[Adsorption behavior and influence factors of p-nitroaniline on high surface area activated carbons prepared from plant stems].

Low-cost and high surface area microporous activated carbons were prepared from Spartina alternilora and cotton stalk with KOH activation under the conditions of impregnation ratio of 3.0, activation temperature at 800 degrees C and activation time of 1.5 h. The adsorption behavior of p-nitroaniline on the activated carbons was investigated by batch sorption experiments. The influences of solution pH value, adsorbent dose and temperature were investigated. The adsorption isotherm and thermodynamic characteristics were also discussed. The Spartina alterniflora activated carbon (SA-AC) has a high surface area of 2825 m2 x g(-1) and a micropore volume of 1.192 cm3 x g(-1). The BET surface area and micropore volume of the cotton stalk activated carbon (CS-AC) are 2135 m2 x g(-1) and 1.011 cm3 x g(-1), respectively. The sorption experiments show that both the activated carbons have high sorption capacity for p-nitroaniline. The Langmuir maximum sorption amount was found to be 719 mg x g(-1) for SA-AC and 716 mg x g(-1) for CS-AC, respectively. The sorption was found to depend on solution pH, adsorbent dose, and temperature. The optimum pH for the removal of p-nitroaniline was found to be 7.0. The Freundlich model and Redlich-Peterson model can describe the experimental data effectively. The negative changes in free energy (delta G0) and enthalpy (delta H0) indicate that the sorption is a spontaneous and exothermic procedure. The negative values of the adsorption entropy delta S0 indicate that the mobility of p-nitroaniline on the carbon surface becomes more restricted as compared with that of those in solution.