Photocatalytic and photoluminescence properties of ZnO/graphene quasi core-shell nanoparticles

In this paper, a combination of in-situ chemical synthesis and electrolysis methods was applied for the preparation of zinc oxide/graphene oxide quasi core-shell nanoparticles. Pure zinc oxide was also prepared using the same method at different temperatures. 100 degrees C was selected for synthesizing the ZnO/GO quasi core-shell (zinc oxide as a core and few layers of graphene oxide as a shell). The particle size was 15 +/- 2 nm in all samples. In both processes, oxygen was the main reason for the connection between the core and the shell. XRD patterns also confirmed the formation of ZnO (with regular wurtzite structure) and ZnO/GO quasi core-shell structures. Raman spectroscopy results confirmed ZnO formation at various temperatures, but little shift was observed for ZnO/GO quasi core-shell after conjugating. HRTEM, BET, PL and UV-Vis were able to define and confirm the formation of the quasi core-shell structure and the mechanism of connection at the interface. Photoluminescence spectroscopy showed a few numbers of PL peaks that were not related to the presence of graphene. These sub-peaks depend on the kind of synthesis and creation of defects (based on defects chemistry). The results indicated that graphene just changed the intensity of the PL peaks. Our data indicated that the rate of MB degradation for ZnO/GO quasi core-shell structures was less than that of the pure zinc oxide. After conjugating between ZnO and GO, two mechanisms are suggested. The first is the band structure modification in the boundary of the core and shell. The second is the diffusion of carbon atoms or functions as dopant in ZnO surface. This report addresses how band structure modification, defect chemistry; microstructural features can affect the photocatalytic and photoluminescence behavior in a specific core-shell structure.