NITROGEN INTERACTION WITH SINGLE-WALL CARBON NANOTUBES PROBED VIA IN-SITU VIBRATIONAL SPECTROSCOPY

摘要

The pore size of a carbon material dictates its performance in gas separation, storage, and catalytic applications. Generally speaking, methods for pore size analysis fall into two categories: (i) Methods that rely on fitting a thermodynamic model or model uptake calculations to experimental adsorption data, and (ii) Methods that attempt to directly characterize the pore structure, such as spectroscopy, diffraction, and electron microscopy. Specifically, small angle X-ray scattering (SAXS) is useful for crystalline porous materials, but generally not applicable to amorphous materials that do not scatter X-rays uniformly[1-3]; positron annihilation lifetime spectroscopy (PALS) is sensitive to pore size, as the lifetime of positronium is sensitive to the high electron density within pores [4-6]; transmission electron microscopy (TEM) and/or scanning electron microscopy (SEM) are useful for visualizing highly localized regions, and may be useful deducing pore size, particularly if or tomography is used [7]. All of these "direct" methods tend to be highly specialized, expensive, and/or not widely available. For porous carbon materials, which generally have irregular pore structure, gas adsorption is by far the most common method for deducing both surface area and pore size distribution. Either nitrogen or argon at their normal boiling points are used most frequently, although carbon dioxide at near ambient temperatures has advantages when there are diffusion limitations in micropores at low temperature [8]. Speaking quite generally, adsorption models can be categorized into classic thermodynamic models (such as the BET, Langmuir, H-K models), models derived from simulations (DFT, Non-local DFT), and/or models based on uniformity of adsorption potential.