Structure of Sulfuric Acid Solutions Using Pair Distribution FunctionAnalysis

Solvation and mesoscale ordering of sulfuric acid and otherstrong acid solutions leads to suppressed freezing points and strongrheological changes with varying concentration. While the solid-statestructures are well-understood, studies focused on the evolving solvationstructure in the solution phase have probed a limited concentration range(similar to 1-6 M). This study applies a total scattering approach in both the wide-angle X-ray scattering (WAXS) and pair distribution function (PDF) regimesto elucidate the evolving solvation structure over its full range of acidconcentration (0-18 M). The emergence of a prepeak in the WAXS regimeat intermediate concentrations indicates a transition from noninteractingsulfate molecules in the dilute limit to sterically limited sulfates at concentrations near its deep eutectic point. Fits to the PDF dataquantify this trend, showing a transition from octahedrally hydrated sulfates up to 6-7 M concentrations, followed by gradualdehydration, and eventually reaching a solution structure similar to that of water-in-salt electrolyte systems at high acidconcentrations

Automated summary

This study used total scattering approach to elucidate the evolving solvation structure of sulfuric acid solutions from 0-18M concentrations. A transition from octahedrally hydrated sulfates up to 6-7 M concentrations, followed by gradual dehydration was observed, reaching a solution structure similar to high acid concentrations water-in-salt electrolyte systems.