X-ray Analyses of Lead Adsorption on the (001), (110), and (012

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X-ray analyses of lead adsorption on the (001), (110), and (012) hematite surfaces Matthew R. Noerpel, Sang Soo Lee, and John J. Lenhart Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.6b03913 • Publication Date (Web): 21 Oct 2016 Downloaded from http://pubs.acs.org on October 22, 2016

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Environmental Science & Technology

X-ray analyses of lead adsorption on the (001), (110), and (012) hematite surfaces

Matthew R. Noerpel,†,§ Sang Soo Lee,‡ and John J. Lenhart†,* † Department of Civil, Environmental, and Geodetic Engineering The Ohio State University, Columbus, Ohio, 43210, United States ‡ Chemical Sciences and Engineering Division, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439, United States § Present Address: United States Environmental Protection Agency, 5995 Center Hill Ave., Cincinnati, OH 45224, United States

October, 2016

*Corresponding Author (614)688-8157 [email protected] 470 Hitchcock Hall, 2070 Neil Avenue Columbus, OH 43210

ACS Paragon Plus Environment


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Abstract

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Predicting the environmental fate of lead relies on a detailed understanding of its

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coordination to mineral surfaces, which in turn reflects the innate reactivity of the mineral

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surface. In this research, we investigated fundamental dependencies in lead adsorption to

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hematite by coupling extended X-ray absorption fine structure (EXAFS) spectroscopy on

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hematite particles (10 and 50 nm) with resonant anomalous X-ray reflectivity (RAXR) to

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single crystals expressing the (001), (012), or (110) crystallographic face. The EXAFS

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showed that lead adsorbed in a bidentate inner-sphere manner in both edge and corner

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sharing arrangements on the FeO6 octahedra for both particle sizes. The RAXR

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measurements confirmed these inner-sphere adsorption modes for all three hematite

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surfaces and additionally revealed outer-sphere adsorption modes not seen in the EXAFS.

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Lead uptake was larger and pH dependence was greater for the (012) and (110) surfaces,

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than the (001) surface, due to their expressing singly- and triply-coordinated oxygen

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atoms the (001) surface lacks. In coupling these two techniques we provide a more

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detailed and nuanced picture of the coordination of lead to hematite while also providing

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fundamental insight into the reactivity of hematite.

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TOC Graphic

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Introduction

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Lead (Pb) is a highly toxic element that negatively influences nearly all bodily systems.1

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Due to decades of use as an additive to gasoline and paint, Pb is among the most widely

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dispersed metal pollutants in the environment, found in locations ranging from remote

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American forests2 and ice sheets in Greenland and Antarctica,3 to urban areas, where it is

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most heavily accumulated.4 Lead can form precipitates under certain environmental

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conditions (e.g., forming pyromorphite in the presence of phosphate5) and has a strong

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affinity for metal oxides6 and as such it is not expected to remain in solution in soil

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systems when these minerals are present.7 Lead associates with iron oxides in aquatic8

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and soil systems,2, 9, 10 and its adsorption onto nano-scale iron (oxyhydr)oxide particles

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could result in enhanced transport should these particles be mobile.7, 11 Adsorption

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reactions are therefore important to the fate and transport of Pb through the environment.

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Hematite, α-Fe2O3, is a naturally occurring iron oxide commonly found in soils at

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both the nano and macro scale.12 It is one of the most thermodynamically stable iron

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oxides and therefore can occur as the end transition form of other less stable iron

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oxides.12 Hematite particles can exhibit a variety of crystal morphologies, from well-

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defined platy crystals to more spherical shapes, depending on the conditions under which

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they were formed.12 The different particle morphologies result in a different distribution

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of crystallographic faces, which may exhibit unique charging and adsorbent

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characteristics.13 While knowledge of the crystal faces for hematite is not as robust as

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other common minerals, it is generally agreed that the most common hematite crystal

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faces are (001), (012) and (110)14, 15 (see Figure S1).


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Lead adsorption on the surfaces of hematite particles has been studied using a

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number of methods both experimental16-18 and theoretical.19 From macroscopic batch

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adsorption studies it is known that the pH dependent adsorption edge of Pb on hematite

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increases sharply between approximately pH 4 and 6 depending on the electrolytes

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present in solution and the solid:solution ratio.20, 21 McKenzie21 reported that the

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maximum surface coverage of Pb on hematite was 2.7 µmol/m2 at pH 5, which is below

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the pH where the total maximum adsorption will occur in their experimental setup, and

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that the adsorbed Pb was not as easily extractable with acetic acid, as it was from the

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goethite surface. This the authors interpreted as indicative of an inner-sphere complex.

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X-ray absorption spectroscopy provides direct information on adsorbed structures that

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macroscopic techniques fail to provide. For example, Bargar et al.16 utilized extended X-

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ray absorption fine structure (EXAFS) spectroscopy to determine at pH 6 – 8 that Pb

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adsorbs on hematite as a mononuclear bidentate inner-sphere complex on an edge of the

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iron oxide octahedra with a Pb – Fe distance of 3.3 Å. Also using EXAFS, Lenhart et

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al.17 corroborated this edge sharing structure and found an additional binuclear bidentate

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corner sharing arrangement of Pb on the hematite surface at pH 6 with a Pb – Fe distance

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of 3.8 Å.

