Evaluation of the effectiveness and mechanisms of acetaminophen and methylene blue dye adsorption on activated biochar derived from municipal solid wastes

Abstract

The adsorption potential and governing mechanisms of emerging contaminants, i.e. acetaminophen or acetyl-para-aminophenol (APAP) and methylene blue (MB) dye, on activated carbon derived from municipal solid waste were investigated in this work. Results showed that MB adsorption was significantly more effective, with a maximum removal of 99.9%, than APAP adsorption (%R_max = 63.7%). MB adsorption was found to be unaffected by pH change, while the adsorption capacity of APAP drastically dropped by about 89% when the pH was adjusted from pH 2 to 12. Surface reactions during APAP adsorption was dominated by both physical and chemical interactions, with the kinetic data showing good fit in both pseudo-first order (R² = 0.986-0.997) and pseudo-second order (R²>0.998) models. On the other hand, MB adsorption was best described by the pseudo-second order model, with R²>0.981, denoting that chemisorption controlled the process. Electrostatic attractions and chemical reactions with oxygenated surface functional groups (i.e., -OH and -COOH) govern the adsorption of APAP and MB on the activated biochar. Thermodynamic study showed that APAP and MB adsorption were endothermic with positive ΔH° values of 16.5 and 74.7 kJ mol^-1, respectively. Negative ΔG° values obtained for APAP (-3.7 to -5.1 kJ mol^-1) and MB (-11.4 to -17.1 kJ mol^-1) implied that the adsorption onto the activated biochar was spontaneous and feasible. Overall, the study demonstrates the effectiveness of activated biochar from municipal solid wastes as alternative adsorbent for the removal of acetaminophen and methylene blue dye from contaminated waters.

Keywords: Acetaminophen; Adsorption; Mechanism; Methylene blue; Municipal solid waste; Pyrolysis biochar.