Evolution of structure and functional groups in the functionalization of graphene oxide with L-cysteine

A one-step method is proposed to fabricate three-dimensional functionalized graphene oxide (3D GOL) using L-cysteine (L-Cys) as grafting modification agent under atmospheric pressure. The emphasis is determining the functional modification mechanism of 3D GOL with characterization of morphology, structure and functional groups through scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The results showed that 3D GOL has a well-connected 3D porous microstructure. With the increase of mass ratio of L-Cys to graphene oxide (GOs), more pores in the microstructure of 3D GOL were formed and the pore size got smaller. The reactions between L-Cys and GOs, such as oxidation-reduction reaction of sulfhydryl with hydroxyl groups, dehydration of sulfhydryl with carboxyl groups, and amidation reaction of amino with carboxyl groups promoted the crosslinking of GOs nanosheets, and induced the GOs nanosheets to assemble into a 3D porous framework.