Gibberellic acid surface complexation on ferrihydrite at different pH values: Outer-sphere complexes versus inner-sphere complexes

2019 ◽  
Vol 650 ◽  
pp. 741-748 ◽  
Author(s):  
Li Zhang ◽  
Liang Chen ◽  
Guoxin Huang ◽  
Fei Liu
Keyword(s):  
Gibberellic Acid ◽  
Surface Complexation ◽  
Outer Sphere ◽  
Ph Values ◽  
Inner Sphere ◽  
Outer Sphere Complexes ◽  
Inner Sphere Complexes

Surface Complexation of Neptunium(V) with Goethite

2006 ◽  
Vol 985 ◽  
Author(s):  
James L Jerden ◽  
A Jeremy Kropf
Keyword(s):  
Sodium Chloride ◽  
Sodium Silicate ◽  
Outer Sphere ◽  
Distribution Coefficients ◽  
Batch Adsorption ◽  
Inner Sphere ◽  
Show Evidence ◽  
X Ray Absorption ◽  
Outer Sphere Complexes ◽  
Inner Sphere Complexes

AbstractBatch adsorption experiments in which neptunium bearing solutions were reacted with goethite (alpha-FeOOH) have been performed to study uptake mechanisms in sodium chloride and calcium-bearing sodium silicate solutions. This paper presents results identifying and quantifying the mechanisms by which neptunium is adsorbed as a function of pH and reaction time (aging). Also presented are results from tests in which neptunium is reacted with goethite in the presence of other cations (uranyl and calcium) that may compete with neptunium for sorption sites. The desorption of neptunium from goethite has been studied by resuspending the neptunium-loaded goethite samples in solutions containing no neptunium. Selected reacted sorbent samples were analyzed by x-ray absorption spectroscopy (XAS) to determine the oxidation state and molecular speciation of the adsorbed neptunium. Results have been used to establish the pH adsorption edge of neptunium on goethite in sodium chloride and calcium-bearing sodium silicate solutions. The results indicate that neptunium uptake on goethite reaches 95% at a pH of approximately 7 and begins to decrease at pH values greater than 8.5. Distribution coefficients for neptunium sorption range from less than 1000 (moles/kg)sorbed / (moles/kg)solution at pH less than 5.0 to greater than 10,000 (moles/kg)sorbed / (moles/kg)solution at pH greater than 7.0. Distribution coefficients as high as 100,000 (moles/kg)sorbed / (moles/kg)solution were recorded for the tests done in calcite equilibrated sodium silicate solutions. XAS results show that neptunium complexes with the goethite surface mainly as Np(V) (although Np(IV) is prevalent in some of the longer-duration sorption tests). The neptunium adsorbed to goethite shows Np-O bond length of approximately 1.8 angstroms which is representative of the Np-O axial bond in the neptunyl(V) complex. This neptunyl(V) ion is coordinated to 5 or 6 equatorial oxygens with Np-O bond lengths of 2.45 angstroms. The absence of a clearly recognizable Np-Fe interaction for the sodium chloride sorption tests suggests that neptunium in these solutions adsorbs as an outer-sphere complex. XAS results from the calcium-bearing sodium silicate sorption tests show evidence for a neptunyl(V) inner-sphere surface complex with a Np-Fe interaction at 3.5 angstroms. Desorption tests indicate that samples in which neptunium is bound as inner-sphere complexes show significant sorption hysteresis relative to samples in which neptunium is bound largely as outer-sphere complexes.

Role of carboxylic and phenolic groups in NOM adsorption on minerals: a review

2006 ◽  
Vol 6 (6) ◽  
pp. 155-164 ◽  
Author(s):  
X.H. Guan ◽  
D.L. Li ◽  
C. Shang ◽  
G.H. Chen
Keyword(s):  
Organic Matter ◽  
Aluminium Hydroxide ◽  
Interaction Strength ◽  
Outer Sphere ◽  
Hydroxyl Groups ◽  
Aromatic Carboxylates ◽  
Inner Sphere ◽  
Outer Sphere Complexes ◽  
Inner Sphere Complexes

This paper presented the current state of our understanding of the roles of carboxylic and phenolic groups in NOM adsorption and reviewed the contradictory opinions in the literatures. Previous studies carried out by other researchers indicated that aromatic carboxylates were adsorbed onto metal (hydr)oxides via outer-sphere complexes under most conditions and phenolic groups were very crucial for formation of inner-sphere complexes between organic acids and metal (hydr)oxides. Adsorption test with in-situ ATR-FTIR spectroscopic investigation were carried out to verify the role of aromatic carboxylic and phenolic groups in the NOM adsorption onto aluminium hydroxide surfaces by using a series of aromatic carboxylic acids and dihydroxybenzoic acids as the surrogate of NOM. Our studies suggested that the formation of outer-sphere complexes dominated the adsorption of most of the aromatic carboxylates over the pH range of 5–9; inner-sphere complexes were only detected at some pH levels for some aromatic carboxylates adsorption; and the aromatic carboxylates were most likely to be adsorbed to the first surface layer of hydroxyl groups and water molecules without forming coordinative bonds with the aluminium hydroxide surfaces but strong hydrogen bonds were formed in this process. Our study also revealed that (1) the presence of phenolic groups can increase the interaction strength of carboxylate groups with aluminium hydroxide; (2) chelate formation involving a carboxylate oxygen atom and ortho-phenolic-oxygen is important for the adsorption of organic matter on aluminium hydroxide at acidic pH; and 3) the phenolic groups adjacent to each other are more important than the carboxylic groups at alkaline pH for organic matter adsorption.

