Adsorption of Trimethyl Phosphate on Maghemite, Hematite and Goethite Nanoparticles
2011 (English)In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 115, no 32, 8948-8959 p.Article in journal (Refereed) Published
Adsorption of trimethyl phosphate (TMP) on well-characterized hematite, maghemite and goethite nanoparticles 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 show 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 Brønstedt 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 towards 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 TMP 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 pathways 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.
Place, publisher, year, edition, pages
American Chemical Society , 2011. Vol. 115, no 32, 8948-8959 p.
Trimethyl phosphate, hematite, maghemite, goethite, nanoparticles, adsorption
IdentifiersURN: urn:nbn:se:umu:diva-45372DOI: 10.1021/jp201065wPubMedID: 21711003OAI: oai:DiVA.org:umu-45372DiVA: diva2:429333
Publication Date (Web): June 28, 20112011-07-042011-07-042012-04-10Bibliographically approved