Journal
ENVIRONMENTAL SCIENCE & TECHNOLOGY
Volume -, Issue -, Pages -Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.est.1c05938
Keywords
humic acid (HA); acidity; solubility; folding; aggregation; mechanisms; simulation and experiment
Categories
Funding
- National Natural Science Foundation of China [22106111, 21473206]
- LiaoNing Revitalization Talents Program [XLYC2002015]
- Fundamental Research Funds for the Central Universities
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This study investigates the dynamics of humic acid (HA) in a water solution and its dependence on pH, temperature, and concentration using molecular dynamics (MD) simulations. The results reveal the compact conformation of HA in water and pH-dependent aggregation. Experimental data support the simulation results.
Molecular dynamics (MD) simulations were performed to investigate the dynamics of humic acid (HA) in an aqueous solution and the influence of pH, temperature, and HA concentration. The HA model employed in MD simulations was chosen and validated using experimental chemical composition data and Fourier transform infrared (FTIR) spectra. The simulations showed that the HA molecule has a strong propensity to adopt a compact conformation in water independent of pH, while the aggregation of HA was found to be pH-dependent. At high pH, the ionized HAs assembled into a thread-like structure, maximizing contact with water. At low pH, the neutral HAs formed a droplet-like aggregate, minimizing contact with the solvent. The simulation results are consistent with experimental data from dynamic light scattering (DLS) measurements and transmission electron microscopy (TEM) imaging. This work provides new insight into the folding and aggregation of HA as a function of pH and a molecular-level understanding of the relationship between the acidity and the structure, solubility, and aggregation of HA, with direct implications for HA-based remediation strategies of contaminated sites.
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