Solvent-free functionalization of graphene oxide powder and paper with aminobenzo-crown ethers and complexation with alkali metal cations

Abstract

Graphene oxide powder and graphene oxide paper were covalently functionalized with the 4′-aminobenzo-15-crown-5 (AB15C5) and 4′-aminobenzo-18-crown-6 (AB18C6) ethers by a solvent-free gas-phase treatment. Then, we attempted the complexation with potassium and sodium cations. A comparative characterization in the functionalized graphene oxide structures was carried out using Fourier-transform infrared (FTIR), Raman and X-ray photoelectron spectroscopy (XPS), thermogravimetric and differential thermal analysis (TGA and DTA, respectively), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The wettability of graphene oxide paper (GOP) samples was analyzed by measuring the contact angle. The degree of covalent functionalization in GO powder with aminobenzo-crown ethers was estimated at 27% (AB15C5) and 19% (AB18C6). The amount of organics attached to GOP samples was approximately 7%. After the interaction with potassium and sodium cations, the functionalized GOP samples showed an increase in the contact angle, followed by a decrease in surface free energy. The complexation with alkali metal cations suggests an uptake of about 3%. However, the cation selectivity for alkali metal ions was dependent on the ions' radius. Surface free energy measurements suggest that complexation with potassium effectively takes place when using AB18C6.