Evidence for negative charge near large area supported graphene in water: A study of silica microsphere interactions

초록

This study addresses the electrostatic and van der Waals interactions at the aqueous interface of large area CVD graphene, 1-3 layers thick on a silica support and assessed by Raman spectroscopy to have exclusive sp2 character. Ionic strength was found to substantially alter the interactions of silica micro spheres with silica-supported graphene. Particles were nonadhesive at large Debye lengths but became irreversibly adherent at reduced Debye lengths about 2 nm or less. This was demonstrated to be qualitatively parallel to the influence of ionic strength on silica-silica interactions. The observed ionic strength effects are best explained by negative charges in the vicinity, within a few nanometers, of the supported graphene. DLVO-based modeling of the silica-water-supported graphene interaction suggests that van der Waals interactions drive particle capture and that the surface potential at the supported graphene surface is at least -10 to -15 mV (corresponding to a charge density of 0.02-0.06/nm(2)). This charge could result from ion adsorption or from charges on silica beneath the graphene. The conclusions are not substantially affected by inclusion of nanometer-scale interfacial roughness in the modeling. 2016 Elsevier Inc. All rights reserved.

키워드