Highly Water Dispersible Functionalized Graphene by Thermal Thiol-Ene Click Chemistry

Abstract

Functionalization of pristine graphene to achieve high water dispersibility remains as a key obstacle owing to the high hydrophobicity and absence of reactive functional groups on the graphene surface. Herein, a green and simple modification approach to prepare highly dispersible functionalized graphene via thermal thiol-ene click reaction was successfully demonstrated on pristine graphene. Specific chemical functionalities (–COO, –NH2 and –S) on the thiol precursor (L-cysteine ethyl ester) were clicked directly on the sp2 carbon of graphene framework with grafting density of 1 unit L-cysteine per 113 carbon atoms on graphene. This functionalized graphene was confirmed with high atomic content of S (4.79 at % S) as well as the presence of C–S–C and N–H species on the L-cysteine functionalized graphene (FG-CYS). Raman spectroscopy evidently corroborated the modification of graphene to FG-CYS with an increased intensity ratio of D and G band, ID/IG ratio (0.3 to 0.7), full-width at half-maximum of G band, FWHM [G] (20.3 to 35.5) and FWHM [2D] (64.8 to 90.1). The use of ethanol as the reaction solvent instead of common organic solvents minimizes the chemical hazards exposure to humans and the environment. This direct attachment of multifunctional groups on the surface of pristine graphene is highly demanded for graphene ink formulations, coatings, adsorbents, sensors and supercapacitor applications.

Chemical Functionalization of Graphene Nanoplatelets with Hydroxyl, Amino, and Carboxylic Terminal Groups

“…The increase in the ID/IG band ratio reveals the covale tionalization, and the ID/IG spatial map indicates the functionalization prefers to o the edges. A thiol-ene click reaction between L-cysteine ethyl ester and graphene was deployed by Dusan's group to introduce amino groups to pristine graphene (Scheme 5) [19]. The functionalized graphene shows a significant increase in the S2p, N1s, and O1s peaks at 164.0 eV, 401.5 eV, and 531.0 eV in the XPS spectra, indicating the presence of L-cysteine ethyl ester.…”

“…The thiol-ene click reaction between L-cysteine ethyl ester and graphene. Reproduced with permission from [19], copyright 2021 Multidisciplinary Digital Publishing Institute.…”

Improved Dispersibility of Graphene in an Aqueous Solution by Reduced Graphene Oxide Surfactant: Experimental Verification and Density Functional Theory Calculation

“…One is the covalent functionalization of graphene by grafting functional groups such as hydroxyl, 10,11 carboxyls, 12,13 or amino groups. 14,15 The other employs non-covalently functionalized graphene flakes to achieve stable dispersion in polar media using specific metal particles, 16 organic molecules, 17,18 polymers, 19−21 and biomolecules 22,23 as stabilizers. One feasible method is to disperse graphene directly in the solvent during the production process.…”

“…However, it is difficult for graphene to be employed in many fields because of its high hydrophobicity and is easily aggregated in solution due to the mismatch of graphene surface tension and the strong π–π interaction between sp 2 -conjugated structures. , To date, two ways have been adopted to increase graphene hydrophilicity. One is the covalent functionalization of graphene by grafting functional groups such as hydroxyl, , carboxyls, , or amino groups. , The other employs non-covalently functionalized graphene flakes to achieve stable dispersion in polar media using specific metal particles, organic molecules, , polymers, − and biomolecules , as stabilizers. One feasible method is to disperse graphene directly in the solvent during the production process. , For example, highly stable reduced graphene oxide (rGO) dispersion was produced by the reducing graphene oxide (GO) method. , In addition, pyrene derivatives , and ionic liquids , can serve as effective stabilizers for graphene in liquid-phase exfoliation and have the potential to achieve high concentrations of graphene in solutions.…”

Graphene and Other 2D Layered Nanomaterials and Hybrid Structures: Synthesis, Properties and Applications

“…The theme of graphene functionalization/dispersion is still very active, particularly for environmentally friendly and effective methods that do not require the use of strong acids or oxidants. Farivar et al [ 16 ] reported a simple and green modification method for preparing highly dispersible functionalized graphene via thermal thiol-ene click reactions. The method provides specific chemical functionalities such as –COO, –NH 2 and –S to the graphene sheets by using modified L-cysteine ethyl ester.…”