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@SCGB) governing adsorption behaviors and mechanisms of arsenic (As) and antimony (Sb) anions from aqueous phases. Post-calcinated LDH@SCGB (PLDH@SCGB) exhibited higher adsorption capacities for As and Sb compared to spent coffee ground biochars (SCGB) and LDH@SCGB as post-calcination of LDH@SCGB enhanced the charge properties (surface zeta potential at pH 7.0: SCGB = -21.8 mV, LDH@SCGB = 28.5 mV, and PLDH@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 and Sb by SCGB, LDH@SCGB, and PLDH@SCGB. Moreover, post-calcination of LDH@SCGB enhanced its selectivity toward As and Sb by reinforcing the electrostatic surface complexation via its improvement of charge properties. Since PLDH@SCGB exhibited the excellent reusability for the adsorption of As (reuse efficiency >63.6%) and Sb (reuse efficiency >52.1%), it can be concluded that post-calcination of LDH@SCGB is a promising method for improving the adsorption capacities for As and Sb in real water matrices.