A Novel Coordination Polymer as Adsorbent Used to Remove Hg(II) and Pb(II) from Water with Different Adsorption Mechanisms

Under the hydrothermal condition, a new type of two-dimensional coordination polymer ([Cd­(D-Cam)­(3-bpdb)]n, Cd-CP) has been constructed. It is composed of D-(+)-Camphoric-Cd­(II) (D-cam-Cd­(II)) one-dimensional chain and bridging 1,4-bis­(3-pyridyl)-2,3-diaza-1,3-butadiene (3-bpdb) ligands. Cd-CP has a good removal effect for Hg­(II) and Pb­(II), and the maximum adsorption capacity is 545 and 450 mg/g, respectively. Interestingly, thermodynamic studies have shown that the adsorption processes of Hg­(II) and Pb­(II) on Cd-CP use completely different thermodynamic mechanisms, in which the adsorption of Hg­(II) is due to a strong electrostatic interaction with Cd-CP, while that of Pb­(II) is through a weak coordination with Cd-CP. Moreover, Cd-CP has a higher affinity for Hg­(II), and when Hg­(II) and Pb­(II) coexist, Cd-CP preferentially adsorbs Hg­(II).