Characterization of Porous Silica Materials with Water at Ambient Conditions. Calculating the Pore Size Distribution from the Excess Surface Work Disjoining Pressure Model

Abstract

Characterization of mesoporous materials today is routinely performed recording the adsorption isotherm of nitrogen at 77 K. The pore size distribution (PSD) can subsequently be determined using either thermodynamics or statistical mechanics based approaches. While nitrogen has evolved as the reference adsorptive, other gases are often used to extract more information from the isotherm. This contribution is focused on the calculation of a PSD from the water vapor isotherm. It is demonstrated that water adsorption provides accurate results comparable to the standard nitrogen adsorption.

The Impact of Cloud Processing on the Ice Nucleation Abilities of Soot Particles at Cirrus Temperatures

“…This is an advantage, given that in terms of ice nucleation ability we are interested in the interaction of soot particles with water vapor. Besides, recent studies have shown that PSD derived from water sorption reveals comparable results to other methods frequently used (Georgi et al, 2017). Finally, we would like to point out the limitations of the method to derive a PSD.…”

“…When studying porous silica particles, n c is often assumed to be equivalent to an adsorbed water monolayer capacity (e.g., Adolphs & Setzer, ; Adolphs, ). Using this monolayer capacity, the film thickness can be calculated at any amount of water adsorbed by where τ is the thickness of a single layer of adsorbate ( nm; Georgi et al., ). What remains to be done is a transformation of the sorption isotherms from V a − p / p 0 coordinates into V a ‐ r coordinates, in order to derive an expression for the dV a / dr term when evaluating equation .…”

“…The water sorption isotherm can also be used to assess particle porosity. When using water sorption isotherms to determine a PSD, the nonlocal density function theory (NLDFT) frequently applied to derive PSD from N 2 sorption on mesoporous silica particles cannot readily be employed (Georgi et al., ). This mainly results from different interaction potentials of polar water molecules with the adsorbent surface, compared to N 2 , which has a symmetric potential that can be described as a Lennard‐Jones potential.…”

“…where τ is the thickness of a single layer of adsorbate (τ H2O ¼0:24 nm; Georgi et al, 2017). What remains to be done is a transformation of the sorption isotherms from V a −p/p 0 coordinates into V a -r coordinates, in order to derive an expression for the dV a /dr term when evaluating equation (5).…”

Connections Matter: On the Importance of Pore Percolation for Nanoporous Supercapacitors

“…[14][15][16][17] However, other gases have also been used, for instance argon and hydrogen 14 as well as the water vapor. 18 The cases of equal and different PSDs obtained by different probes were reported; 16 the differences could be particularly due to inter-pore connectivity, which might appear different for different probes.…”