Highly concentrated polycations-functionalized graphene nanosheets with excellent solubility and stability, and its fast, facile and controllable assembly of multiple nanoparticles

Here we report that branch poly(ethylenimine) (BPEI) could be used as both a stabilizer and a reducing agent in the preparation of long-term stable polycations-functionalized graphene nanosheets (GNs) suspension with concentration as high as 5 mg mL(-1). UV-vis spectroscopy, Fourier transform infrared, X-ray photo-electron spectroscopy, atomic force microscopy, transmission electron microscopy, Raman spectroscopy and X-ray diffraction were used to characterize the reduction process, composition and structure of BPEI functionalized GNs (BGNs). Fourier transform infrared and X-ray photo-electron spectroscopy data revealed that the BPEI was attached to the surface of GNs through covalent bonds such as amide bond and -Ar-NH-C bond, and could prevent their aggregation through strong electrostatic repulsion. From the atomic force microscopy image and height profile of BGNs, the modality of functionalized surface of BGNs should be continuous and compact. The as-obtained BGNs could disperse well not only in water but also in other alkaline solution, salt solution and organic solvents. The as-obtained BGNs containing abundant amino groups were used as effective and controllable templates for fast and facile assembly with a series of negatively charged nanoparticles (NPs), which was probably caused by the strong electrostatic interaction between both components. This paper presents a fast, facile, controllable, efficient and green approach for preparing GNs and GNs/NPs composites of great value for applications in various fields.