Molecular dynamics simulations of nonionic surfactant adsorbed on subbituminous coal model surface based on XPS analysis

ABSTRACT

A molecular dynamics (MD) simulation was conducted to study the adsorption behaviour of a nonionic surfactant adsorbed on low-rank coal. Owing to the complicated chemical component and structure of the coal surface, a modified graphite surface with hydroxyl, carboxyl, and carbonyl groups was utilised for a representation of the subbituminous coal surface model. The compositions of the hydroxyl, carbonyl, and carboxyl groups on the coal surface were found to be at a proportion of 25:3:5 according to the X-ray photoelectron spectroscopy (XPS) results. The interaction of nonylphenol ethoxylate with 8 ethylene oxide groups (NPEO-8) using this coal model in an aqueous phase was then simulated. It was revealed that the nonionic surfactant molecules were adsorbed at the interface between water and coal. This agminated structure of the surfactant molecules on the surface of the coal demonstrated an attachment of the surfactant ethoxylate groups to these solid surfaces and an extension of the remaining hydrophobic portions into the solution. Therefore, a coal surface with greater hydrophobicity was created. The dynamic properties of the water molecules characterised through self-diffusion coefficients indicate greater water mobility resulting from the existence of NPEO-8.

KEYWORDS:

• Subbituminous coal
• nonionic surfactant
• molecular dynamics
• XPS

Acknowledgements

The computation of molecular modelling was performed at China University of Mining and Technology.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by Key Laboratory of Coal Processing and Efficient Utilization, Ministry of Education Foundation: [Grant Number CPEUKF 1802]; SDUST Research Fund: [Grant Number 2018TDJH101].