Abstract
In this work, the functionalization of graphene nanoplatelets (GNPs) performed by a solvent-free cycloaddition reaction on GNPs with iminodiacetic acid (IDA) and paraformaldehyde (PFA), and the functionality analysis of the resulting functionalized GNPs (f-GNPs) by Boehm titration are introduced. The f-GNPs synthesized at different temperatures were characterized by X-ray diffraction (XRD), Raman spectroscopy and scanning electron microscopy (SEM) for structural and morphological properties. Back titration of the f-GNPs selectively identified 3 types of functional groups on the f-GNP surface, carboxylic, lactonic and phenolic, and suggested that 200 °C gives the highest carboxylic group functionality. With the reaction temperature increasing from 180 to 220 °C, a decrease in the phenolic functionality and an increase in that of lactonic are observed. In the case of 250 °C reactions, it was found that the carboxylic functionality is greatly reduced, while the phenolic functionality showed a significant increase. The f-GNP samples were further characterized by thermogravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS), the results of which showed a good agreement with the titration analysis.
Highlights
The 1,3-dipole reacted with HC11 following the cycloaddition scheme and facilitated the formation of a carboxylic acid-terminated pyrrolidine ring covalently bonded to the surface of the HC11, denoted as fGNPs
The electrical conductivity was found to be 298 Æ 3 S mÀ1, 269 Æ 2 S mÀ1, 259 Æ 3 S mÀ1, 253 Æ 2 S mÀ1 and 252 Æ 2 S mÀ1 for HC11, f-graphene nanoplatelets (GNPs)-180, functionalized GNPs (f-GNPs)-200, f-GNPs-220 and f-GNPs-250, respectively. These results show that there is a small decrease in the electrical conductivity going from HC11 to the f-GNPs, all the values are of the same order of magnitude
In the iminodiacetic acid (IDA)–PFA–GNPs-250 sample, the stage (ii) is completely absent and only the stage (iii) was identi ed. These results indicate that despite the high melting point of the IDA, the DCA reaction occurs within the temperature range selected
Summary
The increasing research over the past decade into the excellent properties that graphene possesses has led to fruitful outputs that have demonstrated a wide range of potential applications, where graphene and its composites have played a remarkable role.[1,2,3] Surface modi cation of graphene is a practical method that could on the one hand alter the surface properties, while on the other hand, introduce functional groups covalently/noncovalently into graphene sheets, so that the desired performance could be realized.[4,5,6] It is by such modi cation that the applications of graphene-based materials in the elds of solar cells, supercapacitors, biomedical applications, gas storage, composites and others have been developed.[7,8,9,10,11]. The functionalization of GNPs through the 1,3DCA reaction in the solid state was performed at selected temperatures of 180 C, 200 C, 220 C and 250 C. By comparing the functionality of f-GNP samples, it is revealed that the functionality of f-GNPs synthesized via the solid-state DCA reaction introduced is strongly temperature dependent These results can be correlated with and are in good agreement with TGA and XPS results. The functionality of the pristine HC11 material and the f-GNPs synthesized at different temperatures was studied by Boehm titration in an indirect manner, denoted in the literature as back titration.31 0.75 g of GNPs (pristine HC11 or f-GNPs) was added to 50 mL 0.05 M aqueous solution of one of the three selected bases: NaHCO3, Na2CO3 or NaOH. The selective neutralization of different functional groups by different titrating bases enables the estimation of functionalities of these groups by calculating the difference of the nCSF calculated for different titrating bases: the differences between nCSF (NaHCO3) and nCSF (Na2CO3), and between nCSF (Na2CO3) and nCSF (NaOH) give the functionalities of lactonic groups and phenolic groups, respectively
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