RESULTS AND DISCUSSION
1. Influence of Initial pH The effect of initial pH on bioadsorption of dyes was examined over a range of pH values from 2 to 10 and the results are presented in Fig. 1. As elucidated in Fig. 1, the dye removal was minimum at pH 2 for both adsorbents. The dyes adsorbed increased as the pH was increased from 2 to 7 for APR and from 2 to 8 for RPR. Then, beyond pH 7 and 8 there was no notable change. For this reason, pH 7 and pH 8 was selected for future experiments for APR and RPR respectively. After adsorption experiments, it was found that at low pH and at high pH, the dye become protonated, the electrostatic repulsion between the protonated dyes and positively charged adsorbent sites results in decreased adsorption. Higher adsorption at pH 7 and 8 may be due to increased protonation by the neutralization of the negative charges at the surface of the adsorbent, which facilitates the diffusion process and provides more active sites for the adsorbent. Furthermore, the solution pH is above the zero point charge (pH = 4.8 zpc for APR and 4.4 for RPR) and hence the negative charge density of the surface of the adsorbents increases which favors the adsorption of cationic dye [18].
RESULTS AND DISCUSSION1. Influence of Initial pH The effect of initial pH on bioadsorption of dyes was examined over a range of pH values from 2 to 10 and the results are presented in Fig. 1. As elucidated in Fig. 1, the dye removal was minimum at pH 2 for both adsorbents. The dyes adsorbed increased as the pH was increased from 2 to 7 for APR and from 2 to 8 for RPR. Then, beyond pH 7 and 8 there was no notable change. For this reason, pH 7 and pH 8 was selected for future experiments for APR and RPR respectively. After adsorption experiments, it was found that at low pH and at high pH, the dye become protonated, the electrostatic repulsion between the protonated dyes and positively charged adsorbent sites results in decreased adsorption. Higher adsorption at pH 7 and 8 may be due to increased protonation by the neutralization of the negative charges at the surface of the adsorbent, which facilitates the diffusion process and provides more active sites for the adsorbent. Furthermore, the solution pH is above the zero point charge (pH = 4.8 zpc for APR and 4.4 for RPR) and hence the negative charge density of the surface of the adsorbents increases which favors the adsorption of cationic dye [18].
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