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Adsorption of Trimethyl Phosphate on Maghemite, Hematite, and Goethite Nanoparticles

Makie, Peter; Westin, Gunnar; Persson, Per LU and Osterlund, Lars (2011) In The Journal of Physical Chemistry Part A: Molecules, Spectroscopy, Kinetics, Environment and General Theory 115. p.8948-8959
Abstract
Adsorption of trimethyl phosphate (TMP) on well-characterized hematite, maghemite and goethite nanopartides was studied by in situ DRIFT spectroscopy as a model system for adsorption of organophosphorous (OP) compounds on iron minerals. The iron minerals were characterized by X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), specific surface area, and pore size distribution. The minerals were found to consist of stoichimetrically and morphologically well-defined maghemite, hematite, and goethite nanoparticles. Analysis of in situ diffuse reflectance Fourier transform (DRIFT) spectroscopy shows that TMP bonds mainly to Lewis acid Fe sites through the O phosphoryl... (More)
Adsorption of trimethyl phosphate (TMP) on well-characterized hematite, maghemite and goethite nanopartides was studied by in situ DRIFT spectroscopy as a model system for adsorption of organophosphorous (OP) compounds on iron minerals. The iron minerals were characterized by X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), specific surface area, and pore size distribution. The minerals were found to consist of stoichimetrically and morphologically well-defined maghemite, hematite, and goethite nanoparticles. Analysis of in situ diffuse reflectance Fourier transform (DRIFT) spectroscopy shows that TMP bonds mainly to Lewis acid Fe sites through the O phosphoryl atom (-P=O-Fe) on hematite and maghemite. On goethite most TMP molecules bond to Bronstedt acid surface OH groups and form hydrogen bonded surface complexes. The vibrational mode analysis and uptake kinetics suggest two main reasons for the observed trend of reactivity toward TMP (hematite > maghemite > goethite): (i) larger number of accessible Lewis acid adsorption sites on hematite; (ii) stronger interaction between the Lewis acid Fe sites and the phosphoryl O atom on TAP for hematite and maghemite compared to goethite with concomitant formation of surface coordinated TMP and dimethyl phosphate intermediates. As a result, on the oxides a surface oxidation pathway dominates during the initial adsorption, which results in the formation of surface methoxy and formate. In contrast, on goethite a slower hydrolysis pathway is identified, which eventually yields phosphoric acid. The observed trends of the reactivity and analysis of the corresponding surface structure and particle morphology suggest an intimate relation between the surface chemistry of exposed crystal facets on the iron minerals. These results are important to understand OP surface chemistry on iron minerals. (Less)
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Contribution to journal
publication status
published
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in
The Journal of Physical Chemistry Part A: Molecules, Spectroscopy, Kinetics, Environment and General Theory
volume
115
pages
8948 - 8959
publisher
The American Chemical Society
external identifiers
  • scopus:80051768109
ISSN
1520-5215
DOI
10.1021/jp201065w
language
English
LU publication?
no
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5442a69d-9c59-4147-afa0-12e1c7109168 (old id 4332302)
date added to LUP
2014-03-04 09:45:53
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2017-05-21 03:57:17
@article{5442a69d-9c59-4147-afa0-12e1c7109168,
  abstract     = {Adsorption of trimethyl phosphate (TMP) on well-characterized hematite, maghemite and goethite nanopartides was studied by in situ DRIFT spectroscopy as a model system for adsorption of organophosphorous (OP) compounds on iron minerals. The iron minerals were characterized by X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), specific surface area, and pore size distribution. The minerals were found to consist of stoichimetrically and morphologically well-defined maghemite, hematite, and goethite nanoparticles. Analysis of in situ diffuse reflectance Fourier transform (DRIFT) spectroscopy shows that TMP bonds mainly to Lewis acid Fe sites through the O phosphoryl atom (-P=O-Fe) on hematite and maghemite. On goethite most TMP molecules bond to Bronstedt acid surface OH groups and form hydrogen bonded surface complexes. The vibrational mode analysis and uptake kinetics suggest two main reasons for the observed trend of reactivity toward TMP (hematite > maghemite > goethite): (i) larger number of accessible Lewis acid adsorption sites on hematite; (ii) stronger interaction between the Lewis acid Fe sites and the phosphoryl O atom on TAP for hematite and maghemite compared to goethite with concomitant formation of surface coordinated TMP and dimethyl phosphate intermediates. As a result, on the oxides a surface oxidation pathway dominates during the initial adsorption, which results in the formation of surface methoxy and formate. In contrast, on goethite a slower hydrolysis pathway is identified, which eventually yields phosphoric acid. The observed trends of the reactivity and analysis of the corresponding surface structure and particle morphology suggest an intimate relation between the surface chemistry of exposed crystal facets on the iron minerals. These results are important to understand OP surface chemistry on iron minerals.},
  author       = {Makie, Peter and Westin, Gunnar and Persson, Per and Osterlund, Lars},
  issn         = {1520-5215},
  language     = {eng},
  pages        = {8948--8959},
  publisher    = {The American Chemical Society},
  series       = {The Journal of Physical Chemistry Part A: Molecules, Spectroscopy, Kinetics, Environment and General Theory},
  title        = {Adsorption of Trimethyl Phosphate on Maghemite, Hematite, and Goethite Nanoparticles},
  url          = {http://dx.doi.org/10.1021/jp201065w},
  volume       = {115},
  year         = {2011},
}