Micro-Raman analysis of association equilibria in supersaturated NaClO4 droplets

Abstract

We report an in situ strategy for the quantitative analysis of association equilibria in a single NaClO(4) droplet of nanogram mass deposited on a quartz substrate. In the new approach, the single droplet was forced to enter into a supersaturated state by decreasing the relative humidity (RH) of the environment, allowing accurate control over the concentration of the solute within the droplet. An analysis of the solvated structure of the ClO(4)(-) anion with change in molar water-to-solute ratio (WSR) was performed by micro-Raman spectroscopy within the confines of a single droplet. The symmetric stretching v(1)-ClO(4)(-) band was observed to shift from a Stokes frequency of 935 to 944 cm(-1) and was accompanied by a change in the full width at half-maximum (FWHM) from 11.4 to 16.6 cm(-1) as the WSR decreased from 16.1 to 2.3. From component band analysis of the spectral range of 900-970 cm(-1), four peaks at 933.3, 938.6, 944.1 and 946.0 cm(-1) were identified and assigned to the free solvated perchlorate anion, the solvent-shared ion pair, the contact ion pair and complex ion aggregates, respectively. As expected, the signature of the free solvated ClO(4)(-) ion was observed to decrease in intensity with a decrease in RH over the full range from 94 to 27%. The intensity of the signature from solvent-shared ion pairs was observed to rise with decrease in RH from 94% to 75% before decreasing as the RH was further reduced to 27%. Signatures of the contact ion pair and of complex ion aggregates were shown to increase over the full range of RH as the RH was reduced. Based upon the Eigen mechanism, three association equilibria were used to describe the transformations between the free solvated perchlorate anion, the solvent-shared ion pair, the contact ion pair and complex ion aggregates. The overall association constant K and the stepwise association constants K(i) (i = 1 to 3) were determined separately (0.27 +/- 0.01, 0.03 +/- 0.01, 5.49 +/- 0.95, 0.76 +/- 0.06).

Towards High‐Performance Aqueous Sodium‐Ion Batteries: Stabilizing the Solid/Liquid Interface for NASICON‐Type Na2VTi(PO4)3 using Concentrated Electrolytes

“…The full spectra are shown in Figure S3. [40,41] Upon increasing the NaClO 4 concentration, the contact ion pairs/ionic aggregate band increases, whereas the solvent-separated ion pairs, free solvated ClO 4 À ,a nd overtone band v 2 -ClO 4 features decrease. [34,39] Figure 2a shows the ClO 4 stretching mode at room temperature, occurring in the ñ = 890-970 cm À1 range, whichcan be used for the evaluation of NaClO 4 in aqueous electrolytes.…”

“…By component band analysis, the four Lorentzian-Gaussian bands at ñ % 945.0, 935.0, 925.0, and 915.0 cm À1 can be assignedt oc ontact ion pairs/aggregated ion pairs, solvent-separatedi on pairs, free but solvated ClO 4 À anions, and the v 2 -ClO 4 overtone, respectively. [40,41] Upon increasing the NaClO 4 concentration, the contact ion pairs/ionic aggregate band increases, whereas the solvent-separated ion pairs, free solvated ClO 4 À ,a nd overtone band v 2 -ClO 4 features decrease. However, as ignificant degree of ion pairing and aggregation can be observed in all electrolytes.…”

Heterogeneous Formation of Sulfur Species on Manganese Oxides: Effects of Particle Type and Moisture Condition

“…In eq 6, y 0 is the baseline offset, A is the total area, x c is the peak center, w is the full width of the peak at half-maximum (fwhm), and m u is the profile shape factor. 60,61 During the spectra deconvolution, A and w were taken as variables while the x c and m u remained unchanged. The deconvolution result was not adopted until the correlation coefficient (R 2 ) was higher than 0.90.…”

Complexity of Measuring and Representing the Hygroscopicity of Mixed Component Aerosol

“…51 In the mixtures containing both acidic and basic components in supersaturated solution, charged species in solution could interact more strongly with their contact ion pairs than interactions via hydrogen bonding with water molecules, thereby supressing the hygroscopic response of the solute mixture. 53 In conclusion, available modelling methods and current experimental methods cannot be used to determine the pH at supersaturated solute conditions for mixtures of dicarboxylic and amino acids. Refined models that account for the changes in activity coefficient for these non-ideal solutions with variation in water activity are required.…”