Adsorption of pharmaceutical pollutants on ZnCl2-activated biochar from corn cob: Efficiency, selectivity and mechanism

Abstract

The occurrence of pharmaceuticals in water bodies and drinking water poses risks for the environment and human health, thus it is necessary to study methodologies that allow the efficient removal of these contaminants. In this work, corn cob-derived biochar was obtained by ZnCl₂-activation, and subsequent carbonization at 700 °C. The effect of contact time, temperature, pH, and initial concentration on the adsorption capacity of acetaminophen (ACE) and amoxicillin (AMX) was determined through batch experiments. In addition, the kinetics, isotherms, and thermodynamics parameters were determined. The activated biochar exhibited a maximum adsorption capacity of 332.08 mg/g for ACE and 175.86 mg/g for AMX. The adsorption kinetics and adsorption isotherm of ACE corresponded to the pseudo-second order and Langmuir model, respectively. Meanwhile, pseudo-first-order kinetics and the Freundlich isotherm model were well-fitted to AMX adsorption. The ACE and AMX co-adsorption had a synergistic effect on AMX but an antagonistic effect on ACE removal, achieving a maximum adsorption capacity of 193.51 and 184.58 mg/g, respectively. On the other hand, fixed-bed column experiments showed that the adsorption capacity depends on the influent concentration, and the breakthrough curve fits the Thomas and Yoon-Nelson model. The mechanism adsorption studies showed that surface interactions (hydrogen bonding formation and n-π interactions) are the main driving forces for the adsorption process, and pore filling is the rate-limiting step. In this way, the prepared biochar exhibits a high potential for the adsorption of pharmaceutical compounds from water.