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Aqueous sodium hydroxide (NaOH) solutions at high pressure and temperature: insights from in situ Raman spectroscopy and ab initio molecular dynamics simulations

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Abstract

Hydrothermal diamond anvil cell experiments in combination with Raman spectroscopy and first principles molecular dynamics simulations were performed to investigate the structure and dynamics of aqueous NaOH solutions for temperatures up to 700 °C, pressures up to 850 MPa and two different solute concentrations. The significant changes observed in the O–H stretching region of the Raman spectra between ambient and supercritical conditions are explained by both dynamic effects and structural differences. Especially important are a Grotthuss-like proton transport process and the decreasing network connectivity of the water molecules with increasing temperature. The observed transfer of Raman intensity towards lower wavenumbers by the proton transfer affects a wide range of frequencies and must be considered in the interpretation of Raman spectra of highly basic solutions. We suggest a deconvolution of the spectra using a model with four Gaussian functions, which are assigned to the molecular H2O and OH vibrations, and one asymmetric exponentially modified Gaussian (EMG) function, which is assigned to [HO(H2O)n] vibrations.

Graphical abstract: Aqueous sodium hydroxide (NaOH) solutions at high pressure and temperature: insights from in situ Raman spectroscopy and ab initio molecular dynamics simulations

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Publication details

The article was received on 17 Jan 2018, accepted on 24 Jul 2018 and first published on 24 Jul 2018


Article type: Paper
DOI: 10.1039/C8CP00376A
Citation: Phys. Chem. Chem. Phys., 2018, Advance Article
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    Aqueous sodium hydroxide (NaOH) solutions at high pressure and temperature: insights from in situ Raman spectroscopy and ab initio molecular dynamics simulations

    J. Stefanski, C. Schmidt and S. Jahn, Phys. Chem. Chem. Phys., 2018, Advance Article , DOI: 10.1039/C8CP00376A

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