The Preparation Of Graphene Quantum Dots And The Performance Of Composite Materials Research

In this study, we have focused on the synthesis and characterization of self-assembled graphene quantum dots and its composites. The photocatalytic properties of GQDs composites were also discussed. The thesis included synthesis and preparation of high concentration graphene quantum dots, preparation of graphene quantum dot-based composites and characterization of material’s morphplogy, structure and photoluminesence. Then we explored the composite materials on photocatalytic hydrogen production and photocatalytic degradation. The main results of this study are summarized as followings:（1） The expanded graphite was treated by high-speed cutting and ultrasonic dispersion. Graphite powder was stripped and dispersed, then it was oxidized at a high temperature by improved Hummers methodto obtain high oxidizing graphite oxide（OGO）.（2） Using high graphene oxide（OGO） as raw material, under the action of a strong base, one-step of high temperature and pressure was used to achieve a high purity and a high concentration of yellow light graphene quantum dots（GQDs） by hydrothermal method extraction. The resulting quantum dot solution can be directly written into the word and emit light under 365 nm UV. GQDs quantum yield is 23.6% at 320 nm excitation, which is much higher than most of the previous paper. The analysis of their photoluminescence properties indicated that it has excellent stability and good photoluminescence properties.（3） Using cheap goods titanium dioxide as a raw material, the titania nanotubes（TiO₂NT） was synthesized by hydrothermal method and calcination in sodium hydroxide（NaOH）. The prepared TiO₂ NT had good physical morphology by transmission electron microscopy（TEM） and scanning electron microscopy（SEM）. The diameter of TiO₂ NT is about 30-50 nm, and the length is about-3μm.（4） Graphene quantum dots and titanium dioxide nanotube composite material（GQDs/TiO₂NT） was obtained by one-step of hydrothermal dipping method. By UV-Vis-NIR absorption spectroscopy, transmission electron microscopy（TEM）,electron microscopy（SEM） and high resolution transmission electron microscopy（HRTEM）, the presence of the composite structure was confirmed. The prepared GQDs/TiO₂ NT has good photocatalytic degradation performance, good stability, repeatability and high degradation efficiency. With the increasing amounts of quantum dots, the degradation efficiency was improved first and then declined. When the doping amount is 2.5 % GQDs/TiO₂ NT, the rate of degradation of methyl orange（MO） is 2.67 times of pure TiO₂ NT.（5） Acertain percentage of g-C₃N₄/TiO₂ was obtained by a sol-gel, method and using it as a precursor, one-step of hydrothermal dipping method was used to synthesis graphite carbon nitride and titanium dioxide precursor ternary composite material with graphene quantum dots（g-C₃N₄/TiO₂-GQDs）. The presence of the composite structure was confirmed by characterizing the composite materials. The photocatalytic degradation and photocatalytic hydrogen production properties of the material were also further explored. The photocatalytic degradation of performance has greater improved than the precursor. But the performance of ternary composite is worse than dual composite of graphene quantum dots doped TiO₂ NT. With the increasing amounts of quantum dots, the photocatalytic hydrogen production was declined.