Spontaneous Adsorption of Graphene Oxide to Oil–Water and Air–Water Interfaces by Adsorption of Hydrotropes

Abstract

The interfacial adsorption of graphene oxide (GO) is crucial in phenomena such as emulsification and froth flotation, where presence of 2D nanomaterials facilitates Pickering stabilization. This process usually requires the input of high amounts of shear energy, or is aided by surfactants in order to make it possible at room temperature. In this work, a surfactant‐free method for interfacial enrichment through the use of a family of tetraalkylammonium hydrotropes, the most effective being tetraethylammonium chloride (TEAC), is demonstrated. As both GO and hydrotropes do not spontaneously enrich to interfaces on their own, this synergistic, spontaneous effect highlights that hydrotropes adsorb to GO sheets, decreasing their negative charge while rendering them more amphiphilic and therefore making it thermodynamically favorable for them to adsorb to the interface. Evidence for this adsorption includes increases in surface pressure, as well as emulsion and froth stability when both GO and hydrotropes are present in a system. Hydrotropes perform as well as or better than surfactants. Adsorption is irreversible, with XRR and AFM studies demonstrating that roughness increases with compression of the air‐water interface, showing that GO sheets are crumpling at the interface rather than desorbing, providing new routes to patterned and structured GO layers.

Effects of Ion Adsorption on Graphene Oxide Films and Interfacial Water Structure: A Molecular-Scale Description

“…This rearrangement forces the GO flakes to tilt and generates a rough, crumpled GO film that can, in addition to the adsorbed ions, reflect more signal and be detected using XR. 48 Based on the obtained pressure-area isotherms (Supporting Information), the GO film is likely in the same condensed phase at both 20 and 30 mN/m where GO sheets are touching and overlapping to create a multilayer structure. 45,47,50 This means there is little mechanical difference in between the two film structures at these pressures.…”

“…Langmuir-Blodgett films prepared from GO dispersions successfully spread on aqueous subphases have confirmed surface activity. [44][45][46][47] Although GO is not a traditional surfactant, 8 it can stabilize water-oil emulsions 7,48 with limited studies considering the oil-water interface specifically. 49 The air-water interface is particularly relevant to separation efforts but can be difficult to isolate from the bulk.…”

Spontaneous surface adsorption of aqueous graphene oxide by synergy with surfactants

“…19 To overcome this limitation, additive inclusion to aqueous GO suspensions has been investigated as a potential pathway to achieving spontaneous adsorption of GO. Such additives include quantum dots, 20 hydrotropes, 21 polymers 22 and surfactants. 23,24 These systems work by forming surface active GO/additive composite materials that accumulate at interfaces without requiring adjustment to extreme pH conditions.…”

Control of Water Adsorption via Electrically Doped Graphene: Effect of Fermi Level on Uptake and H2O Orientation

“…Adsorption plays an important role in applications such as condensation-evaporation in thermal power generation, [1,2] ambient air water harvesting, [3,4] ice-nucleation, [5] self-cleaning surfaces, [6,7] and oil-water separation [8,9] The energy efficiency of these adsorption technologies can be improved by tunable adsorption. [10,11] For example, in condensation heat transfer, tunable adsorption could enable a surface to condense more vapor by periodically switching between being easier to form a condensation film to easier to shed condensation.…”

“…This is followed by the creation of hydrogen bonds among water molecules, which coalesce to form droplets. Adsorption of water plays an important role in applications such as condensation–evaporation in thermal power generation, [ 1,2 ] ambient air water harvesting, [ 3,4 ] ice‐nucleation, [ 5 ] self‐cleaning surfaces, [ 6,7 ] oil–water separation, [ 8,9 ] and biological interfaces. [ 10 ] The energy efficiency of these adsorption technologies can be improved by tunable adsorption.…”