At first, before sulfonation, the activated carbon was washed with
distilled water to achieve neutral pH. Then, the washed activated
carbon was dried at 373 K for 4 h.
For sulfonation, 0.01 kg activated carbon and 200 cm
3
concentrated sulfuric acid (98%) were mixed and heated at 428 K under
reflux, stirring, and N2flow for 15 h.
After the treatment, the mixture was cooled to room temperature and 2 cm
3
of distilled water was added to the mixture. Then,
the precipitate was filtered and washed repeatedly by hot distilled water (353 K) and the pH of wash water was measured
continuously. The washing was stopped when the wash water
became neutral. The sulfonated activated carbon was dried at 373 K
in a vacuum oven for 4 h