Molecular dynamics simulation study of covalently bound hybrid coagulants (CBHyC): Molecular structure and coagulation mechanisms

Covalently-bound organic silicate-aluminum hybrid coagulants (CBHyC) have been shown to efficiently remove low molecular weight organic contaminants from wastewater. However, the interaction dynamics and motiva-tions during the coagulation of contaminant molecules by CBHyC are limited. In this study, a molecular dynamics (MD) simulation showed that CBHyC forms core-shell structure with the aliphatic carbon chains gather inside as a core and the hydrophilic quaternary ammonium-Si-Al complexes disperse outside as a shell. This wrapped structure allowed the coagulant to diffuse into solutions easily and capture target contaminants. The adsorption of anionic organic contaminants (e.g., diclofenac) onto the CBHyC aggregates was driven equally by van der Waals forces and electrostatic interactions. Cationic organic contaminants (e.g., tetracycline) were seldom bound to CBHyC because of substantial repulsive forces between cationic molecules and CBHyC. Neutrally-charged organic molecules were generally bound through hydrophobic interactions. For adenine and thymine deoxy-nucleotide, representatives of antibiotic resistance genes, van der Waals forces and electrostatic interaction became the dominant driving force with further movement for adenine and thymine, respectively. Driving forces between target contaminant and coagulant directly affect the size and stability of formed aggregate, following the coagulation efficiency of wastewater treatment. The findings of this study enrich the database of aggregation behavior between low molecular weight contaminants and CBHyC and contribute to further and efficient application of CBHyC in wastewater treatment.

Automated summary

This study used molecular dynamics simulations to investigate the interaction dynamics and motivations during the coagulation of contaminant molecules by covalently-bound organic silicate-aluminum hybrid coagulants (CBHyC). The simulations revealed that CBHyC forms a core-shell structure, with aliphatic carbon chains in the core and hydrophilic quaternary ammonium-Si-Al complexes in the shell. The adsorption of different types of organic contaminants onto CBHyC was driven by varying forces such as van der Waals forces, electrostatic interactions, and hydrophobic interactions. The findings contribute to a better understanding of the aggregation behavior between low molecular weight contaminants and CBHyC, and have implications for improving wastewater treatment efficiency.