Interaction of Chromium(VI) with the α-Aluminum Oxide−Water Interface

Abstract

Interfacial processes can control the transport, speciation, and ultimate fate of aqueous pollutants in groundwater. Here, we apply resonantly enhanced second harmonic generation as well as the χ (3) technique to study the interaction of chromium(VI) with the (11 h02) R-Al 2 O 3 -water interface. Adsorption isotherm measurements yield free energies of adsorption that are consistent with a hydrogen-bonding mechanism mediated through the outer-sphere solvation shell of chromium(VI). Results from measurements regarding the charge state of the R-Al 2 O 3 -water interface as well as the chromium(VI) saturation surface coverages and the pH-dependence of the chromium(VI) equilibrium binding constants are used to develop a thermodynamic and mass-balanced model that describes the interfacial interactions on the molecular level. Special attention is paid to the interfacial speciation state of chromium(VI) as a function of bulk solution pH. Scaling up, we estimate the mobility of chromium(VI) in alumina-rich soils by using the K d model. This work presents a significant advancement in our understanding of the molecular-level interactions between chromium(VI) and R-Al 2 O 3 and improves our ability to predict the environmental mobility, speciation, and ultimate fate of chromium(VI).

Adsorption of Cr(VI) on γ-alumina in the presence and absence of CO2: Comparison of three surface complexation models

“…The TLM requires more parameterization then either the CCM or the DLM, but it has the advantage of allowing sorbates to be explicitly described as inner-or outersphere by placing charges on either the "0" or the "b" plane, and thus allows explicit competition of sorbates with electrolyte cations and anions for adsorption on the "b" plane. Cr(VI) adsorption on substrates including c-alumina (Mikami et al, 1983;Wu et al, 2000;Alvarez-Ayuso et al, 2007), a-alumina (Musorrafiti et al, 2008;Elzinga et al, 2009) and iron oxides (Zachara et al, 1987;Ainsworth et al, 1989;Mesuere and Fish, 1992) is typically assumed to occur via outersphere complexation, although a few studies do suggest innersphere adsorption of Cr on goethite (Fendorf et al, 1997) or a combination of inner-and outersphere complexes (Villalobos et al, 2001). Three reaction stoichiometries were tested using a TLM, two forming outersphere complexes:…”

“…Furthermore, because c-alumina contains both octahedrally and tetrahedrally coordinated aluminum, it has been used as an analog for surface aluminol groups on aluminosilicate minerals (Brady and Walther, 1989;Casey et al, 1989). A few studies demonstrate significant Cr(VI) sorption on c-alumina (Mayer and Schick, 1981;Mikami et al, 1983;Wu et al, 2000;Fritzen et al, 2006;Elzinga et al, 2009), as well as on a-alumina (Honeyman, 1984;Ajouyed et al, 2007;Musorrafiti et al, 2008), which also has a high pH ZPC (5-9.3: Kosmulski, 2002Kosmulski, , 2004Kosmulski, , 2006 but contains only octahedrally-coordinated aluminum.…”

“…A variety of SCMs have been developed to assess potentiometric (Akratopulu et al, 1986;Brady, 1994;Taiwei et al, 1997a,b;Morel et al, 2006), anion sorption (Honeyman, 1984;Manchado et al, 1994;Toner and Sparks, 1995;He et al, 1997;Cheng et al, 2000;Wu et al, 2001;Musorrafiti et al, 2008;Guo et al, 2009) and cation sorption (Brady, 1994;Chang et al, 1994) data for c-alumina. However, SCMs describing Cr(VI) or carbonate sorption on calumina remain scarce.…”

Dye removal using iron–polyphenol complex nanoparticles synthesized by plant leaves

“…It also agrees with the UV/vis spectra of dye removal observed in Figure 4. ΔG ads values are 18 or below, suggesting physical adsorption on to the material as well (Musorrafiti et al, 2008). The negative values of ΔH ads, ΔS ads and ΔG ads indicate that the sorption of dye on Fe-P NPs is spontaneous in nature.…”

Interaction between an organic dye in water and sand packs in a flume system

“…A key feature of environmental chemistry is to understand and predict fluxes of vital and detrimental compounds, because the final destination of high toxicity chemicals can only be properly predicted if all the relevant physical and biogeochemical processes are fully understood [4][5][6][7][8]. Understanding the properties of the interface is particularly important in organic materials and natural sand because of its abundance in the environment and its potential to bind inorganic and organic pollutants [9][10][11][12][13][14].…”