Structural Evolution of Cr(III) Polymeric Species at the -Al2O3/Water Interface
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- 作者：Jeffrey P. Fitts ; Gordon E. Brown ; Jr. ; and George A. Parks
- 刊名：Environmental Science & Technology
- 出版年：2000
- 出版时间：December 15, 2000
- 年：2000
- 卷：34
- 期：24
- 页码：5122 - 5128
- 全文大小：190K
- 年卷期：v.34,no.24(December 15, 2000)
- ISSN：1520-5851
文摘
We have characterized the structure of the predominantCr(III) species present at the 
-Al2O3/water interface as afunction of equilibration time and Cr(III) surface loadingusing X-ray absorption fine structure (XAFS) spectroscopy.The spectroscopic measurements span two distinct timeperiods of Cr(III) uptake. During the initial period (<2 h),which is characterized by rapid uptake, Cr(III) monomersform inner-sphere complexes on the -Al2O3 surfaceby bonding to at least two surface functional groups. Duringthe second period (ranging from 2 h to 1 week), significantquantities of Cr(III) continue to be removed from solution,but sorption proceeds at a greatly reduced rate. The XAFSspectra collected during the period of slow uptake showan increase in scattering contributions from neighboring Cr(III) atoms with increasing equilibration time. The inferredstructural changes are consistent with a progressionfrom hydroxo-bridged Cr(III) dimers to higher-order polymers.In combination with spectroscopic evidence, whichshows that monomeric Cr(III) species are the only significantreactants in solution, the observed evolution of Cr(III)surface species suggests that chemical bonding betweenadsorbed Cr(III) ions and -Al2O3 surface functionalgroups enhances Cr(III) polymerization. The proposedreaction sequence has important implications for surfacecomplexation modeling used to predict Cr(III) partitioningby hydroxide sorbents in wastewater treatment andcontaminant migration scenarios.
-Al2O3/water interface as afunction of equilibration time and Cr(III) surface loadingusing X-ray absorption fine structure (XAFS) spectroscopy.The spectroscopic measurements span two distinct timeperiods of Cr(III) uptake. During the initial period (<2 h),which is characterized by rapid uptake, Cr(III) monomersform inner-sphere complexes on the -Al2O3 surfaceby bonding to at least two surface functional groups. Duringthe second period (ranging from 2 h to 1 week), significantquantities of Cr(III) continue to be removed from solution,but sorption proceeds at a greatly reduced rate. The XAFSspectra collected during the period of slow uptake showan increase in scattering contributions from neighboring Cr(III) atoms with increasing equilibration time. The inferredstructural changes are consistent with a progressionfrom hydroxo-bridged Cr(III) dimers to higher-order polymers.In combination with spectroscopic evidence, whichshows that monomeric Cr(III) species are the only significantreactants in solution, the observed evolution of Cr(III)surface species suggests that chemical bonding betweenadsorbed Cr(III) ions and -Al2O3 surface functionalgroups enhances Cr(III) polymerization. The proposedreaction sequence has important implications for surfacecomplexation modeling used to predict Cr(III) partitioningby hydroxide sorbents in wastewater treatment andcontaminant migration scenarios.