INVESTIGADORES
BARJA Beatriz Carmen
artículos
Título:
Aminomethylphosphonic Acid and Glyphosate Adsorption onto Goethite: A Comparative Study
Autor/es:
B. C. BARJA; M. DOS SANTOS AFONSO
Revista:
ENVIRONMENTAL SCIENCE & TECHNOLOGY
Referencias:
Año: 2005 vol. 39 p. 585 - 592
ISSN:
0013-936X
Resumen:
Glyphosate is a non-selective, broad spectrum, postemergent
herbicide widely used in weed control.
Aminomethylphosphonic acid (AMPA) is one of the main
products of biodegradation of glyphosate in natural systems
before its ultimate mineralization and also the breakdown
product of more complex phosphonates such as nitrilotris-
(methylenephosphonic acid). The adsorption isotherms and
surface coverage of AMPA and glyphosate ( N-phosphomethylglycine,
PMG) in aqueous suspensions of goethite as
a function of pH were measured. Electrophoretic mobility
curves for the PMG/goethite system were also determined.
The ATR-FTIR interfacial spectra of the surface complexes
of AMPA and PMG onto goethite were analyzed as a
function of the pH and the surface coverage. The phosphonate
moiety of these two ligands coordinates to the iron
oxide surface with similar structures as the methylphosphonic
acid despite the presence of the amino and/or carboxylate
groups of their molecules. Two predominating complexes
have been identified where the phosphonate group in PMG
or AMPA bonds monodentately or bridges bidentately to
the surface of iron oxide in an inner sphere mode, while the
carboxylate and amino group are noncoordinated to the
surface. The stability constants of the surface complexes
of AMPA and PMG onto goethite were analyzed as a
function of the pH and the surface coverage. The phosphonate
moiety of these two ligands coordinates to the iron
oxide surface with similar structures as the methylphosphonic
acid despite the presence of the amino and/or carboxylate
groups of their molecules. Two predominating complexes
have been identified where the phosphonate group in PMG
or AMPA bonds monodentately or bridges bidentately to
the surface of iron oxide in an inner sphere mode, while the
carboxylate and amino group are noncoordinated to the
surface. The stability constants of the surface complexes
-FTIR interfacial spectra of the surface complexes
of AMPA and PMG onto goethite were analyzed as a
function of the pH and the surface coverage. The phosphonate
moiety of these two ligands coordinates to the iron
oxide surface with similar structures as the methylphosphonic
acid despite the presence of the amino and/or carboxylate
groups of their molecules. Two predominating complexes
have been identified where the phosphonate group in PMG
or AMPA bonds monodentately or bridges bidentately to
the surface of iron oxide in an inner sphere mode, while the
carboxylate and amino group are noncoordinated to the
surface.
The stability constants of the surface complexes
The stability constants of the surface complexes
FeOP(O)(OH)R, FeOP(O)2R, and (FeO)2P(O)RP(O)(OH)R, FeOP(O)2R, and (FeO)2P(O)R
were calculated using the constant capacitance model.