Activated carbons were prepared from rice husk as following procedures: firstly, the rice husks were washed with water to remove dirt and other contaminants, oven-dried at 110 °C for 12 hrs then grounded and sieved to fractions with average particle size of 1.0 mm. Secondly; the prepared husks were carbonized at 400 °C under nitrogen flow for 90 min. The resulting samples were impregnated with NaOH and dried at 120 °C for 12 hrs. Then, the preparative process was followed by heating at 400 °C for 20 min under nitrogen atmosphere at a flow rate of 300 mL thereafter the temperature was raised to the predetermined temperatures (650–800 °C) at a heating rate of 10 °C and maintained at the final temperature for 60 min to activate the obtained material. Finally, the activated product was grounded, neutralized by HCl solution and washed several times with hot distilled water to a constant pH rate of 6.6–7.0). The washed activated carbon samples were dried under vacuum at 120 °C for 24 h and stored in a desiccator.
Characterization of activated carbons
The surface functional groups of activated carbon samples were identified by Fourier transform infrared spectroscopy using an IR Prestige 21, Shimazu, operating in the range of 4000–500 cm−1 and employing the KBr pellet method. The surface acidity and basicity of the samples were determined by the Boehm method . About 0.2 g of each AC sample was added to 25 mL of one of the four reactants of 0.1 M concentration: NaHCO3, Na2CO3 NaOH and HCl. The mixtures were shaked for 48 h and then filtered to remove the carbon. The excess of base and acid was titrated with 0.1 M HCl solution and 0.1 M NaOH solution, respectively. The numbers of acidic sites were calculated under the assumption that NaOH neutralizes carboxyl, phenolic and lactonic groups; Na2CO3-carboxyl and lactonic groups; and NaHCO3 only carboxyl groups. The number of surface basic sites was calculated from the amount of hydrochloric acid which reacted with the ACs.
Source : https://www.sciencedirect.com/science/article/pii/S1002007114000653
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