Adsorption of Organic Matter at Mineral/Water Interfaces: 7. ATR-FTIR and Quantum Chemical Study of Lactate Interactions with Hematite Nanoparticles
The interaction of the l-lactate ion (l-CH{sub 3}CH(OH)COO{sup -}, lact{sup -1}) with hematite ({alpha}-Fe{sub 2}O{sub 3}) nanoparticles (average diameter 11 nm) in the presence of bulk water at pH 5 and 25 C was examined using a combination of (1) macroscopic uptake measurements, (2) in situ attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy, and (3) density functional theory modeling at the B3LYP/6-31+G* level. Uptake measurements indicate that increasing [lact{sup -1}]{sub (aq)} results in an increase in lact{sup -1} uptake and a concomitant increase in Fe(III) release as a result of the dissolution of the hematite nanoparticles. The ATR-FTIR spectra of aqueous lact{sup -1} and lact{sup -1} adsorbed onto hematite nanoparticles at coverages ranging from 0.52 to 5.21 {mu}mol/m{sup 2} showed significant differences in peak positions and shapes of carboxyl group stretches. On the basis of Gaussian fits of the spectra, we conclude that lact{sup -1} is present as both outer-sphere and inner-sphere complexes on the hematite nanoparticles. No significant dependence of the extent of lact{sup -1} adsorption on background electrolyte concentration was found, suggesting that the dominant adsorption mode for lact{sup -1} is inner sphere under these conditions. On the basis of quantum chemical modeling, we suggest that inner-sphere complexes of lact{sup -1} adsorbed on hematite nanoparticles occur dominantly as monodentate, mononuclear complexes with the hydroxyl functional group pointing away from the Fe(III) center.
- Research Organization:
- Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 1006989
- Journal Information:
- Langmuir, Vol. 24, Issue (13) ; 2008; ISSN 0743-7463
- Country of Publication:
- United States
- Language:
- ENGLISH
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