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While EXAFS provides details of the local coordination environment around the

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target element, it can be difficult to determine exact binding mechanisms as it provides an

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average of the coordination environment in the sample. Thus, in a heterogeneous system,

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all of the local coordinating environments are averaged into a mean condition. The

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results of an EXAFS analysis are also limited to the environment immediately



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surrounding the target atom and in the case of Pb it is only able to probe at most 5 Å from

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the Pb atom.22 This means that details regarding binding at specific crystalline faces and

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contributions from minor coordination modes are lost during sample analyses and data

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fitting.23 Some of these details can be elucidated using single-crystal experiments and

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molecular simulation. For example, Bargar et al.18 applied Grazing Incidence EXAFS

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and X-ray photoelectron spectroscopy (XPS) to single crystals cut to expose the (001)

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and (012) hematite surfaces and identified an oligomeric Pb species not evident in

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previous EXAFS studies.16, 17 Mason et al.19 applied density functional computational

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theory to describe Pb adsorption to the (001) hematite surface and determined a

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prevailing tridentate Pb structure with Pb-O distances slightly shorter than those from

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EXAFS measurements.19

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X-ray reflectivity (XR) is a surface specific technique that provides information on

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the electron density as a function of distance from the surface.24 XR can be combined

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with resonant anomalous X-ray reflectivity (RAXR), which gives the electron density of

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a specific element as a function of distance from the surface,25 to get the total and

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element-specific electron density. As a result, reflectivity allows us to easily see the

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difference between inner-sphere and outer-sphere adsorption processes. This method

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requires that the surface be cut or cleaved to expose a specific plane. Knowing exact

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atomic-level details of the adsorbent surface adds clarity to the adsorption process not

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readily determined with other methods. This increased clarity allows atomic-scale

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observations on the interfacial reactivity, information directly comparable with surface


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complexation models, to be made, and therefore can provide a fundamental

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understanding of lead behavior in natural systems.

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In this paper, two different synchrotron-based X-ray techniques were used to

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elucidate the coordination environment of Pb at the hematite surface, with the objective

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to overcome uncertainties associated with EXAFS determined structures via the direct

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probing of the interface through the use of X-ray reflectivity. EXAFS was performed at

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pH 6, confirming the findings of previous studies that Pb adsorbs in an inner-sphere

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manner to the hematite surface forming both corner sharing and edge sharing bidentate

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complexes on the FeO6 octahedra. XR and RAXR were performed on (001), (012), and

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(110) hematite surfaces at pH 4 and 6. The RAXR analyses indicated that the total Pb

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surface coverage varied between the surfaces studied and also provided evidence that Pb

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was bound to the hematite surfaces not only as an inner-sphere complex but also as an

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outer-sphere complex. Thus, combining single crystal-based XR techniques with

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particle-based EXAFS provides a much more detailed picture of Pb adsorption to

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hematite than did the EXAFS on its own while simultaneously providing fundamental

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details on the reactivity of hematite.

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EXPERIMENTAL

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Hematite. Both hematite particles and single crystals were used in this series of

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experiments. Two sizes of hematite particles were synthesized, nominally 50 nm and 10

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nm, as described in detail in Noerpel and Lenhart26 and summarized in the Supporting

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Information. The 50 nm and 10 nm particles have specific surface areas of

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approximately 35 and 99 m2/g as measured by BET (Micrometrics Flowsorb II 2300),



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and are subsequently referred to as low surface area (LSA) and high surface are (HSA)

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hematite, respectively.

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Crystals, oriented, cut and polished to expose the (001) surface were procured from a

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natural hematite crystal and provided courtesy of Dr. Glenn Waychunas (Lawrence

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Berkeley National Laboratory). Crystals similarly prepared to expose the (012) and (110)

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surfaces were purchased from SurfaceNet GMBH (Rheine, Germany). The crystal

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surfaces were cleaned prior to each experiment following Catalano et al.27, 28 by placing

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each crystal in a methanol bath and sonicating for 5 minutes, followed by 5 minutes in a

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similarly sonicated acetone bath. This was repeated 5 times. Following this, the crystals

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were placed in alternating 10-3 M NaOH and HCl baths and sonicated. Crystals were

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rinsed with DI water (18.2 MΩ-cm from a Millipore system) between baths. Following

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the final acid bath, the crystals were completely rinsed with DI water and annealed at

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450°C for 4 hours and slowly cooled to room temperature.27, 28 We evaluated 3, 2 and 1

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crystals exposing the (001), (110) and (012) faces, respectively, and thus they were

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washed at the conclusion of the experiments (as previously described) and used

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repeatedly.

