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Among the serious environmental problems that attracted much attention from the broader public is the high toxicity of dioxins. Considerable efforts have been made to develop techniques and materials that could help in their efficient removal from the environment. Due to its high specific surface area, numerous active sites, and outstanding structural and electronic properties, antimonene is considered for a variety of potential applications in different fields such as energy storage, electrocatalysis, and biomedicine. The present study adds to this portfolio by suggesting antimonene as a promising candidate for dioxin capture. Using density functional theory calculations, we studied the adsorption of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on pristine as well as Ca-, Ti-, and Ni-doped antimonene. Three spatial configurations of the adsorption of TCDD on antimonene were analyzed. The results obtained from the calculation of adsorption energies, charge transfer, and densities of states provide evidence that antimonene outperforms other nanomaterials that have been previously suggested for dioxin capture applications. Therefore, we propose these substrates (i.e., pristine and doped antimonene) as potential capture agents for removing such toxic organic pollutants. [ABSTRACT FROM AUTHOR]

The soil pH plays a substantial role in controlling phosphorus (P) adsorption and mobilization. These processes are strongly affected by the phosphate interaction strength with P-fixing soil minerals such as goethite. The target of the current contribution is to draw a molecular level picture of the interplay between pH and phosphate binding at the goethite–water interface via a joint experimental–theoretical approach. Periodic density functional theory (DFT) calculations were carried out to provide a molecular level understanding of the pH dependence of P adsorption. To validate the modeling approach, adsorption experiments of phosphate at goethite were performed in the pH range of 4–12. There was agreement between experiments and simulations in the description of the adsorption behavior by two pH-dependent successive stages. The adsorption increases along the pH change from 4 to 8. A further increase of pH leads to a decrease of adsorption. By comparing with literature data it is concluded that the first stage will be observed only if there is no significant change of the surface charge at low pH. Moreover, the molecular modeling results point to the abundance of the monodentate (M) binding motif at both extremely low and high pH ranges. Otherwise, the bidentate (B) one is predominant along the intermediate pH range. These observations could resolve the existing debate about the assignment of phosphate–goethite binding motifs. Furthermore, the results point to a decrease of pH upon phosphate sorption due to an induced acidification of soil solution. The present joint experimental–theoretical approach provides a better understanding and description of the existing phosphate sorption experiments and highlights new findings at the atomistic/molecular scale. [ABSTRACT FROM AUTHOR]

Phosphorus (P) immobilization and thus its availability for plants are mainly affected by the strong interaction of phosphates with soil components especially soil mineral surfaces. The related reactions have been studied extensively via sorption experiments especially by carrying out adsorption of ortho-phosphates onto Fe-oxide surfaces. But a molecular-level understanding of the P-binding mechanisms at the mineral–water interface is still lacking, especially for forest eco-systems. Therefore, the current contribution provides an investigation of the molecular binding mechanisms for two abundant phosphates in forest soils, inositol hexaphosphate (IHP) and glycerolphosphate (GP), at the diaspore mineral surface. Here a hybrid electrostatic embedding quantum mechanics/molecular mechanics (QM/MM) based molecular dynamics simulation has been applied to explore the diaspore–IHP/GP–water interactions. The results provide evidence for the formation of different P-diaspore binding motifs involving monodentate (M) and bidentate (B) for GP and two (2M) as well as three (3M) monodentates for IHP. The interaction energy results indicated the abundance of the GP B motif compared to the M one. The IHP 3M motif has a higher total interaction energy compared to its 2M motif, but exhibits a lower interaction energy per bond. Compared to GP, IHP exhibited stronger interaction with the surface as well as with water. Water was found to play an important role in controlling these diaspore–IHP/GP–water interactions. The interfacial water molecules form moderately strong H-bonds (HBs) with GP and IHP as well as with the diaspore surface. For all the diaspore–IHP/GP–water complexes, the interaction of water with the diaspore exceeds that with the studied phosphates. Furthermore, some water molecules form covalent bonds with diaspore Al atoms while others dissociate at the surface to protons and hydroxyl groups leading to proton transfer processes. Finally, the current results confirm the previous experimental conclusions indicating the importance of the number of phosphate groups, HBs, and proton transfers in controlling the P-binding at soil mineral surfaces. [ABSTRACT FROM AUTHOR]

The interaction between phosphates and soil mineral surfaces, such as Fe- and Al-(oxyhydr)oxides, plays a crucial role in the immobilization of P and thus its availability for plants. The reactions of phosphates with Fe-hydroxides and especially goethite have been studied extensively. But a molecular-level picture of the phosphate binding mechanisms at the goethite–water interface is still lacking. Therefore, in the current contribution we have explored the molecular binding mechanisms for the adsorbed phosphate at the goethite–water interface by performing sorption kinetics experiments for orthophosphate and characterizing the adsorbed species by FT-IR spectroscopy. In parallel, periodic DFT calculations have been performed to explore the interaction mechanisms and to assign the IR spectra for monodentate (M) and bidentate (B) orthophosphate complexes at two different goethite surface planes (010 and 100) in the presence of water. In general, our interaction energy results give evidence that the mono-protonated B phosphate complex is favored to be formed at the goethite–water interface, although the M motif could exist as a minor fraction. Moreover, it was found that water plays an important role in controlling the phosphate adsorption process at the goethite surfaces. The interfacial water molecules form H-bonds (HBs) with the phosphate as well as with the goethite surface atoms. Furthermore, some water molecules form covalent bonds with goethite's Fe atoms while others dissociate at the surface to protons and hydroxyl groups. The present theoretical assignment of IR spectra introduces a benchmark for characterizing experimental IR data for the adsorbed KH2PO4 species at the goethite–water interface. In particular, the IR spectra of the mono-protonated (2O + 1Fe) B complex at the 010 goethite surface plane and the M complex at the 100 goethite surface plane were found to be consistent with the experimental data. In order to explore the role of different abundances of surface planes and binding motifs, IR spectra obtained from weighted averages have been analyzed. The results confirmed the conclusions drawn from interaction energy calculations. [ABSTRACT FROM AUTHOR]

Investigation of the interaction between glyphosate (GLP) and soil minerals is essential for understanding GLP's fate in the environment. Whereas GLP–goethite binding has been discussed extensively, the impact of water as well as of different goethite surface planes has not been studied yet. In this contribution, periodic density functional theory-based molecular dynamics simulations are applied to explore possible binding mechanisms for GLP with three goethite surface planes (010, 001, and 100) in the presence of water. The investigation included several binding motifs of monodentate (M) and bidentate (B) type. It was found that the binding stability increases in the order M@001 ＜ M@010 ＜ (2O + 2Fe) B@100 ＜ M@100 ＜ (1O + 2Fe) B@001 ＜ (2O + 1Fe) B@010. This behavior has been traced to the presence of intramolecular H-bonds (HBs) in GLP as well as intermolecular HBs between GLP and water, GLP and goethite, and water and goethite. These interactions are accompanied by proton transfer from GLP to water and to goethite, and from water to goethite as well as water dissociation at the goethite surface. Further, it was observed that the OH− species can replace the adsorbed GLP at the goethite surface, which could explain the well-known drastic drop in GLP adsorption at high pH. The present results highlight the role of water in the GLP–goethite interaction and provide a molecular level perspective on available experimental data. [ABSTRACT FROM AUTHOR]