In this study, we have investigated oxyanions adsorption reactions on ferrihydrites nanoparticles using flow microcalorimetry (FMC) and density functional theory (DFT). FMC provides a direct, quantitative measure of the heat evolved during a reaction. Besides providing information of thermodynamic significance, i.e., heats of reactions (Q in mJ/mg) and enthalpy changes (DH in kJ.mol-1), FMC can also resolve a complex series of reactions that occur more or less simultaneously but at different rates. The enthalpy values (DH in kJ.mol-1 ) were found to follow a positive Hofmeister series in ΔH Cl- = ΔH NO3- &lt; ΔH SO42- &lt; ΔH PO4- &lt; ΔH AsO42-. Peak shapes analyses revealed that oxyanions reactions differed kinetically in that heat evolution and reactions times were not uniform. DFT simulations used a model nanoparticle that captures step and corner defects rather than modeling 2-D periodic surfaces. While the experimental DHads and DFT DEad seem to agree on the overall trend, there is a discrepancy in their overall magnitudes. Two of the main factors behind this discrepancy are the complex effect of surface coverage and the ability of the DFT modeling to realistically represent the complex experimental system. The real-time collaboration between the experimental and computational work allowed for rapid adjustment of model configurations and computational methods and for the identification of the cause of discrepancies observed between experiments and simulations. The central goal of this work is to close the gap between experimental thermodynamic measurements and theoretical energetic data obtained from computational efforts.

Thermodynamic and kinetic analysis of oxyanions sorption on ferrihydrite using microcalorimetry and density functional theory

2019 Spring National Meeting

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