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[Display omitted] In the adsorption process of functionalized layered double hydroxide (LDH) to target pollutants it, is essential to investigate the role of functional groups. In this work, 2‑mercaptoethane sulfonic acid (MS) was used as an intercalation modifier to prepare functionalized NiFe-LDH by solvothermal method. The interfacial interaction between the functional groups and the NiFe-LDH surface was studied via molecular dynamics simulation. During the intercalation process, the more negatively charged sulfonic acid group tends to self-assemble electrostatically with the LDH laminate, while the sulfhydryl group is involved in complexing heavy metal ions. The adsorption experiments showed that the adsorption performance of the adsorbent for the three ions of Cd2+, Mn2+, and Co2+ at 298.15 K was 266.16 mg/g, 175.60 mg/g, and 106.56 mg/g, respectively, which were 10 times, 8.7 times, and 4.9 times higher than that of unmodified NiFe-LDH. Meanwhile, Multiwfn wavefunction analysis combined Visual Molecular Dynamics (VMD) was applied to analyze and visualize the reaction active sites & the interactions between MS and NiFe-LDH, and the complexation of the functional group of MS with metal ions, to insight the role of the functional groups in MS molecule, and to reveal the cause that the adsorption capacity of modified NiFe-LDH for heavy metals greatly improves from the view of atoms. [ABSTRACT FROM AUTHOR]

In the present work, phosphogypsum (PG) waste was used as a calcium source, and integrated with 2-hydroxyphosphonoacetic acid (HPA) doping, modified inorganic-organic amorphous calcium phosphate hybrid composite was prepared, to remove Cd2+ and Co2+in aqueous solution. The study demonstrated that when pH=8, the equilibrium adsorption capacity of hydroxyapatite (HAP) for Cd2+ and Co2+ can reach 275.84 mg/g and 70.63 mg/g, respectively. After modification with HPA, the adsorption capacity of 20HPA-HAP for Cd2+ and Co2+ was higher at 468.92 mg/g and 171.38 mg/g, respectively. Regeneration experiments show that the adsorbent has good recycling performance, and the adsorbent has a good adsorption effect on low-concentration cadmium and cobalt ions in the actual hard gold electroplating wastewater. Meanwhile, the adsorption mechanism of 20HPA-HAP for Cd2+ and Co2+ was vividly visualized through Multiwfn wavefunction program and VMD program. Therefore, the reason why doping HPA greatly improves the adsorption performance of amorphous calcium phosphate on heavy metal ions was revealed from the atomic point of view. The findings suggest a promising approach for the effective utilization of discarded PG and the effective treatment of heavy metal pollution in industrial wastewater, highlighting the dual benefit of waste material repurposing and pollution control, which was an innovative strategy of turning waste into treasure. [Display omitted] • HPA/HAP was firstly to prepare by PG waste as calcium source and HPA as dopant. • HPA/HAP composite has excellent adsorption properties for Cd2+ and Co2+. • The interaction of HPA with two metal ions was vividly visualized and compared. • This work realized the resource of PG waste and the immobilization of Cd2+ and Co2+. [ABSTRACT FROM AUTHOR]

