Carboxyl asphaltene is commonly discussed in the petroleum industry. In most conditions, electroneutral carboxyl asphaltene molecules can be deprotonated to become carboxylate asphaltenes. Both in crude oil and at the oil/water interface, the characteristics of anionic carboxylate asphaltenes are different than those of the carboxyl asphaltenes. In this paper, molecular dynamics (MD) simulations are utilized to study the structural features of different asphaltene molecules, namely, C5 Pe and anionic C5 Pe, at the molecular level. In crude oil, the electroneutral C5 Pe molecules prefer to form a steady face-to-face stacking, while the anionic C5 Pe molecules are inclined to form face-to-face stacking and T-shaped II stacking because of the repulsion of the anionic headgroups. Anionic C5 Pe has a distinct affinity to the oil/water interface during the simulation, while the C5 Pe molecules persist in the crude oil domain. A three-stage model of anionic C5 Pe molecules adsorbed at the oil/water interface is finally developed.

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The coupling of carbon nanodots (C-Dots) with graphitic carbon nitride (g-CN) has been demonstrated to boost the overall photocatalytic solar water splitting efficiency. However, the understanding on the role of the C-Dots and how the structure of C-Dots influences the photocatalytic reaction is still limited. In this work, we investigate the excited states of some C-Dot/g-CN composites with the C-Dots containing different functional groups including -OH, -CHO and -COOH by first-principles many-body Green's function theory. It is found that the increase of efficiency can be ascribed to the high separation rate and the low recombination rate of the electron-hole pair benefiting from the emergence of the charge-transfer excited state between the C-Dots and g-CN. Functional groups on the C-Dots play a crucial role in determining the charge transfer direction, active sites for reduction reaction and oxidation reaction of water, and whether the reaction is a four-electron process or a two-electron/two-electron process. These results can provide guidance for the design and optimization of the C-Dots for heterojunction photocatalysts.

Two green surfactants, made by dodecyl sulfate (DS−) and laurate (C12) with equimolar choline (Ch+) components as counterions, are studied through all-atom molecular dynamics simulations.

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