Molecular dynamics simulations of nonylphenol ethoxylate on the Hatcher model of subbituminous coal surface

Nonylphenol ethoxylate can be used to improve the performance of low-rank fine coal flotation. Herein, we utilized experimental and computational methods to investigate the adsorption of nonylphenol ethoxylate with 10 ethylene oxide units (NPEO-10) onto the surface of subbituminous coal, revealing that the adsorption could be described by a Langmuir-type isotherm, in agreement with the negative interaction energy calculated by molecular dynamics simulation. X-ray photoelectron spectroscopy analysis showed that the coverage of oxygen-containing surface groups by NPEO-10 improved the hydrophobicity of subbituminous coal. Moreover, the performed simulations indicated that in the presence of NPEO-10, water molecules were more strongly repelled by the coal surface due to its increased hydrophobicity, which was supported by the results of contact angle measurements at low surfactant concentration. Analysis of surfactant molecule aggregates by head and tail group density profiling revealed that these aggregates were attached to the coal surface via ethoxylate groups. The calculated dynamic properties of NPEO-10 showed that its diffusion was most pronounced in the direction perpendicular to the coal surface due to the hydrophobic interactions of alkyl chains. (C) 2018 Elsevier B.V. All rights reserved.