Adsorption of Methylene blue onto hydrophobic activated carbon: Adsorption of Methylene blue onto hydrophobic activated carbon

Abstract

Activated carbon (AC) was prepared from date palm leaflets using NaOH activation. AC was oxidized using concentrated HNO₃ to produce oxidized activated carbon (ON). Alkylamines including methylamine (M), dimethylamine (DM), ethylamine (E), diethylamine (DE), and diisopropylamine (DIP) were covalently immobilized onto ON to produce ONM, ONDM, ONE, ONDE, and ONDIP hydrophobic activated carbons, respectively. The surface area of AC (588 m2/g) decreased on oxidation with a further decrease on functionalization. These carbons were tested for methylene blue (MB) adsorption. Initial pH 7 was found optimum for the adsorption of MB. The hydrophobic activated carbons show faster adsorption (except for ONDE), than AC with adsorption data following well a pseudo-second-order kinetic model. The rate of adsorption increased with temperature rise. The activation energy, E_a, was less than 42 kJ/mol indicating physical adsorption. Equilibrium adsorption follows L-type isotherm with the adsorption data following well the Langmuir model. The adsorption capacity of MB follows the order of ONDIP > ONE > ONDM > AC > ON > ONM > ONDE. Thermodynamic parameters indicate spontaneous and endothermic adsorption. Carbon reuse for MB adsorption was more efficient for ONDIP, ONE, and ONDM than AC