Surface Complexation of Copper(II) on Soil Particles: EPR and XAFS Studies

Abstract

The interactions of transition metals with natural systems play an important role in the mobility and the bioavailability of these metals in soils. In this study, the adsorption of copper(II) onto natural soil particles was studied as a function of pH and metal concentration. The retention capacity of soil particles was determined at pH 6.2 to be equal to 6.7 mg of copper/g of solid. The Langmuir and Freundlich isotherm equations were then used to describe the partitioning behavior of the system at different pH values. A combination of EPR, extended X-ray absorption fine structure (EXAFS), and X-ray absorption near-edge structure (XANES) spectroscopies was used to probe the Cu atomic environment at the soil particles/aqueous interface. The spectroscopic study revealed that copper(II) ions are held in inner-sphere surface complexes. It also revealed that Cu was in an octahedral coordination with first-shell oxygen atoms. A weak tetragonal distortion was pointed out due to the Jahn-Teller effect, with a mean Cu-Oequatorial bond distance of 1.96 A and a Cu-Oaxial bond distance of 2.06 A. A detailed analysis of the spectroscopic data suggested that Cu(II) was bonded to organic matter coated onto the mineral fraction of soil particles.

Mechanisms of competitive adsorption of Pb, Cu, and Cd on peat

“…The average CueO eq bond length is 1.94 Å , and the CueO ax bond length is 2.34 Å . The results of four short equatorial bonds and two elongated axial bonds were due to the JahneTeller effect of Cu(II), which were consistent with many EXAFS studies involving Cu(II) (Flogeac et al, 2004;Palladino et al, 1993 Analysis of the XANES and EXAFS data on Cu(II) adsorbed on peat, Cu in reference compounds of Cu(OH) 2 , Cu(CH 3 CO 2 ) 2 and Cu(NO 3 ) 2 aqueous solution (Fig. 4b) suggests that the coordination environment of Cu(II) adsorbed on peat strongly resembles that of Cu(CH 3 CO 2 ) 2 , where Cu(II) was bonded primarily to carboxylic moieties.…”

“…When Cu 2þ approached, it cannot bond in the equatorial plane with the same degree of angular overlap as water. Thus, it can be concluded that Cu(II) formed inner-sphere complex (Flogeac et al, 2004 Fig. 4.…”

Adsorption of 2,4,6-trichlorophenol by multi-walled carbon nanotubes as affected by Cu(II)

“…The best fit of this peak leads to 4.14 equatorial oxygen atoms at 1.94 Å , 2.64 axial oxygen atoms at 2.20 Å for Cu(II)-MWCNTs15A. The data are consistent with those obtained from XANES (i.e., a slightly distorted octahedral coordination around Cu(II) sorption onto MWCNTs15A) involving Cu(II) (Flogeac et al, 2004). The results of four short equatorial bonds and two elongated axial bonds were due to the Jahn-Teller effect of the Cu(II)-O clusters.…”

Sorption of Anionic Metsulfuron-Methyl and Cationic Difenzoquat on Peat and Soil As Affected by Copper

“…Cu 2+ is a heavy metal with high electronegativity (1.9) and may form outer-and inner-sphere complexes on the soil surface. When an inner-sphere complex is formed, Cu 2+ is bound directly to the peat and soil surface, and the surrounded water molecules are partially displaced by -OH groups of soil minerals and organic matter (27) and by -COOH groups of soil organic matter (28). On the basis of the FTIR data of DZ and Cu 2+ , it appears that competitive sorption between DZ and Cu 2+ for the same sorption sites is occurring, and this is responsible for the observed mutual suppression of sorption of both DZ and Cu 2+ .…”