What Is The Significance Of The Iodine Value Of Activated Carbon?

The iodine number is a measure of the equilibrium mass of iodine adsorbed in excess on the surface of Activated carbon. This is a standard test method.
In adsorption theory, molecules of different sizes/functionalities will correspondingly physisorb at surface sites of different energies. Chemists measure and simulate adsorption in a similar way using different molecules. Since iodine is very small, it is a good indicator of the availability of Activated Carbon in very small/high density pores. The iodine value corresponds to the iodine equilibration capacity of the activated carbon, the amount of adsorbed iodine is related to the increased porosity of the activated carbon and is used as a general performance indicator.
What is iodine value?
Due to its simplicity and quick test of adsorbent quality, iodine number is a widely used parameter for activated carbon testing. It gives estimates of its surface area and porosity. According to the ASTM D4607 standard, when the residual concentration of iodine is 0.02N (0.01 mol L-1), the iodine value is defined as the number of milligrams of iodine adsorbed by 1 gram of material, which is based on the three-point isotherm.
How to measure?

v Treat the sample with 10 mL of 5% (V/V) HCl. Boil the mixture for 30 seconds, then cool to room temperature. Immediately add 100 mL of 0.1 N iodine solution to the mixture and stir for 30 seconds. Then filter the solution, and titrate 50 mL of the filtrate with 0.1N (0.05 mol L-1) sodium thiosulfate solution, using methylammonium (or starch) as an indicator. The amount of iodine adsorbed per gram of adsorbent was plotted against the residual iodine concentration using a logarithmic axis. If the residual iodine concentration is not in the range (0.008-0.04N), repeat the process using a different carbon mass for each isothermal point. Regression analysis was performed on the three points, and the iodine value was calculated as the adsorption amount when the residual iodine concentration was 0.02N.