Our previous studies have shown that the modification of hydroxyapatite with organic phosphonates can greatly improve the adsorption effect of hydroxyapatite on heavy metal ion pollutants. Hydroxyethylydene-1,1-diphosphonate (HEDP) is a widely used multi-purpose chemical agent with the advantage of lower-cost, but the preparation and application of hydroxyapatite composites doped by HEDP have not been reported. Therefore, in the present work, calcium nitrate and diammonium hydrogen phosphate were used as the calcium source and inorganic phosphorus source, respectively. 5%, 10%, 20% and 25% HEDP was added as an organophosphine source in the process of preparing hydroxyapatite （HAP）to obtain inorganic-organic phosphorus hybrid HAP composite materials with different HEDP doping amounts, respectively. XRD characterization showed that when HEDP doping was 20% of total phosphorus, the crystallinity of the resulting composite material was greatly reduced and became amorphous HAP, and the maximum adsorption capacity of the obtained amorphous HAP was 1893.7 mg/g, 239.3 mg/g, 285.4 mg/g, and 339.7 mg/g for Pb2+, Cu2+, Zn2+ and Cd2+, respectively, which was 8.47, 4.25, 3.29, 3.41 times that of the commercial HAP, respectively. Furthermore, Hirshfeld surface analysis specially including fingerprint plot was applied to investigate the interaction between HEDP and HAP, and reduced density gradient (RDG) method was carried out to explore the interaction mechanism of HEDP doping amorphous HAP composite and heavy metal ions. Because of the low price of HEDP, the simple and low-consumption preparation method and the excellent removal effect to various heavy metal pollutants, the inorganic-organic phosphorus hybrid amorphous HEDP-HAP composite material will have broad application prospects in the field of heavy metal pollution control. [Display omitted] • Inorganic-organic phosphorus hybrid amorphous HEDP-HAP was synthesized. • The adsorption capacity of HAP-H-2.0 was much higher than that of HAP. • Hirshfeld surface analysis combined fingerprint plot were applied. • RDG was firstly used to reveal the interaction mechanism among different fragments. [ABSTRACT FROM AUTHOR]

Amino trimethylposphonate(ATMP) functionalized HAP were synthesized with different ATMP addition (0, 5%, 10%, 15%) and the adsorption performance towards Pb2+ and Cd2+ were studied in an aqueous solution. Under the optimum condition, HAP with ATMP addition of 10% (10AT-HAP) displayed the most efficient adsorption performance with the adsorption capacity of 1458.79 mg/g and 321.26 mg/g towards Pb2+ and Cd2+, respectively, which improved 76% and 92% than that of the artificially prepared HAP in the laboratory, respectively. For both heavy metal ions, the adsorption mechanism also included ion exchange and surface complexation, in which the surface complexation played a predominant role. In addition, XRD showed that a new crystal phase was formed after Pb2+ adsorption, while no new phase appeared after Cd2+ adsorption, indicating that the adsorption mechanism of Pb2+ involved dissolution-precipitation. The fitting results of adsorption isotherm and kinetics showed that the adsorption of Pb2+ and Cd2+ on HAP and 10AT-HAP were well fitted by the Langmuir isotherm model and Pseudo-second model. Moreover, Multiwfn wavefunction program based on density functional theory (DFT) was applied to deeply probe and vividly visualize the interaction sites, interaction types, interaction strength and the essence of interactions between HAP and ATMP or ATMP-HAP composite and heavy metal ions. [Display omitted] • The adsorption capacity of 10AT-HAP on Pb2+ and Cd2+ reached 1458.79 and 321.26 mg/g. • The adsorption mechanisms were revealed by experiment and Multiwfn program. • ATMP formed ternary complex with HAP and heavy metal ions. • The oxygen atoms of the phosphate groups of ATMP played a major complexation role. [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]

• Montmorillonite was modified with green and environment-friendly Histidine salt. • His-Mt is proved to be a high-efficiency adsorbent for removal of heavy metal ions. • Maximum adsorption capacity for Pb(II) and Cu(II) with His-Mt is 107.73 mg/g and 30.72 mg/g. • Ion exchange is main mechanism by Na-Mt by forming Pb(CO 3) 2 or Cu(OH) 2. A novel nanocomposite of sodium montmorillonite with L-Histidine (His-Mt), was prepared to remove Pb(II) and Cu(II) from aqueous media. The resulting nanocomposites were characterized by XRD, FT-IR, BET, SEM, TG/DTG, XPS techniques. All characterizations confirmed the anchoring of L-Histidine to Na-Mt, and the packing sequence of His in the interlayer gallery may form a monolayer structure. The His salt obtained a skewed orientation compared to the silicate surface. The single/ co-adsorption of Cu(II) and Pb(II) by pure and modified i.e. Na-Mt and His-Mt were carried out by batch adsorption experiments. The maximum adsorption capacity (q max) of Pb(II) and Cu(II) by Na-Mt and modified His-Mt was 89.08 mg/g, 23.93 mg/g, and 107.73 mg/g, 30.72 mg/g, correspondingly. The pseudo-second-order model (kinetic model) and Langmuir model (isotherm model) well-matched with the adsorption process. The data analysis showed it was an endothermic, favorable and spontaneous process, Cu(II) and Pb(II) showed competitive adsorption in the co-adsorption system. Na-Mt adsorbed M(II) ions by ion exchange mechanism, while M(II) formed complexes with histidine and were adsorbed in the interlayer region or the surface of His-Mt. [ABSTRACT FROM AUTHOR]

