Adsorption properties of templated nanoporous carbons comprising 1–2 graphene layers

Abstract

A variety of vapor adsorption (water, methanol, ethanol, dichloromethane, and n-hexane) is examined on templated nanoporous carbons consisting of 1-2 graphene layers including microporous zeolite-templated carbon (ZTC), mesoporous carbon mesosponge (CMS) and graphene mesosponge (GMS). Conventional nanoporous carbon materials are used as references. While water-vapor adsorption is peculiar because of the repulsion between H2O molecules and hydrophobic carbon, organic-vapor adsorption basically follows the mechanism of typical physisorption. The graphene-based nanoporous materials exhibit a noticeable degree of adsorption-induced expansion from their extraordinary softness except the case of inferior water-vapor adsorption on mesoporous CMS and GMS. CMS exhibits an especially large degree of adsorption-induced expansion, and achieved very high adsorption capacities up to 4.25-4.76 cm 3 g -1 for organic vapors, demonstrating its feasibility as a high-capacity adsorbent. The adsorption isotherms of ZTC at 278 K and 298 K for n-hexane are overlapping well, and it is advantageous for a new type of heat pump working with force-induced phase transition. Moreover, this work provides a general prediction of the ease of organic-vapor adsorption by the product of surface tension and molar volume.

Pore-size control of soft mesoporous carbon by hot pressing

“…This can be ascribed to the fact that the stacking structure is formed not during the CVD process but by capillary force upon drying. Indeed, we were able to control the CVD conditions to achieve the average stacking numbers of graphene between 1.0 and 1.1, 54 and avoid the formation of tightly stacked graphene structures during the CVD process. The structural changes of the graphene walls were analyzed also using Raman spectroscopy (Fig.…”

“…1a) were uniformly coated with a thin carbon layer using CVD with a gas mixture of methane (20 vol%) and N 2 at 900 °C. 54 The CVD time duration was adjusted to achieve the desired carbon-loading amount corresponding to an average graphene stacking number of 1.0 to 1.1, depending on the synthesis scale. The resulting carbon-coated Al 2 O 3 nanoparticles (Fig.…”

“…The evaluation of the graphene edge sites was performed by measuring the amount of desorbed gas from a sample using an in-house temperature-programmed desorption (TPD) device at temperatures up to 1800 °C under vacuum. [51][52][53][54][55] The bulk modulus of the samples were obtained by a mercury-intrusion technique. 41,43 Specifically, the volume change Δ𝑉 is measured when the sample is placed in a vacuum chamber and isotropically compressed by mercury.…”

“…Considering their identical pore structures as well as the average graphene stacking number of their frameworks, 54 the number of edge sites may affect the bulk modulus. We have previously reported that CMS shows a more intense adsorption-induced deformation than GMS, 54 and this was attributed to the softer property of CMS. The bulk moduli determined for CMS and GMS confirm our previous predictions.…”

“…39,49 The difference between CMS and GMS is the number of carbon edge sites, while their porous textures are identical and both of them consist mainly of rarely stacked graphene walls. 54 While GMS is intensively stabilized at 1800 °C and it is hard to change its mesoporous structure by mechanical pressure, 49 CMS is metastable and it is expected that the pore size may be tuned by hot pressing. Herein, we demonstrate the post-synthesis pore-size control in CMS, and discuss the structural changes in detail.…”