Structure and Adsorptive Properties in Wastewater Treatment of Activated Carbon Fiber Based on Kapok

A new kind of activated carbon fiber (ACF) based on kapok was prepared by activation with diammonium hydrogen phosphate [(NH₄)₂HPO_4] at 923 K for 70 min. Two preoxidation methods and one without preoxidation were adopted to produce AK-2, AK-3 and AK-1 respectively. The characteristics of the ACFs were determined with N₂ adsorption-desorption isotherms and Boehm titration. And the process of activation was characterized with thermogravimetric analysis (TG). It was found that preoxidation after impregnation (AK-2) could greatly increase ACF´s BET surface area (1518m²/g) compared to AK-1 without preoxidation (825.1m²/g). And preoxidation before impregnation (AK-3) would slightly decrease BET surface area (799.2 m2/g). Both two preoxidation methods lead to higher concentrations of surface acidic groups. The ACFs were employed in wastewater treatment to adsorb phenol and methylene blue (MB). The results showed that the data of adsorption isotherms all fitted the Freundlich model better except AK-1 in adsorption of MB. Specifically, AK-1 had the biggest adsorption capacity for phenol (up to 65.8 mg/g), and AK-3 for MB (up to 156.7 mg/g). The surface acidic groups were found to decrease the adsorption of both phenol and MB in aqueous solutions.