In-situ ATR-FTIR Kinetic Experiments and DFT Calculations on the Surface Chemistry of Dimethylarsinic Acid with Goethite and Hematite Hind A. Al-Abadleh, Chemistry Department, Wilfrid Laurier University Waterloo, ON N2L 3C5 CANADA Dimethylarsinic Acid (DMA) belongs to an important class of methylated organoarsenical compounds that exist in fossil fuels and biomass as impurities of biogeochemical origins. They lower the purity of fuel and poison catalysts used in refinery processes. Our goal is to investigate fundamental properties of DMA interaction with metal (oxyhydr)oxide surfaces relevant to the petroleum industry.
+ DMA- ·(H2O)4
Fe2(OH)5(OH2)5+ ·(H2O)4
85 5 4 3 2 1
6(H2O)
∆Gads = -145 kJ/mol
Example DFT/B3LYP calculations on the formation of the thermodynamically most stable DMA complex with iron clusters
-3
7x10 -1
Adsorption time (min) 793
920 880 840 800 760 720 -1 Wavenumber (cm )
+ 6 DMA-Fe2(OH)5(OH2)3 ·(H2O)4
840
Absorbance at 840 cm
We utilized the surface-sensitive technique attenuated total internal reflectance Fourier transform infrared spectroscopy (ATR-FTIR) to investigate the kinetics of DMA interaction with goethite and hematite particles. We also calculated the thermodynamics of binding using DFT/B3LYP method.
A 0.002 877 b s o r b a n c e Fe2O3
Exp. data 1-site model 2-site model
6 5 4 3 2 1 0 0.01
0.1 1 10 Adsorption Time (min)
100
Results show fast and slow adsorption rates from spectral data, consistent with the formation of more than one type of adsorbed DMA . Calculated values of ∆Gdes indicate that desorption favorability of DMA complexes increases in this order: bidentate < mondentate < outersphere. Next, we will quantify the binding strength and kinetics of DMA to surface covered with organic acids.
