Abstract:

This study investigated the effects of two different I₂/KI mass ratios on the iodine adsorption value of activated carbon prepared by seven common methods, with specific surface area ranging from 800 to 3 500 m²/g, including steam-activated coconut shell activated carbon(AC-11, AC-12, AC-13), phosphoric acid-activated powdered activated carbon(AC-21, AC-22), and KOH-activated petroleum coke high specific surface area activated carbon(AC-31, AC-32). The influence of specific surface area and pore structure of activated carbon on iodine adsorption value was analyzed. The results show that, activated carbons with a larger specific surface area, developed mesopore structure, and wide mesopore distribution, exhibited a more significant effect of the I₂/KI mass ratio on the iodine adsorption value. The difference between the iodine adsorption value of the test sample AC-31 under m(I₂): m(KI)=1:1.5 and that under m(I₂): m(KI)=1:2 could reach 140 mg/g. For microporous activated carbon AC-13 with iodine adsorption value around 800 mg/g, the difference between the two testing methods was almost negligible, which suggested that the difference between the activated carbon iodine adsorption value obtained by the old and new versions of wood and coal activated carbons iodine adsorption value testing standards was very small. Under the condition of activated carbon iodine adsorption value test, the pore sizes of activated carbon that effectively adsorb iodine molecules were mainly between the range of 0.8-1.5 nm. For microporous activated carbon such as coconut shell activated carbon, the value of the specific surface area was not much difference from the iodine adsorption value, with a certain degree of equivalence. The essence of the I₂/KI mass ratio influence was that the change of the ratio of the two determines the starling concentration of elementary iodine in the iodine stardard solution, which affected the iodine adsorption value of activated carbon.

Key words: activated carbon, iodine adsorption value, mass ratio of iodine and potassium iodide, specific surface area, pore structure