Facet-Dependent Cr(VI) Adsorption of Hematite Nanocrystals

Environ Sci Technol. 2016 Feb 16;50(4):1964-72. doi: 10.1021/acs.est.5b05111. Epub 2016 Feb 4.

Abstract

In this study, the adsorption process of Cr(VI) on the hematite facets was systematically investigated with synchrotron-based Cr K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy, in situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, density-functional theory calculation, and surface complexation models. Structural model fitting of EXAFS spectroscopy suggested that the interatomic distances of Cr-Fe were, respectively, 3.61 Å for the chromate coordinated hematite nanoplates with exposed {001} facets, 3.60 and 3.30 Å for the chromate coordinated hematite nanorods with exposed {001} and {110} facets, which were characteristic of inner-sphere complexation. In situ ATR-FTIR spectroscopy analysis confirmed the presence of two inner-sphere surface complexes with C3ν and C2ν symmetry, while the C3ν and C2ν species were assigned to monodentate and bidentate inner-sphere surface complexes with average Cr-Fe interatomic distances of 3.60 and 3.30 Å, respectively. On the basis of these experimental and theoretical results, we concluded that HCrO4(-) as dominated Cr(VI) species was adsorbed on {001} and {110} facets in inner-sphere monodentate mononuclear and bidentate binuclear configurations, respectively. Moreover, the Cr(VI) adsorption performance of hematite facets was strongly dependent on the chromate complexes formed on the hematite facets.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adsorption
  • Chromates / chemistry
  • Chromium / chemistry*
  • Ferric Compounds / chemistry*
  • Nanoparticles / chemistry*
  • Spectroscopy, Fourier Transform Infrared / methods
  • Water Pollutants, Chemical / chemistry
  • X-Ray Absorption Spectroscopy
  • X-Rays

Substances

  • Chromates
  • Ferric Compounds
  • Water Pollutants, Chemical
  • Chromium
  • chromium hexavalent ion
  • ferric oxide