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EXAFS. Samples were prepared for EXAFS analysis by mixing the hematite particles in

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polycarbonate centrifuge tubes with Pb, supplied from stock solutions of

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Pb(ClO4)2·3H2O, to bring the final concentration of Pb to 0.7 mM for the LSA and 1 mM

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for the HSA. The concentration of LSA hematite was set at 5 g/L (180 m2/L) and the

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HSA, 3 g/L (300 m2/L). Sodium perchlorate was added to set the ionic strength constant

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at 0.1 M. The pH of the stock NaClO4 and Pb(ClO4)2 solutions were adjusted to a value


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of 6 using NaOH or perchloric acid. The pH of the hematite solution was also adjusted to

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6 and it was allowed to equilibrate overnight before the addition of the lead. All solutions

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were CO2-free, and all transfers and measurements were performed under a humidified

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nitrogen atmosphere. Samples were equilibrated on an end-over-end rotator in the dark

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for 24 hours. The pH was checked and adjusted if necessary and the sample was returned

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to the rotator. The solution pH was never more than 0.1 pH units off the target pH of 6.

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At 48 hours, the samples were removed from the rotator and the final pH was determined

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before the samples were centrifuged to separate the solids from the supernatant. The wet

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particle pastes were immediately removed and mounted into PTFE holders that were

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sealed with Kapton tape. The mounted samples were kept in a cool, damp nitrogen

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atmosphere until analyses. The Pb concentration of the supernatant was analyzed with an

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inductively coupled plasma – atomic emission spectrometer (Varian Vista AX CCD-

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Simultaneous ICP-AES), which was subtracted from the initial concentration to

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determine surface coverage.

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Pb LIII EXAFS spectra (binding energy = 13.035 keV) were collected in fluorescence

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mode at beamline 20-BM-B at the Advanced Photon Source at Argonne National

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Laboratory. A Si 111 monochromator was used to select the X-ray energy, and a 1 x 6

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mm2 unfocused incident beam, limited by beam defining slits, was applied to the

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samples. The X-ray beam was detuned by 15% to minimize higher-order harmonics. A

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Canberra 13-element germanium detector was used to measure the samples’

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fluorescence. Several layers of aluminum foil were placed between the sample and

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detector to reduce the iron Kα fluorescence. The detector was set to measure the



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fluorescence from the L3-M5 transition at 10.551 keV. At least 10 scans of all samples

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were taken and merged together to improve the signal to noise ratio. Data analysis was

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performed using Athena and Artemis in the Demeter package.29 To fit the data, a fixed

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amplitude reduction factor, So2, of 0.8425 was used for all elements as has been used in

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previous lead adsorption studies.17, 18 The Debye-Waller function was set to 0.01 for all

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oxygen (O) and iron (Fe) atoms.16-18 The electron binding energy shift, Eo, was

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determined by allowing it to vary in the fit of the first shell oxygen atom and then setting

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the Eo at the determined value to fit the second shell Pb-Fe distances before allowing it to

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vary again during the final fit.17 Input models to FEFF were created by building a

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structure consisting of a Pb atom on Fe oxide octahedra using the chemical modeling

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software GaussView.30

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X-ray Reflectivity. Reflectivity data were collected in situ at beamlines 33-ID-D and 6-

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ID-B at the Advanced Photon Source. Reflectivity experiments were designed to collect

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two complimentary sets of data, with nonresonant XR used to determine the overall

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electron density and RAXR used to determine the Pb specific electron density

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(Supporting Information). The two data sets were collected in series without any changes

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to the setup aside from flushing the crystal surface with fresh solutions in between

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measurements. The samples were prepared by placing clean crystals into a freshly

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prepared 0.1 mM Pb(ClO4)2 solution with 0.1 M sodium perchlorate as a background

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electrolyte, both free of CO2. The solutions were equilibrated in the dark for at least two

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hours, which was shown previously be to sufficient time to achieve equilibrium.18 Each

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surface was tested at pH 4 and pH 6 as the Pb adsorption edge on hematite is located


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within this pH range.21 After equilibration, the crystals were placed in a customized thin-

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film cell covered with a Kapton film.31 The solution used during the crystal surface

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equilibration was subsequently utilized in the cell forming an estimated 2-10 µm thick

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film of water on the crystal surface.32 Care was taken to eliminate air bubbles from the

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system and then excess solution was drained to minimize the amount of solution on the

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crystal surface, which could attenuate the X-ray beam. The holder was placed in the

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diffractometer and the crystal was aligned.

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The XR and RAXR measurement and data analysis followed the approach of Lee et

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al.25 as detailed in the Supporting Information. Briefly, XR data were collected by

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varying the momentum transfer (q = 2πL/d where L is the Bragg index and d is the length

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of the unit cell perpendicular to a surface plane) while keeping the energy constant at 12

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keV, which was not near the absorption edges of any of the elements involved (shown in

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Figures S2 and S3). System stability was monitored in the XR by either returning to a

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specific q value several times during the course of data collection (q = 1.23 and 2.46 Å-1

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on the (001) surface for data collected at 33-ID-D) or by measuring every other data point

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first from high to low q, then back from low to high q to fill in the skipped data points

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(for data collected at 6-ID-B).

