Molecular dynamics simulation of a lignite structure simplified model absorbing water

ABSTRACT

To study the formation mechanism of hydration films, a lignite molecular model based on FTIR analysis was established. Both the positive and negative extreme values (±184.76 kJ/mol) of the electrostatic potential appear around oxygen-containing functional groups. Water molecules are mainly adsorbed near oxygen-containing functional groups. This paper studies the absorption of lignite for water molecules using MD simulation. With the addition of water molecules, the number of polar groups increases, and the electrostatic potential level of the system increases, causing an increase in the number of active sites. When the amount of water is inadequate for covering the surface of lignite, water molecules adsorb at active sites and places with lower z values. As the number of water molecules increase, the average length of hydrogen bonds between water molecules and that between lignite and water are close to the set values (1.97 and 1.8 Å, respectively). The short-range order structure of the interface has little effect on the average bond length of water molecules, but it reduces the average bond angle by 1°~2°. After a hydration film forms, the increase to the thickness of the hydration film is primarily attributed to hydrogen-bond interaction between water molecules.

KEYWORDS:

• Molecular dynamics
• adsorption
• electrostatic potential
• hydration
• oxygen-containing functional groups

Acknowledgments

We thank LetPub (www.letpub.com) for its linguistic assistance during the preparation of this manuscript.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by National Natural Science Foundation of China (grant number 51604273); the Fundamental Research Funds for the Central Universities (grant number 2014QNB14).