High‐ versus Low‐Quality Graphene: A Mechanistic Investigation of Electrografted Diazonium‐Based Films for Growth of Polymer Brushes

Abstract

Electrografting using aryldiazonium salts provides a fast and efficient technique to functionalize commercially available 3-5 layered graphene (vapour-deposited) on nickel. In this study, Raman spectroscopy is used to quantify the grafting efficiency of cyclic voltammetry which is one of the most versatile, yet simple, electrochemical techniques available. To a large extent the number of defects/substituents introduced to the basal plane of high-quality graphene by this procedure can be controlled through the sweeping conditions employed. After extended electrografting the defect density reaches a saturation level ( ∼ 10(13) cm(-2)) which is independent of the quality of the graphene expressed through its initial content of defects. However, it is reached within fewer voltammetric cycles for low-quality graphene. Based on these results it is suggested that the grafting occurs (a) directly at defect sites for, in particular, low-quality graphene, (b) directly at the basal plane for, in particular, high-quality graphene, and/or (c) at already grafted molecules to give a mushroom-like film growth for all films. Moreover, it is shown that a tertiary alkyl bromide can be introduced at a given surface density to serve as radical initiator for surface-initiated atom transfer radical polymerization (SI-ATRP). Brushes of poly(methyl methacrylate) are grown from these substrates, and the relationship between polymer thickness and sweeping conditions is studied.

Functionalized CVD monolayer graphene for label-free impedimetric biosensing

“…After the third cycle, no further change in the Raman spectra was observed, indicating that the graphene surface was covered with monolayer of aryl groups in a good agreement with the observed saturation in CV Faradaic current data explained above. It is worth noting that the estimated defects density obtained using our method for three CV cycles was consistent with that reported for the grafting of carboxyphenyl tetrafluporoborate on graphene supported on SiO 2 using spontaneous electron transfer chemistry [32] as well as on Ni using the electrografting method in acetonitrile [39]. For graphene/Ni electrografting, five CV scans were shown to be necessary for realizing the maximal modification of the graphene surface.…”

“…The authors have demonstrated successful grafting of uniform thin films using electrochemistry and demonstrated modulation of graphene electronic properties by opening a band gap upon functionalization [38]. More recently, a mechanistic investigation of electrografted diazoniumbased films on few layers of graphene (vapordeposited) on nickel has been reported [39]. However, diazonium-functionalized monolayer CVD graphene sheets have not been applied to biosensing.…”

Electrochemical Behaviour of HOPG and CVD‐Grown Graphene Electrodes Modified with Thick Anthraquinone Films by Diazonium Reduction

“…According to the specification from the supplier (i.e., Graphene Supermarket) Ni-Gra is composed of patches of 1-7 layers with dimensions of 3-10 mm. This is in accordance with Raman analysis carried out in a previous study [58]. With an average number of layers equal to 4, Ni-Gra should be considered as multilayer graphene [62].…”

“…Because the measurements were carried out on a dried and therefore collapsed films, the refractive index of the layer was fixed at a constant value (real = 1.55; imaginary = 0), independent of the thickness. The average and the standard deviation values reported correspond to data points obtained from measuring three spots on each plate [58].…”

“…The complex refractive index of the bare substrate was calculated from the D s and y s values. A three-layer optical model consisting of a substrate with a complex refractive index, the grafted layer with a refractive index and thickness and the surrounding medium (air) was used to calculate the overall reflection coefficients for in-plane (R p ) and out-of-plane (R s ) polarized lights [58].…”