MICROSCOPIC IMAGE ANALYSIS TECHNIQUES TO CHARACTERIZE SURFACE MORPHOLOGY AND ADSORPTION MECHANISMS OF ACTIVATED CARBON

Activated carbon is widely used to remove organic contaminants from contaminated water or air. Although the highly active surface properties of the activated carbon are often attributed to the chemical functional groups, surface morphology also plays a significant role in determining the surface availability. The typical surface area of activated carbon ranges from 50 to 120 square meters per gram. Although the activated carbon has significant porosity, the most important part of an activated carbon particle is still the exterior surfaces where the reactive groups are easily accessible. Depending on the preparation methods used, activated carbon contains micropores, mesopores and macropores. The pore size defines which types of molecules could be adsorbed on the carbon surface. The objectives of this study were to evaluate the effect of surface morphology on the adsorption mechanisms of the contaminants on the carbon surface. The surface characteristics of the clean and saturated granular activated carbon particles were analyzed by scanning electron microscope (SEM). The characteristics of SEM images were digitized and analyzed by Image-Pro Plus software. Based on the analysis of the images taken by SEM before and after the adsorption process, two types of adsorption mechanisms were observed: surface adsorption on the smooth surfaces exhibiting a thin uniform layer of contaminant accumulation and linear adsorption exhibiting a line of accumulation on the exterior edges of the surfaces with high roughness. The surface characteristics were analyzed in relation to surface accessibility and pore sizes of the granular activated carbon used.