Adsorption of o-Phthalate at the Water−Boehmite (γ-AlOOH) Interface:  Evidence for Two Coordination Modes

Abstract

Complexation of o-phthalate (1,2-benzenedicarboxylate) at the water−boehmite (γ-AlOOH) interface has been studied in 0.1 N NaCl media at 298.2 K within the range 4.0 < pH < 10.0. Equilibrium measurements were performed as potentiometric titrations and adsorption measurements. Attenuated total reflectance IR spectra were recorded to obtain structural information of the phthalate surface complexes. Additional adsorption and IR spectroscopic measurements were performed as a function of ionic strength. Infrared data strongly indicated the formation of two complexes at the surface, one outer-sphere and one inner-sphere complex with a chelating bidentate structure. The relative concentrations of these complexes were shown to vary with ionic strength and pH. The potentiometric and adsorption data were modeled using the extended constant capacitance approach to describe the electrostatics at the water−boehmite interface. Furthermore, constraints from the infrared spectroscopic results were used in the model. The surface complexation model which provided the best fit to all experimental data included the following equilibria: ⋮AlOH + HL- ↔ ⋮AlOH2 +L2- (outer sphere); ⋮Al(OH)2 + H+ + HL- → ⋮AlL + 2H2O (inner sphere).

Dynamic adsorption process of phthalate at goethite/aqueous interface: An ATR-FTIR study

“…The band centered at ∼1445 cm −1 was attributed to benzene ring vibrations [19]. As suggested by previous studies, the six bands at ∼1423, 1407, 1391, 1378, 1365, and 1356 cm −1 should be all associated with symmetric S(COO − ) modes [1,9,20]. As discussed above, the adsorbed phthalate was in the dianionic form, indicating two symmetric COO − stretch vibrations in a certain surface complex.…”

“…The two peaks at 1383 and 1402 cm −1 were clearly resolved in the characteristic symmetric COO − region [1,9,19,20]. Similarly, the second derivative of the strong peak in the asymmetric COO − region revealed two components at 1554 and 1564 cm −1 , though it was seemed as a broad band at around 1552 cm −1 [9]. The appearance of asymmetric and symmetric vibration modes could be attributed to the two equivalent COO − groups which can move in cooperation or in opposition.…”

“…The B-B configuration was also observed by Dobson and McQuillan [8] for phthalate adsorption on TiO 2 , ZrO 2 , Al 2 O 3 , and Ta 2 O 5 . However, Persson et al [9,10] proposed phthalate adsorption on boehmite, aged ␥-Al 2 O 3 , and goethite in outersphere and mononuclear bidentate (M-B) structures. Furthermore, Hwang [1] found that phthalate formed three surface complexes on hematite, namely a fully deprotonated outer-sphere complex and two inner-sphere complexes with respect to a M-B and a B-B complex involving both carboxylate groups.…”

Adsorption and surface oxidation of Fe(II) on metal (hydr)oxides

“…The fitted Stern layer capacitance is C 1 "C 2 = 1.03 ± 0.02 F/m 2 . For data of (Nordin et al, 1997) the capacitance was lower (C 1 "C 2 = 0.80 F/m 2 ), which might point to a lower contribution of the 0 1 0 face to the overall charging behavior in that preparation.…”

“…The charging behavior of boehmite has been measured by Nordin et al (1997) and Klebanov et al (2001) for particles with a surface area of respectively 180 m 2 /g and 124 m 2 /g. The reported PZC values are respectively about 8.6 and 8.5-8.8 (Klebanov et al, 2001).…”