Interaction of Zn(II) with hematite nanoparticles and microparticles: Part 2. ATR-FTIR and EXAFS study of the aqueous Zn(II)/oxalate/hematite ternary system

Juyoung Ha, Thomas P. Trainor, François Farges, Gordon E. Brown

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Abstract

Sorption of Zn(II) to hematite nanoparticles (HN) (av diam = 10.5 nm) and microparticles (HM) (av diam = 550 nm) was studied in the presence of oxalate anions (Ox (aq) 2-) in aqueous solutions as a function of total Zn(II) (aq) to total Ox (aq) 2- concentration ratio (R = [Zn(II) (aq)] tot/[Ox (aq) 2-] tot) at pH 5.5. Zn(II) uptake is similar in extent for both the Zn(II)/Ox/HN and Zn(II)/Ox/HM ternary systems and the Zn(II)/HN binary system at [Zn(II) (aq)] tot < 4 mM, whereas it is 50-100% higher for the Zn(II)/Ox/HN system than for the Zn(II)/Ox/HM ternary and the Zn(II)/HN and Zn(II)/ HM binary systems at [Zn(II) (aq)] tot > 4 mM. In contrast, Zn(II) uptake for the Zn(II)/HM binary system is a factor of 2 greater than that for the Zn(II)/Ox/HM and Zn(II)/Ox/HN ternary systems and the Zn(II)/HN binary system at [Zn(II) (aq)] tot < 4 mM. In the Zn(II)/Ox/HM ternary system at both R values examined (0.16 and 0.68), attenuated total reflectance Fourier transform infrared (ATR-FTIR) results are consistent with the presence of inner-sphere oxalate complexes and outer-sphere ZnOx (aq) complexes, and/or type A ternary complexes. In addition, extended X-ray absorption fine structure (EXAFS) spectroscopic results suggest that type A ternary surface complexes (i.e., >O 2-Zn- Ox) are present. In the Zn(II)/Ox/HN ternary system at R = 0.15, ATR-FTIR results indicate the presence of inner- sphere oxalate and outer-sphere ZnOx (aq) complexes; the EXAFS results provide no evidence for inner-sphere Zn(II) complexes or type A ternary complexes. In contrast, ATR-FTIR results for the Zn/Ox/HN sample with R = 0.68 are consistent with a ZnOx (s)-like surface precipitate and possibly type B ternary surface complexes (i.e., >O 2-Ox-Zn). EXAFS results are also consistent with the presence of ZnOx (s)-like precipitates. We ascribe the observed increase of Zn (II) (aq) uptake in the Zn(II)/Ox/HN ternary system at [Zn(II) (aq)] tot > 4mM relative to the Zn(II)/Ox/HM ternary system to formation of a ZnOx(s)-like precipitate at the hematite nanoparticle/water interface.

Original languageEnglish
Pages (from-to)5586-5593
Number of pages8
JournalLangmuir
Volume25
Issue number10
DOIs
StatePublished - 19 May 2009

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