Activated carbons can be widely used as industrial carbons have a large Brunauer-Emmett-Teller (BET) adsorbents for separation, purification, and recovery pro-surface area. In addition, experimental results revealed that cesses due to their highly porous texture and large ad-the BET surface area, pore volume, and average pore sorption capacity [1][2][3]. They are also used as catalyst diameter of the resulting porous carbon generally increase supports, chromatography columns and electrode materials with increasing activation time, activation temperature and for batteries and capacitors [4][5][6][7][8][9]. Two general methods ratio of activation agents. are used for the preparation of activated carbon [10,11].
However, this activation process is complicated, not One, the ''physical'' activation, consists of heating at a well understood and very much dependent on many high temperature under a carbon gasification reactant (H O variables. In this sense, the chemical activation process has 2 or CO ). The other method, ''chemical'' activation, con-been studied in this work, including some effects, which 2 sists of heating at a relatively lower temperature with the have not been discussed before. addition of a dehydration agents (e.g., H PO , ZnCl ).
The raw material, rice husk was thoroughly washed with 3 4 2
However in the 1970s, Wennerberg [12,13] described the water to remove adhering soil and clay, and dried at invention of an activated carbon with a high specific 110 8C in an oven overnight. After drying the husk was surface area prepared by the interaction of carbon with carbonized at 400 8C for 4 h to produce the pyrolysate. In potassium hydroxide. Nowadays, there is a great interest in this study, some samples were prepared with KOH, NaOH, the alkali hydroxide activation process in the production of KOH with NaCl addition and NaOH with KCl addition, activated carbons [8,14,15]. using a physical mixing method and considering previous Rice husk, a by-product of the rice milling industry, results [19,20]. The same proportion of metal / pyrolysate accounts for about 20% of the whole rice grain. The as in the case of NaOH or KOH (i.e., ratio NaOH / amount of rice husk was approximately 500 million tons in pyrolysate, 3:1; KOH / pyrolysate, 4:1; total cations used developing countries (Food and Agriculture Organization, about 72 mmol / g of pyrolysate) was maintained. The 1995). Only 100 million tons were available annually for pyrolysate was heated in the presence of the agents at utilization. The amount of rice husk available is far in 400 8C for 0.2 to 1.0 h to dehydrate the combination, excess of any local uses and thus has posed disposal thereafter the temperature was raised (heating rate 15 8C/ problems. Despite the increasing trend of the rice husk min) from 400 8C to the final temperature (650-800 8C) surplus, proper methods of disposal and utilization of rice for 0.5 to 2 h to activate the combination. Finally, the husk have yet to be developed because of its high ash activated product was ground, washed with water and dried content [16]. Many papers have been published on this at 120 8C to form porous carbon. subject [17,18]. In our previous studies [19,20], porous Some samples have been activated with K CO and 2 3 carbons were prepared from rice husks by chemical Na CO , also by a physical mixing method and the 2 3 activation with KOH and NaOH at low temperatures. The pyrolysate in the same proportion as mentioned above for NaOH (KOH), and heat treatment up to the activation temperature (650-750 8C) without dehydrating the mixture