Graphene oxide as surfactant sheets

Abstract

Graphite oxide sheet, now referred to as graphene oxide (GO), is the product of chemical oxidation and exfoliation of graphite powders that was first synthesized over a century ago. Interest in this old material has resurged in recent years, especially after the discovery of graphene, as GO is considered a promising precursor for the bulk production of graphene-based materials. GO sheets are single atomic layers that can readily extend up to tens of microns in lateral dimension. Therefore, their structure bridges the typical length scales of both chemistry and materials science. GO can be viewed as an unconventional type of soft material as it carries the characteristics of polymers, colloids, membranes, and as highlighted in this review, amphiphiles. GO has long been considered hydrophilic due to its excellent water dispersity, however, our recent work revealed that GO sheets are actually amphiphilic with an edge-to-center distribution of hydrophilic and hydrophobic domains. Thus, GO can adhere to interfaces and lower interfacial energy, acting as surfactant. This new property insight helps to better understand GO’s solution properties which can inspire novel material assembly and processing methods such as for fabricating thin films with controllable microstructures and separating GO sheets of different sizes. In addition, GO can be used as a surfactant sheet to emulsify organic solvents with water and disperse insoluble materials such as graphite and carbon nanotubes (CNTs) in water, which opens up opportunities for creating functional hybrid materials of graphene and other π-conjugated systems.

Recyclable magnetic graphene oxide for rapid and efficient demulsification of crude oil-in-water emulsion

“…The exposed amino groups on the functionalized nanoparticles (c-Fe 2 O 3 @SiO 2 -NH 2 ) surface are the active sites to react with GO. After coupling the amino-functionalized nanoparticles on the GO surface, the zeta potential of M-GO were measured to be À35.61 mV, which was slightly smaller than that of GO (range from À42 to 50 mV [30]) due to the influence of acylamino groups and the unreached amino groups on the silica surface. These results from the zeta potential measurements provide convincing evidence that the anticipated nanoparticles were successfully obtained in each step during the preparation of M-GO.…”

Demulsification of Crude Oil-in-Water Emulsions Driven by Graphene Oxide Nanosheets

“…With the decreasing of demulsification pH value, the GO transferred from the water to the oil phase, which can be well explained by the adjustable amphiphilicity of the GO nanosheets. 42,43 The ionization of carboxyl group on the edge of GO can be tuned by 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 16 changing the pH value. 50 Therefore, GO can be reversibly shuttled between water and oil phase, which make it useful for recycling.…”

Magnetic surfactants

“…They readily form stable colloidal dispersions in water as some of the sp2 hybridized carbons atoms are derivatized by epoxide and phenol hydroxyl groups. Unoxidized hydrophobic domains do still exist turning GO into a surfactant sheet, capable of lowering interfacial energies [55]. They have attracted a great deal of interest over the past decade with potential in multifarious applications ranging spectroscopic sensors [56], battery electrodes [57], and more recently water treatment [58,59].…”