Determining the pore structure of activated carbon by nitrogen gas adsorption
When considering a material for use as a catalyst or adsorbent, the pore structure is critical. The structure is defined by the pore size distribution and connectivity between the pores. Often there is a balance between accessibility by having larger pores, and increased dispersion of active sites by having a high surface area created by many smaller pores. Traditionally materials have been characterized by collecting nitrogen adsorption data and fitting this data with various models to obtain the surface area, pore volume, and pore size distribution. These models, however, are often applied incorrectly and without fully understanding their limitations. For non-uniform materials, it may not be obvious when the fit provided by a model is not correct, which adds to the challenge. This article reviews various models and outlines considerations for applying these models to activated carbon materials. The characterization of four carbon materials with different pore structures will be discussed to illustrate the challenges of using nitrogen adsorption to determine pore structures.