The single/co-adsorption characteristics and microscopic adsorption mechanism of biochar-montmorillonite composite adsorbent for pharmaceutical emerging organic contaminant atenolol and lead ions

An eco-friendly corncob biochar based montmorillonite composite (Cc-Mt) was synthesized for the single adsorption and co-adsorption of lead (Pb(II)) and a pharmaceutical emerging organic contaminant Atenolol (ATE). In single adsorption system, the maximum equilibrium capacity of Cc-Mt for Pb (II) and ATE were 139.78 mg g(-1) and 86.86 mg g(-1), respectively, but for montmorillonite just 98.69 mg g(-1) and 69.68 mg g(-1), for corncob biochar just 117.54 mg g(-1) and 47.29 mg g(-1). Meanwhile,co-adsorption properties of ATE and Pb(II) on Cc-Mt composite were performed and found that the influence of ATE on the adsorption of Pb(II) was greater than the effect of Pb(II) on that of ATE. Moreover, Multiwfn program based on quantum chemical calculation was used to quantitatively analyze electrostatic potential (ESP) distribution, average local ionization energy (ALIE) distribution and their minimum points on neutral ATE and protonated ATE (PATE) molecules to reveal the microscopic adsorption mechanism of Cc-Mt composite to ATE, the results showed that the amino N and amide oxygen atom were easier to provide lone pair of electrons, generating hydrogen bonds or strong electrostatic interactions with functional groups on the surface of Cc-Mt, meanwhile hydroxyl 0 atom was also a possible reaction site. For PATE molecules, only the oxygen atom of the amide group was the most likely reactive site.