## 3 Results and Discussion
### Adsorption from Water Solution  
Initially, the adsorption kinetics of three aromatics on the studied carbons were evaluated, in order to assess the time, needed for equilibrium before determining the maximal adsorption capacity of each adsorbent. The kinetics of adsorption of pentachlorophenol, m-aminophenol and p-nitrophenol from aqueous solutions were studied for various concentrations ranging from 100 to 250 mg L\({}^{-1}\) for carbon. The obtained kinetics of adsorption shows the well-known pattern of aromatic compounds described in the literature [18; 19], with a fast uptake of three compounds at the initial stage of the adsorption process (short times), and equilibrium is attained within 40 min in all cases. Moreover, the amounts adsorbed show smooth continuous curves in all the cases, with a well-defined saturation plateau. This behavior is attributed to the decrease in the number of available adsorption sites on the carbon surface as the adsorption proceeds and the first molecules of adsorbate are retained. Since m-aminophenol and p-nitrophenol show rather close solubility in water, 2.6 g and 1.7 g per 100 g H\({}_{2}\)O solution, respectively, the similarities in the rate of adsorption on activated carbon are somewhat expected. Pentachlorophenol shows a small solubility in water--0.03 g per 100 g water solution--which could explain why the adsorption is lower in comparison with the pollutants. The adsorption isotherms of m-aminophenol, pentachlorophenol and m-aminophenol on activated carbon are presented in Figure 4.  
All of them belong to type L of Giles classification, indicating that adsorption proceeds by the formation of a monolayer in the range of concentrations used [20]. Our results show that the adsorption mechanism of pentachlorophenol, m-aminophenol and p-nitrophenol is similar. The experimental data fits well with the Langmuir equation [21]. \[\mathrm{Q_{e}=Q_{o}bC_{e}/(1+bC_{e})}, \tag{1}\]  
where C\({}_{e}\) /relative error of the measurement 1.0%/ is the equilibrium pollutant concentration remaining in solution after adsorption (mg L\({}^{-1}\)), Q\({}_{e}\) /relative error 2.01%/ is the amount of pollutant bound to the adsorbent (mg g\({}^{-1}\)), Q\({}_{o}\) /relative error 0.01%/ is the maximum amount of the pollutant per unit weight of adsorbent (mg g\({}^{-1}\)), and b /relative error 1.0%/ is a constant related to the affinity of binding sites (L mg\({}^{-1}\)). These parameters, together with the relative affinity of the adsorbates towards the surface of the adsorbents--Parameter bQ\({}_{o}\), and the correlation coefficients, are compiled in Table 4. The very good fittings, obtained for the sample, indicate that the Langmuir model is capable of predicting the adsorptive behavior of these carbons towards pentachlorophenol, m-aminophenol and p-nitrophenol. The adsorption capacities of obtained carbon towards the three pollutants studied carbons are high, probably due to the hydrophobic character of the carbon surface. The maximal adsorption capacities calculated from the Langmuir  
Figure 3: IR spectrum of activated carbon. equation are 22 mg/g, 165 mg/g, and 152 mg/g, for pentachlorophenol, m-aminophenol and p-nitrophenol, respectively. These values are higher in comparison to those reported in the literature for activated carbons with higher surface areas [22; 23; 24]. The differences in the uptake of the three pollutants, p-nitrophenol, m-aminophenol and pentachlorophenol, confirm that the adsorptive performance depends on the porosity and the chemical nature of the activated carbon. The slightly lower uptake of p-nitrophenol and lower uptake of pentachlorophenol by the carbon is somewhat expected, implying that these compounds displays a lower water solubility (1.7 g and 2.6 g per 100 g water solution, for p-nitrophenol and m-aminophenol, respectively, and 0.003 g per 100 g water solution for pentachlorophenol).