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 R ct 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.