Removal of an emerging pharmaceutical pollutant (metronidazole) using PPY-PANi copolymer: Kinetics, equilibrium and DFT identification of adsorption mechanism

Present study reports the synthesis of the polyaniline-polypyrrole (PPY-PANi) copolymer and its subsequent application for aqueous metronidazole removal under batch adsorption trials. The experiments were then performed to determine the influence of different adsorption parameters such as adsorbent dose, pH, reaction time, initial concentration and temperature on the adsorption process. The obtained experimental data was further evaluated by using different kinetic, isotherm and thermodynamic modeling. The pseudo-first order model provided the satisfactorily explanation for metronidazole kinetic adsorption over PPY-PANi adsorbent. The equilibrium experimental data was in good agreement with Freundlich model. The thermodynamic parameters reveal that the adsorption was spontaneous and exothermic in nature. Metronidazole adsorption mechanism over PPY-PANi surface sites was further evaluated by employing density functional theory (DFT) method. The calculated data indicated that the metronidazole adsorption was mainly accomplished via nucleophilic groups (containing oxygen atoms) of metronidazole over the electrophilic attack sites (-NH-) of PPY-PANi adsorbent. The interaction energy bond clearly suggests that the adsorption of metronidazole over PPY-PANi is a physisorption in nature. Thus, based on these above-mentioned experimental results and DFT data, we concluded that PPY-PANi copolymer could be taken as an alternative filter material for pharmaceutical contaminated wastewater treatment.