Optimization of 4-nonylphenol adsorption on activated carbons derived from safou seeds using response surface methodology

The fight against environmental pollution by organic compounds has today become a primary necessity for public authorities to ensure sustainable development. This work highlights the removal of 4-nonylphenol (4-NP) in aqueous solution onto two chemically activated carbons (ACs) by optimizing some parameters that influence the adsorption process. Central composite design with four center points was used to optimize the process variables. The concentration of 4-NP solution, adsorbent dosage, stirring time and solution pH on the adsorption capacity were considered while the response measured was the quantity of 4-NP adsorbed. The AC obtained by treatment with sulfuric acid was named NSST and that obtained by treatment with phosphoric acid was named NSPT. Optimal conditions for 4-NP removal were as follows: 4-NP concentration 180 and 100 mg/L for NSST and NSPT respectively. Adsorbent dosage (100 mg), solution pH (9) and stirring time (120 min) were the same for both adsorbents. These optimal conditions resulted in 30.740 and 39.490 mg/g removal for NSST and NSPT respectively. A quadratic model for 4-NP removal was proposed and from it, analysis of variance was approximately in accordance with expectations. Correlation coefficients R2 and R2adj were of 91.00 and 81.32 % for NSPT material and 87.81 and 74.69 % for NSST material. Experimental data obtained from optimal conditions were validated with different isotherms and kinetic models to evaluate the solute interaction behavior and nature of adsorption. A pseudo-second order non-linear kinetic model best described the adsorption kinetics of 4-NP removal onto the ACs. Freundlich's isotherm best described the removal of 4-NP onto NSST and the Langmuir's isotherm did the same with the NSPT