Spontaneous Grafting of Nitrophenyl Groups on Amorphous Carbon Thin Films: A Structure–Reactivity Investigation

Abstract

Amorphous carbon materials find numerous applications in diverse areas ranging from implantable biodevices to electronics and catalysis. The spontaneous grafting of aryldiazonium salts is an important strategy for the modification of these materials and it is widely used in order to display a range of functionalities or to provide anchoring groups for further functionalization. We have investigated the spontaneous attachment of 4-nitrobenzenediazonium salts from aqueous solutions onto amorphous carbon materials that differ in their sp 2 content with the aim of understanding to what extent bulk composition affects rates and yields of aryldiazonium adsorption at the carbon/solution interface. Amorphous carbons were deposited in the form of thin films via reactive magnetron sputtering, and were characterized using a combination of Raman, infrared, UV-Vis and X-ray Photoelectron Spectroscopy in order to determine their sp 2 content. Attenuated Total Internal Reflection Fourier Transform Infrared spectroscopy (ATR-FTIR) was used to monitor in situ and in real time the aryldiazonium adsorption process at the carbon/solution interface. These measurements demonstrate that rates and yields of adsorption for the same aryldiazonium salt increase non-linearly vs. sp 2 concentration. Studies of aryldiazonium salt grafting as a function of time carried out ex situ via cyclic voltammetry showed that the amorphous carbon film with highest sp 2 content displays significantly lower grafting yields than glassy carbon, a material with 100% sp 2 content. Intercalation experiments using 4-nitrobenzylamine suggest that the difference in relative density of graphitic edge planes exposed at the carbon surface is in excellent agreement with the observed relative grafting yields. We discuss the implications of these results for the development of structure/reactivity relationships that can be leveraged for understanding the surface chemistry of disordered carbon materials.

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

“…For spontaneous grafting involving aryldiazonium ions such as 4‐nitrobenzenediazonium an excellent correlation was reported to exist between the grafting yields and the relative density of graphitic edge planes exposed at surfaces of various carbon materials . The same might therefore be anticipated to be the case herein with a fast initial grafting occurring at edges and defect sites of graphene.…”

Remarkable enhancement of the specific activities of Pt catalysts to methanol oxidation through tuning the surface properties of supporting materials by fast microwave treatments

“…Instead, it reaches peak value in Pt-RGO/PF-5. The high-resolution C1s spectrum is deconvoluted into the peak at: 284.5 eV (C]C, sp 2 graphite component), 285.1 eV (CeC, sp 3 carbon) [15,16], 285.9 eV (CeOH, hydroxyl/phenolic group), 286.6 eV (CeOeC, epoxide group), 287.5 eV (C]O, carbonyl group), 289.0 eV (COOH, carboxyl group) [17,18]. For the three catalysts, an additional satellite peak at~290.5 eV (pep*) is involved when fitting [17].…”

Heterogeneous Charge Transfer at the Amorphous Carbon/Solution Interface: Effect on the Spontaneous Attachment of Aryldiazonium Salts

“…This value suggests a significantly greater density of graphitic edge planes at annealed carbon surfaces when compared to the previously reported value for a-C of (3.4 ± 0.9) × 10 −10 mol cm −2 (95% C.I.). 12 Roughness measurements on a-C and a-C700 samples obtained via AFM also show that surface roughness is similar for these two samples; therefore, the observed difference in intercalated 4NBA surface densities cannot arise from differences in surface roughness (see Supporting Information). These results therefore indicate that both an increase in sp 2 carbon and graphitic clusters and edges take place upon annealing; the effect of these changes on adsorption reactions will be discussed in the following section.…”

“…12 These films had been shown to be semimetallic in character and to possess an sp 2 content of (80 ± 4)%, as determined via XPS. 12 a-C films were then annealed under a nitrogen atmosphere in order to increase their sp 2 carbon content. Figure 1a shows the Raman spectra of the as deposited a-C film and of a-C after annealing at 500°C (a-C500) and 700°C (a-C700); the spectrum of glassy carbon (GC) is reported for comparison.…”

“…We have shown that when the electronic properties of amorphous carbon change from metallic to semiconducting, adsorption rates drop dramatically. 12 Conversely, molecular acceptor levels can strongly affect adsorption rates at amorphous carbons. For instance, 13 using in situ spectroscopy we showed that adsorption rates of 4-nitronaphthalene (4NND) and 5-nitronaphthalene (5NND) diazonium tetrafluoroborate, two positional isomers (see Scheme 1b), were remarkably different.…”