h i g h l i g h t sThe M-GO was a high efficiency demulsifier which could be reused for 6-7 times. The non-covalent interaction analysis proved that p-p and r-p interactions between GO materials and asphaltene molecules are the major driven forces for demulsification. Graphene oxide (GO) nanosheets have been experimentally proved to be a highly efficiency, rapid and universal demulsifier to break up the crude oil-in-water emulsion and/or the emulsified oily waste water in our previous study. To recycle the GO nanosheets and avoid the possible contamination of GO for crude oil, in this work, the magnetic graphene oxide (M-GO) was successfully synthesized and used for separating oil/water emulsions. Demulsification tests indicated that M-GO could separate the oil/water emulsions within a few minutes and recycle 6-7 times without losing its demulsification capability. The residual oil content in the separated water was as low as $10 mg/L, corresponding to a demulsification efficiency of 99.98% at an optimal dosage. Quantum chemical calculation results indicated that the p-p/r-p interactions between GO materials and asphaltene molecules are the major driven forces for the high demulsification performance of M-GO nanosheets. This work not only provides a promising demulsifies to demulsify the crude oil-in-water emulsion or the oily wastewater but also give a deep understanding on the intrinsic interaction between demulsifiers and asphaltenes.

Understanding the nature of non-covalent interactions (NCIs) between asphaltene molecules is not only theoretically interesting but also important for practical application. We performed quantum chemical calculations to reveal the configuration feature and intermolecular interaction characteristics of asphaltene dimers using three representative asphaltene model compounds and their derivatives. The frontier molecular orbitals and electrostatic potential map of the model asphaltenes were analyzed to reveal the nature of interaction between the asphaltene monomers. The calculation of binding energies indicates that the stability of asphaltene dimers not only depends upon the number of aromatic rings but also relies on the presence of heteroatoms in the aromatic core and aliphatic side chains, which could change the electrostatic charge distribution on the molecular van der Waals surface. In addition, NCIs and the natural bond order analysis method were used to identify the interactions that promote the formation of asphaltene dimers. It was found that the reduced density gradient isosurfaces could clearly reveal the type of interactions between two asphaltene monomers in their dimers. The results indicate that various interactions possess either an electrostatic or a dispersive nature, including hydrogen-bonding, θ–θ, θ–π, and π–π interactions, among which the π–π stacking interaction is believed to be the major driving force for asphaltene aggregation.

The purpose of this work is to investigate the relationship between the chemical structure of the GO materials and the demulsification performance.