Cardanol surfactant/ultrasound-assisted exfoliation of graphite in a water/ethanol solution

Abstract

Graphene has high electrical and thermal conductivity, high transparency, and chemical stability that stand out compared to those of other materials. An efficient technique for producing few-layers graphene (<5 layers) is the liquid-phase exfoliation of graphite (LPE). LPE is a simple, cost-effective, ecologically friendly technique that without the use of hazardous solvents can produce graphene without defects in its basal plane. The influence of natural surfactant (cardanol), time and type of ultrasound on the properties of exfoliated graphite was studied. The use of tip ultrasound promotes graphite exfoliation in relatively shorter time (20 min) than ultrasonic bath time (360 min). Another factor that determines the effectiveness of the exfoliation is the concentration of cardanol, which, when used at the critical micelle concentration (CMC) value promotes the formation of micelles that help in the exfoliation and stability of the exfoliated graphite. Few-layers graphene with a concentration of 3.00 ± 0.01 mg mL−1 and an average stacked graphene height of up to 3 nm for 30% of the product were produced by combining the appropriate time of tip ultrasound with the use of cardanol at an equal concentration to its CMC. Furthermore, stable suspension of graphene in aqueous medium was achieved for more than 6 months without significant sedimentation. These results are related to the π-π and hydrophobic-hydrophobic interactions between the cardanol molecules and the graphene surface, which promote the adsorption of cardanol molecules on the graphene surface, and the re-stacking and agglomeration can be reduced due to electrostatic repulsion. Few-layers graphene produced from a new green-surfactant is an innovative technology that transforms low cost products into materials with higher added value for applications in supercapacitors, solar cells, and biosensors.