Molecular Dynamics Simulation of the Interaction between Common Metal Ions and Humic Acids

Abstract

Humic acids (HAs) have important environmental and geochemical effects on soil, water environments and sediment. HAs strongly complex some metal ions, which affects the migration of metal ions and the colloidal aggregation of HA. Here, the complexation of Ca2+ and Mg2+ with HA in aqueous solution under neutral conditions has been systematically studied by molecular dynamics (MD) simulation. The results show that the aggregation of HA is caused by the complexation of HA and metal ions, mainly due to the intermolecular bridging between Ca2+, Mg2+ and COO− groups. Monodentate and bidentate coordinations have been found between Ca2+ and COO− groups of different HA molecules in the same simulation system. Mg2+ only has a monodentate coordination with COO− group.

Colloidal Chemistry in Water Treatment: The Effect of Ca2+ on the Interaction between Humic Acid and Poly(diallyldimethylammonium chloride) (PDADMAC)

“…Even in the presence of inorganic cations with the same valency, it was reported that the strength of HA aggregates was higher in the presence of Ca 2+ than for Mg 2+ , which is consistent with higher efficiency of HA coagulation with a cation of a larger ionic radius and the same valency . Such a comparison was further confirmed by an MD simulation study, which clarified the monodentate and bidentate coordination between Ca 2+ and carboxylate groups among the complexation of HA and cationic ions, while for Mg 2+ , only monodentate coordination was found …”

“…35 Such a comparison was further confirmed by an MD simulation study, which clarified the monodentate and bidentate coordination between Ca 2+ and carboxylate groups among the complexation of HA and cationic ions, while for Mg 2+ , only monodentate coordination was found. 36 As Ca 2+ ions are omnipresent in raw water and often become added in the form of lime during the water treatment process, a large number of studies have been dedicated to elucidating the Ca 2+ effect within the conventional water treatment process. For instance, it has been found that the consumption of aluminum sulfate (Al 2 (SO4) 3 ) was sufficiently reduced by around 20% to achieve comparable removal efficiency at pH above 6 when adopting CaCl 2 as a cocoagulant to remove NOM from raw water.…”

Effect of surfactant compounding on the wettability of talcum powder

“…The angle change of the surfactant hydrophobic tail chain and hydrophilic head group characterizes the interaction strength between the surfactant and the talcum powder surface. Also, it reflects the degree of stretching of the surfactant molecule (Wu et al, 2021). The larger the surfactant angle, the stronger the interaction between the hydrophobic tail group and the talcum powder surface, the more stable the adsorption.…”

Interfacial interactions of humic acids with polystyrene nano-plastics in aqueous/ionic environments: a molecular dynamics exploration

“…The molecular structure of the TNB molecule comprises three carboxylic (R-COOH) groups, three carbonyls (R-CO), two phenolic (R-OH) groups, two amines (R-NH 2 ), and four other alcohol groups and has a chemical composition of (C 36 H 40 O 16 N 2 ). 24 The carboxylated groups of the TNB molecule were deprotonated in the pH range of 4-9 (pK a = 4-5), whereas the phenolic (pK a = 9) and amine groups (pK a = 4.6) were in a protonated state. 25 Five such molecules of TNB were distributed randomly over the simulation box of size 9 × 9 × 9 nm 3 , with the PSslab being at its center, as shown in Fig.…”