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The RAXR scans were collected by varying the photon energy across the LIII edge of

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Pb at 13.035 keV while maintaining a constant q. This was repeated for multiple values

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of q (shown in Figures S4 and S5). The spectrum at a specific q value (q ~ 0.6 Å-1) was

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measured repeatedly throughout the collection of spectra to gauge the stability of the

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system and ensure that the X-ray beam was not changing the system. If the spectrum at



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the specified q value changed from the previous spectrum at that q in amplitude or phase,

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the sample was flushed with fresh solution and moved so that a new spot was illuminated

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by the X-ray beam. The stability of the system was mostly dependent on the surface.

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Measurement of the (001) surface required movement several times an hour whereas the

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(012) and (110) surfaces required movement only a few times per sample.25 All analyses

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were conducted in the dark in order to avoid any complications associated with light

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exposure.25, 33 All of the crystals had a degree of miscut (ca. 1° for the (001) and (012)

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and 0.2° for the (110) surface) to them as evidenced by an additional reflection of the

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incident beam around the midpoint of the Bragg peaks. The miscuts were accounted for

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during data reduction by summing the intensities arising from both signals to get the total

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intensity.28 Data was collected as image files using either a CCD or Pilatus detector. The

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XR and RAXR data were fit using MATLAB (Version 2013b, The MathWorks®, USA)

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using the hematite models of Catalano et al.15, 28, 35-37 which are elaborated on in the

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Supporting Information.

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RESULTS AND DISCUSSION

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EXAFS. The EXAFS spectra (Figure 1, Table 1) were dominated by contributions from

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the backscattering of the first-shell oxygen atoms at an average distance of ~2.30 Å for

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both hematite particle sizes (Table 1). Bargar et al.16 reported aqueous Pb2+ having an

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average Pb-O distance of 2.5 Å. The significant difference in the Pb-O bond distance for

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adsorbed Pb compared to that for dissolved Pb was indicative of the Pb being bound

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directly to oxygen atoms on the hematite surface. The Pb-Fe distance of 3.3 - 3.4 Å was

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consistent with edge sharing bidentate adsorption, whereas a distance greater than 3.9 Å


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suggests that Pb adsorbed in a corner sharing bidentate or a monodentate mononuclear

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manner.16, 17 The second shell Pb-Fe influence can be seen in the χ(k) plot (Figure 1A)

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where the drop in the amplitude of the third antinode was attributed to destructive

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interference in the Pb-Fe and Pb-O oscillations (visualized in Figure S6 and in the Fourier

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Transform, Figure 1B) between 2.5 and 4 Å. The LSA hematite has Pb-Fe distances of

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3.30 and 3.89 Å and the HSA has Pb-Fe distances of 3.34 and 3.94 Å. The Pb-O

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coordination numbers were between 2 and 3 for both particle sizes which reflects the

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distorted trigonal geometry of the doubly coordinated Pb adion.16, 17

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Overall, the results were consistent with previously published Pb EXAFS performed

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on hematite particles.16, 17 The Pb surface coverage for the HSA and LSA hematite was

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3.82 and 3.08 µmol/m2 respectively falling in between the 1.5 µmol/m2 reported by

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Lenhart et al.17 and the 6.7 µmol/m2 reported by Bargar et al.16 There was little

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discernable size dependency in the coordination of Pb on the hematite particles tested.

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This result was different from that presented by Madden et al.38 who found a difference in

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the macroscopic adsorption trends of copper on hematite particles as the particle size

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increased from 7 to 25 nm. Madden et al.38 attributed the increase in adsorption with

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decreasing particle size to an increase in edge sites which copper prefers relative to the

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total number of sites. This suggests that the reactivity of the crystal is dependent on the

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exhibition of specific surfaces. Although we did see evidence for edge-sharing

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coordination, in the form of Pb-Fe distance of 3.3 Å, the relative magnitude of this

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coordination mode for the different sized hematite could not be determined due to the

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uncertainty in the coordination number commonly considered ±20%.16



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X-Ray Reflectivity: (001) Surface. The (001) face, the basal surface of the hexagonal

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crystal structure, is considered the most stable crystalline face on natural hematite14 and

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thus it is the most studied hematite surface.39 The (001) face ideally consists entirely of

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oxygen atoms doubly coordinated to Fe atoms (see Figure S1)40 forming a molecularly

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flat surface.15 On the ideal termination, between pH 2 to 10 these oxygen atoms are

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singly protonated and, therefore, the surface is uncharged41 resulting in the (001) face

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being relatively inert.13

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In DI water the total electron density of the (001) surface exhibits a consistently

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well-defined single-layer termination as evident by the distinct and rapid transition from

248

the narrow, high electron density peaks associated with the bulk crystal to the lower

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broad peaks of the weakly layered water (Figure 2). There is some disagreement in the

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literature as to the actual termination of the (001) hematite surface. For example, in their

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XR study of the (001) hematite face, Trainor et al.35 concluded the termination was not

