Fabrication of noncovalently functionalized brick-like β-cyclodextrins/graphene composite dispersions with favorable stability

Abstract

Noncovalently functionalized β-cyclodextrins (β-CDs)/graphene composite dispersions have been fabricated through layer-by-layer self-assembly. Scanning electron microscope and transmission electron microscopy characterization confirm that the β-CDs/graphene composites possess brick-like sandwich-type structure. X-ray diffraction results illustrate that β-CDs covering on the surface of graphene possess channel-type structures. Moreover, the obtained β-CDs/graphene composites exhibit good dispersibility in common polar solvents and could exist for several weeks. In particular, the composites could be dispersed well in water at concentrations up to 2 mg mL⁻¹ and stably exist at pH values from 4 to 12. The facts indicate that there exist certain forces between graphene and β-CDs. In order to clarify the interaction between them, we adopt a molecular mechanics (MM) method to evaluate the driving force. According to MM simulations, van der Waals forces should be the driving force for the formation of the well-defined β-CDs/graphene composites, and hydrogen-bonding interaction between adjacent β-CD molecules is another driving force for the formation of this stable graphene dispersion, which is similar to that of the β-CDs/carbon nanotubes composite. But the binding energy of the β-CDs/graphene composite is larger than that of the latter, suggesting much stronger interaction between graphene and β-CD molecules due to the two-dimensional flat-structure of graphene offering more and efficient sites to interact with β-CD molecules compared to carbon nanotubes with large interfacial curvature. These theoretical data for the existence of these interactions are further confirmed by experimental results from Raman and thermogravimetric analysis-differential scanning calorimetry.