Retracted Article: Enhanced adsorption of Eu(iii) on mesoporous Al2O3/expanded graphite composites investigated by macroscopic and microscopic techniques

2012 ◽  
Vol 41 (43) ◽  
pp. 13388-13394 ◽  
Author(s):  
Yubing Sun ◽  
Changlun Chen ◽  
Xiaoli Tan ◽  
Dadong Shao ◽  
Jiaxing Li ◽  
...  
Keyword(s):  
Adsorption Mechanism ◽  
Surface Complexation ◽  
Expanded Graphite ◽  
Outer Sphere ◽  
Sphere Surface ◽  
Inner Sphere ◽  
Retracted Article ◽  
Enhanced Adsorption ◽  
Graphite Composites ◽  
Microscopic Techniques

The adsorption mechanism between Eu(iii) and mesoporous Al2O3/EG composites shifts from outer-sphere to inner-sphere surface complexation with increasing pH.

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.

Surface complexation modelling of uranyl adsorption onto kaolinite based clay minerals using FITEQL 3.2

2006 ◽  
Vol 94 (12) ◽  
Author(s):  
Deniz Arda ◽  
Julide Hizal ◽  
Resat Apak
Keyword(s):  
Clay Minerals ◽  
Surface Complexation ◽  
Outer Sphere ◽  
Uranyl Ion ◽  
Sphere Surface ◽  
Hexavalent Uranium ◽  
Inner Sphere

The aim of this study is to explain how the kaolinite-based clay minerals adsorb hexavalent uranium (uranyl ion), and to model uranyl adsorption based on inner-sphere surface complexation with the kaolinite edge hydroxyl sites and outer-sphere complexation with the permanent charge sites. The adsorption of UO

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.

Protonation effects on dynamic flux properties of aqueous metal complexes

2009 ◽  
Vol 74 (10) ◽  
pp. 1543-1557 ◽  
Author(s):  
Herman P. Van Leeuwen ◽  
Raewyn M. Town
Keyword(s):  
Complex Formation ◽  
Metal Ion ◽  
Good Description ◽  
Minor Component ◽  
Outer Sphere ◽  
Metal Species ◽  
Central Metal ◽  
Inner Sphere ◽  
A Minor ◽  
Protonated Ligand

The degree of (de)protonation of aqueous metal species has significant consequences for the kinetics of complex formation/dissociation. All protonated forms of both the ligand and the hydrated central metal ion contribute to the rate of complex formation to an extent weighted by the pertaining outer-sphere stabilities. Likewise, the lifetime of the uncomplexed metal is determined by all the various protonated ligand species. Therefore, the interfacial reaction layer thickness, μ, and the ensuing kinetic flux, Jkin, are more involved than in the conventional case. All inner-sphere complexes contribute to the overall rate of dissociation, as weighted by their respective rate constants for dissociation, kd. The presence of inner-sphere deprotonated H2O, or of outer-sphere protonated ligand, generally has a great impact on kd of the inner-sphere complex. Consequently, the overall flux can be dominated by a species that is a minor component of the bulk speciation. The concepts are shown to provide a good description of experimental stripping chronopotentiometric data for several protonated metal–ligand systems.

scholarly journals RuIII(edta) complexes as molecular redox catalysts in chemical and electrochemical reduction of dioxygen and hydrogen peroxide: inner-sphere versus outer-sphere mechanism

RSC Advances ◽  
2021 ◽  
Vol 11 (35) ◽  
pp. 21359-21366
Author(s):  
Debabrata Chatterjee ◽  
Marta Chrzanowska ◽  
Anna Katafias ◽  
Maria Oszajca ◽  
Rudi van Eldik
Keyword(s):  
Hydrogen Peroxide ◽  
Electron Transfer ◽  
Electrochemical Reduction ◽  
Molecular Oxygen ◽  
Outer Sphere ◽  
Transfer Processes ◽  
Edta Complexes ◽  
Inner Sphere ◽  
Electron Transfer Processes ◽  
Sphere Mechanism

[RuII(edta)(L)]2–, where edta4– =ethylenediaminetetraacetate; L = pyrazine (pz) and H2O, can reduce molecular oxygen sequentially to hydrogen peroxide and further to water by involving both outer-sphere and inner-sphere electron transfer processes.

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