Mesoporous materials are widely used in adsorption, separations, drug delivery, gas storage and as catalytic supports, among others. For these and other applications, characterization of their pore structure is needed for full optimization of their surface area properties. The General Adsorption Isotherm (GAI) developed for ordered porous materials fails when applied to disordered pore constructs. Specifically, the GAI makes an assumption of a metastable or equilibrium adsorption thermodynamic process, with the metastable branch popularly employed on adsorption. In disordered porous materials, however, complexity of the pore architecture allows for an interplay of both metastable and equilibrium thermodynamic processes on adsorption. Analogous to sorption studies, freezing-melting of liquids similarly allows for quantitative analysis of confined spaces.
Herein, we employ the serially-connected pore model (SCPM) which builds on the GAI, by incorporating both equilibrium and metastable thermodynamic conditions for different parts of the system, to offer a more accurate characterization toolbox. Modelled as statistical linear chains of pores, we prove that this model is able to characterize both ordered and disordered porous materials of similar construct. Particularly, we perform Nuclear Magnetic Resonance (NMR) cryoporometry (freezing-melting) studies of water in MCM-41 porous materials to validate the model and show disorder in SBA-15 porous materials.
References [1] Schneider D.; Kondrashova D.; Valiullin R., 2017, “Phase transitions in disordered mesoporous solids”, Scientific Reports, 7, 7216. [2] Schneider, D. and Valiullin R., 2019, “Capillary condensation and evaporation in irregular channels: Sorption isotherm for serially connected pore model”, Journal of Physical Chemistry C, 123, 16239. [3] Enninful H.R.N.B., Schneider D., Hoppe A., König S., Fröba M., Enke D. and Valiullin R., 2019, “Comparative gas sorption and cryoporometry study of mesoporous glass structure: Application of the serially connected pore model”, Frontiers in Chemistry, doi: 10.3389/fchem.2019.00230. [4] Enninful H.R.N.B., Schneider D., Kohns R., Enke D. and Valiullin R., 2020, “A novel approach for advanced thermoporometry characterization of mesoporous solids: Transition kernels and the serially connected pore model”, Microporous and Mesoporous Materials 309, 110534. [5] Enninful H.R.N.B., Schneider D., Enke D. and Valiullin R., 2021, “Impact of Geometrical Disorder on Phase Equilibria of Fluids and Solids Confined in Mesoporous Materials”, Langmuir, Accepted.