Effects of Surface Coordination on the Temperature-Programmed Desorption of Oxalate from Goethite

Abstract

The temperature-programmed desorption (TPD) of electrostatically, hydrogen-, and metal-bonded oxalate complexes at the goethite surface was investigated with concerted Fourier transform infrared (FTIR) measurements (TPD-FTIR) to 660 K and mass spectrometer analyses of the evolved gases to 900 K. These reactions took place with the concomitant dehydroxylation reaction of goethite to hematite and decarbonation of bulk-occluded carbonate. The measurements revealed three important stages of desorption. Stage I (300-440 K) corresponds to the desorption of electrostatically and/or unbound oxalate molecules in the goethite powder with a thermal decomposition reaction pathway characteristic of oxalic acid. Stage II (440-520 K) corresponds to the desorption of hydrogen-bonded surface complexes due to the loss of surface hydroxyls at 3660 and 3550 cm -1 , leading to a partial desorption via oxalic acid thermal decomposition pathways and to a partial conversion to metal-bonded surface complexes. Finally, Stage III (520-660 K) corresponds to the thermal decomposition of the metal-bonded oxalate complex, proceeding through a two-electron reduction pathway.

Inner-Helmholtz potential development at the hematite (α-Fe2O3) (001) surface

“…The model also provides evidence for additional reactive adsorption centers on a rough (0 0 1) surface resulting from acid-etching and iron surface complexation/precipitation reactions. The oxalate dianion, a strong chelator which can form stable five-membered chelate complexes on mineral surfaces (Duckworth and Martin, 2001;Yoon et al, 2004;Persson and Axe, 2005;Axe et al, 2006;Boily et al, 2007b), is shown to be reactive with the (0 0 1) surface, yielding drastic changes in electrode potential consistent with the findings of Yanina and Rosso (2008). The thermodynamic model is successful at describing all features of the data set over the 0-14 pH range, and is proposed as a new tool to predict the potentials of hematite electrodes.…”

Water Structure and Hydrogen Bonding at Goethite/Water Interfaces: Implications for Proton Affinities

“…Of these, protonation reactions involving various surface (hydr)­oxo groups are of central importance − to understand interfacial water structure, electric double layer formation, and the overall reactivity of this environmentally important mineral. Although goethite particles of various sizes and morphologies have been the subject of a large number of experimental − and theoretical − studies, unambiguous elucidation of interfacial water structures and proton affinity constants continue to face numerous challenges. Experimental studies of synthetic particles with well-defined crystal habits have been particularly attractive in this regard through a priori knowledge of (hydr)­oxo group identity and disposition.…”

Two-dimensional correlation spectroscopy — Biannual survey 2007–2009

“…Breaking away of absorbed water and weakening of inter-and intrachain hydrogen bonding were observed. Boily et al [178] reported 2D IR study based on temperature-programmed desorption of oxalate complexes at goethite surfaces.…”

“…Norén et al [46,47] studied the adsorption of monocarboxylates, such as acetate, benzoate, and cyclohexanecarboxylate, and ethylenediaminetetraacetate at water interface of iron oxide goethite. Boily et al [178,230] studied desorption of oxalate complexes at goethite surfaces and protonation of oxo-and hydroxo groups at the surface of geothite particles. Shin et al [181] used 2D IRRAS for the thermal behavior of self-assembled monolayers having hydrogen-bonding groups like urea.…”