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Chemical speciation of N-(phosphonomethyl)glycine in solution and at mineral interfaces
Umeå universitet, Teknisk-naturvetenskaplig fakultet, Kemi.
Umeå universitet, Teknisk-naturvetenskaplig fakultet, Kemi.
Umeå universitet, Teknisk-naturvetenskaplig fakultet, Kemi.
Umeå universitet, Teknisk-naturvetenskaplig fakultet, Kemi.
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2004 (Engelska)Ingår i: Surface and Interface Analysis, ISSN 0142-2421, Vol. 36, nr 8, s. 1074-7Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

The chemical speciation of the zwitterionic compound N-(phosphonomethyl)glycine (PMG) was studied in solution and at the mineral/water interface at different pH. Results from vacuum techniques such as XPS were compared with previously published conventional batch experiments. It was shown that by keeping the samples frozen during XPS analyses it was possible to keep a water interface. The frozen interface enables studies of the protonation of the nitrogen group which has previously been difficult using XPS. The protonation in frozen solutions was compared with literature data and the differences discussed. Furthermore, the speciation of PMG at the surface of manganite (-MnOOH) and goethite (-FeOOH) was studied. It was found that at least one of the protonation constants for surface-bound PMG differs significantly from the protonation constants in a pure PMG solution. The formation of different surface complexes is discussed together with differences between the sorption capacities of PMG onto the minerals studied.

Ort, förlag, år, upplaga, sidor
2004. Vol. 36, nr 8, s. 1074-7
Nyckelord [en]
XPS, cryogenics, solid-liquid interface, manganite, goethite, phosphonomethylglycine
Identifikatorer
URN: urn:nbn:se:umu:diva-14084DOI: doi:10.1002/sia.1844OAI: oai:DiVA.org:umu-14084DiVA, id: diva2:153755
Tillgänglig från: 2007-05-22 Skapad: 2007-05-22 Senast uppdaterad: 2018-06-09Bibliografiskt granskad
Ingår i avhandling
1. Chemical Processes at the Water-Manganite (γ-MnOOH) Interface
Öppna denna publikation i ny flik eller fönster >>Chemical Processes at the Water-Manganite (γ-MnOOH) Interface
2004 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Alternativ titel[sv]
Kemiska Processer vid gränsytan mellan vatten och manganit (γ-MnOOH)
Abstract [en]

The chemistry of mineral surfaces is of great importance in many different areas including natural processes occurring in oceans, rivers, lakes and soils. Manganese (hydr)oxides are one important group to these natural processes, and the thermodynamically most stable trivalent manganese (hydr)oxide, manganit (γ-MnOOH), is studied in this thesis.

This thesis summarises six papers in which the surface chemistry of synthetic manganite has been investigated with respect to surface acid-base properties, dissolution, and adsorption of Cd(II) and the herbicide N-(phosphonomethyl)glycine (glyphosate, PMG). In these papers, a wide range of analysis techniques were used, including X-ray photoelectron spectroscopy (XPS), extended X-ray absorption fine structure (EXAFS) spectroscopy, Fourier transform infra-red (FTIR) spectroscopy, atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray diffraction (XRD), potentiometry, electrophoretic mobility measurements and wet chemical techniques, in order to obtain a more complete understanding of the different processes occurring at the manganite-water interface.

From the combined use of these techniques, a 1-pKa acid-base model was established that is valid at pH>6. The model includes a Na+ interaction with the surface:

=MnOH2+½ --> =MnOH-½ + H+ log β0 (intr.) = -8.20 = -pHiep

=MnOH2+½ + Na+ --> =MnOHNa+½ + H+ log β0 (intr.) = -9.64

At pH<6 the manganite crystals dissolve and disproportionate into pyrolusite (β-MnO2) and Mn(II)-ions in solution according to:

2 γ-MnOOH + 2H+ --> β-MnO2 + Mn2+ + 2H2O log K0 = 7.61 ± 0.10

The adsorption and co-adsorption of Cd(II) and glyphosate at the manganite surface was studied at pH>6. Cd(II) adsorption displays an adsorption edge at pH~8.5. Glyphosate adsorbs over the entire pH range, but the adsorption decreases with increasing pH. When the two substances are co-adsorbed, the adsorption of Cd(II) is increased at low pH but decreased at high pH. The adsorption of glyphosate is increased in the entire pH range in the presence of Cd(II). From XPS, FTIR and EXAFS it was found that glyphosate and Cd(II) form inner sphere complexes. The binary Cd(II)-surface complex is bonded by edge sharing of Mn and Cd octahedra on the (010) plane of manganite. Glyphosate forms inner-sphere complexes through an interaction between the phosphonate group and the manganite surface. The largest fraction of this binary glyphosate complex is protonated throughout the pH range. A ternary surface complex is also present, and its structure is explained as type B ternary surface complex (surface-glyphosate-Cd(II)). The chelating rings between the Cd(II) and glyphosate, found in aqueous complexes, are maintained at the surface, and the ternary complex is bound to the surface through the phosphonate group of the ligand.

Förlag
s. 74
Nyckelord
Inorganic chemistry, manganite, γ-MnOOH, mineral surface, acid-base properties, adsorption, Cd(II), N-(phosphonomethyl)glycine, glyphosate, PMG, surface complex, dissolution, disproportionation, XPS, EXAFS, infrared spectroscopy, SEM, AFM, potentiometry, electrophoresis, Oorganisk kemi
Nationell ämneskategori
Oorganisk kemi
Forskningsämne
oorganisk kemi
Identifikatorer
urn:nbn:se:umu:diva-253 (URN)91-7305-634-0 (ISBN)
Disputation
2004-05-19, KB3B1, KBC, Umeå University, Umeå, 13:00 (Engelska)
Opponent
Handledare
Tillgänglig från: 2004-04-29 Skapad: 2004-04-29 Senast uppdaterad: 2018-06-09Bibliografiskt granskad

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Ramstedt, MadeleineShchukarev, AndreySjöberg, Staffan

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