Sodium lignosulfonate (Na-LS) was used to modified montmorillonite to form lignosulfonate-montmorillonite (LS-MMT). The as-prepared samples were characterized by various equipment to analyze the surface morphology and structure of the pure and reformed samples. The adsorption capability (q e , mg/g) of LS-MMT or Ca/Na-MMT for Pb(II) and Cu(II) at different reaction intervals, the concentration of metal ions, temperature, and pH were studied by batch adsorption experiments. The results revealed that LS-MMT displayed a higher adsorption capacity than Ca/Na-MMT. The pH of solutions had a great influence on the q e of the two adsorbents, and the q e was slightly enhanced with temperature increasing. The isotherm and kinetic experiments studies indicated that the adsorption of heavy metal on LS-MMT or Ca/Na-MMT fit well with the Langmuir model and pseudo-second-order kinetic model. The competitive adsorption showed that LS-MMT had a stronger affinity for Pb(II) than Cu(II), which was different from Ca/Na-MMT. Additionally, the desorption experiment showed that LS-MMT had a stronger ability to lock heavy metal ions than Ca/Na-MMT in an acidic environment with pH ranging from 3 to 5. Unlabelled Image • Lignin is a non-toxic natural polymer comprising many functional groups, i.e. carboxy, phenol, hydroxyl and methoxy groups. • The results revealed that LS-MMT displayed a higher adsorption capacity than Ca/Na-MMT. • The isotherm and kinetic experiments fit well with the Langmuir model and pseudo-second-order kinetic model. • The competitive adsorption showed that LS-MMT had a stronger affinity to Pb(II) than Cu(II). • LS-MMT had a stronger ability to lock heavy metal ions in an acidic environment with a pH range from 3 to 5. [ABSTRACT FROM AUTHOR]

[Display omitted] • High dispersion and stable attachment of LDH on nitrogen and sulfur doped porous carbon (NSPC). • The synergistic effect of LDH and NSPC enhances the adsorption of heavy metal ions. • The adsorption mechanism was attributed to surface complexation. Layered double hydroxides (LDHs) composites (NSPC@LDH) were successfully prepared on nitrogen and sulfur-doped porous carbon (NSPC) by a simple co-precipitation method. The synergistic effect between the modified porous carbon and LDH enhanced its adsorption performance. Compared with pure LDH, the composite had a larger specific surface area (188.78 m2/g) and pore structure with a smaller crystallite size (4.56 nm). The porous carbon carrier effectively mitigated the aggregation effect of LDH. The maximum adsorption capacities of NSPC@LDH for Zn2+ (100 ppm) and Cu2+ (100 ppm) were 125.7 mg/g and 137.5 mg/g, respectively, which were 2.85 and 2.39 times the original LDH. The XRD and XPS studies of the adsorbent after adsorption revealed that surface complexation and physical adsorption played a dominant role in the removal of Zn2+ and Cu2+, and the introduction of N, S heteroatoms provided more active centers for heavy metal ions. Moreover, after five desorption cycles, NSPC@LDH still exhibited high removal efficiency. The results indicated that the synthesized NSPC@LDH composites have great potential for removing Zn2+ and Cu2+ from aqueous solutions. [ABSTRACT FROM AUTHOR]

