
Surface Hydroxyl ◽  
Naturally Occurring

AbstractSorption behaviors of neptunium (V) on naturally-occurring magnetite (Fe3O4) and goethite (α-FeOOH) in 0.1M NaN03 electrolyte solution under aerobic conditions were interpreted using the surface complexation model (SCM). The surface properties of these materials were experimentally investigated by C02-free potentiometric titration, and SCM parameters for the constant capacitance model, such as protonation/deprotonation constants of the surface hydroxyl group, were determined. The number of negatively charged sorption sites of goethite rapidly increased with the increase of the bulk solution pH compared with that of magnetite and this tendency was similar to the pH dependence of neptunium sorption. This implies that the neptunyl cation, NpO2+, plays a dominant role in possible sorption reactions. Assuming that the dominant surface complex is XO-NpO2, modeling by means of SCM was carried out, and the results were found to agree with experimental data.

scholarly journals Antimony (V) Adsorption at the Hematite–Water Interface: A Macroscopic and In Situ ATR-FTIR Study

Soil Systems ◽  
2021 ◽  
Vol 5 (1) ◽  
pp. 20
Author(s):  
Jerzy Mierzwa ◽  
Rose Mumbi ◽  
Avedananda Ray ◽  
Sudipta Rakshit ◽  
Michael E. Essington ◽  
...  
Keyword(s):  
Iron Oxide ◽  
Adsorption Mechanism ◽  
Surface Complexation ◽  
Outer Sphere ◽  
Surface Complexation Modeling ◽  
Surface Complexes ◽  
Ph Values ◽  
Oxide Minerals ◽  
Complexation Mechanism

The environmental mobility of antimony (Sb) is largely unexplored in geochemical environments. Iron oxide minerals are considered major sinks for Sb. Among the different oxidation states of Sb, (+) V is found more commonly in a wide redox range. Despite many adsorption studies of Sb (V) with various iron oxide minerals, detailed research on the adsorption mechanism of Sb (V) on hematite using macroscopic, spectroscopic, and surface complexation modeling is rare. Thus, the main objective of our study is to evaluate the surface complexation mechanism of Sb (V) on hematite under a range of solution properties using macroscopic, in situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopic, and surface complexation modeling. The results indicate that the Sb (V) adsorption on hematite was highest at pH 4–6. After pH 6, the adsorption decreased sharply and became negligible above pH 9. The effect of ionic strength was negligible from pH 4 to 6. The spectroscopic results confirmed the presence of inner- and outer-sphere surface complexes at lower pH values, and only outer-sphere-type surface complex at pH 8. Surface complexation models successfully predicted the Sb (V) adsorption envelope. Our research will improve the understanding of Sb (V) mobility in iron-oxide-rich environments.

scholarly journals Evaluation of a Novel Water Treatment Residual Nanoparticles as a Sorbent for Arsenic Removal

2015 ◽  
Vol 2015 ◽  
pp. 1-10 ◽  
Author(s):  
Elsayed Elkhatib ◽  
Ahmed Mahdy ◽  
Fatma Sherif ◽  
Hala Hamadeen
Keyword(s):  
Water Treatment ◽  
Arsenic Removal ◽  
Batch Adsorption ◽  
Hydroxyl Groups ◽  
Surface Complexes ◽  
Surface Hydroxyl ◽  
Ph Values ◽  
First Order Kinetics ◽  
The Stability ◽  
Water Treatment Residual

A novel sorbent, water treatment residual nanoparticles (nWTR), was synthesized and used to remove As(V) from water solutions. The kinetics and equilibrium of As(V) adsorption by nWTR were evaluated. The kinetic data for nWTR at 3 different pH values indicate that As(V) sorption is biphasic, is favored at low pH values, and followed the power function and first-order kinetics models fit. The results of the batch adsorption study showed that nWTR was effective in As(V) removal and its removal capability was 16 times higher than that of bulk WTR. Fourier transmission infrared (FTIR), SEM-EDX spectra, and As fractionation results indicate the crucial role of surface hydroxyl groups in As retention onto nWTR and the high capability of nWTR to immobilize As(V). The stability of As-nWTR surface complexes is suggested as less than 2% of adsorbed As(V) was released from nWTR after 4 consecutive desorption cycles.

HYPERBRANCHED ALIPHATIC POLYESTER MODIFIED ACTIVATED CARBON PARTICLES WITH HOMOGENIZED SURFACE GROUPS

2007 ◽  
Vol 14 (06) ◽  
pp. 1025-1032 ◽  
Author(s):  
PENG LIU ◽  
LIUXUE ZHANG
Keyword(s):  
Activated Carbon ◽  
Photoelectron Spectroscopy ◽  
Active Sites ◽  
Hydroxyl Groups ◽  
Surface Groups ◽  
Aliphatic Polyester ◽  
One Pot ◽  
Surface Hydroxyl ◽  
Carbon Particles ◽  
Activated Carbon Particles

The hyperbranched aliphatic polyester grafted activated carbon (HAPE-AC), was successfully prepared by the simple "one-pot" method. The surface functional groups of commercial activated carbon particles were homogenized to hydroxyl groups by being oxidized with nitric acid and then reduced with lithium tetrahydroaluminate ( LiAlH 4) at first. Secondly, the surface hydroxyl groups were used as the active sites for the solution polycondensation of the AB2 monomer, 2, 2-bis(hydroxymethyl)propionic acid (bis-MPA), with the catalysis of p-toluenesulfonic acid (p-TSA). The homogenization of the surface groups of the activated carbon particles and the graft polymerization of the hyperbranched aliphatic polyester were investigated by X-ray photoelectron spectroscopy (XPS) technique. The products were also characterized with Fourier transform infrared (FT-IR) and scanning electron microscope (SEM). The competitive adsorption properties of the products toward the heavy metal ions ( Cu (II), Hg (II), Zn (II), and Cd (II)) also proved the translations of the surface groups.

scholarly journals Adsorption of strontium on manganese oxide (δ-MnO2) at elevated temperatures: experiment and modeling

2019 ◽  
Vol 64 (10) ◽  
pp. 1091-1104
Author(s):  
O. N. Karaseva ◽  
L. I. Ivanova ◽  
L. Z. Lakshtanov
Keyword(s):  
Ionic Strength ◽  
Elevated Temperatures ◽  
Equilibrium Constants ◽  
Surface Complexation ◽  
Outer Sphere ◽  
Acid Base ◽  
Surface Complexes ◽  
Different Temperatures ◽  
Low Ionic Strength ◽  
Outer Sphere Complexes

Strontium adsorption has been studied by the method of acid-base potentiometric titrations at three different temperatures: 25, 50, 75C. The effect of pH, ionic strength, sorbate/sorbent ratio, and temperature on adsorption was investigated. Experimental data were simulated using two various surface complexation models, with two different electrostatic descriptions of the interface: the constant capacitance model (CCM) and the triple-layer model (TLM). Although the both models used are able to account for the acid-base reactions and surface complexation of strontium on birnessite, we consider that the TLM is more applicable for a description of heterophaseous system H+ MnOH Sr2+. Under conditions of low ionic strength and negatively charged surface, Sr2+ ions compete with the electrolyte ions and form outer-sphere complexes along with inner-sphere complexes. Consequently, using the CCM for description of strontium adsorption data could be mathematically satisfactory, but physically senseless. The equilibrium model proposed here consists of the complexes of inner (MnOHSr2+, MnOSr+, MnOSrOH0) and outer types ([MnO Sr2+]+). The corresponding intrinsic equilibrium constants of the formation of these surface complexes were calculated for 25,50, and 75C.

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