Charge-Driven Selective Adsorption of Sodium Dodecyl Sulfate on Graphene Oxide Visualized by Atomic Force Microscopy

Using liquid-cell atomic force microscopy, we investigated molecular adsorption of sodium dodecyl sulfate (SDS) from aqueous solution onto single-layer graphenes that were oxidized to different degrees. SDS did not adsorb onto graphene oxide (GO) featuring an atomic carbon:oxygen (C:O) ratio of 2.0. Reduced GO (C:O ratio: 10.7), in contrast, was covered with micellar SDS aggregates, featuring a height of approximate to 2 nm and lateral feature sizes of approximate to 5 nm. This selective adsorption depending on the degree of oxidation can be explained by electrostatic repulsion between the negatively charged SDS head groups and the negatively charged hydroxyl groups on oxidized graphene. Our results suggest it will be possible to translate this adsorption selectivity into separation techniques that fractionate GO into subsets featuring different degrees of oxidation. Such fractionation techniques are likely to enable the preparation of GO with more well-defined electronic properties and make GO interesting as a band gap material.