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ideal and that there were additional FeO6 octahedra “adsorbed” onto the surface breaking

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up the ideal, flat (001) surface. This study was conducted under humidified helium gas

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and vacuum conditions. Similarly, Eggleston et al.42 applied scanning tunneling

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microscopy in water to the (001) hematite surface and reported the existence of a mixed

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oxygen and iron terminated surface. Catalano,37 however, applied XR to the surface and

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determined that the surface was ideally terminated. They observed a very weakly ordered

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water layer and significant relaxation of the surface Fe atoms. Catalano37 conducted

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measurements under in situ conditions that covered the crystal surface with a thin film of

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water. Thus, it seems likely that differences in crystal surface structure observed in the


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literature for the (001) surface reflect sample preparation. We attempted to fit our data

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using a model that included an additional partial layer termination. The optimization led

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to an extremely small partial layer coverage ( (110) > (001) and at pH 4, (110) > (012) > (001). The pH

442

dependence on Pb uptake was most apparent on the (012) face which might be related to

443

the abundance of singly and triply coordinated oxygen atom “ridges” and “valleys” along

444

the [121ത] direction on the surface, or potentially owing to the formation of Pb oligomers

445

at this specific surface at pH 6 (the mechanism of which could not be resolved from this

446

study).

447

Overall, the results for the (110) and (012) faces better match the adsorption of Pb on

448

hematite particles where pH is a controlling factor.21 This was significant as the (001)

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surface is often considered the most abundant in natural hematite39 and since it was the

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least reactive face for Pb adsorption at the tested pH values it likely does not reflect the

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pH dependent behavior observed for Pb adsorption on hematite particles.21 Thus, the

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reactivity of hematite in natural systems likely reflects a combination of surface

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imperfections35,43 that impart reactivity to the (001) surface and the presence of the more

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corrugated surfaces such as those on the (110) and (012) faces. This finding, along with

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the newly identified outer-sphere complex provides insight into the reactivity of hematite



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and can be used to better constrain surface complexation models to form a more complete

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characterization of adsorbed lead.

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Associated Content

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The Supporting Information contains methods for the synthesis and characterization of

460

the hematite nanoparticles. Additional details of the approach to model the X-ray

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reflectivity data are also included, as well as are the absolute reflectivity, relative

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reflectivity and RAXR results for the (001), (110) and (012) surfaces and the shell-by-

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shell EXAFS for lead adsorbed to HSA hematite.

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Acknowledgements

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This work was supported by the U.S. Department of Energy, Office of Science, Office of

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Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences Division under

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Contracts DE-AC02-06CH11357 to UChicago Argonne, LLC as operator of Argonne

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National Laboratory (for S.S.L.) and by the National Science Foundation under Grant No.

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0954991. All X-ray work was performed at the Advanced Photon Source, sectors 6, 20,

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and 33. This research used resources of the Advanced Photon Source, a U.S. Department

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of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science

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by Argonne National Laboratory under Contract No. DE-AC02-06CH11357.

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References

476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518

1. Casas, J. S.; Sordo, J. Lead: Chemistry, Analytical Aspects, Environmental Impact and Health Effects. 1st Ed.; Elsevier: 2006. 2. Kaste, J. M.; Bostick, B. C.; Friedland, A. J.; Schroth, A. W.; Siccama, T. G. Fate and apeciation of gasoline-derived lead in organic horizons of the Northeastern USA. Soil Science Society of America Journal 2006, 70 (5), 1688. 3. Boutron, C. F.; Candelone, J.-P.; Hong, S. Past and recent changes in the large-scale tropospheric cycles of lead and other heavy metals as documented in Antarctic and Greenland snow and ice: A review. Geochimica et Cosmochimica Acta 1994, 58 (15), 3217-3225. 4. Mielke, H. W.; Laidlaw, M. A.; Gonzales, C. R. Estimation of leaded (Pb) gasoline's continuing material and health impacts on 90 US urbanized areas. Environment International 2011, 37 (1), 248-257. 5. Ryan, J. A.; Scheckel, K. G.; Berti, W. R.; Brown, S. L.; Casteel, S. W.; Chaney, R. L.; Hallfrisch, J.; Doolan, M.; Grevatt, P.; Maddaloni, M. Reducing children's risk from lead in soil. Environmental Science & Technology 2004, 38 (1), 18A-24A. 6. O'Reilly, S. E.; Hochella Jr, M. F. Lead sorption efficiencies of natural and synthetic Mn and Fe-oxides. Geochimica et Cosmochimica Acta 2003, 67 (23), 4471-4487. 7. Hassellov, M.; von der Kammer, F. Iron oxides as geochemical nanovectors for metal transport in soil-siver systems. Elements 2008, 4 (6), 401-406. 8. Taillefert, M.; Lienemann, C.-P.; Gaillard, J.-F.; Perret, D. Speciation, reactivity, and cycling of Fe and Pb in a meromictic lake. Geochimica et Cosmochimica Acta 2000, 64 (2), 169-183. 9. Schroth, A. W.; Bostick, B. C.; Kaste, J. M.; Friedland, A. J. Lead sequestration and species redistribution during soil organic matter decomposition. Environmental Science & Technology 2008, 42 (10), 3627-3633. 10. Kaste, J.; Friedland, A.; Miller, E. Potentially mobile lead fractions in montane organic-rich soil horizons. Water, Air, & Soil Pollution 2005, 167 (1-4), 139-154. 11. Lofts, S.; Tipping, E. Solid-solution metal partitioning in the Humber rivers: application of WHAM and SCAMP. Science of the total environment 2000, 251, 381399. 12. Cornell, R. M.; Schwertmann, U. The Iron Oxides: Structure, Properties, Reactions, Occurrences and Uses. Wiley-vch: 2003. 13. Venema, P.; Hiemstra, T.; Weidler, P. G.; van Riemsdijk, W. H. Intrinsic proton affinity of reactive surface groups of metal (hydr) oxides: Application to iron (hydr) oxides. Journal of Colloid and Interface Science 1998, 198 (2), 282-295. 14. Mackrodt, W. C.; Davey, R. J.; Black, S. N.; Docherty, R. The morphology of αAl2O3 and α-Fe2O3: The importance of surface relaxation. Journal of Crystal Growth 1987, 80 (2), 441-446. 15. Catalano, J. G.; Fenter, P.; Park, C. Water ordering and surface relaxations at the hematite (110)‚ water interface. Geochimica et Cosmochimica Acta 2009, 73 (8), 22422251. 16. Bargar, J.; Brown, G.; Parks, G. Surface complexation of Pb (II) at oxide-water interfaces: II. XAFS and bond-valence determination of mononuclear Pb (II) sorption



