Fluorinated Reduced Graphene Oxide-Encapsulated ZnO Hollow Sphere Composite as an Efficient Photocatalyst with Increased Charge-Carrier Mobility.

Zinc oxide (ZnO) hollow spheres were prepared by the hydrothermal method and encapsulated with fluorinated reduced graphene oxide (FRGO) using a tetra- n-butylammonium bromide (TBAB) linker to give an FRGO/ZnO composite. X-ray diffraction and microscopic studies revealed their hexagonal-wurtzite structure, spherical morphology, and size of the crystallite to be 26.7 nm. Diffuse reflectance UV-visible spectroscopy showed an optical band gap and semiconductive nature of the composite. Atomic force microscopy images show the surface topography of FRGO-encapsulated ZnO hollow spheres. The photoluminescence spectra depicted the electron-hole pair recombination order to be ZnO > RGO/ZnO > FRGO/ZnO. The electrochemical impedance spectroscopy (EIS) demonstrates the increased charge-carrier mobility of the FRGO/ZnO composite; the Rct values of ZnO, RGO/ZnO, and FRGO/ZnO were found to be 6.18 × 103, 4.07 × 103, and 3.45 × 103 Ω, respectively. All the three materials were employed as photocatalysts in the degradation of methylene blue under UV-365 nm radiation and the results exposed the higher photocatalytic activity of reduced fluorinated graphene oxide/ZnO than RGO/ZnO and bare ZnO hollow spheres. The increased photocatalytic activity of the composite is due to the enhanced vectorial transport of charge carriers at the interface of the FRGO/ZnO composite and suppression of charge-carrier recombination. The presence of fluorine in the RGO sheet introduces additional defects and leverages heterogeneous electron transport. In turn, mobility of light-generated charge carriers is increased and results in suppression of their recombination, which facilitates the photocatalytic process.