Arsenate adsorption on ruthenium oxides: A spectroscopic and kinetic investigation

• Published in: Journal of colloid and interface science 2008-09, Vol.325 (1), p.23-30
• Main Authors: Luxton, Todd P., Eick, Matthew J., Scheckel, Kirk G.
• Format: Article
• Language: English
• Subjects: ADSORPTION; ARSENATES; Arsenates - chemistry; Arsenic; Chemistry; Colloidal state and disperse state; DESORPTION; Exact sciences and technology; EXAFS; General and physical chemistry; Hydrogen-Ion Concentration; INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; KINETICS; Organometallic Compounds - chemistry; Oxides - chemistry; Pressure-jump relaxation; RELAXATION; Ruthenium - chemistry; Ruthenium oxide; RUTHENIUM OXIDES; Solutions - chemistry; SORPTIVE PROPERTIES; Spectrometry, X-Ray Emission; Surface physical chemistry; Surface Properties
• ISSN: 0021-9797; 1095-7103
• DOI: 10.1016/j.jcis.2008.05.022

Arsenate adsorption on amorphous (RuO 2⋅1.1H 2O) and crystalline (RuO 2) ruthenium oxides was evaluated using spectroscopic and kinetic methods to elucidate the adsorption mechanism. Extended X-ray absorption fine structure spectroscopy (EXAFS) was used to determine the local coordination environment of adsorbed arsenate. Additionally, pressure-jump (p-jump) relaxation spectroscopy was used to investigate the kinetics of arsenate adsorption/desorption on ruthenium oxides. Chemical relaxations resulting from the induced pressure change were monitored via electrical conductivity detection. EXAFS data were collected for two initial arsenate solution concentrations, 3 and 33 mM at pH 5. The collected spectra indicated a similar coordination environment for arsenate adsorbed to RuO 2⋅1.1H 2O for both arsenate concentrations. In contrast the EXAFS spectra of RuO 2 indicated differences in the local coordination environments for the crystalline material with increasing arsenate concentration. Data analysis indicated that both mono- and bidentate surfaces complexes were present on both RuO 2⋅1.1H 2O and RuO 2. Relaxation spectra from the pressure-jump experiments of both ruthenium oxides resulted in a double relaxation event. Based on the relaxation spectra, a two step reaction mechanism for arsenate adsorption is proposed resulting in the formation of a bidentate surface complex. Analysis of the kinetic and spectroscopic data suggested that while there were two relaxation events, arsenate adsorbed to ruthenium oxide surfaces through both mono- and bidentate surface complexes. Schematic representation of the proposed arsenate adsorption mechanism on ruthenium oxide.