The iodine number as a quality control parameter of activated carbon
The iodine number (or “iodine value”) (ASTM D4607) is an indication of the available surface area in m2/gram of virgin carbon. Although the Iodine number has become synonymous with the “activity” of activated carbon and it is widely used as a quality control (QC) parameter in production and reactivation of activated carbon, it does not necessarily provide a measure of the carbon's ability to adsorb other species. Generally the iodine number is 50 to 100mg/g lower compared to the BET surface area.
It is well known that the iodine adsorption from aqueous solutions is affected by carbon surface oxygen complexes, pH and ash constituents. When a virgin activated carbon is wetted with water and dried, the iodine number for that carbon will drop 20 - 50 points because the surface oxygen complex has been changed. Therefore QC samples should be taken dry and not wet in an activated carbon filter!