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Adsorption of trimethyl phosphate and triethyl phosphate on dry and water pre-covered hematite, maghemite, and goethite nanoparticles

Makie, Peter; Persson, Per LU and Osterlund, Lars (2013) In Journal of Colloid and Interface Science 392. p.349-358
Abstract
Adsorption of trimethyl phosphate (TMP) and triethyl phosphate (TEP) on well-characterized nanopartides of hematite (alpha-Fe2O3), maghemite (gamma-Fe2O3), and goethite (alpha-FeOOH) has been studied by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), 2D correlation DRIFTS analysis, and X-ray photoelectron spectroscopy (XPS) on dry and water pre-covered surfaces. It is shown that, at room temperature and low coverage, both TMP and TEP coordinate to Lewis acid Fe sites through the O phosphoryl atom on hematite and maghemite, while hydrogen bonding to Bronstedt acid surface OH groups dominates on goethite. At room temperature, slow dissociation of TMP occurs on the iron (hydr)oxide nanoparticles, whereby a... (More)
Adsorption of trimethyl phosphate (TMP) and triethyl phosphate (TEP) on well-characterized nanopartides of hematite (alpha-Fe2O3), maghemite (gamma-Fe2O3), and goethite (alpha-FeOOH) has been studied by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), 2D correlation DRIFTS analysis, and X-ray photoelectron spectroscopy (XPS) on dry and water pre-covered surfaces. It is shown that, at room temperature and low coverage, both TMP and TEP coordinate to Lewis acid Fe sites through the O phosphoryl atom on hematite and maghemite, while hydrogen bonding to Bronstedt acid surface OH groups dominates on goethite. At room temperature, slow dissociation of TMP occurs on the iron (hydr)oxide nanoparticles, whereby a methoxy group is displaced to form surface methoxy, leaving adsorbed dimethyl phosphate (DMP). Methoxy is further decomposed to formate, suggesting an oxidative degradation pathway in synthetic air on the oxide particles. Relatively, larger amounts of DMP and surface methoxy form on maghemite, while more formate is produced on hematite. Upon TMP adsorption on dry goethite nanoparticles, no oxidation surface products were detected. Instead, a slow TMP hydrolysis pathway is observed, yielding orthophosphate. It is found that pre-adsorbed water stimulates the hydrolysis of TMP. In contrast to TMP, TEP adsorbs molecularly on all iron hydr(oxide) nanoparticles. This is attributed to the longer aliphatic chain, which stabilizes the loss of charge on the methoxy C-O bonds by charge redistribution upon phosphoryl O coordination to Fe surface atoms. The presented results implicate different reactivity depending on specific molecular structure of the organophosphorus compound (larger functional groups can compensate loss of charge due to surface coordination) and iron (hydr)oxide surface structure (exposing Lewis acid or Bronstedt acid sites). (c) 2012 Elsevier Inc. All rights reserved. (Less)
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author
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published
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in
Journal of Colloid and Interface Science
volume
392
pages
349 - 358
publisher
Elsevier
external identifiers
  • scopus:84872358280
ISSN
1095-7103
DOI
10.1016/j.jcis.2012.10.012
language
English
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no
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c3a43f9e-add6-4bd3-b46d-e048d676b04a (old id 4332217)
date added to LUP
2014-03-04 09:44:56
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2019-07-02 01:15:22
@article{c3a43f9e-add6-4bd3-b46d-e048d676b04a,
  abstract     = {Adsorption of trimethyl phosphate (TMP) and triethyl phosphate (TEP) on well-characterized nanopartides of hematite (alpha-Fe2O3), maghemite (gamma-Fe2O3), and goethite (alpha-FeOOH) has been studied by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), 2D correlation DRIFTS analysis, and X-ray photoelectron spectroscopy (XPS) on dry and water pre-covered surfaces. It is shown that, at room temperature and low coverage, both TMP and TEP coordinate to Lewis acid Fe sites through the O phosphoryl atom on hematite and maghemite, while hydrogen bonding to Bronstedt acid surface OH groups dominates on goethite. At room temperature, slow dissociation of TMP occurs on the iron (hydr)oxide nanoparticles, whereby a methoxy group is displaced to form surface methoxy, leaving adsorbed dimethyl phosphate (DMP). Methoxy is further decomposed to formate, suggesting an oxidative degradation pathway in synthetic air on the oxide particles. Relatively, larger amounts of DMP and surface methoxy form on maghemite, while more formate is produced on hematite. Upon TMP adsorption on dry goethite nanoparticles, no oxidation surface products were detected. Instead, a slow TMP hydrolysis pathway is observed, yielding orthophosphate. It is found that pre-adsorbed water stimulates the hydrolysis of TMP. In contrast to TMP, TEP adsorbs molecularly on all iron hydr(oxide) nanoparticles. This is attributed to the longer aliphatic chain, which stabilizes the loss of charge on the methoxy C-O bonds by charge redistribution upon phosphoryl O coordination to Fe surface atoms. The presented results implicate different reactivity depending on specific molecular structure of the organophosphorus compound (larger functional groups can compensate loss of charge due to surface coordination) and iron (hydr)oxide surface structure (exposing Lewis acid or Bronstedt acid sites). (c) 2012 Elsevier Inc. All rights reserved.},
  author       = {Makie, Peter and Persson, Per and Osterlund, Lars},
  issn         = {1095-7103},
  language     = {eng},
  pages        = {349--358},
  publisher    = {Elsevier},
  series       = {Journal of Colloid and Interface Science},
  title        = {Adsorption of trimethyl phosphate and triethyl phosphate on dry and water pre-covered hematite, maghemite, and goethite nanoparticles},
  url          = {http://dx.doi.org/10.1016/j.jcis.2012.10.012},
  volume       = {392},
  year         = {2013},
}