Phosphate Ion Adsorption Properties of Polyacrylonitrile (PAN) Activated Carbon Fiber

In this study, the activated polyacrylonitrile (PAN) -based carbon fibers were evaluated as phosphate ion adsorbents in water. The activated PAN-based carbon fibers were prepared from commercially available oxidized black colored PAN fiber by ammonia gas activation at 950 ̊C, and KOH activation and/or steam activation at 800 ̊C under helium gas flow. The adsorption amount of phosphate ion was improved from 0.1 mmol/g for ammonia gas activated PAN-based carbon fiber to 0.24 mmol/g for ammonia gas and steam activated PAN-based carbon fiber. Characterizations of activated PAN-based carbon fibers were carried out using the nitrogen adsorption-desorption analysis at –196 ̊C and elemental analysis. The BET surface area and pore volumes were increased by any activation method employed, but the pore diameter and nitrogen content tended to be decreased during the high temperature treatment. Using the fiber showing the highest adsorption capacity, the adsorption isotherm, the effect of pH, and the reusability of the adsorbent were investigated. The steam activated PAN-based carbon fibers with pre- and post-ammonia treatment had higher adsorption capacity and Langmuir adsorption affinity than other prepared adsorbents, and the adsorption amount of phosphate ion achieved the highest at the equilibrium pH range of 6–7.