519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563

products and surface functional groups on iron oxides. Geochimica et Cosmochimica Acta 1997, 61 (13), 2639-2652. 17. Lenhart, J. J.; Bargar, J. R.; Davis, J. A. Spectroscopic evidence for ternary surface complexes in the lead(II)–malonic acid–hematite system. Journal of Colloid and Interface Science 2001, 234 (2), 448-452. 18. Bargar, J. R.; Trainor, T. P.; Fitts, J. P.; Chambers, S. A.; Brown Jr, G. E. In situ grazing-incidence extended X-ray absorption fine structure study of Pb (II) chemisorption on hematite (0001) and (1-102) surfaces. Langmuir 2004, 20 (5), 1667-1673. 19. Mason, S. E.; Iceman, C. R.; Tanwar, K. S.; Trainor, T. P.; Chaka, A. M. Pb (II) Adsorption on Isostructural Hydrated Alumina and Hematite (0001) Surfaces: A DFT Study. The Journal of Physical Chemistry C 2009, 113 (6), 2159-2170. 20. Bargar, J.; Brown Jr, G.; Parks, G. Surface complexation of Pb (II) at oxide-water interfaces: III. XAFS determination of Pb (II) and Pb (II)-chloro adsorption complexes on goethite and alumina. Geochimica et Cosmochimica Acta 1998, 62 (2), 193-207. 21. McKenzie, R. M. The adsorption of lead and other heavy metals on oxides of manganese and iron. Soil Research 1980, 18 (1), 61-73. 22. Templeton, A. S.; Trainor, T. P.; Spormann, A. M.; Newville, M.; Sutton, S. R.; Dohnalkova, A.; Gorby, Y.; Brown, Jr. G. E. Sorption versus biomineralization of Pb(II) within Burkholderia cepacia biofilms. Environmental Science & Technology 2003, 37 (2), 300-307. 23. Nelson, R. C.; Miller, J. T. An introduction to X-ray absorption spectroscopy and its in situ application to organometallic compounds and homogeneous catalysts. Catalysis Science & Technology 2012, 2 (3), 461-470. 24. Fenter, P. X-Ray Reflectvity as a Probe of Mineral-Fluid Interfaces: A User Guide. Reviews in Mineralogy and Geochemistry, 2002, 49, 149-221. 25. Lee, S. S.; Nagy, K.; Park, C.; Fenter, P. Heavy metal sorption at the muscovite (001)-fulvic acid interface. Environmental Science & Technology 2011, 45 (22) 95749581. 26. Noerpel, M. R.; Lenhart, J. J. The impact of particle size on the adsorption of citrate to hematite. Journal of Colloid and Interface Science 2015, 460, 36-46. 27. Catalano, J. G.; Park, C.; Fenter, P.; Zhang, Z. Simultaneous inner- and outer-sphere arsenate adsorption on corundum and hematite. Geochimica et Cosmochimica Acta 2008, 72 (8), 1986-2004. 28. Catalano, J.; Fenter, P.; Park, C. Interfacial water structure on the (012) surface of hematite: Ordering and reactivity in comparison with corundum. Geochimica et Cosmochimica Acta 2007, 71 (22), 5313-5324. 29. Ravel, B.; Newville, M. ATHENA, ARTEMIS, HEPHAESTUS: data analysis for Xray absorption spectroscopy using IFEFFIT. Journal of synchrotron radiation 2005, 12 (4), 537-541. 30. Dennington, R.; Keith, T.; Millam, J. GaussView, version 5. Semichem Inc., Shawnee Mission, KS 2009. 31. Bellucci, F.; Lee, S. S.; Kubicki, J. D.; Bandura, A.; Zhang, Z.; Wesolowski, D. J.; Fenter, P. Rb+ adsorption at the quartz(101)–aqueous interface: Comparison of resonant anomalous X-ray reflectivity with ab initio calculations. The Journal of Physical Chemistry C 2015, 119 (9), 4778-4788.


