Post-calcination as an effective approach to enhance adsorption of arsenic and antimony anions by Mg/Al layered double hydroxide-decorated spent coffee ground biochars: Role of charge properties and active sites

This study evaluated the effects of post-calcination on the charge properties and active sites of Mg/Al layered double hydroxide-decorated spent coffee ground biochars (LDH_MgAl@SCGB) governing adsorption behaviors and mechanisms of arsenic (As^V) and antimony (Sb^V) anions from aqueous phases. Post-calcinated LDH_MgAl@SCGB (PLDH_MgAl@SCGB) exhibited higher adsorption capacities for As^V and Sb^V compared to spent coffee ground biochars (SCGB) and LDH_MgAl@SCGB as post-calcination of LDH_MgAl@SCGB enhanced the charge properties (surface zeta potential at pH 7.0: SCGB = −21.8 mV, LDH_MgAl@SCGB = 28.5 mV, and PLDH_MgAl@SCGB = 34.4 mV) and increased active sites by eliminating the anions (i.e., Cl⁻ ions) and water molecules at its interlayers. The calculated kinetic, intra-particle diffusion, and isotherm parameters indicated that the chemisorption and intra-particle diffusion were mainly responsible for the adsorption of As^V and Sb^V by SCGB, LDH_MgAl@SCGB, and PLDH_MgAl@SCGB. Moreover, post-calcination of LDH_MgAl@SCGB enhanced its selectivity toward As^V and Sb^V by reinforcing the electrostatic surface complexation via its improvement of charge properties. Since PLDH_MgAl@SCGB exhibited the excellent reusability for the adsorption of As^V (reuse efficiency >63.6%) and Sb^V (reuse efficiency >52.1%), it can be concluded that post-calcination of LDH_MgAl@SCGB is a promising method for improving the adsorption capacities for As^V and Sb^V in real water matrices.