Application of the Long-Period X-ray Standing Wave Technique to the Analysis of Surface Reactivity:  Pb(II) Sorption at α-Al₂O₃/Aqueous Solution Interfaces in the Presence and Absence of Se(VI)

Abstract

A long-period X-ray standing wave (XSW) study of the reactivity of mineral surfaces in contact with metal(loid)-bearing aqueous solutions is presented. Experimental XSW fluorescence yield data for Pb(II) and Pb(II)/Se(VI) adsorption on α-Al2O3(0001) and -(11̄02) surfaces under in situ conditions are described, and the details of the data modeling approach are presented. XSW results for Pb(II) uptake (at [Pb] = 6−600 μM) on the (11̄02) and (0001) surfaces of α-Al2O3 in the absence of Se(VI) confirm that the (11̄02) surface has an overall higher affinity for Pb(II) uptake than the (0001) surface at pH 4.5. The presence of Se(VI) at 600 μM appears to result in a significant diffuse-layer accumulation of Pb, likely because of a large negative surface charge on the α-Al2O3(11̄02) surface, but to exert only a small influence at the (0001) surface. The observed reactivity differences are discussed in terms of the surface structures of the hydrated α-Al2O3(0001) and -(11̄02) substrates.

CTR diffraction and grazing-incidence EXAFS study of U(VI) adsorption onto α-Al2O3 and α-Fe2O3 (11̄02) surfaces

“…As CTR is not sensitive to U(VI) adsorbed onto defect sites, there appears to be an intrinsic difference in the affinity toward U(VI) adsorption between the ␣-Fe 2 O 3 and ␣-Al 2 O 3 (11 02) surfaces. While this difference in reactivity is not as large as that seen for cation adsorption onto the (0001) surfaces of ␣-Al 2 O 3 and ␣-Fe 2 O 3 (Bargar et al, 1997;Templeton et al, 2001;Trainor et al, 2002d), which was due to substantially different surface terminations , it still suggests that there is a structural or electronic difference between ␣-Al 2 O 3 and ␣-Fe 2 O 3 (11 02) surfaces.…”

Mineral-Aqueous Solution Interfaces and Their Impact on the Environment

“…Hydration of the a-Al 2 O 3 (0001) surface essentially passivates it to further rapid reaction with water . In contrast, the hydrated a-Al 2 O 3 (1-102) surface has about equal proportions of one-, two-, and three-coordinated oxygens, based also on CTR diffraction data (Trainor et al ., 2002a;Fig . 10 .…”

“…This method was introduced by Batterman and Golovchenko and co-workers in several classic papers (Batterman, 1964(Batterman, , 1969Golovchenko et al ., 1974;Cowan et al ., 1980) that pointed out the utility of both long-period and short-period (or Bragg) XSW-FY spectroscopy for probing the distribution of metal ions at buried interfaces . Subsequently, the long-period XSW-FY (LP-XSW-FY) method has been used to probe the vertical distribution of atoms at a number of different types of interfaces, including electrochemical interfaces (Bedzyk et al ., 1986;Abruna et al ., 1990); biological membranes (Bedzyk et al ., 1988(Bedzyk et al ., , 1989(Bedzyk et al ., , 1990Wang et al ., 1991Wang et al ., , 2001, organic thin films (Bedzyk, 1992), mineral-water interfaces (Trainor et al ., 2002a;Levard et al ., 2011b) and mineral surfaces coated with microbial biofilms or thin organic films (Templeton et al ., 1999(Templeton et al ., , 2001(Templeton et al ., , 2003bYoon et al ., 2005a) . Bedzyk and Cheng (2002) and Trainor et al (2006) provide excellent reviews of these various applications of LP-XSW-FY spectroscopy through 2006 .…”

Determining the Conformation of an Adsorbed Br−PEG−Peptide by Long Period X-Ray Standing Wave Fluorescence

“…[8][9][10][11] The tunable nature of synchrotron radiation also permits the use of element specific spectroscopic methods, allowing one to investigate various marker atoms in an adsorbed species. Long period x-ray standing wave fluorescence (XSW) and x-ray reflectivity techniques are employed in this work to probe the conformation of molecular adsorbates at the hydrated interface of synthetic biomaterials.…”

“…XSW has been successfully applied to the characterization of various interfacial problems including membrane protein adsorption, Langmuir-Blodgett films, self-assembled monolayers, biofilms on mineral surfaces, and polymer films. 8,10,[19][20][21][22][23] The present study applies XSW to probe the conformation of a model peptide construct at the solid-liquid interface. A bromine (Br) labeled-peptide-polyethylene glycol construct is used to mimic the adsorption of small biological molecules.…”