Bimetallic coordination polymer for highly selective removal of Pb(II): Activation energy, isosteric heat of adsorption and adsorption mechanism

[Display omitted] •A novel bimetallic coordination polymer adsorbent was synthesized.•The adsorbent had a maximum adsorption capacity of 175 mg/g for Pb(II).•Ti/Zr-DBMD achieved a good Pb(II) removal effect in a wide range of pH 3–7.•The adsorbent had good selectivity and reusability.•The adsorption mechanism was electrostatic attraction and chelation. The efficient removal of toxic Pb(II) from water was a serious problem for human. Herein, a bimetallic coordination polymer adsorbent (Ti/Zr-DBMD) was synthesized by 2,5-dimercaptoterephthalic acid ligand. The batch adsorption was performed and the relevant adsorption behavior was surveyed. Ti/Zr-DBMD had an outstanding adsorption performance in the range of pH = 3–7. The adsorption reached equilibrium at 120 min and the maximum adsorption capacity was 175 mg/g at 298 K. The adsorption of Pb(II) on Ti/Zr-DBMD conformed to pseudo-second order kinetic and Langmuir isotherm models. The activation energy (Ea) revealed a chemical adsorption in which the adsorption rate decreased with the increase of temperature. Thermodynamic analysis showed that the adsorption of Pb(II) by Ti/Zr-DBMD was a spontaneous exothermic behavior. Isosteric heat of adsorption (ΔHx) indicated that the energy heterogeneity of Ti/Zr-DBMD surface was low. The competitive adsorption experiment indicated that Ti/Zr-DBMD had the strongest affinity with Pb(II). Five adsorption–desorption cycles confirmed that Ti/Zr-DBMD had excellent regeneration performance. Furthermore, the adsorption mechanism is electrostatic attraction and chelation based on Zeta potential and XPS analysis. This study proved that Ti/Zr-DBMD had broad prospects in removing Pb(II).