Abstract
Multivalent cations primarily exist as polynuclear hydroxo and oxyhydroxo clusters and/or nanoparticles (NPs) in aqueous environments, where their interactions with mineral surfaces can be influenced by complexing anions. Here, we investigated the distribution of tetravalent Zr adsorbed on the negatively charged basal surface of muscovite mica in four background electrolytes (0.1 M NaClO4, 0.1 M NaCl, 0.04 M Na2SO4, and 0.045 M Na2HPO4) at constant pH (=3), total Zr(IV) concentration (=0.1 mM), and ionic strength (=0.1 M). The results show that aqueous Zr speciation determined by reactions with anions controls the formation and structure of Zr-containing adsorbates on the mica surface. The Zr coverages measured by X-ray fluorescence in ClO4 - and Cl- systems were 1.3 and 2.1 Zr/AUC (where AUC = 46.72 Å2 is the area of the unit cell of the mica (001) surface), respectively, and mostly remained unchanged during the reaction time from 6 to 50 h. In these conditions, Zr adsorption occurred both as small NPs (with an average height of ∼4 nm observed by ex situ atomic force microscopy, AFM) and in a ∼2 nm-thick molecular layer (observed by in situ resonant anomalous X-ray reflectivity, RAXR). In comparison, higher Zr coverages that increased with reaction time (i.e., from ∼4 to ∼7 Zr/AUC from 6 to 50 h reactions) were observed in the SO4 2- system. Ex situ AFM revealed that the Zr uptake in this system occurred predominantly as NPs that were ∼5-15 nm tall and 20-40 nm wide, but no evidence of the interfacial molecular-layer formation was observed by RAXR. In the HPO4 2- solution, all measurements unequivocally showed no significant Zr sorption, in stark contrast to the observations in the other solutions. Details of the Zr surface coverage and sorption modes are consistent with the known clustering of tetravalent Zr in solutions in the presence of these anions. These results demonstrate the significant impact of anions on the adsorption affinity and mechanism of Zr on the negatively charged mica surface.
| Original language | English |
|---|---|
| Pages (from-to) | 16699-16710 |
| Number of pages | 12 |
| Journal | Journal of Physical Chemistry C |
| Volume | 123 |
| Issue number | 27 |
| DOIs | |
| State | Published - Jun 10 2019 |
Funding
This work was supported by U.S. Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences Division under Contract DE-AC02-06CH11357 to UChicago Argonne, LLC, as operator of Argonne National Laboratory (“Argonne”), a U.S. Department of Energy Office of Science laboratory. M.S. has received funding from the Helmholtz Gemeinschaft Deutscher Forschungszentren by supporting the Helmholtz–Nachwuchsgruppe “Structures and Reactivity at the Water/Mineral Interface” (VH-NG-942). This research used resources of the Advanced Photon Source, a U.S. DOE Office of Science User Facility, beamlines 6-ID-B, 12-ID-D, and 33-ID-D, operated for the DOE Office of Science by Argonne under contract no. DE-AC02-06CH11357. The U.S. Government retains for itself, and others acting on its behalf, a paid-up nonexclusive, irrevocable worldwide license in said article to reproduce, prepare derivative works, distribute copies to the public, and perform publicly and display publicly, by or on behalf of the Government. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan.
| Funders | Funder number |
|---|---|
| DOE Office of Science | |
| Helmholtz Gemeinschaft Deutscher Forschungszentren | VH-NG-942 |
| Office of Basic Energy Sciences | |
| U.S. Department of Energy Office of Science Laboratory | |
| U.S. Department of Energy | |
| Office of Science | |
| Argonne National Laboratory | |
| Chemical Sciences, Geosciences, and Biosciences Division | DE-AC02-06CH11357 |