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• Surface grafted HEDP-HAP composite was applied to the removal of Pb2+ and Cu2+. • The maximum uptake amount of Pb2+ and Cu2+ was 1521 mg/g and 168.9 mg/g, respectively. • Quantitative molecular surface analysis was applied to predict the active sites. • Becke surface analysis was implemented to reveal the H-bond between HEDP2− and HAP. • IGM and VMD were performed to visualize the interaction among different fragments. A simple hydrothermal method was employed to prepare the surface grafted 1-hydroxyethylidene-1,1-diphosphonic acid-hydroxyapatite (HEDP-HAP) composites, which were termed as 0.2HEDP-HAP, 0.5HEDP-HAP and 1HEDP-HAP respectively, according to the HEDP content. Adsorption experiments showed that the maximum adsorption capacity of 0.5HEDP-HAP for Cu2+ reached 168.9 mg/g, which was 4.19 times that of HAP, while the maximum adsorption capacity of 1HEDP-HAP for Pb2+ was as high as 1521 mg/g, which was approximately 10 times that of HAP. For the first time, the interaction mechanism of HEDP with HAP, or HEDP-HAP composite with the two heavy metal ions was illustrated by the combination of quantum chemistry (QC) calculation, quantitative analysis of molecular surface, Becke surface analysis and Independent Gradient Model (IGM) method. The active reaction sites, the types, relative strength and essence of the interactions were revealed based on the visual analysis of interactions. The results demonstrated that the phosphonic acid group (PO 3 H−) of HEDP2- can form hydrogen bonds with the phosphate group (PO 4 3-) and the hydroxyl group (OH) of HAP. The oxygen atom of PO 3 H- provided lone pair electrons to form chelate with Ca2+ of HAP, which resulted in the strong affinity of HEDP with HAP. Moreover, the significant improvements of uptake of surface grafted HEDP-HAP for Cu2+ and Pb2+ were due to the formation of the ternary surface complexes. [ABSTRACT FROM AUTHOR]

• AL-HAP was synthesized and used to remove heavy metals from wastewater firstly. • AL-HAP had a huge improvement on the adsorption capacity to Pb2+, Cu2+ and Cd2+. • DFT, HOMO, ESP and IGM were firstly applied to explore the properties of AL-HAP. • AL and metal ions form a ternary complex with HAP to improve removal of metal ions. • There were ionic bond, hydrogen bonds and van der Waals interactions. In this paper, a new nanobiomaterial, alendronate hydroxyapatite (AL-HAP), was synthesized by the conventional co-precipitation method with alendronate (AL) as dopant, and applied in the removal of heavy metal contaminants for the first time. The characterization results showed that the crystallinity of the AL-HAP nanocomposite biomaterials after doping has been greatly deteriorated, and the pore volume and pore size increased. When the doping amount of AL was 10 %, the maximum adsorption capacity of AL-HAP for Pb2+, Cd2+ and Cu2+ can reach 1431.8, 469 and 226.6 mg/g, respectively, which was much higher than that reported in other literature. Meanwhile, the adsorption mechanism of AL-HAP for heavy metal ions was discussed from both the views of experimental and Multiwfn program theoretical calculation based on density functional theory (DFT). Quantitative molecular surface analysis was carried out for the first time to study the minimum points and the positions of electrostatic potential (ESP) and average local ionization energy(ALIE), as well as the exact values, giving more accurate and reliable analysis conclusions for the reaction sites and binding mode. In addition, the independent gradient model (IGM) method was also firstly applied to investigate the interactions between AL and HAP or AL-HAP nanocomposite with metal ions. AL-HAP is a potential adsorption material for heavy metal wastewater treatment and soil remediation because of its advantages such as convenient synthesis, excellent adsorption performance and no secondary pollution. [ABSTRACT FROM AUTHOR]

• Ternary core-shell CS@PANI@LDH composite was synthesized and characterized. • The maximum adsorption capacity of CS@PANI@LDH was 618.16 mg/g for DCF. • Multiwfn, Chimera, VMD, and IGM were combined to reveal the adsorption mechanism. • Deduced binding mechanism was electrostatic, hydrogen bonding, and π–π interaction. The efficient removal of Diclofenac sodium (DCF), a nonsteroidal anti-inflammatory drug, has attracted more and more attention. In this work, ternary core-shell CS@PANI@LDH composite was synthesized via the in-situ growth of Mg/Al layered double hydroxide plates onto polyaniline-wrapped carbon sphere and applied for DCF removal. Various influence factors like concentration, pH, time, temperature, and background electrolytes were systematically investigated. The maximum adsorption capacity was 618.16 mg/g. Besides, after 5 regeneration cycles, CS@PANI@LDH still retained high adsorption capacity. The adsorption mechanism was investigated by Fourier transformed infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) characterization analyses. Simultaneously, the Multiwfn program combined the Chimera program was applied to calculate and visualize the localized orbit locator (LOL) of π electrons in DCF− molecule, which explored the π electronic structure and conjugation characteristics of DCF− molecule. Moreover, the Independent Gradient Model (IGM) analysis based on pro-molecular density revealed the interaction sites and interaction strength between DCF and LDH. The adsorption mechanism could be explained through electrostatic interaction and hydrogen bonding between LDH and DCF, π-π interaction between DCF and PANI. It was the synergistic effects of different interactions that improved the adsorption of DCF by CS@PANI@LDH composite. [ABSTRACT FROM AUTHOR]

• Adsorption mechanism is elucidated by experimental and theoretical methods. • The Interface FF is introduced into Forcite module to study adsorption behavior. • Adsorption sites in PBTC are revealed by quantitative analysis on vdW surface. • Adsorption interactions are vividly shown by IGM and Hirshfeld surface analyses. • Hydrogen bond interaction may be the main force for the adsorption process. Two clay minerals, kaolinite (Kaol) and montmorillonite (Mt) with different crystal structures were chosen to investigate the comparative adsorption of 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTC) through batch control experiments and theoretical studies. The systematical isotherm and kinetic studies agreed with Langmuir model and pseudo-second-order model, confirming a monolayer and chemisorption interaction process, respectively. The maximum removal capacities of Kaol and Mt for PBTC were 72.297 mg/g and 121.163 mg/g at pH=3.0 and T=298 K, respectively. Furthermore, the adsorption mechanisms were investigated by molecular dynamic (MD) simulations and density functional theory (DFT). The Interface force field (IFF) was firstly introduced into Materials Studio package to explore the microscopic mechanism of clay mineral interface. The dynamics behaviors verified that the oxygen (O) atom of carboxyl group has stronger affinity at the external surface of Mt, which consistent with the experimental data well. For DFT calculations, quantitative analysis around molecular van der Waals (vdW) surface was adopted to predict reactive sites for the electrophilic reaction. Independent Gradient Model (IGM) and Hirshfeld surface analyses in Multiwfn indicated that the high adsorption effect mainly attributes to hydrogen bond action. These findings improve our ability to explore the related properties occurring at the interface of different clay minerals. [ABSTRACT FROM AUTHOR]