Page 26 of 34

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564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606


32. Lee, S. S.; Fenter, P.; Park, C. Optimizing a flow-through X-ray transmission cell for studies of temporal and spatial variations of ion distributions at mineral–water interfaces. Journal of synchrotron radiation 2013, 20 (1), 125-136. 33. Francis, A. J.; Dodge, C. J. Influence of complex structure on the biodegradation of iron-citrate complexes. Applied and environmental microbiology 1993, 59 (1), 109-113. 34. Lee, S. S.; Fenter, P.; Nagy, K. L.; Sturchio, N. C. Monovalent ion adsorption at the muscovite (001)-solution interface: relationships among ion coverage and speciation, interfacial water structure, and substrate relaxation. Langmuir 2012, 28 (23), 8637-8650. 35. Trainor, T. P.; Chaka, A. M.; Eng, P. J.; Newville, M.; Waychunas, G. A.; Catalano, J. G.; Brown, Jr. G. E. Structure and reactivity of the hydrated hematite (0001) surface. Surface science 2004, 573 (2), 204-224. 36. Catalano, J.; Zhang, Z.; Park, C.; Fenter, P.; Bedzyk, M. Bridging arsenate surface complexes on the hematite (012) surface. Geochimica et Cosmochimica Acta 2007, 71 (8), 1883-1897. 37. Catalano, J. G. Weak interfacial water ordering on isostructural hematite and corundum (001) surfaces. Geochimica et Cosmochimica Acta 2011, 75 (8), 2062-2071. 38. Madden, A.; Hochella, M.; Luxton, T. Insights for size-dependent reactivity of hematite nanomineral surfaces through Cu2+ sorption. Geochimica et Cosmochimica Acta 2006, 70 (16), 4095-4104. 39. Guo, H.; Barnard, A. S. Thermodynamic modelling of nanomorphologies of hematite and goethite. Journal of Materials Chemistry 2011, 21 (31), 11566-11577. 40. Barron, V.; Torrent, J. Surface hydroxyl configuration of various crystal faces of hematite and goethite. Journal of Colloid and Interface Science 1996, 177 (2), 407-410. 41. Hiemstra, T.; Van Riemsdijk, W. H. Effect of different crystal faces on experimental interaction force and aggregation of hematite. Langmuir 1999, 15 (23), 8045-8051. 42. Eggleston, C. The structure of hematite (α-Fe2O3) (001) surfaces in aqueous media: scanning tunneling microscopy and resonant tunneling calculations of coexisting O and Fe terminations. Geochimica et Cosmochimica Acta 2003, 67 (5), 985-1000. 43. Zarzycki, P.; Chatman, S;; Preocanin, T.; Rosso, K. M. Electrostatic potential of specific mineral faces. Langmuir 2011, 27 (13), 7986-7990. 44. Chatman, S.; Zarzycki, P.; Rosso, K. M. Surface potentials of (001), (012), (113) hematite (α-Fe2O3) crystal faces in aqueous solution. Physical Chemistry Chemical Physics 2013, 15, (33) 13911-13921. 45. Kershner, R. J.; Bullard, J. W.; Cima, M. J. Zeta potential orientation dependence of sapphire substrates. Langmuir 2004, 20 (10), 4101-4108. 46. Eggleston, C.; Jordan, G. A new approach to pH of point of zero charge measurement: Crystal-face specificity by scanning force microscopy (SFM). Geochimica et Cosmochimica Acta 1998, 62 (11), 1919-1923. 47. Lutzenkirchen, J.; Heberling, F.; Supljika, F.; Preocanin, T.; Kallay, N.; Johann, F.; Weisser, L.; Eng, P. Structure-charge relationship - the case of hematite (001). Faraday Discussions 2015, 180, 55-79. 48. Fenter, P.; Sturchio, N. C. Mineral–water interfacial structures revealed by synchrotron X-ray scattering. Progress in Surface Science 2004, 77 (5–8), 171-258.



