Identification of Fluoride and Phosphate Binding Sites at FeOOH Surfaces

Abstract

Iron oxyhydroxide minerals occur widely in nature and play important roles in environmental and industrial processes. Owing to their high reactivity, these minerals can act as sinks and/or transformation centers for a variety of inorganic and organic ions. Interfacial reactions are often mediated by surface (hydr)oxo groups. These groups can be singly, doubly, or triply coordinated with respect to underlying Fe atoms. In order to investigate the reactivity of these differently coordinated groups, Fourier transform infrared (FTIR) spectroscopy was used to examine adsorption products formed on iron oxyhydroxide surfaces. The absence of water was required to probe the O–H stretching region after initial reactions in aqueous media. This work was specifically focused on synthetic, submicrometer-sized lepidocrocite and goethite particles reacted with aqueous solutions of sodium fluoride and monosodium phosphate. Langmuir–Freundlich adsorption isotherms were calibrated on adsorption data in aqueous media at various pH values to obtain the maximum sorption densities for these ions under these conditions. FTIR measurements of the resulting solids dried under N2(g) show that fluoride and phosphate ions preferentially exchange with singly coordinated hydroxyls. Doubly coordinated groups can, however, be exchanged with fluoride ions at relatively high loading densities. Triply coordinated groups remain, in contrast, resilient to exchange. They may, however, stabilize phosphate species by hydrogen bonding. These findings add further constraints to our understanding of adsorption reactions and to the formulation of molecularly adequate thermodynamic models.

Molecular-Scale Study of Salicylate Adsorption and Competition with Catechol at Goethite/Aqueous Solution Interface

“…Goethite was selected as the model mineral due to its widespread occurrence in terrestrial soils and sediment. 18,19 The configurations of catechol on goethite are in M-M and B-B structures, and its dynamic adsorption process has been reported in our previous study. 20 The objective of this study was to explore the interfacial configurations of salicylate on goethite under the effect of pH, concentration, ionic strength, and the competition with catechol.…”

Phosphate alteration of chloride behavior at the boehmite–water interface: New insights from ion-probe flow adsorption microcalorimetry

“…Experiments were conducted using 25.0-57.0 mg of c-AlOOH packed inside the micro-cell which was flanked by the reference thermistor and calibrating resistor on the leading/influent end, and the column thermistors on the downstream/effluent end. Solutions containing the ion-probe molecule (Cl À ) as well as NO 3 À and phosphate were advanced through the cell at a solution flow rate of 0.29 -0.34 mL min À1 . The reference thermistor senses the temperature of the incoming solution while the column thermistor senses the temperature of the effluent after reacting with the c-AlOOH sample.…”

“…surface area, particle size, isoelectric point and crystallinity) which are governed largely by the identity and structure of the lattice metal or by molar ratios of individual metal centers in double-hydroxides and mixed-metal oxides. For example, because of their high reactivity at environmental pH values, aluminum (Al) and iron (Fe)-(hydr)oxides can interact strongly with a variety of solutes, including inorganics [1][2][3][4][5], metals [6][7][8], and organic ions [9][10][11][12][13]. The second interpretation considers physicochemical and catalytic properties (chemical surface heterogeneity) based on morphology of the (hydr)oxide surface, particularly the Lewis (or Brønsted) acidity and basicity of hydroxyl groups.…”

Identifying Phase‐Dependent Electrochemical Stripping Performance of FeOOH Nanorod: Evidence from Kinetic Simulation and Analyte–Material Interactions

“…For β‐FeOOH, the absorption peaks at 3367 cm −1 are the OH stretching vibrations of physically absorbed H 2 O or structural OH − groups . The peak at 892 and 796 cm −1 appeared in the curve of α‐FeOOH can be contributed to FeOH bending vibrations, while for β‐FeOOH it is at 846 cm −1 . The band at 639 cm −1 is attributed to FeO and FeOH stretching in both curves .…”

“…Elucidating the electrochemical behavior determined by the FeOOH crystal phase is of great significance for the design of highly sensitive sensing interface. In addition, the growth processes and the interior structures of α‐ and β‐FeOOH crystal phases in the format of nanorods have been studied and predicted theoretically . However, direct experimental observation in terms of the real morphology and the crystal phases for the 1D nanostructures is still rare …”