Concentrated aqueous dispersions of low-defect few-layer thick graphene using surface active ionic liquid for enhanced enzyme activity

Abstract

Low energy ultrasonic assisted aqueous phase exfoliation of defect free graphene (D/G = 0.19) in a high yield (3.0 mg ml-1) is achieved using benzimidazolium based surface active ionic liquid (SAIL) appended with an ester functionalized alkyl chain. The obtained dispersions are found to be stable against agglomeration or sedimentation for at least 15 days, owing to coulombic repulsions offered by electron deficient π-conjugated SAIL ions adsorbed onto graphene. The exfoliated few-layer thick graphene sheets (2 layers 53% and 3-5 layers 20%) offer a high surface area in conjunction with high concentration, which is exploited for the efficient loading of an enzyme, cellulase, via hydrophobic interactions. The graphene appended cellulase is found to exhibit a remarkable increase in the enzyme activity (13-fold) as compared to cellulase in the buffer. It is expected that the present results would act as a platform for the synthesis and utilization of new SAILs for graphene exfoliation, stabilization, and functionalization required to widen the application arena of graphene.