(155e) Utilizing Ultrasound to Complement Adsorption Characterization of Porous Materials

Physisorption is a standard technique for characterization of nanoporous materials. Adsorption isotherms provide information on the specific surface area of porous samples as well as the pore size distribution [1]. Recent studies showed that the measurements of the speed of ultrasound propagation through a porous sample during gas adsorption can complement the information available from volumetric or gravimetric measurements [2-4].

The speed of ultrasound propagation v in a medium is related to the elastic modulus M and the density of the medium ρ, by a simple equation v = (M/ρ)^1/2. If the medium is porous and it is gradually filled with fluid, its average density is increasing, causing the decrease of the speed of sound. When pores are filled with a dense liquid-like condensate, which has a much modulus compared to vapor, the overall modulus of the medium increases, causing the increase of the speed of sound. Therefore, the ultrasonic signal has the information on the pore filling. Furthermore, molecular simulations suggest that the modulus of the fluid adsorbed in nanopores, is higher than the modulus of the same fluid in bulk, and depends on the pore size [2]. This deviation helps extract the information about the pore size from the speed of sound data. So far, the use of ultrasound is limited to monolithic samples, and in this presentation I will show recent results on combination of adsorption with ultrasound on nanoporous glasses, carbon xerogels and zeolites.

[1] Thommes, M., Kaneko, K., Neimark, A.V., Olivier, J.P., Rodriguez-Reinoso, F., Rouquerol, J. and Sing, K.S., 2015. Physisorption of gases, with special reference to the evaluation of surface area and pore size distribution (IUPAC Technical Report). Pure and Applied Chemistry, 87(9-10), pp.1051-1069.

[2] Maximov, M.A. and Gor, G.Y., 2018. Molecular simulations shed light on potential uses of ultrasound in nitrogen adsorption experiments. Langmuir, 34(51), pp.15650-15657.

[3] Dobrzanski, C.D., Gurevich, B. and Gor, G.Y., 2021. Elastic properties of confined fluids from molecular modeling to ultrasonic experiments on porous solids. Applied Physics Reviews, 8(2), p.021317.

[4] Ogbebor, J., Valenza, J.J., Ravikovitch, P.I., Karunarathne, A., Muraro, G., Lebedev, M., Gurevich, B., Khalizov, A.F. and Gor, G.Y., 2023. Ultrasonic study of water adsorbed in nanoporous glasses. Physical Review E, 108(2), p.024802.