Adsorption of Pb(II) from aqueous solution by pomelo fruit peel-derived biochar

Abstract

Removing hazardous metals from aqueous solution using biomaterials synthesized from waste resources with low cost is a novel strategy in environmental science and application. Among those hazardous metals, lead is one of the most dangerous elements because it significantly affects human-body organs. In the present study, biochar prepared from pomelo fruit peel using a green synthesized method was utilized to remove Pb(II) from aqueous solution. The effects of pH, adsorption time, ion strength, and Pb(II) initial concentration on the Pb(II) adsorption of this material were investigated. The Langmuir, Freundlich, Sip, pseudo-first-order, pseudo-second-order, and intra-diffusion models were used to study the isotherm and kinetic properties of the material. Results showed that the uptake followed the intra-diffusion kinetic model and the maximum Pb(II) mono-adsorption capacity determined from the Langmuir equation was 92.13 mg/g at 303 K. Furthermore, by combining conventional characterization methods as SEM-EDX, BET-BJH and FT-IR with advanced nuclear analytical techniques as positron annihilation lifetime (PAL) and electron momentum distribution (EMD), we found that the Pb(II) adsorption should be occurred via three stages, namely (i) electrostatic attractions that affect the external diffusion; (ii) ion-exchanges that control the internal diffusion; and (iii) chemical interactions. In particular, the PAL and EMD analyses provided, for the first time, an in-depth study on the adsorption mechanism that the ion-exchanges and/or electrostatic interactions occurred due to the diffusion of Pb(II) ions into the defects, vacancies, and/or vacancy clusters and/or the filling of Pb(II) ions into the micropores of biochar.