Quantitative assessment of pores in oxidized carbon spheres using scanning tunneling microscopy

Surface heterogeneity, particularly shape and size of pores on the surface of activated carbon spheres were studied by using scanning tunneling microscopy (STM) and field-emission type scanning electron microscopy (FE-SEM). Spheres were carbonized either in N₂ or CO₂ atmosphere and oxidized ones were used as samples. A new numerical method based on the determination of contour maps from STM images was proposed in order to determine the size distribution in micropores. These results were discussed with respect to the adsorption of gas and liquid molecules. A good correlation between Brunaner, Emmett, and Teller (BET) surface area determined from adsorption isotherms of N₂ at 77 K and the number of pores with the size of 0.5–1.8 nm was observed, indicating that the proposed procedure to analyze the pore size distribution is effective.