The phosphonate functionalized layered double hydroxide constructed through intercalation reaction, and efficiently applied to capture toxicant metal ions. The characterization results indicated that the functionalized composite with many functional groups has adsorption potential to heavy metals. The strong chelation of the phosphonate groups with heavy metal ions proved it an excellent adsorbent leading to a maximum adsorption capacity of 156.95 mg/g (Cr3+) and 198.34 mg/g (Cd2+) separately. The data of kinetics and isotherm revealed that the chelating adsorption was dominated by chemisorption and monolayer interaction. Notably, the spent adsorbent presented satisfactory reusability after six cycles. Furthermore, the Forcite simulation with the CLAYFF-CVFF force field implied that the critical mechanism for modifiers and the surface sites of the interlayer is electrostatic interaction. Our in-depth exploration in terms of the weak interactions not only demonstrated the strength and nature but also provided a novel way to intuitively capture the type of interactions that occurred around interesting regions. In the end, we made detailed investigations on the chelation mechanism, and the covalent nature played a leading role in the binding interaction. This work provides a valuable strategy for researchers to design novel materials in practice. [Display omitted] • Functionalized LDH increased removal of Cr3+ (156.95 mg/g) and Cd2+ (198.34 mg/g). • Possible adsorption mechanisms included electrostatic interaction and chelation. • CLAYFF-CVFF force field was applied to Forcite code to study intercalation process. • The vdW potential of clay interface was intuitively exhibited for the first time. • Topology analysis and orbital interaction were used to study chelation mechanism. [ABSTRACT FROM AUTHOR]

• The high adsorption capacity of A-LDH is due to the metal-chelating function. • The reactive sites in ATMP are firstly revealed by Multiwfn calculation. • The non-covalent interactions of water/clay interface are firstly presented by IGM. • IGM analysis confirmed that ATMP/LDH is combined together mainly by H-bond. • The reactive sites and non-covalent interactions support experimental results. Phosphonates are environmental friendly materials, and can be potentially employed to improve the removal efficiency of the clay materials. In the present work, Zn-Al layered double hydroxide (LDH) intercalated with amino trimethylene phosphonic acid (ATMP) by a facile technique and employed as an adsorbent for Cu2+ and Pb2+ from wastewater. The adsorption characteristics and microscopic mechanism of ATMP in the interlayer space were explored by a combination of experimental and density functional theory (DFT). The adsorption capacity for Cu2+ and Pb2+ could reach 42.02 mg.g−1 and 84.06 mg.g−1, respectively. The adsorption kinetics curves were matched well with the pseudo-second-order model, indicating chemical adsorption via electrostatic interaction mechanism. Based on Multiwfn and VMD program calculation, the ways of electrostatic potential and average local ionization energy were firstly applied to predict reactive sites of ATMP molecule and corresponding anion, suggesting that anion state was more easily to provide lone pair electrons for electrophilic reaction. The weak interaction analysis indicated that interactions among ATMP and LDH are mainly dominated by H-bond. These results recommended that modified LDH can be a promising adsorbent for the adsorption of toxic metal ions in practical applications. [ABSTRACT FROM AUTHOR]

• PA -PPG was successfully synthesized via a radical polymerization method. • PA-PPG demonstrated a pH-dependent adsorption. • High adsorption capacities for Cd (216 mg/g), and Pb (732.4 mg/g). • PA-PPG is reusable without any loss of its adsorption capacity after four adsorption cycles. In the present work, a novel material consisting of phytic acid-functionalized poly-phenylglycine (PA-PPG) was successfully synthesized through radical polymerization and used for the removal of heavy metals ions from water. Microscopic images revealed the formation of homogenous particles in aggregated form. The chemical composition of the PA-PPG was examined using X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy. The influence of various experimental parameters such as solution pH, alkaline metals, and initial concentration of Cu, Pb, Cd ions on the removal efficiency of PA-PPG was assessed by using absorption atomic spectroscopy (AAS). The PA-PPG sample exhibited high maximum adsorption capacity of 90.5, 732.4, and 216 mg/g for Cu, Pb, and Cd ions, respectively. The PA-PPG demonstrated a pH-dependent adsorption with a maximum adsorption capacity achieved at pH 5.2. The Langmuir and Temkin models described well the adsorption isotherm data and a probable adsorption mechanism based on complexation and electrostatic attraction was proposed. Moreover, the developed PA-PPG can be reused for four cycles without any apparent loss of its adsorption capacity. The obtained results prove the efficiency of phytic acid, validate and promote the idea of using an active molecule to enhance the capacity of poly-phenylglycine for environmental remediation. [ABSTRACT FROM AUTHOR]