Molecular-Sieving Capabilities of Mesoporous Carbon Membranes

Abstract

The size-sieving properties of a mesoporous carbon membrane were studied via molecular permeation and cyclic voltammetry experiments. Two phenomena, simple diffusion and electrochemically aided diffusion, were investigated. Molecular diffusion through the membrane was caused by a concentration gradient across the membrane and was facilitated by electrosorption of ions under an externally applied electric field. The diffusion of molecules transported through the membrane was characterized by the values of permeability and apparent diffusion coefficient in the membrane. Because larger molecules are more restricted in terms of penetrating the pores, the size-based selectivity of the mesoporous carbon membrane could be readily observed. For example, in the two-component permeation experiment, a high selectivity (alpha=56.9) of anilinium over Rhodamine B was found. It is inferred that the diffusive transport of the larger Rhodamine B molecules with a more extensive retardation comes from the competitive mechanism between the two kinds of molecules in accessing the pore. A series of voltammetric experiments involving a mesoporous carbon membrane immersed in various electrolytes with ions of different sizes allowed the observation of ion-exclusion phenomena. It was found that the size effect is significant for electrochemically aided diffusion and electrosorption processes. The number of cations inside the pores of the membrane decreases with increasing cation size. This phenomenon is due to the size-exclusion effect, which could be demonstrated by the values of electrical double-layer capacitance for sodium, magnesium, and tetrahexylammonium cations, at potentials ranging from negative values to the point of zero charge, corresponding to 86.7, 73.1, and 50.0 F/g, respectively. The findings of this work manifest that the relationship between the pore size and the dimensions of the molecules determines the transport and sorption behavior of nanoporous carbon materials.

Engineering Photocatalytic Cements: Understanding TiO2 Surface Chemistry to Control and Modulate Photocatalytic Performances

“…15. Large molecules like Rhodamine B, with an average molecular diameter of about 1.6 nm, 54 can penetrate only with difficulty the interior of an n ‐TiO 2 cluster (pore size around 8 nm), but readily can access m ‐TiO 2 clusters (see Table I). Moreover, RhB sticks on the cement specimen surface and does not penetrate inside the cement pore structure.…”

Fluidic Carbon Precursors for Formation of Functional Carbon under Ambient Pressure Based on Ionic Liquids

“…Carbon materials are central to many important applications because of their wide availability and superior physicochemical properties, such as electric and thermal conductivities, chemical stabilities, and low densities 1–3. For example, they have been extensively used as electrode materials for batteries,4, 5 fuel cells,6, 7 and supercapacitors8–10 as well as effective supports for catalysis,11–13 separation,14 and gas storage 15. Conventionally, carbon materials can be synthesized by the pyrolysis and physical or chemical activation of low‐vapor‐pressure polymeric precursors derived from either synthetic (e.g., polyacrylonitrile (PAN) and phenolic resins) or natural (e.g., coal, pitch, and shell nuts) polymeric sources at elevated temperatures 16, 17.…”

Highly Ordered Mesoporous Silica Films with Perpendicular Mesochannels by a Simple Stöber‐Solution Growth Approach

“…[10,11] Among these, mesoporous thin films have attracted significant attention owing to their unique structures and functions. [12][13][14][15] Previously, ordered mesoporous silica films have been synthesized by selfassembly of silica precursors with surfactant templates at air-water [16] or water-oil interfaces, [17] or by using the evaporation-induced self-assembly (EISA) approach. [18] As the surfactant micelles tend to orient parallel to substrates to reduce the surface energy at interfaces, the mesochannels obtained are always oriented parallel to the film surfaces.…”