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49. Bargar, J. R.; Towle, S. N.; Brown, Jr. G. E.; Parks, G. A. Outer-sphere Pb(II) adsorbed at specific surface sites on single crystal [alpha]-alumina. Geochimica et Cosmochimica Acta 1996, 60 (18), 3541-3547. 50. Lee, S. S.; Fenter, P.; Park, C.; Sturchio, N. C.; Nagy, K. L. Hydrated cation speciation at the muscovite (001) - water interface. Langmuir 2010, 26 (22), 1664716651. 51. Rustad, J. R.; Wasserman, E.; Felmy, A. R. Molecular modeling of the surface charging of hematite: II. Optimal proton distribution and simulation of surface charge versus pH relationships. Surface science 1999, 424 (1), 28-35. 52. Ostergren, J. D.; Trainor, T. P.; Bargar, J. R.; Brown Jr, G. E.; Parks, G. A. Inorganic ligand effects on Pb(II) sorption to goethite (α-FeOOH): I. Carbonate. Journal of Colloid and Interface Science 2000, 225 (2), 466-482. 53. Mason, S. E.; Trainor, T. P.; Chaka, A. M. Hybridization-reactivity relationship in Pb(II) adsorption on α-Al2O3-water interfaces: A DFT Study. The Journal of Physical Chemistry C 2011, 115 (10), 4008-4021.


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10 nm Pb (Γ = 3.08 µmol/m2)

k3χ(k)

−4

|χ(R)| (Å )

(B)

50 nm Pb (Γ = 3.82 µmol/m2)

2

622 623 624 625

(A)

3

4

5

6

−1

7

8

9

10

0

1

2

3

4

R (Å)

k (Å )

Figure 1. Least-squared fits (red line) to the experimental results (blue circles) of lead LIII EXAFS spectra at pH 6 represented as (A) k3 weighted χ(k) functions and (B) their Fourier transforms.


5


626 627 628 629 630

Figure 2. Electron density profiles for lead on the (001) surface of hematite at pH 4 and pH 6 determined from the RAXR experiments. The solid black line is the overall electron density and the red area is the lead specific electron density. The blue dashed line is the electron density of the (001) surface in DI water.

631


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632 633 634 635 636 637 638


Figure 3. Electron density profiles for lead on the (012) surface of hematite at pH 4 and pH 6 determined from the RAXR experiments. The solid black line is the overall electron density and the red area is the lead specific electron density. The blue dashed line is the electron density of the (012) surface in DI water. The significant peak above a height of 0 in the total and DI water electron density reflects the presence of a half layer termination.

639



640 641 642 643 644

Figure 4. Electron density profiles for lead on the (110) surface of hematite at pH 4 and pH 6 determined from the RAXR experiments. The solid black line is the overall electron density and the red area is the lead specific electron density. The blue dashed line is the electron density of the (001) surface in DI water.

645


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646 647


Table 1. Fits to Pb LIII EXAFS at pH 6. σ2 was fixed at 0.01 for all elements and the amplitude reduction factor was fixed at 0.8425.16, 17

648 Particle

Pb-O

Pb-Fe

Pb-Fe

Size

CN

R (Å)

CN

R (Å)

CN

R (Å)

E0

R-factor

50 nm

2.94

2.31 (0.01)

0.66

3.30 (0.03)

0.93

3.89 (0.04)

-6.61 (1.02)

0.009

10 nm

2.51

2.30 (0.01)

0.8

3.34 (0.02)

0.59

3.94 (0.04)

-6.60 (0.99)

0.006



649 650 651

Page 34 of 34

Table 2. Best fit model parameters from the RAXR data describing the proximity of lead to the three hematite surfaces. The value in the parenthesis represents the 1σ uncertainty of the last digit(s) of the fitting parameter. The total lead coverage is presented in both µmol /m2 and lead atoms per surface oxygen (Pb/O).

652 χ2

653

First Peak

R-Factor

Second Peak

Third Peak z

Crystal

pH

z

c

µ

z

c

µ

µmol/m

Pb/O

(001)

4

4.14

0.009

1.45 (5)

0.48 (4)

0.48 (10)

7.43 (17)

0.24 (6)

0.89 (29)

0.71 (7)

0.031 (4)

(001)

6

1.51

0.005

1.58 (12)

0.37 (10)

0.58 (15)

3.95 (30)

0.49 (12)

1.22 (28)

0.86 (15)

0.038 (9)

(110)

4

4.84

0.061

0.60 (2)

1.38 (9)

0.22 (3)

3.09 (2)

1.53 (7)

0.25 (3)

6.28 (13)

0.80 (11)

0.82 (17)

3.71 (16)

0.15 (1)

(110)

6

4.12

0.016

0.76 (1)

2.26 (4)

0.26 (2)

3.13 (3)

1.34 (5)

0.38 (3)

6.75 (9)

0.99 (10)

1.29 (16)

4.58 (13)

0.18 (1)

(012)

4

2.27

0.013

1.62 (2)

0.71 (2)

0.2 (f)

4.08 (2)

1.01 (3)

0.59 (3)

1.72 (4)

0.071 (2)

(012)

6

3.51

0.021

1.23 (5)

0.99 (6)

0.2 (f)

3.96 (2)

5.00 (22)

0.57 (3)

6.94 (12)

3.65 (31)

1.56 (12)

9.63 (39)

0.40 (2)

2

z = height above the surface (Å); c = occupancy of the layer (µmol/m ); µ = rms width


c

total µ

2

X-ray Analyses of Lead Adsorption on the (001), (110), and (012

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