Preparation And Characterization Of Multistimuli-Responsive Graphene Quantum Dots

In this dissertation, oxidized graphene sheet (OGS) was treated with ahyperbranched polyethylenimine (PEI) under the hydrothermal condition to generatethe graphene quantum dot (GQD) functionalized with PEI (GQD-PEI). Subsequently,isobutyric amide (IBAm) groups were attached to GQD-PEI through the amidationreaction of isobutyric anhydride and the PEI moiety, which resulted in thethermoresponsive T-GQDs. The details were as follows:1. The influence of reaction temperature and the feed ratio of PEI/OGS on thephotoluminescent property of GQD-PEIs were studied. The optimized reactiontemperature is found to be around180℃. When the PEI/OGS ratio is in the rangeof0.3-5, the maximum emission wavelength of the obtained GQDs ranges from430nm to460nm.2. The obtained GQD-PEIs were characterized by TEM, dynamic light scattering. Itis found that in the obtained GQD-PEIs there exist not only the individualGQD-PEIs, but also the GQD-PEI microgels.3. The obtained T-GQD nanocomposites were thermoresponsive. It is clear thatlowering the degree of amidationof isobutyric amidecan effectively increase thecloud point temperature (Tcp) of the aqueous solution of T-GQD. Increasing theacidity significantly increases Tcp. I-exhibits the significant salting-in effect,whereas Cl-and SO42-show the obvious salting-out effect. Furthermore, SO42-ismore efficient to lower the Tcpthan Cl-. Asprin guest can increase the TcpwhereasPBA guest leads to the decrease of Tcp.4. All the obtained T-GQDs are photoluminescent. These outer stimuli have noinfluence on the maximum emission wavelength of T-GQD. The pH value, NaCl,Na2SO4and aspirin guest have a little or even negligible influence on the emissionof T-GQD. Whereas, NaI and PBA can effectively quench the luminescence ofT-GQD.