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

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• 作者：Aaron W. Chen ; Bing Fang ; Hyunbok Lee ; Alejandro L. Briseno ; Maria M. Santore ; ^{Santore@mail.pse.umass.edu}
• 关键词：Pristine graphene ; Chemically-deposited graphene ; Wetting transparency ; Surface charge ; Dispersion forces ; Double layer ; Aqueous ; Secondary minima
• 刊名：Journal of Colloid and Interface Science
• 出版年：2017
• 出版时间：15 April 2017
• 年：2017
• 卷：492
• 期：Complete
• 页码：15-24
• 全文大小：1654 K
• 卷排序：492

文摘

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 microspheres 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/nm2). 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.