Abstract
Due to their outstanding physicochemical properties, the next generation of the graphene family—graphene quantum dots (GQDs)—are at the cutting edge of nanotechnology development. GQDs generally possess many hydrophilic functionalities which allow their dispersibility in water but, on the other hand, could interfere with reactions that are mainly performed in organic solvents, as for cycloaddition reactions. We investigated the 1,3-dipolar cycloaddition (1,3-DCA) reactions of the C-ethoxycarbonyl N-methyl nitrone 1a and the newly synthesized C-diethoxyphosphorylpropilidene N-benzyl nitrone 1b with the surface of GQDs, affording the isoxazolidine cycloadducts isox-GQDs 2a and isox-GQDs 2b. Reactions were performed in mild and eco-friendly conditions, through the use of a natural deep eutectic solvent (NADES), free of chloride or any metal ions in its composition, and formed by the zwitterionic trimethylglycine as the -bond acceptor, and glycolic acid as the hydrogen-bond donor. The results reported in this study have for the first time proved the possibility of performing cycloaddition reactions directly to the p-cloud of the GQDs surface. The use of DES for the cycloaddition reactions on GQDs, other than to improve the solubility of reactants, has been shown to bring additional advantages because of the great affinity of these green solvents with aromatic systems.
Highlights
IntroductionGraphene quantum dots (GQDs), zero-dimensional carbon-based nanomaterials with graphene structures, have received significant interest from academia and industry in recent years [1]
Graphene quantum dots (GQDs), zero-dimensional carbon-based nanomaterials with graphene structures, have received significant interest from academia and industry in recent years [1].Their outstanding physicochemical properties enabled novel and extraordinary applications in several fields including physics, chemistry, materials science, biology and medicine [2]
The graphene quantum dots (GQDs) used for this study were synthesized by a top-down procedure previously reported by us [34], starting from multi-walled carbon nanotubes (MWCNTs) in order to obtain nanodots with many oxygen-containing functional groups [38] and were characterized by Raman, high-resolution transmission electron microscopy (HRTEM), dynamic light scattering (DLS), UV-VIS, and photoluminescence (PL) analyses
Summary
Graphene quantum dots (GQDs), zero-dimensional carbon-based nanomaterials with graphene structures, have received significant interest from academia and industry in recent years [1]. Both band-gap and photoluminescence can be tuned during the GQDs synthesis by controlling their size, shape, charge transfer between functional groups and graphene surface, and by doping with heteroatoms [3] Because of their unique optical properties, these nanomaterials have been designed for application in photovoltaics, for the development of flexible devices and in biosensing [4,5]. The used NADES does not contain chloride or metal ions in its composition, with both components derived fNraonmomsatuergiaalsr2b0e20e,t1, 0a, n25d49is cheap, recyclable and shows advantageous physical properties such as loofw viscosity and low melting point [32] The use of this green solvent has been shown to exert a positive effect for the reactions’ outcomes, improving the solubility of the water insoluble reactants and oinf GorQdDers,tobetceastusites orfeatchteivgitryeawt iatfhfinniatnyoo-sfctahleedsodlivpeonlat rwopithhiltehseacnadrbfoonr tshpe npertewseonrcke. Atomic force microscopy (AFM) images of the samples surface were obtained with a microscope NT-MDT NTEGRA Spectra and using a Si-cantilever operating in semi-contact mode
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