Adsorptive removal of Bisphenol A by biomass activated carbon and insights into the adsorption mechanism through density functional theory calculations

Activated carbon was synthesized from Tithonia diversifolia biomass using potassium hydroxide as the chemical activating reagent. Taguchi's experimental design approach was applied to determine the best preparation conditions. An optimum 2:1 impregnation ratio and 700 °C activation temperature produced the best carbon with a high 854.44 m²g^-1 surface area, 0.445 cm³g^-1 total pore volume and 18.3% yield. From the analysis of variance (ANOVA), the impregnation ratio was found to be the most influential factor in preparing activated carbon with the maximum surface area. SEM and XRD studies revealed the porous microcrystallite structure of the obtained activated carbon. Batch adsorption studies were performed to test the efficiency of Tithonia diversifolia activated carbon for the removal of Bisphenol A (BPA) from aqueous solution. A maximum 98.2% removal percentage was attained at optimum conditions of 0.2 g adsorbent dose, pH 7, 80 min contact time and 40 mg L^?1 initial BPA concentration. The Langmuir isotherm model described the equilibrium adsorption of BPA well with a maximum adsorption capacity(q_m) of 15.69 mg g^?1 while the kinetic adsorption study indicated a pseudo second order model. A theoretical investigation suggested that the adsorption of BPA onto the activated carbon mainly proceeds via chemisorption and the presence of a carboxyl functional group on the activated carbon surface yielded a greater adsorptive impact on BPA. This study indicates that Tithonia diversifolia could be used as a potential raw material for preparing activated carbon for removing of BPA from water.