Coordination Complexes of p-Hydroxybenzoate On Fe Oxides

Abstract

Abstract--Adsorption ofp-hydroxybenzoate anion on synthetic Fe oxides, hydroxides, and oxyhydroxides (hereafter referred to as oxides) was measured at pH 5.5, and the organic-oxide interaction was characterized using diffuse-reflectance Fourier-transform infrared (DRIFT) spectroscopy. Surface complexes with ferrihydrite, hematite, goethite, and noncrystalline Fe oxide were investigated. Infrared (IR) spectra of the oxides after separation from p-hydroxybenzoate solutions showed the organic to be coordinated by an inner-sphere mechanism to the oxide surface through the carboxylate group. Bidentate binding of the carboxylate was identified to be the dominant type of complexation on the oxides. Although the IR study suggested that goethite formed the strongest surface iron-carboxylate bond, the total amount of organic adsorbed was the least on this oxide. This result suggested that bond energy was less important than adsorption site density in determining the amount of organic anion adsorption. Increasing ionic strength had little effect on adsorption by the noncrystalline Fe oxide, but dramatically decreased adsorption on hematite and goethite. This difference might have been due to anion competition for binding sites. At pH 5.5, the amount of organic adsorbed per unit weight of oxides (in 0.05 M NaC104) followed the order: ferrihydrite > noncrystalline Fe oxide > hematite >> goethite. Adsorption per unit of surface area however, followed the order: ferrihydrite > hematite > noncrystalline Fe oxide >> goethite. The hematite adsorption reaction appeared to be driven by entropy, inasmuch as the reaction was endothermic. The difference among the oxides in surface reactivity toward p-hydroxybenzoate is hypothesized to have been caused by differences in both quantity and structural arrangement of reactive sites on the oxide surface.

Adsorption of 4-Nitrocatechol, 4-Nitro-2-Aminophenol, and 4-Nitro-1,2-Phenylenediamine at the Metal (Hydr)Oxide/Water Interface: Effect of Metal (Hydr)Oxide Properties

“…comparison of adsorption behavior have been reported (20,22,23,(25)(26)(27), and others), they provide important insight The elemental abundance of aluminum (8.3%), iron into mineral surface property effects on adsorption. An ATR-(6.2%), and titanium (0.63%) in the earth's crust is over-FTIR study of salicylate adsorption onto a-, d-, and g-Al 2 O 3 , a-Fe 2 O 3 (hematite), and a-and g-FeOOH (goethite and 1 Present address: Nicholas School of the Environment, Duke University, lepidocrocite, respectively) conducted by Biber and Stumm PO Box 90328, Durham, NC 27708 ( 22 ) revealed that salicylate does not bind identically on 2 To whom correspondence should be addressed: phone, (919) 613-8039; fax, (919) 684-8741; e-mail, dharni@duke.edu.…”

Modelling of the adsorption of phenolic acids onto α,γ–alumina particles

“…Indeed, they were evidenced in several humus of soils and in fruit peels [14][15][16][17][18][19][20] and these three acids differ only by adding an OH group on the aromatic ring. Adsorption of organic acids onto oxides is maximum for pH values around the pK a of acids [10,[21][22][23][24] and depends on several parameters such as pH, ionic strength, and number and position of ionizable polar functional groups [21,[24][25][26][27][28][29][30][31][32].…”

Elucidating the Mode of Action of a Corrosion Inhibitor for Iron

“…Completing the coordination requirements of the iron(iii) ions are the carboxylate oxygen atoms of fifteen L 1 ligands that each span pairs of adjacent edge-sharing pseudo-octahedral iron atoms. The iron ± oxygen(oxido) bond lengths are much shorter (av 1.909 (17) ) than the iron ± oxygen(hydroxido) bond lengths (av 2.096(40) ), which allows clear distinction between these two ligand types. In complex 2, as in 1, L 1 binds to adjacent iron(iii) atoms through its carboxylate function in a 1,3-bridging mode.…”

“…In other work, [17] DRIFT spectroscopy has been used to demonstrate the 1,3-bridging mode of coordination of a carboxylate ligand to the surface of goethite.…”